Chemistry

 When NH4Cl is added to an 0.10 M NH3 solution, the pH of this solution:

(a) increases 

(b) decreases

 (c) remains the same

  (d) increases at first and then decreases.

     (e) decreases at first and then increases.

 Which of the following would make the best buffer?

 (a) a mixture of HCl and NaCl

(b) a mixture of NaOAc and NH3

(c) a mixture of HOAc and NH4Cl

(d) a mixture of NaOAc and NH4Cl

(e) a mixture of NH3 and NH4Cl
 

 How would you increase the buffering capacity of a buffer made by adding NaHCO2 to an aqueous solution of HCO2H?

         (a) increase the concentration of HCO2H.

         (b) increase the concentration of NaHCO2.

          (c) increase the concentrations of both HCO2H and NaHCO2.

         (d) increase the ratio of the concentration of HCO2H to NaHCO2.

         (e) increase the ratio of the concentration of NaHCO2 to HCO2H.

 Calculate the pH of a buffer prepared by mixing 0.10 mol of sodium formate and 0.05 mol of formic acid in 1.0 L of solution. (HCO2H: Ka = 1.8 x 10-4)

 (a) 1.8 x 10-4

 (b) 3.44

(c) 4.05

 (d) 5.31

 (e) none of the above
 

Which of the following solutions will show the largest pH change when 10 mL of 1 M NaOH is added to it?

   (a) 10 mL of 1 M NaOH  

  (b) 100 mL of water

   (c) 10 mL of 1 M NaNO3

    (d) 10 mL of 0.01 M HOAc

      (e) 100 mL of 0.1 M HOAc and 0.1 M NaOAc
 

Which of the following equations accurately describes an 0.10 M H2Gly solution?

(a) [H3O+] ≈ [H2Gly]

 (b) [H3O+] > [H2Gly]

 (c) [H3O+] < [HGly-] 

(d) [H3O+] ≈ [HGly-]

 (e) [H3O+] > [HGly-]
 

 At what point in the following titration curve would the pH of the solution be equal to the pKa of the acid?11.gif

 (a) 0 mL

 (b) 50 mL

 (c) 95 mL 

(d) 100 mL

 (e) 120 mL

 In a 0.10 M solution of H2Se, the Se2- concentration is:

  (a) [Se2-] = 0.10 x Ka2 = 1.0 x 10-11       (b) [Se2-] = Ka2 = 1.0 x 10-10

   (c) [Se2-] = (0.10 x Ka2)1/2 = 3.2 x 10-6   (d) [Se2-] = (0.10 x Ka1)1/2 = 4.1 x 10-3

     (e) none of the above

For a weak diprotic acid, H2A, for which Ka1 = 2.1 x 10-7 and Ka2 = 4.3 x 10-13 the A2- ion concentration at equilibrium will be:

         (a) approximately equal to the initial concentration of H2A.

          (b) roughly equal to Ka2.

          (c) roughly equal to the HA- concentration.

         (d) much larger than the HA- concentration.

         (e) approximately equal to the H3O+ concentration