Chem 2113

Test 2

Fall 1996

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:

a) 0.015 M Na₂O

b) The resultant solution after mixing 15.0 mL of 0.10 M HCl with 15.0 mL of 0.10 M NaOH.

c) The resultant solution after mixing 15.0 mL of 0.10 M HCl with 15.0 mL of 0.20 M NaNO₂.

d) The solution obtained after mixing 25.0 mL of 0.10 M HC₂H₃O₂ with 10.0 mL of 0.15 M NaC₂H₃O₂.

e) The resulting solution when 5.00 mL of 0.10 M HCl is added to the solution from (d).

2. Consider the titration of 50.0 mL of 0.10 M propanoic acid with 0.10 M NaOH. 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 50.0 mL of titrant is added;

e) After 62.5 mL of titrant is added.

3. Consider the titration of 50.0 mL of 0.050 M o-phthalic acid with 0.10 M NaOH. 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. A sample of dog food is analyzed for protein content. A 2.50 g sample of the dog food was ground up and digested in sulfuric acid, using a copper sulfate catalyst. Upon completion of the digestion the solution was distilled into 50.0 mL of 0.0517 M H₂SO₄. After the distillation was complete, the sulfuric acid solution was titrated with 0.0846 M NaOH, requiring 15.7 mL. If the gravimetric factor for the protein in the dog food is 6.25, calculate (a) the % nitrogen and (b) the %protein in the original sample.

5. An impure mixture that may contain NaOH, Na₂CO₃, and/or NaHCO₃ with other inert matter was analyzed. A 1.500 g sample of the impure mixture was obtained. 0.5000 g of this sample was titrated to the phenolphthalein endpoint with 0.1042 M NaOH, requiring 16.33 mL. A second 0.5000 g sample was titrated to the modified methyl orange endpoint, requiring 48.15 mL. Determine (a) the component(s) present from the three listed; and (b) the % composition of each of the component(s) that are(is) present.

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