1: Reaction Stoichiometry

1: Reaction Stoichiometry

Drill 9/5 (A Day) 9/6 (B Day) Gather all items by the door
Find your seat number Drill 9/5 (A Day) 9/6 (B Day) Outcome: I can use sig figs to correctly measure quantities. Goal: CW 1, CW 2

CW 1: Safety in the Chemistry Lab
Who has responsibilities for safety? The student and the teacher. What types of clothing are appropriate to wear during a lab? Goggles, closed toe shoes, no baggy/ loose clothes, no dangling jewelry, tie back hair. What should you do with backpacks and extra personal belongings during lab? Put away unnecessary items in backpacks under your desk. Keep walkways clear. What do you never ever do in a science laboratory? Eat or drink anything.

What are the two types of safety equipment? Give an example of each. Classroom: Eye wash, fire blanket, fire extinguisher, first aid, safety shower. Personal: Goggles, gloves, apron. What does this acronym stand for when using a fire extinguisher? P: Pull the pin A: Aim at the base of the flame S: Squeeze the handle S: Sweep back and forth

What is the correct way to smell a substance? Gently waft. How should you transport chemicals across a classroom? Walk defensively, elbows in, use both hands. How should you clean up broken glass? Use a dust pan and broom. Only pick up glass with safety gloves.

Where are the following located? Door Eyewash station Safety shower Fire extinguisher Fire blanket First aid kit Waste beakers

What should you do if you are unsure of how to proceed during an experiment? Ask for help. Why should you not immerse hot glassware into cold water? It can shatter. Where should you dispose of chemical wastes? As directed by your teacher. Do not return unused chemicals to their containers. Do not pour substances down the drain without checking with your teacher. Where should you point a mouth of a test tube that is being heated? Away from yourself and others.

Safety Quiz Complete the safety quiz by bubbling in your scan sheet.
If you finish early, start working individually on CW 2.

CW 2: Measurement and Uncertainty
Precision and Accuracy Accuracy refers to the agreement of a measurement with the true value. Precision refers to the degree of agreement among several measurements of the same quantity. Both relate to error. A random error means that the measurement has an equal probability of too high or too low. This type of error occurs when you estimate the last digit of a measurement. A systematic error occurs in the same direction each time – it is always too high or too low.

To check the accuracy of a graduated cylinder, a student measured of water using a buret, placed it into a graduated cylinder, and recorded the volume. Is this data accurate? Precise? Explain. Not accurate: the graduated cylinder reads 25 mL, the buret is reading 1 mL high Precise: all measurements are very close. What type of error does the data show? Explain. Systematic error: always too high Does the student have good measurement technique? Provide evidence. Yes, the measurements vary at most by 0.09 mL

Correct Measurement To correctly measure a quantity, determine what increments the measuring device uses, then measure out to one smaller place. For example, if a ruler goes by 1 cm increments, then your measurement from that ruler should have one decimal place.

Measure the following. Is it possible that each of the three beakers contain the same amount of water? If no, why? If yes, did you report the same values in the previous question? Explain. Yes, they may all have the same amount of water, but they have different precisions, so that amount may be measured differently. 32.7 mL 32 mL 32.75 mL

Sketch two pieces of glassware showing the proper graduations: one that can measure with a precision of ±0.1 mL and one that can measure with a precision of ±0.01 mL. ±0.1 mL: Goes by 1 (each mark = 1) ±0.01 mL: Goes by 0.1 (each mark = 0.1)

Rules for Counting Significant Figures Nonzero integers. Nonzero integers are always significant. Zeros. There are three classes of zeros: Leading zeros precede all the nonzero digits. They are placeholders and are not significant. For example, g has two significant figures. Captive zeros are between nonzero digits. They are significant. For example, 107 g and 1.07 g both have three significant figures. Trailing zeros are found at the right end of a number. They are only significant if there is a decimal point in the number. For example, 100 g has one significant figure, while 100. g has three significant figures. Exact numbers. These arise from counted quantities (10 experiments, 28 students) and from definitions, such as conversion factors (1 in = 2.54 cm). Scientific notation. When written in scientific notation, all digits are significant. For example, x108 g has five significant figures.

Determine how many significant figures are in the following. 6.07x10–15 17.00 8x108 300 301 300. 3 SF 4 SF 4 SF 1 SF 7 SF 1 SF 3 SF 3 SF

Round off each of the following numbers to the indicated number of significant figures. to three sig figs x102 to four sig figs to five sig figs 3.365x105 to three sig figs Use scientific notation to express the number 385,500 to One significant figure Two significant figures Three significant figures Five significant figures 103.4x102 1.7992 3.37x105 4x105 3.9x105 3.86x105 3.8550x105

Addition and Subtraction The number of significant figures in the answer depends on the least precise place of the measurements.

Multiplication and Division The number of significant figures in the answer is the same as the number of significant figures in the least precise measurement.

Order of Operations In multistep operations, ensure that you use the correct order of operation (PEMDAS). Mentally keep track of how many significant figures you are left with after each step, but do not round until all steps are complete.

Perform the following operations and express each result to the correct number of significant figures. 188.1 12 4x10–7 6.3x10–26 4.89 0.22%

Perform the following operations and express each result to the correct number of significant figures. (6.404×2.91)/(18.7−17.1) = 2 SF 3 SF 4 SF =188.1 3 SF = =12 1 decimal place, 2 SF

Perform the following operations and express each result to the correct number of significant figures. 6.071× 10 −5 −8.2× 10 −6 −0.521× 10 −4 (3.8× 10 − × 10 −13 )/(4× × ) = =4× 10 −7 38× 10 −13 4× 10 12 4× 10 −13 63× 10 12 42× 10 −13 67× 10 13 2 SF 42× 10 −13 67× = × 10 −27 =6.3× 10 −27 2 SF

Perform the following operations and express each result to the correct number of significant figures. 8.925− ×100 (Assume you are taking the average of 4 numbers, thus 4 is an exact number.) 9.5 3 SF 4.1 = 2.8 =4.89 3.175 19.575 (This is a percent error calculation, thus 100 is an exact number.) 2 SF 8.925 ×100= 8.905 =0.22% 4 SF 0.020

Summary 9/5 (A Day) 9/6 (B Day)
Complete CW 1 and CW 2 HW 0: Things to Do Get you syllabus and safety contract signed Order your lab notebook from Amazon Sign up for OWL Locate and bring in your goggles Summary 9/5 (A Day) 9/6 (B Day) Outcome: I can use sig figs to correctly measure quantities. Goal: CW 1, CW 2

2NaHCO3(s) + heat  Na2CO3(s) + CO2(g) + H2O(g)
If 3.80 g of H2O are produced, what mass of NaHCO3 reacted? Drill 1 9/7 (A Day) 9/10 (B Day) 2NaHCO3(s) + heat  Na2CO3(s) + CO2(g) + H2O(g) Outcome: I can apply green chemistry principles to the purification of a mixture. Goal: CW 3, CW 4 Prelab Hand In: syllabus, safety contract, googles

CW 3: Classification of Matter
For each of the following mixtures, suggest a physical means of separation. A mixture of pen inks with different polarities. Chromatography A mixture of water and isopropyl alcohol. Distillation A mixture of a precipitate formed in aqueous solution. Filtration A mixture of solid sodium carbonate and sodium hydrogen carbonate. Different chemical reactions: NaHCO3 decomposes when heated, NaCO3 does not.

Complete the chart below using the word bank from the reading. Matter Pure substances Mixtures Heterogenous Homogenous Elements Compounds Solution Atoms

For each of the following, check the appropriate categories of the substances listed. Substance Heterogenous Homogenous Pure substance Solution Element Compound Mixture Lead metal x Sodium chloride x Raw egg Oxygen

CW 4: Purification of a Mixture
12 Principles of Green Chemistry Create no waste Nothing should be left over No toxicity Green products must work as well as non-green products Get rid of all nonessential additives Reduce energy usage Use renewable materials Get rid of as many steps as possible Make use of a reusable method to speed up a reaction Use materials that break down in the environment (biodegradable) Check everything you do against the other principles Safety first

% 𝐴𝑡𝑜𝑚 𝐸𝑐𝑜𝑛𝑜𝑚𝑦= 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑑𝑒𝑠𝑖𝑟𝑒𝑑 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑎𝑙𝑙 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑 ×100 When the percent atom economy equals 100%, then there is nothing left over because there is only one product, the desired one. If the ratio is less than 100%, it is because there are products that are wastes. The lower the ratio, the less product is produced in comparison to the wastes produced. The atom economy is therefore a measure of how green, or efficient, a chemical process is. The higher the atom economy is, the greener the process is, and the more efficient the process is for producing the desired product.

Select one of the principles of green chemistry. Explain in your own words how this principle shifts chemistry toward more environmentally conscious practices. How is this relevant to considering the benefits and risks when making decisions about which of two (or more) possible chemical processes is better?

The following two reactions are possible methods for refining copper in the final step of a smelting process, i.e., getting pure copper (Cu) from copper ores found in rocks. Calculate the theoretical atom economy for each reaction. 2 CuO (s) + C (s) → 2 Cu (s) + CO2 (g) CuO (s) + CO (g) → Cu (s) + CO2 (g) 2 𝐶𝑢 2 𝐶𝑢+ 𝐶𝑂 2 ×100%= 2 (63.55) 2 (63.55) ×100%= 74.28% 𝐶𝑢 𝐶𝑢+ 𝐶𝑂 2 ×100%= ×100%= 59.08%

Use your calculations from the previous question to answer the following. Which one of the methods for refining copper ore is greener according to the atom economy principle of green chemistry? Method A Why is a calculation of atom economy helpful in comparing two chemical reactions to determine which one is greener? In other words, what does atom economy tell you about “greenness”? Atom economy compares what fraction of the products represents the intended products. Higher economy = greener What is another possible consideration from the principles of green chemistry that could tell you more about comparing the “greenness” of these two reactions? How much energy is needed per mole for each reaction How renewable starting/ ending materials are How environmentally damaging the starting/ ending materials are

Peer review is a critical component of how scientists communicate what they have learned and contribute new knowledge. What is peer review? Why do you think that scientists believe it is important for published work to be peer-reviewed prior to publication? Why is peer review an important part of considering benefits and risks? Why might peer review be important in chemists reporting results of a chemical process? Peer review is the process of scientists reviewing each others’ work. This gives scientists confidence in what they report.

What is a substance? What is a mixture? How are they related? A substance is a pure sample of one chemical (NaCl). A mixture is composed to two or more substances (NaCl and NaCO3 mix) What are the general characteristics of substances chemists use to separate mixtures into individual substances? Every substance has unique properties what can be used to separate them. Distillation: separates liquid mixtures based on the different boiling points of the components. Filtration: separates smaller particles from larger particles, such as a sieve. Chromatography: separates mixtures based on different affinities for the stationary phase and the mobile phase. This involves different strength intermolecular forces.

How are the two ways of measuring the efficiency of a reaction the same? How do they differ? Based on experimental results Financial cost Percent Yield Ratios of values involving the desired product Both Based on theoretical masses Environmental cost Atom Economy

What are some reasons the percent yield of a reaction may be less than 100%? Incomplete reactions/ side reactions What are some reasons percent atom economy may be less than 100%? More than one product besides the desired one

A group of students heated of mixture of NaHCO3 and Na2CO3. Their data is found below. Determine what percentage of the mixture is NaHCO3 and Na2CO3. Before Heating After 1st heating After 2nd heating After 3rd heating 5.045 g 3.770 g 3.766 g 3.767 g 𝑚𝑎𝑠𝑠 𝑙𝑜𝑠𝑡=5.045 𝑔 −3.766 𝑔=1.279 𝑔 Mass is lost as H2O and CO2 during heating 𝑚𝑎𝑠𝑠 𝑙𝑜𝑠𝑡= 𝑥 𝑔 𝑚𝑜𝑙 + 𝑥 𝑔 𝑚𝑜𝑙 Mole ratio is 1:1 so mol H2O = mol CO2 Let x = mol H2O = mol CO2 1.279 𝑔=18.016𝑥+44.01𝑥 1.279 𝑔=62.026𝑥 𝑥= 𝑚𝑜𝑙 𝐶 𝑂 2 Solve for x Convert mol CO2 to g NaHCO3 𝑚𝑜𝑙 𝐶 𝑂 2 1 × 2 𝑚𝑜𝑙 𝑁𝑎𝐻𝐶 𝑂 3 1 𝑚𝑜𝑙 𝐶𝑂 2 × 𝑔 𝑁𝑎𝐻𝐶 𝑂 3 1 𝑚𝑜𝑙 𝑁𝑎𝐻𝐶 𝑂 3 = 𝑔 𝑁𝑎𝐻𝐶 𝑂 3 𝑔 𝑁𝑎𝐻𝐶 𝑂 𝑔 𝑚𝑖𝑥𝑡𝑢𝑟𝑒 ×100%=68.67 % 𝑁𝑎𝐻𝐶 𝑂 3 Find % NaHCO3 in mixture

Pre-Laboratory Work Introduction: Explain theory behind the lab, as well as any equations, graphs, or mathematical equations that will be required. Procedure: Write a procedure for this experiment in your lab notebook. Some tips: Plan to use 4 to 5 g of the mixture. Conduct at least 2 trials with different samples. Take masses using the analytical balance. Heat the sample to constant mass. Plan to complete one heating and take the mass in class, then allow the sample to heat over night before taking the second mass. Use a crucible with the lid askew to hold the sample. Materials: List all chemicals and equipment (including type and size). Look up the MSDS for the chemicals listed below and list major hazards (typically in the Hazards Identification section). Sodium carbonate Sodium hydrogen carbonate

During Laboratory Work Data: Create a data table and record data in your lab notebook. Don’t forget to make detailed observations in addition to any measurements.

Post-Laboratory Work: Word Processed and Printed Analysis: In your lab notebook, use your data to determine the % NaHCO3 in the mixture for both trials. Find the average. Show all work neatly. Report this data by sharing it on the class spreadsheet. Calculate the atom economy of the reaction. Conclusion: Rather than completing a traditional lab report, you will instead review lab manuscripts, and make suggestions for how they may be improved. Each group will receive a copy of a lab report. There are different lab reports, each one written by a scientist who conducted a similar investigation using the same chemical sample you used, with a report of the results of the investigation. Each lab report has some information that is reported well, and some information that is reported poorly. As a group, you will complete the review template, which provides more specific questions to help you assess the manuscripts. Download the template from in Unit 1.

Summary 1 9/7 (A Day) 9/10 (B Day)
Complete the following for CW 4 Complete Class Discussion Questions 3 Complete Prelab Introduction Materials We will write the procedure and do the lab next class HW 1: Stoichiometry I, due 9/11 (A) & 9/12 (B) through OWL. Summary 1 9/7 (A Day) 9/10 (B Day) Outcome: I can apply green chemistry principles to the purification of a mixture. Goal: CW 3, CW 4 Prelab Hand In: syllabus, safety contract, googles

Agenda 9/11 (A Day) 9/12 (B Day)
Check your work on CW 4 question 10 Develop a procedure to conduct the experiment, pay attention to the hints given under Procedure on Page 23 Masses to take: Empty crucible and lid Crucible, lid, and sample before heating Crucible, lid, and sample after heating Crucible, lid, and sample after heating again Conduct the experiment, get 2 masses, put in oven over night, final mass next class Begin working on the conclusion (report review in groups) Next class: Take final mass, do calculation in notebook Lab assessment (one AP FRQ) Continue working on the conclusion Agenda 9/11 (A Day) 9/12 (B Day) Outcome: I can apply green chemistry principles to the purification of a mixture. Goal: Complete two heat/ cool/ mass cycles.

Post-Laboratory Work: Word Processed and Printed Complete the following once the experiment is complete. Analysis: In your lab notebook, use your data to determine the % NaHCO3 in the mixture for all trials. Find the average. Show all work neatly. Report this data by sharing it on the class spreadsheet. Calculate the atom economy of the reaction. Conclusion: Rather than completing a traditional lab report, you will instead review lab manuscripts, and make suggestions for how they may be improved. Each group will receive a copy of a lab report. There are different lab reports, each one written by a scientist who conducted a similar investigation using the same chemical sample you used, with a report of the results of the investigation. Each lab report has some information that is reported well, and some information that is reported poorly. As a group, you will complete the review template, which provides more specific questions to help you assess the manuscripts. Download the template from in Unit 1.

Submitting Laboratory Work
Lab Guidelines Submitting Laboratory Work Complete all sections as described. Create a cover sheet for the lab that includes your name, your partner(s) name(s), your class period, due date, and the title of the experiment. Staple all sections (hand written carbon copies and printed papers) in order and hand in during class. Students who did not complete the pre-laboratory work before the lab day must make up the experiment at the instructor’s nearest convivence. 10% of points will be deducted. If you were absent, make sure to include the day you were absent and the day you made up the lab. Otherwise, the normal late policy (10% off per day) applies.

Lab Guidelines Other Notes
Write in your lab notebook in pen only. The notebook will make a “carbon” copy of your work. This copy is submitted with your typed post-laboratory work or may be collected after you complete your experiment in class. Use the provided separation sheet in the lab notebook so that the copy is transferred to only one yellow sheet at a time. Press hard enough for the copy to be clear. Cite any outside of class resources that you use using APA format. Keep Organized! Develop a file naming system that makes sense for the word-processed portion of the document and save all files in the same place. Analogously, keep all hand-written work organized in your lab notebook. You may be able to use these documents to seek additional college credits. Helpful videos can be found here:

Lab Guidelines Rubric Item Points Note:
Students are required to work in lab groups. Students who are working in the same groups may share data that is collected during class, but all other parts are individual. Pre-Laboratory Work Introduction /10 Materials Procedure During-Laboratory Work Data Collection Post-Laboratory Work Data Analysis /20 Sample Calculations Conclusion /30 TOTAL: /100

Summary 9/11 (A Day) 9/12 (B Day)
HW 2: Stoichiometry II, due 9/13 (A) & 9/14 (B) through OWL Purification of a Mixture Report Review (one per group), 9/20 (A Day) and 9/21 (B Day) Summary 9/11 (A Day) 9/12 (B Day) Outcome: I can apply green chemistry principles to the purification of a mixture. Goal: Complete two heat/ cool/ mass cycles.

A molecule containing only nitrogen and oxygen contains 36
A molecule containing only nitrogen and oxygen contains 36.8% N (by mass). What is the empirical formula of this compound? Drill 2 9/13 (A Day) 9/14 (B Day) 𝑁 2 𝑂 3 Outcome: I can apply green chemistry principles to the purification of a mixture. Goal: Complete data collection and analysis, lab assessment, lab report review 36.8 𝑔 𝑁 1 × 1 𝑚𝑜𝑙 𝑁 𝑔 𝑁 = 𝑚𝑜𝑙 𝑁 =1 𝑚𝑜𝑙 𝑁 2 100%−36.8%=63.2% 𝑂 63.2 𝑔 𝑂 1 × 1 𝑚𝑜𝑙 𝑂 𝑔 𝑂 =3.95 𝑚𝑜𝑙 𝑂 =1.5 𝑚𝑜𝑙 𝑁 3

Post-Laboratory Work: Word Processed and Printed Complete the following once the experiment is complete. Analysis: In your lab notebook, use your data to determine the % NaHCO3 in the mixture for all trials. Find the average. Show all work neatly. Report this data by sharing it on the class spreadsheet. Calculate the atom economy of the reaction. Conclusion: Rather than completing a traditional lab report, you will instead review lab manuscripts, and make suggestions for how they may be improved. Each group will receive a copy of a lab report. There are different lab reports, each one written by a scientist who conducted a similar investigation using the same chemical sample you used, with a report of the results of the investigation. Each lab report has some information that is reported well, and some information that is reported poorly. As a group, you will complete the review template, which provides more specific questions to help you assess the manuscripts. Download the template from in Unit 1.

2 NaHCO3 (s) + heat  Na2CO3 (s) + CO2 (g) + H2O (g)
Agenda Collect last mass Complete analysis % NaHCO3 Atom economy of the reaction (what is the desired product?) 2 NaHCO3 (s) + heat  Na2CO3 (s) + CO2 (g) + H2O (g) Work in groups on conclusion (lab report review, one per group due 9/20 and 9/21) Lab Assessment (timed 15:00 min)

HW 3: Stoichiometry III, due 9/17 (A) & 9/18 (B) through OWL Purification of a Mixture Report Review (one per group), 9/20 (A Day) and 9/21 (B Day) Summary 2 9/13 (A Day) 9/14 (B Day) Outcome: I can apply green chemistry principles to the purification of a mixture. Goal: Complete data collection and analysis, lab assessment, lab report review

Write: review lab assessment in your drill space
Get out a grading pen Drill 3 9/17 (A Day) 9/18 (B Day) Outcome: I can complete solution stoichiometry problems. Goal: CW 5, CW 6

Purification of a Mixture Lab Assessment
Make sure to read exactly what the problem is asking you – don’t make the question harder than it is. Just because we used an equation to solve for moles in the lab doesn’t mean you have to do the same thing on the assessment. Watch your time – go for the low hanging fruit. Show your work – the AP exam does give partial credit. Box your final answers and write neatly.

The Nature of Aqueous Solutions
CW 5: Solutions The Nature of Aqueous Solutions A solution is a homogenous mixture, made by dissolving a solute in a solvent. There are three types of aqueous solutions, based on how well they conduct electricity. Strong electrolytes include soluble salts, strong acids, and strong bases. These compounds are completely ionized when added to water. There are seven strong acids to memorize: HCl, HBr, HI, HNO3, HClO4, H2SO4, and HClO3. Strong bases to memorize include group one hydroxides, the most common being NaOH and KOH. Weak electrolytes exhibit a small amount of ionization when added to water. These include weak acids and weak bases. Nonelectrolytes are substances that dissolve in water, but do not produce any ions. For example, when ethanol dissolves, entire C2H5OH molecules are dispersed in the water.

CW 5: Solutions Match each name below with the following microscopic pictures of that compound in aqueous solution. Barium nitrate Sodium chloride Potassium carbonate Magnesium sulfate MgSO4 NaCl K2CO3 Ba(NO3)2 Ba2+ NO3– Ba(NO3)2 Na+ Cl– NaCl K+ CO3–2 K2CO3 Mg2+ SO42– MgSO4

CW 5: Solutions Which picture best represents HNO3(aq)?
HNO3(aq)  H+(aq) + NO3–(aq) Best matches the NaCl beaker Why aren’t any of the pictures a good representation of HC2H3O2? HC2H3O2 is a weak acid: we should see some ionized H+ and C2H3O2– as well as some unionized HC2H3O2

CW 5: Solutions Molarity
The concentration of a solution is most often expressed as molarity (M), which is defined as moles of solute per volume of solution in liters. When the concentration of a solution is accurately known, either from its preparation or from experimental determination, it is called a standard solution. 𝑀=𝑚𝑜𝑙𝑎𝑟𝑖𝑡𝑦= 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒 𝑙𝑖𝑡𝑒𝑟𝑠 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 To save space in a laboratory, concentrated stock solutions are often prepared. Water is added to achieve the desired molarity, in a process is called dilution. When diluting a solution, remember that the moles of solute before dilution is equal to the moles of solute after dilution. A helpful equation when doing dilutions is below, where M is molarity and V is volume. 𝑀 1 𝑉 1 = 𝑀 2 𝑉 2

CW 5: Solutions Hint for #4 5.14 M C2H5OH
g Na 2.355 M PO43– and M K+ Question 7: Add mL of the 18 M solution to 1 L H2O Add g of the solid to 1 L H2O Add mL of the 16 M solution to 1 L H2O Add g of the solid to 1 L H2O 𝐷𝑒𝑛𝑠𝑖𝑡𝑦= 0.79 𝑔 𝑐𝑚 3 = 0.79 𝑔 𝑚𝐿

CW 5: Solutions A solution of ethanol (C2H5OH) in water is prepared by dissolving mL of ethanol (density = 0.79 g/cm3) in enough water to make mL of solution. What is the molarity of this solution? 𝐷𝑒𝑛𝑠𝑖𝑡𝑦= 0.79 𝑔 𝑐𝑚 3 = 0.79 𝑔 𝑚𝐿 75.0 𝑚𝐿 1 × 0.79 𝑔 1 𝑚𝐿 =59.25 𝑔 𝐶 2 𝐻 5 𝑂𝐻 59.25 𝑔 𝐶 2 𝐻 5 𝑂𝐻 1 × 1 𝑚𝑜𝑙 𝐶 2 𝐻 5 𝑂𝐻 𝑔 𝐶 2 𝐻 5 𝑂𝐻 × 𝐿 = 𝑀 𝐶 2 𝐻 5 𝑂𝐻 =5.14 𝑀 𝐶 2 𝐻 5 𝑂𝐻

CW 5: Solutions The sodium level in a patient’s blood was measured at 137 mmol/L. If 15.0 mL of blood is drawn from this patient, what mass of sodium would be present? 15.0 𝑚𝐿 1 × 1 𝐿 1000 𝑚𝐿 × 137 𝑚𝑚𝑜𝑙 1 𝐿 × 1 𝑚𝑜𝑙 1000 𝑚𝑚𝑜𝑙 × 𝑔 𝑁𝑎 1 𝑚𝑜𝑙 𝑁𝑎 = 𝑔 𝑁𝑎 = 𝑔 𝑁𝑎 137 𝑚𝑚𝑜𝑙 1 𝐿 × 1 𝑚𝑜𝑙 1000 𝑚𝑚𝑜𝑙 × 1 𝐿 1000 𝑚𝐿 × 15.0 𝑚𝐿 1 × 𝑔 𝑁𝑎 1 𝑚𝑜𝑙

K3PO4(aq)  3 mol K+(aq) + PO43–(aq)
CW 5: Solutions If g of potassium phosphate is dissolved in mL of solution, what is the concentration of each ion? 𝑔 𝐾 3 𝑃𝑂 𝑚𝐿 × 1 𝑚𝑜𝑙 𝐾 3 𝑃𝑂 𝑔 𝐾 3 𝑃𝑂 4 × 1000 𝑚𝐿 1 𝐿 = 𝑀 𝐾 3 𝑃𝑂 4 =2.355 𝑀 𝐾 3 𝑃𝑂 4 K3PO4(aq)  3 mol K+(aq) + PO43–(aq) =7.066 𝑀 𝐾 + =2.355 𝑀 𝑃𝑂 4 3−

CW 5: Solutions How would you prepare 1.00 L of a 0.50 M solution of each of the following? H2SO4 from concentrated (18 M) sulfuric acid solution NiCl2 from the salt NiCl2·6H2O 𝑀 1 =18 𝑀 𝑀 1 𝑉 1 = 𝑀 2 𝑉 2 Add mL of the 18 M solution to 1.00 L H2O 𝑉 1 = ? (18 𝑀)(𝑥)=(0.50 𝑀)(1.00 𝐿) 𝑀 2 =0.50 𝑀 𝑥= 𝐿 𝑉 2 =1.00 𝐿 0.50 𝑚𝑜𝑙 1.00 𝐿 × 𝑔 𝑁𝑖𝐶𝑙 2 ∙6 𝐻 2 𝑂 1 𝑚𝑜𝑙 𝑁𝑖𝐶𝑙 2 ∙6 𝐻 2 𝑂 = 𝑔 𝑁𝑖𝐶𝑙 2 ∙6 𝐻 2 𝑂 1.00 𝐿 Add g of NiCl2·6H2O(s) to 1.00 L H2O

Add 31.25 mL of the 16 M solution to 1.00 L H2O
CW 5: Solutions How would you prepare 1.00 L of a 0.50 M solution of each of the following? HNO3 from concentrated (16 M) reagent Sodium carbonate from the pure solid 𝑀 1 =16 𝑀 𝑀 1 𝑉 1 = 𝑀 2 𝑉 2 Add mL of the 16 M solution to 1.00 L H2O 𝑉 1 = ? (16 𝑀)(𝑥)=(0.50 𝑀)(1.00 𝐿) 𝑀 2 =0.50 𝑀 𝑥= 𝐿 𝑉 2 =1.00 𝐿 0.50 𝑚𝑜𝑙 1.00 𝐿 × 𝑔 𝑁𝑎 2 𝐶𝑂 3 1 𝑚𝑜𝑙 𝑁𝑎 2 𝐶𝑂 3 = 𝑔 𝑁𝑎 2 𝐶𝑂 𝐿 Add g of Na2CO3(s) to 1.00 L H2O

CW 6: Precipitation Reactions
Simple Rules for the Solubility of Salts in Water Most nitrate (NO3–) salts are soluble. Most salts containing the alkali metal (group 1) ions (Li+, Na+, K+, Cs+, Rb+) and the ammonium (NH4+) ion are soluble. Most chloride, bromide and iodide salts are soluble. Exceptions are salts containing the ions Ag+, Pb2+, and Hg2+. Most sulfate salts are soluble. Notable exceptions are BaSO4, PbSO4, HgSO4 and CaSO4. Most hydroxide salts are only slightly soluble. The important soluble hydroxides are NaOH and KOH. The hydroxides of barium, strontium and calcium are marginally soluble. Most sulfide (S2–), carbonate (CO32–), chromate (CrO42–), and phosphate (PO43–) salts are only slightly soluble.

The phrase slightly soluble used in the solubility rules above means that a very small amount of solid dissolves, but the solid appears to be insoluble to the naked eye. Thus, the terms insoluble and slightly soluble are often used interchangeably. Determine if the salt is soluble or insoluble in aqueous solution. Calcium carbonate Strontium hydroxide Calcium sulfate Potassium nitrate Iron (II) nitrate Lead (IV) carbonate Insoluble (s) (slightly) Soluble (s) Insoluble (s) Soluble (aq) Soluble (aq) Insoluble (s)

Double Displacement Reactions Another name often used for a precipitation reaction is a double replacement reaction. This is incorrect. Precipitation reactions occur because the formation of a solid on the product side drives the reaction to completion. Double replacement reactions also include those that are driven by the formation of a gas or water on the product side. There are only 3 types of reactions! Redox Reactions Single Replacement Synthesis Decomposition Combustion Precipitation Reactions “Double Replacement” with a solid formed Acid-Base Reactions “Double Replacement” with H2O formed

Consider the reaction between K2CrO4(aq) and Ba(NO3)2(aq). What ions are formed when K2CrO4 is added to water? K2CrO4(s)  2K+(aq) + CrO42–(aq) What ions are formed when Ba(NO3)2 is added to water? Ba(NO3)2(s)  Ba+2(aq) + 2 NO3–(aq) When these two solutions are mixed, what are the products of the reaction? Which is a solid? Write the net ionic equation for this reaction. 2 K+(aq) + CrO42–(aq) + Ba+2(aq) + 2 NO3–(aq)  BaCrO4(s) + 2 KNO3(aq) CrO42–(aq) + Ba+2(aq)  BaCrO4(s)

Consider the reaction between K2CrO4(aq) and Ba(NO3)2(aq). Draw an atomic representation of what the product mixture looks like in terms of ions and precipitates present. Include a key. K2CrO42–(aq) + Ba(NO3)2(aq)  BaCrO4(s) + 2 KNO3(aq) K+(aq) CrO42–(aq) Ba2+(aq) NO3–(aq)

Write the balanced formula and net ionic equations for the reaction that occurs when the contents of the two beakers are added together.

Write the balanced formula and net ionic equations for the reaction that occurs when the contents of the two beakers are added together. CuSO4(aq) + Na2S(aq)  CuS(s) + Na2SO4(aq) Cu2+(aq) + S2–(aq)  CuS(s)

Write the balanced formula and net ionic equations for the reaction that occurs when the contents of the two beakers are added together. CoCl2(aq) + 2 NaOH(aq)  Co(OH)2(s) + 2 NaCl(aq) Co2+(aq) + 2 OH–(aq)  Co(OH)2(s)

Write the balanced formula and net ionic equations for the reaction that occurs when the contents of the two beakers are added together. AgNO3(aq) + KI(aq)  AgI(s) + KNO3(aq) Ag+(aq) + I–(aq)  AgI(s)

A sample may contain any the following ions: Hg22+, Ba2+, Mn2+. No precipitate formed when NaCl(aq) was added to the solution. No precipitate formed when Na2SO4(aq) was added to the solution. A precipitate formed when NaOH(aq) was added to the solution. Which ion or ions are present in the sample solution? Hg22+ Ba2+ Mn2+ Cl–(aq) SO4– 2(aq) OH–(aq) Hg2Cl2(s) BaCl2(aq) MnCl2(aq) Hg2SO4(s) BaSO4(s) MnSO4(aq) Hg2OH(s) Ba(OH) 2(s) Mn(OH) 2(s) Only Mn2+ is present!

What volume of M Na3PO4 is required to precipitate all the lead (II) ions from mL of M Pb(NO3)2?

What volume of M Na3PO4 is required to precipitate all the lead (II) ions from mL of M Pb(NO3)2? 𝐿 1 × 𝑚𝑜𝑙 𝑃𝑏 (𝑁𝑂 3 ) 2 1 𝐿 = 𝑚𝑜𝑙 𝑃𝑏 (𝑁𝑂 3 ) 2 2 Na3PO4(aq) + 3 Pb(NO3)2(aq)  Pb3(PO4)2(s) + 6 NaNO3(aq) 𝑚𝑜𝑙 𝑃𝑏 (𝑁𝑂 3 ) 2 1 × 2 𝑚𝑜𝑙 𝑁𝑎 3 𝑃𝑂 4 3 𝑚𝑜𝑙 𝑃𝑏 (𝑁𝑂 3 ) 2 = 𝑚𝑜𝑙 𝑁𝑎 3 𝑃𝑂 4 𝑚𝑜𝑙 𝑁𝑎 3 𝑃𝑂 4 1 × 1 𝐿 𝑚𝑜𝑙 𝑁𝑎 3 𝑃𝑂 4 =0.250 𝐿

Purification of a Mixture Lab
Create a typed cover page with the lab title, your first and last name, your partners’ first and last name, due date, and class period. Put all your handwritten pages in order from your lab notebook. Should include: Introduction Procedure Materials (including MSDS warnings for chemicals) Data (collected by your group) Analysis (finding % NaHCO3 and atom economy) Complete the lab report review (one per group) as the conclusion

Complete CW 5 and CW 6 Purification of a Mixture Report Review (one per group), 9/20 (A Day) and 9/21 (B Day) Lab next class, bring goggles and closed toe shoes Summary 3 9/17 (A Day) 9/18 (B Day) Outcome: I can complete solution stoichiometry problems. Goal: CW 5, CW 6

CaCl2(aq) + 2AgNO3(aq)  2AgCl(s) + Ca(NO3)2(aq)
0.100 L of 0.25 M CaCl2 solution reacts with L of 0.30 M AgNO3. How many moles of solid form? Drill 4 9/20 (A Day) 9/21 (B Day) CaCl2(aq) + 2AgNO3(aq)  2AgCl(s) + Ca(NO3)2(aq) Outcome: I can determine water hardness through gravimetric analysis. Goal: CW 7 Hand In: Purification of a Mixture lab 0.100 𝐿 1 × 0.25 𝑚𝑜𝑙 𝐶𝑎𝐶𝑙 2 𝐿 × 2 𝑚𝑜𝑙 𝐴𝑔𝐶𝑙 1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑙 2 =0.05 𝑚𝑜𝑙 𝐴𝑔𝐶𝑙 0.100 𝐿 1 × 0.30 𝑚𝑜𝑙 𝐴𝑔𝑁𝑂 3 𝐿 × 2 𝑚𝑜𝑙 𝐴𝑔𝐶𝑙 2 𝑚𝑜𝑙 𝐴𝑔𝑁𝑂 3 =0.03 𝑚𝑜𝑙 𝐴𝑔𝐶𝑙 0.03 mol AgCl(s) can be formed, then the reaction runs out of AgNO3(aq).

Schedule This Class 9/20 9/21 Next Class 9/24 9/25 Class After 9/26
9/27 Complete CW 7 Complete Skills Lab Complete actual lab – need to complete pre-lab items on page 37 in the unit packet before this class period HW 4 due in OWL

CW 7: Gravimetric Analysis
Challenge Three samples of water will be analyzed for their quantities of water hardness through principles of metal ion precipitation and separation. The samples will then be ranked in order of increasing water hardness.

Background Hard water is commonly expressed as mg CaCO3/L, the amount of Ca2+ in the water identifies how hard the water is. This analyte can be isolated by mixing it with a solution of Na2CO3 to form the slightly soluble salt CaCO3. Ca2+(aq) + Na2CO3(aq)  CaCO3(s) + Na+(aq) When completing a gravimetric analysis, an important consideration is that the analyte (metal ion) is completely precipitated. This is accomplished by ensuring that the analyte acts as the limiting reactant in the precipitation reaction. Once the salt has precipitated, it can be collected through filtration. The impurities should be removed from the precipitate through washing and drying of the solid.

Go to the simulation and answer the following. Under the Table Salt tab, shake the salt shaker. Describe what happens to the solid table salt, NaCl. The solid NaCl begins to separate into its individual ions. Click Reset All. Shake the salt shaker until some of the particles are designated as Bound. How many sodium ions are designated as Dissolved? How many sodium ions are designated as Bound? Use the simulation to describe what bound means. About 180 dissolved sodium ions to make 8 bound sodium ions. Bound means that the ionic compound precipitated.

Go to the simulation and answer the following. Click the Slightly Soluble Salts tab. Using the pull-down menu, select Mercury (II) Bromide. Slowly shake the salt shaker until some of the ions are designated as Bound. How many shakes did it take? Compare how this mercury (II) bromide is different from table salt. It takes more shakes than the NaCl shaker, around 4 or 5. The mercury(II) bromide solution has significantly fewer dissolved ions, making the salt slightly soluble. This is different than NaCl, where lots of ions can be dissolved before any become bound. Shake a large amount of mercury (II) bromide into the container. How do the number of dissolved ions change as more mercury (II) bromide is added to the container? The number of dissolved ions does not change if more solid is added.

Go to the simulation and answer the following. Slowly drain some of the mixture out of the container and stop. Where do the dissolved ions go as the solution is drained? What else do you notice as the mixture is drained? If the mixture left the container through a long pipe as it was drained, how might problems arise inside the pipe? Dissolved ions may become bound along the sides of the pipe, forming solid crystals. This can clog pipes. How might the simulation look different if the mercury (II) bromide was created from two salts, such as mercury (II) nitrate and sodium bromide, rather than added directly? Some spectator ions floating around. Predict an appropriate method to collect the bound mercury (II) bromide. Collect the solid via filtration.

Watch the following video: After watching the video, describe what you believe to be hard water. Water that contains ions that form insoluble salts. Discuss the extent to which you agree/disagree with the idea that pure soap doesn’t have any chemicals in it (as the demonstrator states in the video). If there were no chemicals, how did the water form a precipitate? Ask the adults in your household if you have a softener system at home. If so, research online and describe how it works. If not, research online and describe a way that water can be softened. Ms. L has an ion exchange water softener system.

A reaction occurs between solutions of strontium bromide and silver nitrate. SrBr2(aq) + 2 AgNO3(aq) → Sr(NO3)2(aq) + 2 AgBr(s) If grams of the precipitate is formed, how many moles of strontium bromide were reacted? If mL of strontium bromide were reacted in Part a, what is the molarity of the strontium bromide solution that was used? 3.491 𝑔 𝐴𝑔𝐵𝑟 1 × 1 𝑚𝑜𝑙 𝐴𝑔𝐵𝑟 𝑔 𝐴𝑔𝐵𝑟 × 1 𝑚𝑜𝑙 𝑆𝑟𝐵𝑟 2 2 𝑚𝑜𝑙 𝐴𝑔𝐵𝑟 = 𝑚𝑜𝑙 𝑆𝑟𝐵𝑟 2 𝑚𝑜𝑙 𝑆𝑟𝐵𝑟 2 1 × 𝑚𝐿 × 1000 𝑚𝐿 1 𝐿 = 𝑀 𝑆𝑟𝐵𝑟 2 = 𝑀 𝑆𝑟𝐵𝑟 2

A reaction occurs between solutions of strontium bromide and silver nitrate. SrBr2(aq) + AgNO3(aq) → Sr(NO3)2(aq) + AgBr(s) In collecting the precipitate, why would it be inappropriate to heat the reacted mixture and evaporate off the water? The spectators ions would be left behind.

Ksp is a measure of solubility for slightly soluble salts. The larger the Ksp value, the more soluble the salt. Based on this data, which anion would you use to remove each of the following cations from a water sample: Mg2+, Ca2+, and Fe2+. Want to form the least soluble salt possible. Mg2+: Combine with OH– Ca2+: Combine with F– Fe2+: Combine with OH– Mg2+ Ion Ksp Value Ca2+ Ion Fe2+ Ion MgCO3 3.5x10–8 CaCO3 2.8x10–9 FeCO3 3.2x10–11 MgC2O4 1.0x10–8 CaC2O4 4.0x10–9 FeC2O4 3.2x10–7 MgF2 6.5x10–9 CaF2 4.0x10–11 FeF2 2.4x10–6 Mg(OH)2 1.8x10–11 Ca(OH)2 5.0x10–6 Fe(OH)2 8.0x10–16

Complete pre-laboratory work as outlined on the lab guidelines sheet. HW 4: Precipitation Reactions, due 9/26 (A) & 9/27 (B) through OWL Summary 4 9/20 (A Day) 9/21 (B Day) Outcome: I can determine water hardness through gravimetric analysis. Goal: CW 7

Drill: 9/24 (A Day) 9/25 (B Day)
Have a seat until Ms. L takes attendance, then immediately begin working in groups on the skills lab (Page 36). Drill: 9/24 (A Day) 9/25 (B Day) Outcome: I can determine water hardness through gravimetric analysis. Goal: Skills Lab, Excel Work

Skills Lab Follow the procedure as it is written, recording data in your lab notebook (you can call this the Gravimetric Analysis Skills Lab) Complete the analysis questions in your lab notebook while discussing with your groups – you can answer in bullets Once you are finished, you can start working on the Pre-Laboratory Work in your lab notebook, as outlined on the guidelines sheet

Using Excel to Find Standard Deviation
We are going to work on computers to complete some calculations using Excel. Grab a laptop and logon. Watch this video while you wait. Follow along with the directions. The final product is posted on LeffelLabs in unit 1 for you to review if you get stuck. Ask if you need help. Help each other. Finish this at home if you don’t here.

Pre-Laboratory Work Complete the following sections in your lab notebook before doing the experiment. Introduction Explain theory behind the lab, as well as any equations, graphs, or mathematical equations that will be required. Procedure Write a procedure for this experiment in your lab notebook. Some tips: Recall what you did during the Skills Lab. You will be given a water sample (already dissolved) to analyze. You must react the Ca2+ with Na2CO3 such that the calcium ion is the limiting reactant and is completely precipitated. Materials List all chemicals and equipment (including type and size). Look up the MSDS for the chemicals listed below and list major hazards (typically in the Hazards Identification section). Calcium chloride Sodium chloride Sodium carbonate, anhydrous

Summary: 9/24 (A Day) 9/25 (B Day)
Put away laptops. Complete pre-laboratory work as outlined on the lab guidelines sheet. Complete analysis questions BEFORE doing the prelab. HW 4: Precipitation Reactions, due 9/26 (A) & 9/27 (B) through OWL. Summary: 9/24 (A Day) 9/25 (B Day) Outcome: I can determine water hardness through gravimetric analysis. Goal: Skills Lab, Excel Work

Drill: 9/24 (A Day) 9/25 (B Day)
Prepare for lab! Drill: 9/24 (A Day) 9/25 (B Day) Outcome: I can determine water hardness through gravimetric analysis. Goal: Lab

Hard water samples are in the back. They have been concentrated x100. There are two stations with pipettes. Does it matter how much Na2CO3(s) you use? There are about 2.2 g CaCl2 (s) per 50 mL. How much Na2CO3(s) should you use? Dissolve the Na2CO3(s) in DI before mixing – we don’t want any solid left over. Do not put beakers on the analytical balance. Fold up your filter paper and write your names in pencil before massing. I will monitor your samples in the oven. What is the residue in your beakers? Will it impact your experiment?

Use the masses of sodium carbonate and calcium chloride to predict the mass of calcium carbonate that will form in your experiment. (HINT: limiting reactant) If one more gram of sodium carbonate was used, how would it affect the amount of calcium carbonate that you calculated would form? Which mass of the precipitate, the first or second, better represents the amount of dry precipitate collected? What mass of precipitate did you collect? Is the mass you measured close to the expected mass you calculated based on stoichiometry in Question 1? What may be the reason(s) for any differences? Would the mass of precipitate that you measured be larger or smaller if you did not wash the precipitate before drying it? If the precipitate was weighed without drying, would you believe that you had started with 2 grams of calcium chloride? Explain. Do you feel that the second weighing of your precipitate was dry? What experimental changes could be made to improve this portion of the procedure?

Post-Laboratory Work: Word Processed and Printed Analysis Data analysis: Access your class set of data using Perform all required calculations using a spreadsheet program such as Excel or Goggle Sheets. Ensure all displayed numbers show the correct sig figs. Copy and paste into the lab report such that it is readable when the page is printed. Complete the following data analysis: Calculate the mass of precipitate formed in grams for each water sample. Calculate the hardness, in mg/L as CaCO3 of each water sample. Calculate the average hardness, in mg/L as CaCO3 for each water sample. Calculate the standard deviation in the measurement of the hardness. Report your answer as average hardness ± standard deviation. Sample calculations: Show one typed worked example for each major required calculation. You do not need to show sample calculations for finding standard deviation. Include the unrounded answer and the answers with correct sig figs. It is recommended that you use the equation editor feature.

Post-Laboratory Work: Word Processed and Printed Conclusion Include the following in narrative form: Discussion of what you did, including the purpose/ goal of the experiment. Describe any changes to the procedure from what you wrote in your lab notebook. Describe major findings and make claims with supporting evidence from the lab. Report calculated numbers, averages, and standard deviations as required. Many water softeners rely on precipitation softening, or as ion exchange. Based on the reactants used (Na2CO3 and CaCl2), what ions would remain in the softened water? What could be some negative aspects of consuming these ions? Comment on error, both inherit error (due to precision of equipment) and experimental/ human error. Remember that “the lab would have been better if we did it correctly” or “human errors were made” are not discussion of error. Errors should be clearly described along with how they impacted the calculations in the data analysis. Describe refinements or future experiments. What can we study next and why? Once you have completed your conclusion, print and highlight the answers to the above questions. Complete all sections as described. Create a cover sheet for the lab that includes your name, your partner(s) name(s), your class period, due date, and the title of the experiment. Staple all sections (hand written carbon copies and printed papers) in order and hand in during class.

Gravimetric Analysis Lab Report, 10/2 (A Day) and 10/3 (B Day) HW 5: Acid-base Reactions, due 10/4 (A) & 10/5 (B) through OWL Summary: 9/24 (A Day) 9/25 (B Day) Outcome: I can determine water hardness through gravimetric analysis. Goal: Lab

Drill 5: 9/28 (A Day) 10/1 (B Day)
A 11.7 g sample of an aqueous solution of nitric acid contains an unknown amount of the acid. If mL of 1.06 M sodium hydroxide are required to neutralize the nitric acid, what is the percent by mass of nitric acid in the mixture? Drill 5: 9/28 (A Day) 10/1 (B Day) Outcome: I can find the amount of citric acid in a sample of juice. Goal: CW 8, CW 9

Drill A 11.7 g sample of an aqueous solution of nitric acid contains an unknown amount of the acid. If 28.7 mL of 1.06 M sodium hydroxide are required to neutralize the nitric acid, what is the percent by mass of nitric acid in the mixture?

Acid Naming Rules –ide: hydro_____ic acid HCl H2S –ate: _____ic acid
HClO4 H2SO4 –ite: _____ous acid HClO2 H2SO3

Gravimetric Analysis Lab
Let’s get our class data together. Lab Assessment

CW 8: Acid-Base Reactions
There are several definitions of acidity and basicity. We will consider the Bronsted-Lowry definition, which states that acids are proton (H+ ion) donors, and bases are proton (H+ ion) acceptors. Like precipitation reactions, when an acid or base is dissolved in water, the ions separate, and a solution is formed. We describe the concentration of an acid or a base by molarity. When an acid and base are mixed, the ions react to form products. The products are typically a soluble salt and water, thus acid-base reactions are also known as neutralization reaction.

Strong vs. Weak Another important consideration is if the acid or base is strong or weak. A strong acid or base is one that ionizes completely when added to water. There are seven strong acids to memorize: HCl, HBr, HI, HNO3, HClO4, H2SO4, and HClO3. Strong bases to memorize include group one hydroxides, the most common being NaOH and KOH. A weak acid or base does not ionize completely, usually only around 5% (or fewer) of the particles are ionized. This is important because it limits the amount of acid or base that is available to react. When working with chemical reactions in solution, it is important to consider each ion and how it may react. For example, consider the reaction of acetic acid with potassium hydroxide. KOH(aq) + HC2H3O2(aq)  KC2H3O2(aq) + H2O(l) The hydroxide ion is such a strong base that it will strip the H+ from the HC2H3O2. For stoichiometry purposes, we can assume that hydroxide always reacts completely with any weak acid it encounters. We can write the net ionic equation as below. OH–(aq) + HC2H3O2(aq)  C2H3O2–(aq) + H2O(l)

Write the balanced formula and net ionic equations for each of the following. HClO4 (aq) + Mg(OH)2 (s)  HCN(aq) + NaOH(aq)  2+ – + – 2 Mg ( ) ClO4 + 2 H OH (aq) (l) 2 2 H+ (aq) + 2 OH– (aq)  2 H2O(l) + – + – Na CN + H OH (aq) (l) H+ (aq) + OH– (aq)  H2O(l)

What acid and base would react in aqueous solution to form the following salts? Potassium perchlorate Calcium iodide + – K ClO4 KOH HClO4 2+ – Ca I 2 Ca(OH)2 Hl

What volume of each of the following bases will react completely with mL of M HCl? 0.100 M NaOH M Sr(OH)2 𝐿 𝐻𝐶𝑙 1 × 𝑚𝑜𝑙 𝐻𝐶𝑙 1 𝐿 𝐻𝐶𝑙 × 1 𝑚𝑜𝑙 𝑁𝑎𝑂𝐻 1 𝑚𝑜𝑙 𝐻𝐶𝑙 × 1 𝐿 𝑚𝑜𝑙 𝑁𝑎𝑂𝐻 = 𝐿 𝐿 𝐻𝐶𝑙 1 × 𝑚𝑜𝑙 𝐻𝐶𝑙 1 𝐿 𝐻𝐶𝑙 × 1 𝑚𝑜𝑙 𝑆𝑟 (𝑂𝐻) 2 2 𝑚𝑜𝑙 𝐻𝐶𝑙 × 1 𝐿 𝑚𝑜𝑙 𝑆𝑟 (𝑂𝐻) 2 = 𝐿

Acid-Base Titrations Volumetric analysis is a technique that is used to determine the amount of a substance by completing a titration. A titration involves reacting a known volume solution whose concentration is known with a known volume of another solution whose concentration is unknown. The point where enough titrant has been added to react completely with the analyte is called the equivalence point. This point is often marked with an indicator, a substance that changes color at or near the equivalence point. The point where the color really changes is called the end point. The goal is to choose an indicator such that the end point (where the indicator changes color) occurs at the equivalence point (where enough titrant has been added to react completely with the analyte).

Hydrochloric acid (75.0 mL of M) is added to mL of M Ba(OH)2 solution. What is the concentration of the excess H+ and OH– ions left in solution? What is the pH of the solution? 2 HCl (aq) + Ba(OH)2 (aq)  BaCl2 (aq) + 2 H2O (l) HCl L 0.250 M = mol 𝑚𝑜𝑙 𝐻𝐶𝑙 1 × 1 𝑚𝑜𝑙 𝐵𝑎 (𝑂𝐻) 2 2 𝑚𝑜𝑙 𝐻𝐶𝑙 = 𝑚𝑜𝑙 𝐵𝑎 (𝑂𝐻) 2 Limiting! Ba(OH)2 L M = mol mol – mol = mol leftover 𝑚𝑜𝑙 𝐵𝑎 (𝑂𝐻) 2 1 × 2 𝑚𝑜𝑙 𝑂𝐻 1 𝑚𝑜𝑙 𝐵𝑎 (𝑂𝐻) 2 × 𝐿 = 𝑀 𝑂𝐻

Hydrochloric acid (75.0 mL of M) is added to mL of M Ba(OH)2 solution. What is the concentration of the excess H+ and OH– ions left in solution? What is the pH of the solution? 𝑝𝑂𝐻=−log⁡[𝑂𝐻] 𝑀 𝑂𝐻 𝑝𝐻=−log⁡[𝐻] 𝑝𝐻+𝑝𝑂𝐻=14 𝑝𝑂𝐻=−log⁡[𝑂𝐻] 𝑝𝐻+𝑝𝑂𝐻=14 =−log⁡[0.0200] 𝑝𝐻+1.70=14 =1.70 𝑝𝐻=12.30

The concentration of sodium hydroxide solution was determined by titration of potassium hydrogen phthalate (KHP). KHP is an acid with one acidic hydrogen and a molar mass of g/mol. In the titration, mL of the sodium hydroxide solution was required to react with g KHP. KHC8H4O4 + NaOH  KNaC8H4O4 + H2O 𝑔 𝐾𝐻𝑃 1 × 1 𝑚𝑜𝑙 𝐾𝐻𝑃 𝑔 𝐾𝐻𝑃 × 1 𝑚𝑜𝑙 𝑁𝑎𝑂𝐻 1 𝑚𝑜𝑙 𝐾𝐻𝑃 × 𝐿 𝑁𝑎𝑂𝐻 = 𝑀 𝑁𝑎𝑂𝐻

CW 9: How Much Acid is in Drinks?
Challenge One of the major goals of industry chemists is to test products and foods through titrations. Examples include pharmacists who compound formulas to match a patient’s body weight and medical condition or neutralizing free fatty acids in oil before refining it into biodiesel. You will act as a food chemist with the FDA to test the amount of citric acid present in juices.

Using the structural formula of citric acid, determine the molecular formula of citric acid and calculate its molar mass (g/mole). C6H8O7 g/mol Acidic protons! Acidic protons: hydrogen atoms chemically bound to highly electronegative elements (F, O, N) Easily interact with H2O due to large polarity of bonds, forms H3O+

A 10.0-mL sample of pineapple juice was titrated with M sodium hydroxide solution. The average volume of NaOH required to reach the endpoint was 12.8 mL. Calculate the number of moles of sodium hydroxide required to reach the endpoint. Using the mole ratio for the neutralization reaction shown below, determine the number of moles of citric acid in 10.0 mL of pineapple juice. 𝐿 𝑁𝑎𝑂𝐻 1 × 𝑚𝑜𝑙 𝑁𝑎𝑂𝐻 1 𝐿 𝑁𝑎𝑂𝐻 = 𝑚𝑜𝑙 𝑁𝑎𝑂𝐻 𝑚𝑜𝑙 𝑁𝑎𝑂𝐻 1 × 1 𝑚𝑜𝑙 𝐶 6 𝐻 7 𝑂 8 3 𝑚𝑜𝑙 𝑁𝑎𝑂𝐻 =4.27× 10 −4 𝑚𝑜𝑙 𝐶 6 𝐻 7 𝑂 8

A 10.0-mL sample of pineapple juice was titrated with M sodium hydroxide solution. The average volume of NaOH required to reach the endpoint was 12.8 mL. Multiply the number of moles of citric acid by its molar mass to calculate the mass of citric acid in 10.0 mL of the juice. The concentration of acid in juices is usually expressed in grams of acid per 100 mL of juice. What is the concentration of citric acid in pineapple juice? 4.27× 10 −4 𝑚𝑜𝑙 𝐶 6 𝐻 7 𝑂 8 1 × 𝑔 𝐶 6 𝐻 7 𝑂 8 1 𝑚𝑜𝑙 𝐶 6 𝐻 7 𝑂 8 = 𝑔 𝑔×10=0.820 𝑔 𝑖𝑛 100 𝑚𝐿

The titration curves for hydrochloric acid and acetic acid with sodium hydroxide are shown below. Distinguish between the strong and weak acid in terms of the initial pH, the pH at the equivalence point, and the overall shape of the titration curve. Equivalence Point: mol H+ = mol OH– Strong Acid + Strong Base Weak Acid + Strong Base Initial pH 2 – 3 3 – 4 e.p. 7 9 Shape Angry snake Less Angry Snake

Summary 5: 9/28 (A Day) 10/1 (B Day)
Gravimetric Analysis Lab Report, 10/2 (A Day) and 10/3 (B Day) HW 5: Acid-base Reactions, due 10/4 (A) & 10/5 (B) through OWL Summary 5: 9/28 (A Day) 10/1 (B Day) Outcome: I can find the amount of citric acid in a sample of juice. Goal: CW 8, CW 9

Drill 6: 10/2 (A Day) 10/3 (B Day)
An aqueous solution of nitric acid is standardized by titration with a 14.4 mL of M solution of calcium hydroxide. If mL of nitric acid was used, what is its molarity? Drill 6: 10/2 (A Day) 10/3 (B Day) Outcome: I can find the amount of citric acid in a sample of juice. Goal: CW 9 Hand In: Gravimetric Analysis Report

Skills Lab Follow the procedure as it is written, recording data on a sheet of paper. Complete the analysis questions while discussing with your groups – you can answer in bullets Once you are finished, you can start working on the Pre-Laboratory Work in your lab notebook, as outlined on the guidelines sheet

Procedure Label three test tubes B, P and T (bromthymol blue, phenolphthalein, and thymol blue). Using a 10-mL graduated cylinder, measure and pour 2.0 mL of 0.1 M acetic acid into each test tube. Rinse the graduated cylinder with distilled water and dry the cylinder. Add 1−2 drops of each indicator to the appropriate test tube. Record the initial indicator color in each test tube. Add 10 drops (1 mL) of 0.1 M NaOH to the acetic acid solution in test tube B. Record the indicator color. Repeat two more times, for a total of 30 drops (3 mL). Note the approximate volume of NaOH that has been added when the indicator color changes. Repeat steps 4 and 5 for test tubes P and T. Rinse the test tubes with distilled water and return all materials.

Choose a suitable indicator for determining the endpoint in the neutralization of a weak acid with a strong base. Explain your reasoning based on Class Discussion Question 3. Would you choose a different indicator to titrate a strong acid such as HCl? Why or why not? A standard solution is often used in titrations. Explain what this means, identify the titrant, and obtain the known molarity from your instructor. Review the setup shown in the background section. The buret should be cleaned and rinsed with the titrant before beginning the titration. Explain why this is necessary. Do you need to know the precise volume of beverage that will be titrated? Explain. Why is a buret used to add and measure the volume of titrant? During the experiment, you should occasionally rinse the sides of the reaction vessel using distilled water. Explain why you don’t need to know the volume of rinse water.

Examine a buret and explain how to read the volume of titrant in the buret. To what precision should you measure? What data must be measured to obtain a titration curve for an acidic beverage? What is an appropriate volume interval for obtaining this data during the titration? Explain. Write a detailed, step-by-step procedure for titrating a beverage to determine the concentration of weak acid, if present. Include the reagents needed, the glassware and equipment that will be used, and the appropriate measurements and observations that must be made.

Pre-Laboratory Work Introduction: Explain theory behind the lab, as well as any equations, graphs, or mathematical equations that will be required. Procedure: Write a procedure for this experiment in your lab notebook. Some tips: Consider what your group discussed during the skills lab. You will be given one of the fruit juices described in the background section. Plan to use about 15 mL of the juice. You will conduct two trials using two samples of juice. You will use a probe to monitor the pH as the NaOH is added. Don’t worry about including details for how these work, you will be given directions about how to use the probes. You will add some NaOH, the record the pH and the total volume of NaOH added. Materials: List all chemicals and equipment (including type and size). Look up the MSDS for the chemicals listed below and list major hazards (typically in the Hazards Identification section). Sodium hydroxide Phenolphthalein

HW 5: Acid-base Reactions, due 10/4 (A) & 10/5 (B) through OWL Complete prelab Summary 6: 10/2 (A Day) 10/3 (B Day) Outcome: I can find the amount of citric acid in a sample of juice. Goal: CW 9 Hand In: Gravimetric Analysis Report

Drill: 10/4 (A Day) 10/5 (B Day)
Get ready for lab Drill: 10/4 (A Day) 10/5 (B Day) Outcome: I can find the amount of citric acid in a sample of juice. Goal: CW 9

Concentration NaOH: M (refill burettes) You need to know the exact volume of juice added – use a graduated cylinder Plan on using mL of juice per trial and 2 drops of indicator Initially, add the base 0.50 mL to mL at a time. As you approach the equivalence point, slow down and add smaller volumes You must determine the volume of NaOH added to reach the equivalence point – see procedure Save your file where you can access it later Keep the stir plate on the lowest setting and don’t let the stir bar hit the probe Indicator molecule shape changes with pH, changes how light interacts with molecule, which changes color Phenolphthalein

How to Save Data from Logger Pro Method 1 Copy and paste the data: 1. Select the data in the Logger Pro table. 2. Choose Copy from the Edit menu. 3. Switch to Excel and paste the data into the Excel sheet. Method 2 Export the data from Logger Pro 3 to a file that can be opened in a spreadsheet program: 1. Choose Export As from the File menu. 2. Select CSV as the export file type. 3. Name and save the file. This file can be opened in any spreadsheet program, such as Microsoft Excel, OpenOffice, or Google Docs.

Post-Laboratory Work: Word Processed and Printed Analysis: Access your class set of data using Perform all required calculations using a spreadsheet program such as Excel or Goggle Sheets. Ensure all displayed numbers show the correct sig figs. Copy and paste into the lab report such that it is readable when the page is printed. Complete the following data analysis: Calculate the grams of acid per 100 mL for each trial. Calculate the average grams of acid per 100 mL for all trials. Calculate the standard deviation in the measurement of the acid. Report your answer as average g/100 mL ± standard deviation. Sample calculations: Show one typed worked example for each major required calculation. You do not need to show sample calculations for finding standard deviation. Include the unrounded answer and the answers with correct sig figs. It is recommended that you use the equation editor feature.

Post-Laboratory Work: Word Processed and Printed Conclusion: Include the following in narrative form: Discussion of what you did, including the purpose/ goal of the experiment. Describe any changes to the procedure from what you wrote in your lab notebook. Describe major findings and make claims with supporting evidence from the lab. Report calculated numbers, averages, and standard deviations as required. Comment on error, both inherit error (due to precision of equipment) and experimental/ human error. Remember that “the lab would have been better if we did it correctly” or “human errors were made” are not discussion of error. Errors should be clearly described along with how they impacted the calculations in the data analysis. Describe refinements or future experiments. What can we study next and why? Once you have completed your conclusion, print and highlight the answers to the above questions. Complete all sections as described. Create a cover sheet for the lab that includes your name, your partner(s) name(s), your class period, due date, and the title of the experiment. Staple all sections (hand written carbon copies and printed papers) in order and hand in during class.

HW 6: Redox Reactions, due 10/10 (A) & 10/11 (B) through OWL Acid in Drinks Lab Report, 10/18 (A Day) and 10/19 (B Day) Summary: 10/4 (A Day) 10/5 (B Day) Outcome: I can find the amount of citric acid in a sample of juice. Goal: CW 9

Drill 7: 10/8 (A Day) 10/9 (B Day)
How many mL of 0.10 M HCl are required to react completely with mL of 0.25 M NaOH? Drill 7: 10/8 (A Day) 10/9 (B Day) Outcome: I can balance oxidation reduction reactions. Goal: CW 10

CW 10: Oxidation-Reduction Reactions
We have seen that many important substances are ionic. Sodium chloride, for example, can be formed by the reaction of sodium metal with chlorine gas. 2 Na(s) + Cl(g)  2 NaCl(s) In this reaction, the sodium loses an electron, while the chlorine gains an electron, forming Na+ and Cl– ions. Reactions like this, where one or more electrons are transferred, are called oxidation- reduction reactions or redox reactions.

Photosynthesis in plants, reactions used for energy production, and the oxidation of sugars, fats, and proteins in the human body are all redox reactions. Combustion reactions, which provide most of the energy to power our civilization, also involve oxidation and reduction. CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(g) Even though none of the reactants or products are ionic, the reaction still involves a transfer of electrons from carbon to oxygen. To explain this, we must introduce the concept of oxidation states.

Oxidation States Oxidation states are a method to keep track of electrons in redox reactions, especially when covalent substances are involved. Recall that electrons are shared in covalent bonds. The oxidation states of such atoms are determined by assigning electrons to atoms. For a covalent bond between two identical atoms, the electrons are spilt equally. If the two atoms are not identical, the shared electrons are assigned to the atom that has a stronger attraction for electrons. The following rules should be used to determine oxidation states.

Rules to Determine Oxidation States The oxidation state of… Summary Examples An atom in elemental form is zero Element = 0 Na(s), O2(g), O3(g), Hg(l) A monatomic ion is the same as its charge Monatomic ion = charge of ion Na+, Cl– Fluorine is –1 in its compounds Fluorine = –1 HF, PF3 Oxygen is usually –2 in its compounds (exception: peroxides, containing O22–, in which oxygen is –1) Oxygen = –2 H2O, CO2 Hydrogen is +1 in its covalent compounds Hydrogen = +1 H2O, HCl, NH3 Remember that… The sum of oxidation states is zero for an electrically neutral compound For an ion, the sum of the oxidation states must equal the charge of the ion.

Identify the oxidation state of each element in the following equations. 2 Na(s) + Cl2(g)  2 NaCl(s) CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(g) 2 PbS(s) + 3O2(g)  2 PbO(s) + 2SO2(g) PbO(s) + CO(g) Pb(s) + CO2(g) +1 –1 –4 +1 +4 –2 +1 –2 +2 –2 +2 –2 +4 –2 +2 –2 +2 –2 +4 –2

In a redox reaction, oxidation must always be paired with reduction. Oxidation is an increase in oxidation state, caused by the loss of electrons. Reduction is a decrease in oxidation state, due to a gain of electrons. The oxidizing agent is the electron acceptor, while the reducing agent is the electron donor.

Identify which compound is oxidized, which compound is reduced, as well as the oxidizing agent and the reducing agent. 2 Na(s) + Cl2(g)  2 NaCl(s) Oxidized (reducing agent): Reduced (oxidizing agent): CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(g) +1 –1 Na Cl2 –4 +1 +4 –2 +1 –2 CH4 O2

Identify which compound is oxidized, which compound is reduced, as well as the oxidizing agent and the reducing agent. 2 PbS(s) + 3O2(g)  2 PbO(s) + 2SO2(g) Oxidized (reducing agent): Reduced (oxidizing agent): PbO(s) + CO(g) Pb(s) + CO2(g) +2 –2 +2 –2 +4 –2 PbS O2 +2 –2 +2 –2 +4 –2 CO PbO

Balancing Oxidation-Reduction Reactions Balancing redox reactions involves more than simply being atom balanced, the reaction must be balanced with respect to electrons transferred as well. This is most easily accomplished through the half reaction method.

Steps to Balance: Neutral and Acidic Conditions Spilt the reaction into two half reactions. Balance elements in the equation other than O and H. Balance the oxygen atoms by adding the appropriate number of water (H2O) molecules to the opposite side of the equation. Balance the hydrogen atoms (including those added in step 2 to balance the oxygen atom) by adding H+ ions to the opposite side of the equation. Add up the charges on each side. Make them equal by adding enough electrons (e–) to the more positive side. (Rule of thumb: e– and H+ are almost always on the same side.) The e– on each side must be made equal; if they are not equal, they must be multiplied by appropriate integers (the lowest common multiple) to be made the same. The half-equations are added together, canceling out the electrons to form one balanced equation. Common terms should also be canceled out.

Cr2O72–(aq) + HNO2(aq)  Cr3+(aq) + NO3–(aq) +6 –2 +1 +3 –2 +3 +5 –2 reduction oxidation 6e– + 14 H+ + Cr2O72–  Cr3+ 2 + 7 H2O +14 –2 +12 +6 3( ) H2O + HNO2  NO3– + 3 H+ + 2e– +2

5 4 6e– + 14H+ + Cr2O72–  2Cr3+ + 7H2O 3H2O + 3HNO2  6e– + 3NO3– + 9H+ 5H+ + Cr2O72– + 3HNO2  2Cr3+ + 4H2O + 3NO3–

Steps to Balance: Basic Conditions Complete steps 1 to 6, as you would for neutral or acidic conditions. Add OH– ions to each side to balance out H+ ions and form water.

Ag(s) + Zn2+(aq)  Ag2O(aq) + Zn(s) +2 +1 –2 reduction oxidation 2OH– + H2O + 2 Ag  Ag2O + 2 H+ + 2e– + 2OH– +2 2e– + Zn2+  Zn +2

2e– + Zn2+  Zn 1 2OH– + H2O + 2Ag  Ag2O + 2e– + 2H2O 2OH– + 2Ag + Zn2+  Ag2O + H2O + Zn

Balance the following oxidation-reduction reactions using the half reaction method. Label each half reaction as oxidation or reduction. Zn(s) + H+(aq)  Zn2+(aq) + H2(g) in acidic solution I–(aq) + NO2–(aq)  I2(s) + NO(g) in acidic solution Oxidation: Zn(s)  Zn2+(aq) + 2e– Reduction: 2H+(aq) + 2e–  H2(g) Zn(s) + 2H+(aq)  Zn2+(aq) + H2(g) Oxidation: 2I–(aq)  I2(s) + 2e– Reduction: 2[2H+(aq) + NO2–(aq) + 1e–  NO(g) + H2O(l)] 2I–(aq) + 4H+(aq) + 2NO2–(aq)  2NO(g) + 2H2O(g) + I2(s)

Balance the following oxidation-reduction reactions using the half reaction method. Label each half reaction as oxidation or reduction. MnO4–(aq) + Cl–(aq)  Mn2+(aq) + Cl2(g) in neutral solution MnO4–(aq) + Cl–(aq)  Mn2+(aq) + Cl2(g) in basic solution Oxidation: 5[2Cl–(aq)  Cl2(g) + 2e–] Reduction: 2[8H+(aq) + 5e– + MnO4–(aq) Mn2+(aq) + 4H2O(l)] 16H+(aq) + 2MnO4–(aq) + 10 Cl–(aq)  2Mn2+(aq) + 8H2O(l) + 5Cl2(g) Oxidation: 5[2Cl–(aq)  Cl2(g) + 2e–] Reduction: 2[8H+(aq) + 8OH –(aq) + 5e– + MnO4–(aq) Mn2+(aq) + 4H2O(l) + 8OH –(aq)] 8H2O(l) + 2MnO4–(aq) + 10 Cl–(aq)  2Mn2+(aq) + 5Cl2(g) + 16OH –(aq)

Balance the following oxidation-reduction reactions using the half reaction method. Label each half reaction as oxidation or reduction. Br2(l)  BrO3–(aq) + Br–(aq) in basic solution Oxidation: 6H2O(l) + 12OH–(aq) + Br2(l)  BrO3–(aq) + 12H+(aq) + 12e– + 12OH– Reduction: 5[2e– + Br2(l)  2Br–] Zn(s) + 2H+(aq)  Zn2+(aq) + H2(g)

Each of the following results in a chemical reaction. Which of these is not a redox reaction? In all cases, determine the oxidation states for each of the elements. Methane gas is burned in air. A piece of silver metal is placed in an aqueous solution of copper (II) nitrate. Aqueous solutions of lead (II) nitrate and sodium iodide are mixed together. CH4(g) + O2(g)  CO2(g) + H2O(g) –4 +1 +4 –2 +1 –2 2Ag(s) + Cu(NO3)2(aq)  2AgNO3(aq) + Cu(s) +2 +5 +1 +5 –2 –2 Pb(NO3)2(aq) + 2NaI(aq)  2NaNO3(aq) + PbI2(s) +2 +5 –2 +1 –1 +1 +5 –2 +2 –1

What does it mean for a substance to be oxidized? The term oxidation originally came from substances reacting with oxygen gas. Explain why a substance which reacts with oxygen gas will always be oxidized. O2 has an oxidation state of 0 If it reacts and forms any compound, the oxidation state will no longer be 0 If an element is a reactant or product in a chemical reaction, the reaction must be an oxidation-reduction reaction. Why is this true? Any pure element has an oxidation state of 0 To form or break down an element, electrons must be transferred The equation Ag+ + Cu  Cu2+ + Ag has equal numbers of each type of element on each side of the equation. This equation, however, is not balanced. Why is this equation not balanced? Balance the equation. This equation is atom balanced, not electron balanced

If mL of M potassium dichromate solution is required to titrate 30.0 g of blood plasma, determine the mass percent of alcohol in the blood. Cr2O72–(aq) + C2H5OH(aq)  Cr3+(aq) + CO2(g) +6 –2 –2 +1 –2 +1 +3 +4 –2 reduction oxidation 2( ) 6e– + 14 H+ + Cr2O72–  Cr3+ 2 + 7 H2O +14 –2 +6 +12 +6 3H2O + C2H5OH CO2 2 + 12 H+ + 12e– +12 +12

If mL of M potassium dichromate solution is required to titrate 30.0 g of blood plasma, determine the mass percent of alcohol in the blood. 12e– + 28H+ + 2Cr2O72–  4Cr H2O 3H2O + C2H5OH  2CO2 + 12H+ + 12e– C2H5OH + 16H+ + 2Cr2O72–  2CO2 + 4Cr H2O 31.05 𝑚𝐿 1 × 𝑚𝑜𝑙 𝐶𝑟 2 𝑂 7 2− 𝑚𝐿 × 1 𝑚𝑜𝑙 𝐶 2 𝐻 5 𝑂𝐻 2 𝑚𝑜𝑙 𝐶𝑟 2 𝑂 7 2− × 𝑔 𝐶 2 𝐻 5 𝑂𝐻 1 𝑚𝑜𝑙 𝐶 2 𝐻 5 𝑂𝐻 = 𝑔 𝐶 2 𝐻 5 𝑂𝐻 𝑔 𝐶 2 𝐻 5 𝑂𝐻 30.0 𝑔 𝑏𝑙𝑜𝑜𝑑 ×100%=0.143% 𝐶 2 𝐻 5 𝑂𝐻

HW 6: Redox Reactions, due 10/10 (A) & 10/11 (B) through OWL Acid in Drinks Lab Report, 10/18 (A Day) and 10/19 (B Day) Determining Percent H2O2 Lab Report, 10/29 (A Day) and 10/30 (B Day) Summary 7: 10/8 (A Day) 10/9 (B Day) Outcome: I can balance oxidation reduction reactions. Goal: CW 10

Agenda 10/10 (A ) and 10/11 (B) Continue working on CW 10
Complete CW 11 questions 1 to 3 Complete prelab as outlined in CW 11 Lab Assessment Redos

Drill: 10/12 (A Day) 10/15 (B Day)
Prepare for Lab Drill: 10/12 (A Day) 10/15 (B Day) Outcome: I can calculate the percent H2O2 in a drugstore peroxide solution by completing a redox titration. Goal: CW 10

CW 11: Determining Percent H2O2
Challenge Hydrogen peroxide is regarded as an “environmentally friendly” alternative to chlorine for water purification and treatment. Because hydrogen peroxide decomposes in the presence of heat, light, or other catalysts, the quality of a hydrogen peroxide solution must be checked regularly to ensure its effectiveness. The concentration of hydrogen peroxide can be analyzed by redox titration with potassium permanganate.

Background Titration involves the use of volume measurements to analyze the concentration of an unknown. The most common types of titrations are acid–base titrations, in which a solution of an acid is analyzed by measuring the amount of a standard base solution required to neutralize a known amount of the acid. A similar principle applies to redox titrations. If a solution contains a substance that can be oxidized, then the concentration of that substance can be analyzed by titrating it with a standard solution of a strong oxidizing agent. The equation for an oxidation–reduction reaction can be balanced by assuming that it occurs via two separate half-reactions. In this experiment, potassium permanganate will be used as the titrant to analyze the concentration of hydrogen peroxide in a commercial antiseptic solution. The permanganate ion acts as an oxidizing agent—it causes the oxidation of hydrogen peroxide.

Background The oxidation half-reaction shows that two electrons are lost per molecule of hydrogen peroxide that is oxidized to oxygen gas (Equation 1). The permanganate ion, in turn, is reduced from the +7 oxidation state in MnO4– to the +2 oxidation state in Mn2+. The reduction half-reaction shows a gain of five electrons (Equation 2). H2O2(aq)  O2(g) + 2H+ +2e– Equation 1 MnO4–(aq) + 8H+(aq) + 5e–  Mn2+(aq) + 4H2O(l) Equation 2

Combine the oxidation and reduction half-reactions for hydrogen peroxide and permanganate ion, respectively, and write the balanced chemical equation for the overall reaction between H2O2 and MnO4– in acid solution (HINT: The number of electrons transferred must cancel out). 2MnO4–(aq) + 6H+(aq) + 5H2O2(aq)  5O2(g) + 2Mn2+(aq) + 8H2O(l) 5( ) H2O2(aq)  O2(g) + 2H+ +2e– 5H2O2(aq)  5O2(g) + 10H+ +10e– MnO4–(aq) + 8H+(aq) + 5e–  Mn2+(aq) + 4H2O(l) 2MnO4–(aq) + 16H+(aq) + 10e–  2Mn2+(aq) + 8H2O(l) 2MnO4–(aq) + 6H+(aq) + 5H2O2(aq)  5O2(g) + 2Mn2+(aq) + 8H2O(l) 2( )

What is the mole ratio of hydrogen peroxide to permanganate ion in the balanced chemical equation determined in Question #1? How many moles of hydrogen peroxide will be oxidized by moles of potassium permanganate in acidic solution? 5 𝑚𝑜𝑙 𝐻 2 𝑂 2 2 𝑚𝑜𝑙 𝐾𝑀𝑛𝑂 4 𝑚𝑜𝑙 𝐾𝑀𝑛𝑂 4 1 × 5 𝑚𝑜𝑙 𝐻 2 𝑂 2 2 𝑚𝑜𝑙 𝐾𝑀𝑛𝑂 4 = 𝑚𝑜𝑙 𝐻 2 𝑂 2

Review the procedure. Is it necessary to know the exact volume of: (a) Hydrogen peroxide solution added to the flask in step 4? (b) Water added to the flask in step 4? Why or why not? Yes: we are trying to find a mass percent of H2O2, so we need to known the total mass of solution we use so we can divide to get percent. No: this does not change the moles of H2O2 available to react.

Demo use of micropipettes Sulfuric acid stations Hand stirring Waste beaker Clean Up: Rinse out glassware with tap water twice, then distilled water Refill burettes (carefully) Organize all items into the bin

Pre-Laboratory Work Introduction: Explain theory behind the lab, as well as any equations, graphs, or mathematical equations that will be required. Procedure: The procedure is given below. Paraphrase the procedure your lab notebook. Materials: Copy the materials list into your lab notebook. Look up the MSDS for the chemicals listed below and list major hazards (typically in the Hazards Identification section). Hydrogen peroxide Potassium permanganate Sulfuric acid

Post-Laboratory Work: Word Processed and Printed Analysis: Access your class set of data using Perform all required calculations using a spreadsheet program such as Excel or Goggle Sheets. Ensure all displayed numbers show the correct sig figs. Copy and paste into the lab report such that it is readable when the page is printed. Complete the following data analysis: Calculate the grams of H2O2 present in each trial. Calculate the percent by mass of H2O2 present in each trial by dividing the grams of H2O2 by the mass of the H2O2 added, then multiply by You can find the mass of the H2O2 added using the 1.00 mL volume you added and by assuming that the density of the solution is 1.00 g/mL. Calculate the average percent by mass. Calculate the standard deviation in the average percent by mass. Report your answer as average % ± standard deviation. Sample calculations: Show one typed worked example for each major required calculation. You do not need to show sample calculations for finding standard deviation. Include the unrounded answer and the answers with correct sig figs. It is recommended that you use the equation editor feature.

Post-Laboratory Work: Word Processed and Printed Conclusion: Include the following in narrative form: Discussion of what you did, including the purpose/ goal of the experiment. Describe any changes to the procedure from what you wrote in your lab notebook. Describe major findings and make claims with supporting evidence from the lab. Report calculated numbers, averages, and standard deviations as required. Comment on error, both inherit error (due to precision of equipment) and experimental/ human error. Remember that “the lab would have been better if we did it correctly” or “human errors were made” are not discussion of error. Errors should be clearly described along with how they impacted the calculations in the data analysis. Describe refinements or future experiments. What can we study next and why? Once you have completed your conclusion, print and highlight the answers to the above questions. Complete all sections as described. Create a cover sheet for the lab that includes your name, your partner(s) name(s), your class period, due date, and the title of the experiment. Staple all sections (hand written carbon copies and printed papers) in order and hand in during class.

Acid in Drinks Lab Report, 10/18 (A Day) and 10/19 (B Day) Determining Percent H2O2 Lab Report, 10/29 (A Day) and 10/30 (B Day) HW 7: Review for Unit Test Summary: 10/12 (A Day) 10/15 (B Day) Outcome: I can calculate the percent H2O2 in a drugstore peroxide solution by completing a redox titration. Goal: CW 10

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