1. Today is Thursday, December 3 rd, 2015 Pre-Class: I’m giving you back your Baking Soda/HCl Labs as these are good study tools for the core assessment. If you don’t understand why you got the grade you did, please talk to me after class. While I may not give you points, the important part is to be able to do this core assessment right. FOR NOW: HAVE YOUR LAB MATERIALS READY TO GO.

2. Today’s Agenda Review and stuff.

3. Core Assessment Details You will perform the “lab” portion with a partner of your choosing at your lab table. – Speaking to anyone other than your lab partner (and softly) is prohibited and will result in loss of points. When the lab portion is complete, you will complete the remainder at your desks individually. Grading is done on the district rubric.

4. Core Assessment Details What to study? – Your Baking Soda/HCl Lab Including the procedure – Mole Conversions – Mole Ratios and Stoichiometry – Limiting Reagents and Percent Yield – Writing, balancing, and identifying chemical reactions.

5. Mole Conversion 1-Slide Review To go from moles to grams you… – Multiply by formula mass. To go from particles to moles you… – Divide by Avogadro’s Number (6.02 x 10 23 ). To go from moles to liters you… – Multiply by 22.4. To go from liters to grams, you… – Convert liters to moles (divide by 22.4) and multiply by molar mass.

6. Empirical Formula Remember that an empirical formula is the most “reduced” chemical formula possible. Another way to phrase it: It’s the lowest ratio between atoms in a formula. Example: – Glucose is C 6 H 12 O 6. That’s its molecular formula. – Empirical formula: CH 2 O. If you need to, please take out my “directions” for solving these. – Don’t have that anymore? It’s on my website.

7. Empirical Formula Example #1 A compound was analyzed and found to contain 13.5g Ca, 10.8g O, and 0.675g H. What is the empirical formula? – First, convert each to moles. 0.337 mol Ca 0.675 mol O 0.668 mol H

8. Empirical Formula Example #1 Next, select the smallest mole quantity and divide each by that number. This is the ratio part. – 0.337 / 0.337 = 1 Ca – 0.675 / 0.337 = 2 O – 0.668 / 0.337 = 1.98 H = 2 H Last, since they’re all integers, let’s make the formula: – CaO 2 H 2 or Ca(OH) 2

9. Empirical Formula Example #2 NutraSweet is an artificial sweetener found in many processed foods in the grocery store. Nutrasweet is 57.14 % C, 6.16% H, 9.52% N, and 27.18% O. The molar mass of Nutrasweet is 294 g/mol. What is the empirical formula and the molecular formula? – First, convert each to moles. We’ll assume that we have 100 grams of Nutrasweet to make things easier. 57.14g C = 4.76 mol 6.16g H = 6.10 mol 9.52g N = 0.68 mol 27.18g O = 1.70 mol

10. Empirical Formula Example #2 Next, divide each by the smallest number of moles. – 4.76 / 0.68 = 7 C – 6.10 / 0.68 = 8.97 = 9 H – 0.68 / 0.68 = 1 N – 1.70 / 0.68 = 2.5 O Oxygen is too far to round up or down, so we must multiply all numbers until they are each integers themselves. 2 is the best factor to eliminate a value of 0.5.

11. Empirical Formula Example #2 Multiply each number by two to eliminate the decimal. – 4.76 / 0.68 = 7 C * 2 = 14 C – 6.10 / 0.68 = 8.97 = 9 H * 2 = 18 H – 0.68 / 0.68 = 1 N * 2 = 2 N – 1.70 / 0.68 = 2.5 O * 2 = 5 O Write the empirical formula: – C 14 H 18 N 2 O 5

12. Empirical Formula Example #2 But we’re not done! The problem wants us to find the molecular (real) formula too. First, find the molar mass of the empirical formula: – Molar mass equals [approximately] 294 g/mol. – Since our empirical formula has the same mass as the molecular formula, they are the same. In other cases, they may not be. Example next slide…

13. Empirical Formula Problem #2 If I were to have told you that the molecular formula was not 294 g/mol but instead was 882 g/mol. – That would mean that the molecular formula weighed three times as much as the empirical formula. – That would also mean that there were three times as many of each atom as before. – Thus, the molecular formula would be C 42 H 54 N 6 O 15

14. Other Stuff to Review Chemical Reactions – Balancing. – Types. – States of matter. Basic Stoichiometry – Here is a quantity of a reactant. How much product could I produce? And vice versa… Percent Yield – I could have produced that much, but I only produced this much. What percent is that? Limiting Reagents – Here are two reactants. According to this reaction, which one will run out first? (that’s the limiter; the other is excess)

15. And now… Let’s go back to our “new review” type of problem. – You write an answer, your partner writes an answer, and you both compare.

16. Review Question 1 What is the chemistry term for the process of calculating quantities in a chemical reaction? – Stoichiometry

17. Review Question 2 What is the empirical formula of a compound whose molecular formula is C 13 H 52 O 26 ? – CH 4 O 2

18. Review Question 3 If a different compound with empirical formula CH 4 O 2 is determined in a lab to have a molar mass of 144 g/mol, what is its molecular formula? – C 3 H 12 O 6

19. Review Question 4 What are the most likely products in this reaction: CH 4 + O 2  _________ – CO 2 and H 2 O

20. Review Question 5 What type of reaction is it? CH 4 + O 2  _________ – Combustion

21. Review Question 6 Which two types of elements (must get both for credit) tend to do the replacing in a single replacement reaction? – Metals and halogens

22. Review Question 7 BONUS NON-CHEMISTRY QUESTION You may wager any/all of your points. Category: Exploration Early explorers of North America, when not looking for the Fountain of Youth, were seeking to find a potential water route from the Atlantic Ocean to the Pacific Ocean. What was the name they gave to this non-existent pathway? – The Northwest Passage.

23. Review Question 8 In a reaction between two known quantities of reactants, what determines the amount of product formed? – The limiting reagent/reactant.

24. Review Question 9 Water forms when hydrogen gas reacts with oxygen gas. What’s the skeleton equation? – H 2 + O 2  H 2 O

25. Review Question 10 Water forms when hydrogen gas reacts with oxygen gas. What’s the balanced equation? – 2H 2 + O 2  2H 2 O

26. Review Question 11 What kind of reaction was that? – Synthesis or Combustion

27. Review Question 12 Which elements form diatomic molecules? (need all for credit) – Bromine – Iodine – Nitrogen – Chlorine – Hydrogen – Oxygen – Fluorine

28. Review Question 12 Which elements form diatomic molecules, and what does it mean to be diatomic? (need all elements and both answers for credit) – Bromine – Iodine – Nitrogen – Chlorine – Hydrogen – Oxygen – Fluorine

29. Review Question 13 BONUS NON-CHEMISTRY QUESTION You may wager any/all of your points. Category: Currency What is the largest paper money bill currently printed by the U.S. Treasury? – $100

30. Review Question 14 Here’s a balanced molecular equation: Ni(NO 3 ) 2 (aq) + 2NaOH (aq)  Ni(OH) 2 (s) + 2Na(NO 3 ) 2 (aq) What is the net ionic equation? – Ni 2+ (aq) + 2OH - (aq)  Ni(OH) 2 (s)

31. Review Question 15 Okay, so this one isn’t really a question. It’s hard for me to put calculation problems up here, so let me give you one last set of worksheets. They’re the most involved of all the ones we’ve done, and so they make great study guides. – Stoichiometry Review worksheet – Unit 4 Monster Problem Please note that they are not sufficient study materials on their own.