Chemistry 1212 5 Name______

Chemistry 1212

Exam III

Spring, 2008

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 7 problems on 5 pages with some extra credit offered on the fifth page. 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 MUST show your work clearly for each problem in order to receive full credit. Please include an explanation whenever asked to or whenever necessary to make your answer clear. If I cannot understand it -- it is wrong. Please put your name on every page of the exam.

There are scratch papers and periodic tables available for your use. If you require more data, please ask.

As usual, no cheating is allowed. Good Luck!

DATA

Ka (HF) = 7.2 x 10-4 Kw = 1.0 x 10-14 (25 ºC)

Ka (acetic acid, HAc) = 1.8 x 10-5 Kb (NH3) = 1.8 x 10-5

Ksp (Mg(OH)2) = 5.6 x 10-12 Ksp (CaF2) = 5.3 x 10-11

Ksp (BaF2) = 1.8 x 10-7


1.(10) A 0.025 M solution of hydroxylamine has a pH of 9.11. What is the value of Kb for this weak base? Show all work clearly for full credit.

2.(10) Will a precipitate of Mg(OH)2 form when 25.0 ml of 0.010 M NaOH is combined with 75.0 ml of a 0.10 M solution of magnesium chloride? Show all work clearly for full credit.


3.(15) What will be the pH change when 2.0 g of NaOH (MW = 40) is added to 1.0 L of a buffer solution consisting of 0.169 M NH3 and 0.183 M NH4Cl? Assume no volume change upon addition of the solid. Show all work clearly for full credit. Hint: What is the pH before the addition?


4.(15) A solution of hydrofluoric acid, HF, has a pH of 2.30. Calculate the equilibrium concentrations of HF, F¯, and H3O+, and calculate the amount of HF originally dissolved per liter of the solution. Label things carefully. Show all work clearly for full credit.

5.(15) Calculate the pH of the solution that results when 22.0 ml of 0.15 M acetic acid, HAc, is titrated with 0.10 M NaOH. Also, indicate which of the indicators shown below would be a good choice for this titration. Show all work clearly for full credit.

6.(15) In principle, the ions Ba2+ and Ca2+ can be separated by the difference in solubility of their fluorides, BaF2 and CaF2. If you have a solution that is 0.10 M in both Ba2+ and Ca2+, CaF2 will begin to precipitate first as the fluoride ion is added slowly to the solution. Show all work clearly for each part below for full credit.

A. What will be the concentration of the fluoride ion when it precipitates the maximum amount of Ca2+ ion without precipitating BaF2?

B. What concentration of Ca2+ remains in solution when BaF2 just begins to precipitate?

7.(20) Short answers, no work need be shown, answer is everything.

A. & B. Write balanced reactions showing how the hydrogen oxalate ion, HC2O4¯, can be both a Brønsted acid and a Brønsted base.

Acid: ______

Base: ______

C. What is the pH of a 0.0015 M solution of Ba(OH)2? ______

D. Ammonium bromide in water gives an acidic solution. Write the reaction that shows how this occurs.

______

E. A weak acid has a Ka value of 6.5 x 10-5. What is the value of pKa? ______

F. A weak base has a Kb value of 1.5 x 10-9. What is the value

of the Ka of its conjugate acid? ______

G. Consider a solution of the salt KCN. Would you expect it

to be acidic, basic, neutral or undeterminable? ______

H. If I add ammonium chloride to a solution of NH3, would

you expect the pH to increase, decrease or stay the same? ______

I. Would you expect solid silver chloride to be more soluble in

pure water or a 0.001 M solution of AgNO3? ______

J. Would you expect the pH of 0.10 M HBr to be greater than,

less than or equal to the pH of 0.10 M HCN? ______