All notes, books, etc., must be placed out of sight. Please read each of the problems carefully. If
something is not clear, please ask.
The exam consists of 10 problems on 5 pages. Make sure your exam is complete. The exam is
worth 100 points with each of the problems labeled as to its point value.
Answers should be placed in the space provided and written legibly. If I cannot read it--it is
wrong. You should show your work clearly for each of the problems. Please include
explanations whenever asked or whenever necessary to make your answer clear. Please put your
name on every page of the exam.
There is scratch paper and periodic tables available for your use. If you require more data, ask.
As usual, no cheating will be tolerated.
Data will be found on the next page.
Kw = 1.0 x 10-14 Ksp(Fe(OH)2) = 7.94 x 10-16
Ka(NH4+) = 5.6 x 10-10 Ksp(Ca(OH)2) = 5.50 x 10-6
Kb(NH3) = 1.8 x 10-5 Ksp(Mg(OH)2) = 1.82 X 10-11
Ka(HAc) = 1.8 x 10-5 Ksp(Fe(OH)3) = 3.00 x 10-39
Kb(Ac-) = 5.6 x 10-10 Ksp(Al(OH)3) = 2.00 x 10-31
Ksp(AgCl) = 1.8 x 10-10
Ksp(PbI2) = 8.7 x 10-9 Ksp(AgBr) = 5.0 x 10-13
Ksp(PbCO3) = 1.5 x 10-13 Ksp(AgI) = 1.0 x 10-16
Indicator pH Range Color Change
Thymol Blue 1.2 2.8 red yellow
Methyl Yellow 2.5 4.5 yellow blue
Bromophenol Blue 3.0 4.6 yellow blue
Congo Red 3.0 5.0 blue red
Methyl Orange 3.2 4.4 red yellow
Bromcresol Green 4.0 5.0 yellow blue
Methyl Red 4.8 6.0 red yellow
Bromcresol Purple 5.2 6.8 yellow purple
Bromthymol Blue 6.0 7.0 yellow blue
Cresol Red 7.0 8.8 yellow red
Phenolphthalein 8.2 10.0 colorless pink
Thymol Blue 8.5 9.5 yellow blue
Thymolphthalein 9.3 10.5 colorless blue
Alizarin Yellow R 10.3 11.3 yellow red
Representative Weak Acids
HNO2 Nitrous acid 5.01 x 10-4
HF Hydrofluoric acid 3.55 x 10-4
HCHO2 Formic acid 1.82 x 10-4
C6H5CO2H Benzoic acid 6.46 x 10-5
HC2H3O2 Acetic acid 1.78 x 10-5
H2S Hydrosulfuric acid 8.91 x 10-8
HClO Hypochlorous acid 3.02 x 10-8
H3BO3 Boric acid 7.24 x 10-10
HCN hydrocyanic acid 4.00 x 10-10
Chemistry 152 Exam III Page 1 Name
1.(5) A 0.025 M solution of hydroxylamine has a pH of 9.11. What is the value of Kb for this
weak base? Show work clearly for full credit.
H2NOH (aq) + H2O (l) H3NOH+(aq) + OH-(aq)
2.(5) To make up an unknown solution for the students in your laboratory, you dissolve
1.0 x 10-5 mole of AgNO3 in 1.0 liter of water. Unfortunately, you used a liter of tap
water instead of distilled water. If the chloride ion concentration in tap water is
2.0 x 10-4 M, is your error revealed immediately by the formation of a white precipitate of
AgCl? Show work to support your answer.
Chemistry 152 Exam III Page 2 Name
3.(15) You titrate 25.0 ml of 0.0256 M aqueous solution of aniline, C6H5NH2 (MW = 93), a
weak base with 0.0195 M HCl. Kb (aniline) = 4.0 x 10-10
a. Calculate the pH of the aniline solution before the titration. Show all work clearly for each
part of this problem.
b. Determine the pH at the equivalance point of the titration.
c. Select an indicator from the data list that would be suitable. Explain your choices.
Chemistry 152 Exam III Page 3 Name
4.(10) About this time, you may be wishing you had an aspirin. Aspirin (MW = 180) is an
organic acid with a Ka = 3.27 x 10-4 for the reaction shown below. You have two tablets,
each having 0.325 grams of aspirin (mixed with a neutral “binder” to hold the tablet
together), which you dissolve in a glass of water (200 ml). What is the pH of this
solution? Show all work clearly.
HC9H7O4 (aq) + H2O (l) C9H7O4-(aq) + H3O+(aq)
5.(10) A solution contains 0.10 M iodide ion, I-, and 0.10 M carbonate ion, CO3-2.
A. If solid Pb(NO3)2 is slowly added to the solution, which salt precipitates first, PbI2 or PbCO3?
Convince me of your answer.
B. What is the concentration of the first ion that precipitates (CO3-2, or I-) when the second, or
more soluble, salt begins to precipitate? Show your work clearly for full credit.
Chemistry 152 Exam III Page 4 Name
6.(10) A saturated solution of Mg(OH)2 has a pH of 10.49. Use this information to calculate the
Ksp of Mg(OH)2. Show your work clearly for full credit.
7.(10) Sodium cyanide is the salt of the weak acid HCN. Calculate the concentration of H3O+,
OH-, HCN, and Na+ in a solution prepared by dissolving 10.8 grams of NaCN (MW = 49)
in 500 ml of pure water at 25C. Show all of your work clearly.
8.(16) What is the pH change when 0.010 mole of NaOH is added to 100.0 ml of a buffer
solution consisting of 0.169 M NH3 and 0.183 M NH4Cl? Assume no volume change
upon the addition. Show your work clearly for full credit.
Chemistry 152 Exam III Page 5 Name
9.(10) Nicotine, C10H14N2, (abbreviated Nic below) has two basic nitrogen atoms, and both can
react with water to give a basic solution as shown below. If Kb1 = 7.0 x 10-7, and Kb2 =
1.1 x 10-10 determine the pH and [NicH2+2(aq)] of a 0.50 M nicotine solution. Show all of
your work clearly for full credit.
Nic (aq) + H2O (l) NicH+(aq) + OH-(aq) NicH+(aq) + H2O (l) NicH2+2(aq) + OH-(aq)
10.(9) Does the pH of a solution increase, decrease or stay the same when you:
A. Add solid ammonium chloride to a dilute aqueous solution of NH3?
B. Add solid sodium acetate to a dilute aqueous solution of acetic acid?
C. Add solid KCl to a dilute aqueous solution of KOH?