AP Chemistry Midterm “Buy-Back” Total Points = 16
Answer the following questions and submit the answers to me via email no later than Sunday, January
25 at 12:00 noon DST. No late responses will be read.
1. List 3 observations which tell you a chemical reaction has occurred. (1 pt)
A
B
C
2. Is it possible to READ 843 ml of water in a beaker? What piece of glassware could you READ if it
contained 843 ml of water? (1 pt)
When reporting a value for Density, what other value must you always report along with it? (1 pt)
3. The bond energy for a new diatomic element Z2 is measured to be 425kJ/mole. Assuming that
one photon is required to break one bond, what is the maximum wavelength (in nm) of
radiation you could use to break the Z-Z bond? SHOW ALL WORK FOR CREDIT. (3 pts)
4. What is shielding? Give an example by drawing a diagram. (2 pts)
5. For elements Li  Ne, calculate the effective nuclear charge for each; THEN explain the trend in
atomic radius as you move across the second period; finally, explain the trend in 1st ionization
energy as you move across the second period. (3 pts)
6. 125 ml of 2.2M Ca(NO3)2(aq) is mixed with 40 ml of 1.6M Na2SO4(aq). What is the resulting
concentration of nitrate ions? (1 pt)
7. List three scenarios which represent an increase in the entropy of a system when a reaction
proceeds. (1 pt)
What does it mean when is ∆Suniv is positive? (1 pt)
What does it mean when ∆Suniv = 0? (1 pt)
8. When you see a multi-step problem on the AP test in May and you are clueless as to how to do
the first step, what should you do? (1 pt)