NAME:
Chemistry 232
Analytical Chemistry
Show all calculations for partial credit
1. (10 points) What is the difference between a 0.25 M solution of BaCl2 and a 0.25m
solution? Would I use different glassware in making up 1L of each of these solutions?
2. (10 points) Concentrated Nitric Acid is 15.9 M, how much concentrated Nitric Acid do
I need to make 2L of a 2.0 M Nitric Acid solution.
3. (10 points) I titrated a 25.00±.05 mL solution of NaOH with 21.34±.02 mL of .1007M
HCl. What is the molarity of my NaOH solution, and what is the uncertainty in this
molarity?
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4. (10 points) I do 5 experiments and get a mean and standard deviation. I then do 45
additional experiments and find that neither my mean nor my standard deviation
change significantly. The extra experiments seem like a waste of time, yet my text book
tells me that I should have more confidence in my mean value. Why is this? Can you
show numbers of equations to back this up?
5. (10 points) I do 5 experiments to determine the %Mn in a sample of steel. In these
experiments I have a mean value of 0.678% Mn with a standard deviation of .001%. If I
want to be right 95% of the time, what is the confidence interval I should establish from
this data.
6. (10 points) The energy difference between a folded protein (native) and an unfolded
protein (denatured) may be only 2 kJ (i.e. the )G of the reaction native6unfolded = +2
kJ). What is the K associated with this reaction?
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7. (10 points) The ‘lime’ deposit you get from hard water is CaCO3. The Ksp of CaCO3 is
4.5x10-9. What is the solubility of Ca2+ in hard water?
8. (10 points) The carbonate in lime actually comes from CO2 in the air. CO2 in the air
dissolves in water for form H2CO3. H2CO3 then undergoes two simple acid reactions:
H2CO3 W HCO3- + H+
Ka1 = 4.45x10-7
HCO3- W CO32- + H+
Ka2 = 4.69x10-11
(A.) Based on the above equilibria how you expect the solubility of Ca2+ to
change if you heated the water to drive off the CO2? Why?
(B.) Based on the above equilibria how would you expect the solubility of Ca2+ to
change if you increased the pH of the water? Why?
(C.) Based on the above equilibria how would you expect the solubility of Ca2+ to
change if you decreased the pH of the water? Why?
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9A (5 points) In class I mentioned that the K for the dissociation of water is Kw = 1x10-14
= [H+][OH-]. Calculate the pOH of a solution if the pH is 7.37
9B (5 points) One easy way to convert from pH to pOH is to remember that pOH = 14pH. Why is this equation true?
10 (10 points - Hard question) A. In class we talked about how Mg(OH)2 is used as an
antacid. Yet I showed that it has a very low solubility (Ksp = 7.1x10-12). I said the
reason it is used as an antacid is that the OH- reacts with the H+ to form water. The K
for this reaction is 1x10+14. So what is the K for the net reaction of Mg(OH)2 dissolving
in water and then reacting with H+ ?
I.e. The reaction : Mg(OH)2 (s)+ 2 H+(aq) W Mg2+ (aq) + 2H2O(l)
B. If I swallow enough Mg(OH)2 so I have some solid laying undissolved in my
stomach, and the stomach acid has been completely neutralized to the pH of the
stomach juice is pH 7, what is the concentration of Mg2+ in the stomach juice?
(Warning- You may get a funny looking answer.)