Chemistry 222 - Problem Sets

Professor Ralph Allen

Individual Problems

Set 1

1-1) Calculate the concentration of barium in the solution at equilibrium when 15.0 mL of 0.200 M K2CrO4 is added to 25.0 mL of 0.100 M BaCl2.
1-2) What must be the concentration of Ag+ to just start precipitating 0.10 M PO4-3? 0.10 M Cl-?
1-3) What weight of Ag3AsO4 will dissolve in 250 mL water?

Make up problems - Set 1

M1-1) What must be the concentration of PO4-3 to just start precipitation of Ag3PO4 in a 0.10 M AgNO3 solution?
M1-2) What is the solubility of Ag2CrO4 in 0.10 M K2CrO4?
M1-3) Bismuth iodide, BiI3, has a solubility of 7.76 mg/L. What is its Ksp?

Set 2

2-1) The solubility product of Bi2S3 is 1 x 10-97 and that of HgS is 4 x 10-53. Which is the least soluble?
2-2) How many grams CuO would 1.00 g Paris green, Cu3(AsO3)2 2As2O3 Cu(C2H3O2)2, give? Of As2O3?
2-3) A Mixture containing only BaO and CaO weighs 2.00 g. The oxides are converted to the corresponding mixed sulfates, which weight 4.00 g. Calculate the percent Ba and Ca in the original mixture.

Make up problems - Set 2

M2-1) What is the concentration of Ag+ and CrO4-2 in a saturated solution of Ag2CrO4?
M2-2) A student proposes to analyze barium gravimetrically by precipitating BaF2 with NaF. Assuming a 200-mg sample of Ba+2 in 100 mL is to be precipitated and that the precipitation must be 99.9% complete for quantitative results, comment on the feasibility of the analysis.
M2-3) A mixture containing only BaSO4 and CaSO4 contains one-half as much Ba+2 as Ca+2 by weight. What is the percentage of CaSO4 in the mixture?

Set 3

3-1) What is the pH of 0.0100 M solution of phthalic acid?
3-2) What is the pH of a 0.0100 M solution of potassium acid phthalate (KHP)?
3-3) What is the pH of a solution that is 0.20 M in phthalic acid (H2P) and 0.10 M in potassium acid phthalate (KHP)?

Make up problems - Set 3

M3-1) What is the pH of a 0.0100 M solution of potassium phthalate?
M3-2) Calculate the pH of a 0.600 M solution of NaHS.
M3-3) An acetic acid-solution acetate buffer of pH 5.00 is 0.100 M in NaOAc. Calculate the pH after the addition of 10 mL of 0.1 M NaOH to 100 mL of the buffer.

Set 4

4-1)Balance the following reactions:
a) MnO4-2 ---> MnO2 + MnO4- (alkaline solution)
b) MnO4- + H2S ---> Mn+2 + S
c) SbH3 + Cl2O ---> H4Sb2O7 + HCl
d) FeS + NO3- ---> Fe+3 + NO2 + S (acid solution)
4-2)Balance the following reactions:
a) Al + NO3- ---> AlO2- + NH3
b) FeAsS + ClO2 ---> Fe+3 + AsO4-3 + SO4-2 + Cl- (acid solution)
c) K2NaCo(NO2)6 + MnO4- ---> K+ + Na+ + Co+3 + NO3- + Mn+2 (acid solution)

Make up problems - Set 4

M4-1) Balance the following reactions:
a) IO3- + I- ---> I2 (acid solution)
b) Se2Cl2 ---> H2SeO3 + Se + HCl
c) H3PO3 + HgCl2 ---> Hg2Cl2 + H3PO4 + HCl
M4-2) From the standard potentials of the following half-reactions, determine the reaction that will occur, and calculate the cell voltage from the reaction:
PtCl6-2 + 2e- ---> PtCl4-2 + 2Cl- Eo = 0.68 V
V+3 + e- ---> V+2 Eo = -0.255 V

Group Problems:

These are to be worked by your group and submitted with all names. It is up to you to be sure that everyone knows and understands how to do the problems. I may call on members of the group at random and ask them to explain the problem and the results. Grades for the entire group will thus depend upon the understanding of that member chosen to respond. Remember that there are no make up problems so you want to be sure that you are correct the first time. If it is wrong you will have to work the problem and it could be a subject in the oral exam for the group.

Group Problem Set 1

G1-1) Fe+2 and Cr2O7-2 react as follows: 6Fe+2 + Cr2O7-2 + 14H+ = 6Fe+3 + 2Cr+3 + 7H2O. The equilibrium constant for the reaction is 1 x 1057. Calculate the equilibrium concentrations of the iron and chromium species if 10 mL each of 0.02 M K2Cr2O7 in 1.14 M HCl and 0.12 M FeSO4 in 1.14 M HCl are reacted.
G1-2) A and B react as follows: A + B = C + D. The equilibrium constant is 2.0 x 103. If 0.30 moles of A and 0.80 mol of B are mixed in a liter, what are the concentrations of A, B, C, and D after reaction?
G1-3) The dissociation constant of salicylic acid, C6H4(OH) COOH is 1.0 x 10-3. Calculate the percent dissociation of a 1.0 x 10-3 M solution (there is only one dissociable proton). What is the percent dissociation if the solution also contains 1.0 x 10-2 M sodium salicylate (the salt of the acid)? Would you expect the addition of sodium chloride to have the same impact or different impact upon the dissociation? Explain your answer.

Group Problem Set 2

G2-1) A divalent metal forms chelates with two different chelating agents, HA and HB. Ka of HA is 10-5 and Ka of HB is 10-10. The two chelates have equal stability and are equally soluble in the two phases (), as are the chelating agents (). Calculate the relative percent of each chelate extracted at a given pH and reagent concentration and with equal volumes of the two phases.

Group Problem Set 3

G3-1) Aspirin (acetylsalicylic acid) is absorbed from the stomach in the free (un-ionized) acid form. If a patient takes an antacid that adjusts the pH of the stomach contents to 2.95 and then takes two 5-grain aspirin tablets (total 0.65 g), how many grams of aspirin are available for immediate absorption from the stomach, assuming immediate dissolution. Also assume that aspirin does not change the pH of the stomach contents. The pKa of aspirin is 3.50, and its formula weight is 180.2.
G3-2) Tris(hydroxymethyl)aminomethane [(HOCH2)3CNH2Tris, or THAM] is a weak base frequently used to prepare buffers in biochemistry. Its Kb is 1.2 x 10-6 and pKb is 5.92. The corresponding pKa is 8.08, which is near the pH of the physiological buffers, and so it exhibits good buffering capacity at physiological pH. What weight of THAM must be taken with 100 mL of 0.50 M HCl to prepare 1 liter of a pH 7.40 buffer?