Video 2.1 Moles and Molar Mass.

Video 2.1 Moles and Molar Mass

Objectives By the end of this video you should be able to…
Calculate the molar mass of an element or a compound.

Stoichiometry The Mole represents a specific amount of any substance.
It always measures 6.02x1023 particles such as atoms and molecules.

The Mole = 6.02x1023 The mole is based on the fact that 12 grams of Carbon-12 has a mole of atoms. A mole means you have 6.02x1023 particles.

Molar Mass Molar Mass (aka gram formula mass or molecular mass) is the mass of one mole of a substance. Element’s molar masses are reported on the periodic table.

Molar Mass Examples: Elements
What is the molar mass of iron? What is the molar mass of copper? 55.8 g/mol 63.5 g/mol

Molar Mass Examples: Compounds

Objectives Now you should be able to…
Calculate the mass of an element or a compound.

Video 2.2 Calculating Moles

Use dimensional analysis to calculate the moles of a substance.

Example 1 Calculate the mass of 6.70 moles of carbon.

Example 2 Calculate the mass of 0.023moles of lithium.

Example 3 Calculate the mass of moles of Ca3(PO4)2.

Example 4 Determine the number of moles in 8.0 grams of Boron.

Example 5 Determine the number of moles in grams of Helium.

Example 6 Find the number of moles in 1230 grams of MgSO4.

DA pointers summarized
Start with the number given as a numerator over 1. MULTIPLY by a new fraction Place a conversion with the same unit on the denominator of the new fraction. Multiply numerators, divide denominators. (maybe pause and copy all this?)

Use dimensional analysis to calculate the moles of a substance.

Molar Volume and Particles
Video 2.3 Molar Volume and Particles

Use dimensional analysis to calculate the moles of a substance based on molar volume and particles.

Mole Road Map Gram formula mass Gases at STP: use 22.4L
volume Gases at STP: use 22.4L particles Atoms or molecules: use 6.02x1023

Atom versus molecule Atoms are one particle of an element.
H2O CO2 Atoms are one particle of an element. Molecules are multiple atoms stuck together that forms a compound.

Examples 1. a. Calculate the number of molecules in 4.37 moles of Lithium sulfide. b. Calculate the number of atoms in the sample

Examples 2. What is the volume of 7.89 moles of He gas at STP?

Examples 3. a. How many molecules are present in Liters of P2O5 gas at STP? b. How many atoms are present in the sample?

Examples 4. How many moles are present in 5.67x1024 molecules of H2O(l)?

THINK Why do chemists use moles to measure substances? Why aren’t grams, liters and molecules enough?

Use dimensional analysis to calculate the moles of a substance based on molar volume and particles.

Video 2.4 Moles to Coefficients

Use dimensional analysis to calculate the moles of various substances in a chemical reaction. Determine if a substance is excessive or a limiter.

Reactions Mix + 2 Eggs + 1 cup water = Cake Reactants Products 2 Mix = 2 Cakes 6 Eggs = 3 Cakes

Coefficients 4Al + 3O2  2Al2O3 reactants products
Coefficients: How many moles of the substance are needed in a reaction.

Relating Moles To relate moles of one substance to another, simply create a proportion: 4Al + 3O2  2Al2O3 If 3 moles of oxygen react, how many moles of Aluminum oxide form? If 4 moles of aluminum react, how many moles of oxygen are needed? If 4 moles of aluminum oxide are formed, how many moles of oxygen were used? If 8 moles of aluminum react, how many moles of oxygen are needed? 2 3 6 6

Example 1 16 Al + 3S8  8Al2S3 If 2.50 moles of sulfur react, how many moles of aluminum sulfide form?

Example 2 16 Al + 3S8  8Al2S3 If 3.75 moles of aluminum react, how many moles of sulfur are needed?

THINK Why do chemists use moles to measure substances? Why aren’t grams, liters and molecules enough?

Video 2.5 Limiting Reactants

Limiting Reagents Given: 20 11 36 1 sandwich = 2 1 3
1 sandwich = How many sandwiches can I make if I used all of the bread with unlimited other resources? How many sandwiches can I make if I used all of the cheese with unlimited other resources?

Limiting Reagents Given: 20 11 36 1 sandwich = 2 1 3
1 sandwich = 3. How many sandwiches can I make if I used all of the ham with unlimited other resources? 4. How many sandwiches can I make if I used only what is given? 5. What ingredient was the limiter? Why?

Limiting Reagents Examples
1. S + 3F2  SF6 Suppose you have 4 moles of sulfur and 2 moles of fluorine, which is the limiter and which is in excess? How many moles of SF6 can be produced? 4S produces 4 SF6 2F2 produces 0.6 moles of SF6 (F2 Limiter!)

2. 2NH3 + CO2  (NH2)2CO + H2O If grams of ammonia react with grams of carbon dioxide, find the limiter and the amount of urea produced.

4. 5Ca + V2O5  5CaO + 2V 1.96x103 grams of calcium react with 1.54x 103 grams of V2O5. Find the limiter and the amount of V produced.

Use dimensional analysis to calculate the moles of various substances in a chemical reaction. Determine if a substance is excessive or a limiter.

Molarity and Dilutions
Video 2.6 Molarity and Dilutions

Calculate the molarity of a solution. Calculate the molarity of a solution after it is diluted.

Concentration Concentrated solutions contain large amounts of solutes dissolved in the solvent. Dilute solutions contain small amounts of solutes dissolved in solvent. Which is concentrated?

Molarity The amount of solute (dissolvable substance) in a solvent (does the dissolving like water) is known as concentration and can be represented many ways. Molarity is the moles of solute per liter of solution. Find this on your reference tables! The units for molarity are mol/L or mol.L-1 or just M. If you don’t know what this means, maybe write a note to ask me in class…

Molarity (M) mol of solute M = L of solution
Because volume is temperature dependent, molarity can change with temperature.

Examples can be done without a calculator!
If 3.0 moles of NaCl are dissolved in 6.0L of water, what is the molarity? If 29 grams of NaCl are dissolved in one liter of water, what is the molarity? 3moles/6L = 0.50M 29g/58g = 0.50moles 0.5moles/1L = 0.50M

Examples may need a calculator or can be estimated
If 100. grams of KF are dissolved in 300.ml of water, what is the molarity? Calculate the volume needed to create a 2.0M solution with 3.5 moles of Li2O. 100g/58.1g =1.72mol 1.72mol/.300L = 5.70M 2.0M=3.5mol/x X = 1.8L

THINK If you have 3.12g of HCl and 250mL of H2O, what is the molarity of the acid? If 250mL of H2O is added again, how does the molarity change? M decreases by half

THINK If the glass of iced tea I made is too strong for you, what could you do to make it weaker? This process is known as dilution. It is very important in chemistry because we often purchase large quantities of highly concentrated chemicals. In order to use the chemicals in class, for labs, teachers must dilute the chemicals so they aren’t as dangerous.

Dilutions A dilution is a procedure for preparing a less concentrated solution from a more concentrated (or stock) solution. Use the formula: M1V1 = M2V2

Calculations 240mL of a 3.5M solution is diluted to 300 mL of solution. Calculate the new molarity. 7.8L of 2.0M solution is diluted by the addition of 10.0L of water. Calculate the new molarity. 3.5(240) = x(300) 2.8M 2.0(7.8) = x(17.8) 0.88M

Calculations What volume of 9.3M H2SO4 is needed to obtain 450mL of 2.0M H2SO4? What always happens to the molarity when water is added? 9.3(x) = 2.0(450) 97mL M decreases What would you have to do in order to have the molarity increase? Increase moles or evaporate water

Calculate the molarity of a solution. Calculate the molarity of a solution after it is diluted.

Video 2.7 Balancing

Balance reactions to show conservation of mass using coefficients. Identify types of reactions.

Conservation of Mass In a reaction, atoms and molecules cannot appear or disappear. Mass must stay constant from the beginning to the end of the reaction. H2 + O2  H2O ___H2 + ___O2  ___ H2O 2 2

Balancing Reactions ___ N2 + ____H2  ____ NH3 ___Li + ____O2  ___Li2O 3 2 4 2

Balancing __Pb(NO3)2 +__K2CrO4___PbCrO4 + ___KNO3
___C4H8 + ___O2  ___CO2 + ___H2O 2 6 4 4

Types of Reactions Synthesis: A + 2B  AB2 Decomposition: AB2  A + 2B
Combustion: CH4 + O2  CO2 + H2O Single Replacement: AB + C  CB +A Double Replacement: AB + CD  AD + CB * Notice synthesis and decomposition are opposites. Also, combustion can have any carbon compound as a reactant.

Balance reactions to show conservation of mass using coefficients. Identify types of reactions.

Video 2.8 Percent Composition

Calculate the percent composition of an element in a compound. Define hydrate and anhydrate.

Percent Composition Nutrition Facts on foods can tell you just how much of a substance you are consuming and how that relates to how much you should eat in a day. It is equally important to know how much of a element or compound is in a mixture.

Percent Composition % By mass: mass part x 100 total mass
Find the % by mass of phosphoric acid. H3PO4 3(1.0) x 100 3(1.o) (16.0) = 3.02%

Example 2 Find the percent by mass of Ca in Ca(OH) x (16.0)+2(1.0) = 54.1%

Find the percent by mass of Na:
NaClO NaCl NaOH 23.0/74.5 *100 = 30.9% 23.0/58.5 *100 = 39.3% 23.0/40.0 *100 = 57.5%

Percent Composition Examples
A sample of a substance containing only magnesium and chlorine was tested in the laboratory and found to be composed of 74.5% chlorine by mass. If the total mass of the sample was grams, what is the mass of the magnesium? (190.2) = 141.7 grams

Hydrates Hydrates contain a specific number of moles of water attached to a molecule: CuSO4.5H2O When the water is heated off, the new substance is known as an anhydrate. The words are red because they are vocab words!!!!

Which is the hydrate and the anhydrate?

Hydrates The reaction must be performed in a crucible on a clay triangle on a ring stand. Clean and heat crucibles before use Careful they get really hot! Always reheat your sample to ensure all water has left the hydrate Record all measurements!

Hydrates Once the hydrate is heated, you can calculate the moles of water that evaporated, and figure out the formula. The steps are as follows: Calculate the mass of hydrate, anhydrate and water by subtraction. Find the moles of anhydrate and water separately. Find the mole ratio of anhydrate to water (1 to ?). Hint: write this down so you have it for the lab!

Hydrate Example: Data:
Mass of crucible: g Mass of crucible and hydrate: g Mass of crucible and anhydrate: g Calculate the hydrate formula and the percent water if the anhydrate is CuSO4.

Answer = 1.60 g of hydrate = 1.24 g of anhydrate = 0.36 g of water 0.36/1.60 * 100 = 23% water 0.36/ = moles of water 1.24/159.6 = moles of anhydrate CuSO4.3H2O

Calculate the percent composition of an element in a compound. Define hydrate and anhydrate.

Empirical and Molecular Formulas
Video 2.9 Empirical and Molecular Formulas

Identify empirical and molecular formulas Calculate empirical formulas from percent. Calculate molecular formulas from empirical formulas.

Empirical Formulas Empirical formula refers to any molecular formula in it’s reduced form. Are these empirical? If not, reduce them: C2H2 C6H12O6 NO2 Na2(OH)2 CH CH2O NO2 NaOH

Molecular Formulas Molecular Formulas are some multiple of the empirical formula. If the empirical formula is CH4 a molecular formula could be CH4, C2H8, C3H12 etc. A compound whose empirical formula is NH3 has a mass of 34 g/mol. What is the empirical formula? NH3 = 17.0 g/mol /17 = 2 2NH3 = N2H6

Steps: Find the mass of the empirical formula.
Divide the mass given by the empirical mass. Distribute your answer through the empirical formula. If a compound has a mass of 45 g/mol and an empirical formula of CH3, what is the molecular formula? CH3 = 15 g/mol /15 = 3 3CH3 = C3H9

Calculating Empirical Formulas From Percent Composition
Find the empirical formula of a compound with 40.92% C, 4.58% H and 54.50% O by mass. Rules: Convert the % to grams, assuming the total mass of the sample is 100 grams. 40.92g C, 4.58g H, 54.50g O Convert mass to moles, using atomic masses. 40.92/12 = 3.40 moles C 4.58/ = 4.58 moles H 54.50/16 = 3.4o moles O Divide each element’s moles by the smallest number of moles. 1 mole C, 1.5 mole H, 1 mole O Find a whole number ratio. C2H3O2

Now try these… A sample of nitrogen and oxygen contains 1.52 g N and 3.47g O and a molar mass of about 90 grams. Find the empirical and molecular formulas.

Examples 2. Find the empirical and molecular formula of a 30 gram sample with 6.44 grams of Boron and grams of hydrogen.

Identify empirical and molecular formulas Calculate empirical formulas from percent. Calculate molecular formulas from empirical formulas.

Video 2.10 Binary Compounds

Write the name of binary compounds. Write the formula of binary compounds.

What is the difference between an element and a compound?

Definitions Elements cannot be broken down by physical or chemical changes. Compounds are composed of 2 or more elements that can be broken down by chemical change.

Ions Ions are elements with a charge. The reference table lists these charges for each element. If the element is positive, it is called a cation. Cations are named the same as the element. (Example: Ca=Calcium atom / Ca+2=Calcium ion) If the element in negative, it is called an anion. Anions are named ending with “-ide” (Example: N=Nitrogen atom / N-3 = Nitride ion)

Examples Mg+2 K+ O-2 F- Li+ I-

Binary Compounds Binary Compounds consist of only two of elements. To name: write the complete name of the first element. The second element should then be named, ending in “-ide.” NaCl sodium chloride KI potassium iodide MgCl2 Ca3N2 magnesium chloride calcium nitride

Examples Li3P Al2S3 SrBr2 Rb2O BaSe CsI Lithium Phosphide
Aluminum sulfide Strontium bromide Rubidium oxide Barium selenide Cesium iodide

Writing Formulas The ions in the formula have charges that must sum to zero. Look up ion charges on the top right corner of every element box on the periodic table. For negatively charged ions (anions) only use the top charge listed. Sodium Chloride Na+ and Cl-  Magnesium Chloride Mg+2 and Cl-  Sodium Oxide Na+ and O-2  Magnesium Oxide Mg+2 and O-2  Magnesium Nitride Mg+2 and N-3  NaCl Mg+2 Cl- Cl- MgCl2 Na+ Na+ O-2 Na2O MgO Mg+2 Mg+2 Mg+2 N-3 N-3 Mg3N2

Criss-Cross Rule To write a formula, write the two ions separately showing their charges. Charges are on the periodic table. Then, swap the two numbers and drop the sign: Calcium nitride:Ca N-3 Ca3N2 Lithium oxide: Li+ O-2 Li2O Notice, we don’t write ones!

Examples Sodium iodide Lithium sulfide Potassium nitride
Magnesium chloride Calcium oxide Strontium phosphide Aluminum iodide Na+ I- = NaI Li+ S-2 = Li2S K+ N-3 = K3N Mg+2 Cl- = MgCl2 Ca+2 O-2 = CaO Sr+2 P = Sr3P2 Al+3 I = AlI3

Write the name of binary compounds. Write the formula of binary compounds.

Video 2.11 The Stock System

Write the name of binary compounds using the stock system. Write the formula of binary compounds using the stock system.

Problem: FeCl2 and FeCl3 are different compounds but seem to have the same name. How can we name them different? FeCl2 is iron (II) chloride FeCl3 is iron (III) chloride. What do the roman numerals represent?

Transition Metals and Nonmetals
Transition Metals are in the middle group of the periodic table. I II Nonmetals are on the right side of the staircase. III They have multiple charges or oxidation numbers and so you must show which charge you are using with roman numerals: IV V VI VII

Try these… LOOK UP THE ANION
FeCl2 CuF MnO2 ZnO N2O3 PCl3 Cl- F- O-2 Iron (II) chloride Copper (I) fluoride Manganese (IV) oxide Zinc oxide Nitrogen (III) oxide Phosphorous (III) chloride

Try these… Copper (II) flouride Iron (III) telluride
Manganese (VII) oxide Gold (I) Bromide Vanadium (V) sulfide Cu+2 F- = CuF2 Fe+3 Te-2 = Fe2Te3 Mn+7 O-2 = Mn2O7 Au+ Br- = AuBr V+5 S-2 = V2S5

Write the name of binary compounds using the stock system. Write the formula of binary compounds using the stock system.

Video 2.12 Ternary Compounds

Write the name of ternary compounds using the stock system. Write the formula of ternary compounds using the stock system.

Ternary Compounds When compounds have more than 2 elements, it contains a polyatomic ion. Polyatomic ion are a group of 2 or more atoms that are bonded very strongly and act as one ion. AgNO3 silver nitrate

Polyatomic ions You are given a list of polyatomic ions. Naming compounds with these ions are easy once you familiarize yourself with the list. CaCO3 calcium carbonate LiClO2 lithium chlorite NaOH sodium hydroxide (NH4)3PO4 ammonium phosphate

Examples K2SO4 CsNO2 Ba(SCN)2 SrClO3 Al(HCO3)3 RbCN Potassium sulfate
Cesium nitrite Barium thiocyanate Strontium chlorate Aluminum hydrogen carbonate Rubidium cyanide

Writing Formulas To write the formulas, you are using the same rules:
The charges must balance to zero Criss cross or drop and swap your numbers Ca+2 reacts with CO3-2  CaCO3 Li+ reacts with SO4-2 Li2SO4 Mg+2 reacts with NO3-  MgNO32? MgNO3 2? Mg(NO3)2

Examples Potassium chlorate K+ and ClO3-  KClO3
sodium carbonate Magnesium acetate Strontium phosphate K+ and ClO3-  KClO3 Na+ and CO3-2  Na2CO3 Mg+2 and C2H3O2-  Mg(C2H3O2)2 Sr+2 and PO4-3  Sr3(PO4)2

Write the name of ternary compounds using the stock system. Write the formula of ternary compounds using the stock system.

Video 2.1 Moles and Molar Mass.

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