CHEM 2113

Test 2

Spring 1997

All questions are worth 25 points. Omit one question by leaving completely blank or by clearly writing OMIT on the page. Show your work and circle your answers where appropriate for full credit. Good Luck!

1. Calculate the pH of the following solutions:

0.045 M benzoic acid

0.027 M Hydrazine

0.20 M Potassium hydrogen phthalate

0.025 M Sodium cyanide

2 x 10^-7 M Perchloric acid

2. Consider the titration of 50.0 mL of 0.10 M chloroacetic acid with 0.10 M sodium hydroxide. Calculate the pH at the following points along the titration curve:

a) before any titrant is added;

b) after 25.0 mL of titrant is added;

c) after 45.0 mL of titrant is added;

d) after 50.0 mL of titrant is added;

e) after 60.0 mL of titrant is added.

3. Consider the titration of 50.0 mL of 0.05 M ethylene diamine with 0.10 M hydrochloric acid. Calculate the pH at the following points along the titration curve:

a) before any titrant is added;

b) after 12.5 mL of titrant is added;

c) after 25.0 mL of titrant is added;

d) after 37.5 mL of titrant is added;

e) after 50.0 mL of titrant is added.

4. One of the major pollutants in coal is sulfur - as sulfur when burned will react with water to form acid rain. All major consumers of coal for industrial purposes must therefore have a method to remove sulfur from the effluent gases. Your corporation is considering the purchase of coal from a new mine located in Wyoming, but the sulfur content is questionable. The scrubbers at you factory can handle coal with a sulfur content of up to 750 ppm. A sample of coal was sent to you, and you choose to determine the sulfur content by combustion analysis. A 10.00 g sample of the coal was burned, and the effluent was bubbled through a 3% solution of hydrogen peroxide to convert the effluent to sulfuric acid. This sample was then titrated with NaOH, which required 45.17 mL of the 0.01087 M NaOH to reach the endpoint. Write the reaction for the sulfuric acid with NaOH, and calculate the ppm sulfur in the sample, and make a recommendation as to the feasibility of this purchase. The reactions of sulfur are:

S + O₂ SO₂

SO₂ + H₂O₂ H₂SO₄

5. Calculate the hydrogen ion concentration and the pH for a 0.0200M solution of HCN under the following conditions:

a) in water

b) in a 0.100 M solution of HCl

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