CHEMISTRY 152

Exam III

Winter, 1998

Name______

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 8 problems on 4 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.

DATA

Kw = 1.0 x 10-14 Ksp(Zn(OH)2) = 1.2 x 10-17

Ka(NH4+) = 5.6 x 10-10 Ksp(Cu(OH)2) = 1.58 x 10-44

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

Ka

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 4 Name

1.(10) The pH of an 0.060 M solution of a weak acid is 2.71. Identify the acid from among those listed on the data page. Show work and explain your reasoning.

2.(5) In aqueous solution, amino acids exist as zwitterions, compounds in which internal proton transfer give a molecule with two charged functional groups. Draw structures that clearly illustrate the proton transfer from the acid functional group (-COOH) to the amine functional group (-NH2) to produce the zwitterion form of the amino acid glycine.

H—CH¾COOH

½

NH2

3.(10) If 0.10 g of Zn(OH)2 is added to 1.00 liter of water, what mass will dissolve? (Assume the solid does not increase the volume of solution upon addition) Show all work clearly for full credit.

4.(30) A. Compute the pH of a 0.0200 M NH4NO3 solution. Show all work clearly.

B. If you now add 0.0100 mole of NH3 to 1 liter of the solution above, what will be the new pH? Show all work clearly for full credit.

C. If you now add 0.0010 mole of NaOH to the solution in B above, what will be the new pH? Show all work clearly for full credit.

5.(15) Find the concentrations of all ions in the solution at equilibrium after 500 ml of 0.30 M aqueous Cu(NO3)2 solution has been mixed with 500 ml of 0.40 M aqueous KOH solution. Show all of your work clearly for full credit.

6.(10) Phthalic acid, H2C8H4O4, is a diprotic acid used in the systhesis of phenolphthalein indicator. Ka1= 1.2 x10-3 and Ka2= 3.9 x 10-6. Determine the pH and the [C8H4O4-2] in a 1.0 M phthalic acid solution. Show all work clearly for full credit.

7.(5) What is the pH of a solution that is 0.10 M KNO2 and 0.15 M HNO2 (nitrous acid). Show all work clearly for full credit.

8.(15) A laboratory technician wants to determine the aspirin content of a headache pill by acid-base titration. Aspirin has a Ka = 3.0 x 10-4. If the pill is dissolved in water to give a solution that is 1.0 x 10-2 M and is then titrated with KOH solution (assume no volume change), find the pH at each of the following points, showing all work for each part to receive full credit.

A.  before titration begins

B.  at the midpoint of the titration

C.  at the equivalence point of the titration

D. Extra Credit(2): Select a suitable indicator:______