CHEM 113

HOMEWORK 9

NAME_________________

DUE Wed. March 14, 2001

 

COMP. HMWRK: 19.Buf and Hydr. 1-5

1. The single equilibrium equation written below can be applied to a number of different phenomena. HC2H3O2 + H2O = H3O+ + C2H3O2- Ka = 1.74 x 10-5. Indicate the phenomenon-ionization of pure acid, common ion (H+ or OH-) effect, buffer formation, hydrolysis - for each of the following combinations of concentrations.

[C2H3O2-] is high; [HC2H3O2] and [H3O+] are very low

pure acid

common ion

buffer

hydrolysis

[HC2H3O2] is high; [H3O+] and [C2H3O2-] are low

pure acid

common ion

buffer

hydrolysis

[H3O+] and [HC2H3O2] are high; [C 2H3O2-] is low

pure acid

common ion

buffer

hydrolysis

[HC2H3O2] and [C2H3O2-] are high; [H3O+] is low

pure acid

common ion

buffer

hydrolysis

.

  1. Calculate the number of grams of NH4Br that have to be dissolved in 1.00 L of water at 25oC to have a solution with a pH of 5.16.

 

 

 

 

Mass = _______________

3. The salt, calcium propionate, is used as a preservative in bread. What is the mole ratio of [CH3CH2COOH]/[CH3CH2COO-] that would give a pH of 4.15. The Ka for propionic acid is 1.3 x 10-5.

 

 

 

ratio = |________________

4. Calculate the pH of a solution that is 1.50 M in HN3 (hydrazoic acid) and 0.750 M in KN3.

 

 

 

 

 pH = |__________________

5. If 8.0 ml of 2.00 M HCl are added to 100 ml of the buffer prepared in problem #4, what is the final pH of the solution .

 

 

pH = |__________________

 

  1. Calculate the concentrations of all solute species present in 0.75 M selenous acid, H2SeO3

Ka1 = 3.5 x 10-3 and Ka2= 5.0 x 10-8.

 

[H2SeO3] = |___________

[HSeO3-1] = |___________

[SeO3-2] = |___________

 

7. Calculate the pH of a (see previous problem for Ka's)

a. 0.50 M Na 2SeO3 solution.

 

pH = |___________________

b. 1.25 M Na HSeO3 solution.

 

 

 

pH = |___________________

c. a solution that contains 0.125 M Na2SeO3 and 0.50 M NaHSeO3.

 

 

pH = |___________________

8. Calculate the pH of a solution at the equivalence point in the titration of 0.1035 M HCl with 25.00 mL of 0.1148 M NH3 (aq)

 

 

pH = |_____________

9. Calculate the pH at the first and second equivalence points in the titration of 0.612 g of Na2CO3 with 0.1014 M HCl and then suggest an indicator that might be appropriate for each of these equivalence points.

pH(1) = |___________

Indicator(1) = |____

pH(2) = |___________

Indicator(2) = |____