Chem 2113

Test 2

Fall 2000

Questions are worth 25 points each. OMIT ONE QUESTION by clearly writing OMIT in the space provided for your work. If you fail to mark OMIT on a question I will omit the last question of the test. Show your work and circle your answers for full credit.

1. Calculate the pH of the following solutions:

1.5 x 10^-7 M HNO₃

0.0015 M HCOOH (Formic acid)

0.025 M C₆H₅NH₂ (Aniline)

0.075 M NaHC₆H₄(COO)₂ (Sodium biphthalate)

0.010 M KClO₄

2. Consider the titration of 50.0 mL of 0.10 M sodium phenolate with 0.10 M HClO₄. Calculate the pH of the solution at the following points along the titration curve:

a) Before any titrant is added;

b) After 15.0 mL of titrant is added;

c) After 25.0 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 25.0 mL of 0.20 M malonic acid with 0.20 M NaOH. Calculate the pH of the solution 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. A popular brand of cat food is analyzed using the Kjeldahl method. A 3.29 g sample of the cat food was performed, with the products of the digestion of the cat food being distilled into 100.0 mL of 0.1000 M HCl. The excess HCl was back titrated with 7.21 mL of 0.1057 M NaOH. Determine the percent by mass for nitrogen in the sample, and assuming a gravimetric factor of 6.25 for the protein relative to the nitrogen content (16.0% nitrogen in the protein), calculate the percent (by mass) protein in the cat food.

5. Consider a mixture that may contain NaOH (39.997), Na₂CO₃ (105.989) and NaHCO₃ (84.007). A 6.125 g sample of an unknown was dissolved and diluted to 250.0 mL. A 100.0 mL aliquot of this solution was titrated to a phenolphthalein endpoint , which required 32.15 mL of 0.1012 M HCl. A 50.00 mL aliquot was titrated to a bromocresol green endpoint with 47.22 mL of the 0.1012 M HCl. Determine the identity of the active component(s), and calculate the percentage of each present in the original mixture.

Comments? E-mail me.

Return to my homepage.