Total points: 33

General
•	Closed book. You may use a (one page) note sheet, plus a periodic table. 
•	Calculators “required”. 
•	If a question isn’t clear, please ask me about it. 
•	In multi-part questions, if a difficulty with one part is keeping you from going on, please ask about it. 
•	Some questions request a simple answer and an explanation. It’s the explanation that is important. No credit for answer without a requested explanation. 
•	For chemical equations: be sure they are balanced, and show phases for all species. 
•	Show work and show units on all calculations. Use dimensional analysis for all unit conversions. Show correct number of significant figures in final results.

N = 6.02x1023 		R = 0.0821 L·atm/(mol·K)		T(K) = T(C) + 273
Kw, the equilibrium constant for the ionization of water, is 10-14 M2. 

1. (2 pts.) Why does water have a much higher boiling point than methane (CH4), even though both have about the same molar mass? Include Lewis structures in your explanation; explain why they are relevant.

2. (3 pts.) Consider nitric acid, HNO3, and acetic acid, HC2H3O2. (Only the first H of acetic acid is acidic. If you want, you can write acetic acid as HAc.)

[The parts of this problem are closely related. Later parts may help you with earlier ones.]

a. (1/2 pt.) Which of these is the stronger acid? 

b. (1 pt.) What is the conjugate base of each of these acids?

c. (1/2 pt.) Which of the two bases (which you listed in part b) is the stronger base?

d. (1 pt.) Write a balanced chemical equation showing the proton transfer reaction that would be most likely between these two acid-base pairs. Write the equation so that the major reaction goes from left to right.

3. (1 pt.) The mineral olivine is a solid solution of two silicates, Mg2SiO4 and Fe2SiO4. What are the likely oxidation numbers for the metal atoms in each of these two compounds? Briefly explain how you can tell or figure it out. (No knowledge about silicate(s) is assumed. The two compounds are closely related. Think about which atoms are easily predicted, from the PT -- and which are not.)

4. (1 pt.; no credit without explanation) Assume that we have a saturated solution of sodium chloride, with excess solid NaCl present. A friend suggests that if you could put a tag on particular sodium ions in the solid phase, you would find that some of those ions actually move from the solid phase into the solution (over time). Is this correct? Explain. (Assume equilibrium conditions, and that they remain constant -- which is slightly redundant.)

5. (1 pt.) Consider the following six “things”: proton, the sun, chlorine atom, chlorine molecule, electron, a salt crystal. Put them in order by mass, smallest first.

6. (2 pts.) 
a. (1 pt.; 1/2 pt. each) For each chemical listed, tell whether it is a strong electrolyte, weak electrolyte, or non-electrolyte when it is dissolved in water.

–	cesium sulfate 
	
–	ethylene glycol (antifreeze), C2H6O2 (entirely covalent; neither acidic nor basic)

b. (1 pt.) When cesium sulfate is dissolved in water, the major species actually in the solution are Cs+(aq) and SO42-(aq). What is/are the major species when ethylene glycol is dissolved in water? Be sure your answer is consistent with what you wrote in part a.

7. (3 pts.) Reminder: In all gas problems, assume that variables not mentioned remain constant.

a. (1 pt.; no explanation required) Qualitatively, what happens to the volume of a gas when it is cooled? Choose one: increases OR does not change OR decreases.

b. (2 pts.) The temperature of a 6.8 L sample of helium gas is changed from 30 C to -60 C. What is the new volume? Show clear work. Show proper SF.

8. (2 pts.; 1 pt. per part) In each part, give the correct chemical formula for the indicated chemical species and draw a Lewis structure (electron dot formula). (Points will be for the Lewis structure, but you must have the correct formula first to write the Lewis structure.)

				formula		Lewis structure

a. a nitrogen molecule				

b. a nitride ion

9. (2 pts.; 1 pt. per part) You want to make 650 mL (6.50x102) mL of 0.150 M potassium hydrogen phosphate. In each part, show clear work and proper SF; use dimensional analysis.

a. How many moles of potassium hydrogen phosphate do you need?

b. You have a stock solution that is 0.800 M potassium hydrogen phosphate. How much of this solution would you use to make your solution?

10. (3 pts.; 1 pt. per part) In parts a & b, what is the pH

[I would prefer that you show some work on parts a and b, so that I can provide you feedback if there are problems. However, if you find these “obvious”, correct answers are ok for full credit.]

a. if [H+] = 10-9 M

b. if [OH-] = 10-11 M

c. (No credit without explanation.) Which (one) of the two solutions above is more acidic? How can you tell?

11. (3 pts.) Consider the single replacement reaction of zinc metal with hydrochloric acid (a good way to make a little hydrogen):

Zn (s) + 2 HCl (aq)  ZnCl2 (aq) + H2 (g)		

(You can do the parts independently, but some are somewhat related. For example, atoms or ions that are spectators obviously did not gain or lose electrons.)

a. (1/2 pt.) Which atom gains electrons? 

b. (1/2 pt.) Which atom loses electrons? 

c. (2 pts.) Write the net ionic equation for this reaction. Show how you work it out. Be sure phases are clear at each step.

12. (1 pt.) Which (one) of the following compounds is more likely to be an ionic compound: CaCl2 or SCl2? Explain how you can tell, based on the periodic table?

13. (2 pts.) You have a solution that is 15.0% sucrose by weight (w/w). If you want 0.824 mol of sucrose, how much of this solution do you need? Show clear work. Show proper SF. (Sucrose is C12H22O11, with molar mass = 342.30.)

14. (1 pt.; no credit without explanation) Consider the following three bonds: C-F, F-F, O-F. Which is most polar? How can you tell?

15. (1 pt.; 1/2 pt. per part; no explanation required)  Imagine that you are a molecule. In each part below, tell which of the common states of matter (e.g., gas) is being described.

a. You look around you and see the same neighbors (in the same place) each time you look.

b. You look around you, and have trouble seeing any neighbors at all.

16. (3 pts.; 1 pt. per part) 
a. Draw a Lewis structure for arsenic trichloride. 
	b. Mark the bond polarity on one of the bonds; show which end is which.

c. What is the shape of this molecule? In particular, why is it not planar?

17. (2 pts.) In a recent remarkable piece of work, scientists measured production of ATP by individual molecules of the key energy-generating enzyme (isolated from bacteria). In one experiment, they reported that 2000 molecules of ATP were made, giving a concentration of 500 nM (nanomolar; nano = 10-9). What is the volume of the container? (This is a fairly complex question. Think out the unit path before doing any calculations. Show me your set-up, if you wish.)

18. (1 millipoint) In what sport might you suspect that the ball has OH- ions on it? Explain.

cq\pq3	(Spring 05)	5/3/05