Chemistry 1110                                                                                                Dr. Shane Phillips

Fall 1999                                                                                                          Nov. 8, 1999

 

 

EXAM 3

 

 

 

Name                                                                                      

 

Student I.D. Number                                                               

 

 

Please wait for the instruction to begin before starting to work on this exam.

 

 

 

            This is a closed book exam.  It should contain 6 pages including this cover sheet.  The multiple choice should be answered on a Scantron form (882-ES).  Please be sure your exam is complete with your name and student I.D. number entered in the space provided above.  You may use an approved calculator.  

 

 

 

Problems

Pts. Poss.

Pts. Earned

Multiple Choice

75

 

Work-out

25

 

Total

100

 

 

 

Potentially Useful Information

 

Kw = 1.0 x 10-14 (room temperature)

 

 

 

      1.   Calculate the concentration of H3O+ for an aqueous solution with a pH of 8.20.

 

      a)   1.6 ΄ 10–6 M    b)  0.91 M    c)  1.4 ΄ 10–3 M    d)  6.3 ΄ 10–9 M    e)  1.0 ΄ 10–14 M

 

      2.   All of the following are strong acids except _____________.

 

      a)   HF    b)  HClO4   c)  HI    d)  HBr    e)  HNO3

 

      3.   All of the following are strong bases except ____________.

 

      a)   NH2OH    b)  NaOH    c)  LiOH    d)  KOH    e)  Ba(OH)2

 

      4.   Which of the following is the strongest base?

 

      a)   ammonia (pKb = 4.75)                                  d)   pyridine (pKb = 8.75)

      b)   methylamine (pKb = 3.44)                             e)   morphine (pKb = 5.79)

      c)   urea (pKb = 13.90)

 

      5.   Which of the following is the strongest acid?

 

      a)   H2O    b)  CH4   c)  H2S    d)  H2Se    e)  H2Te

 

      6.   Which of the following has the highest pKa?

 

      a)   HClO    b)  HClO2   c)  HClO3   d)  HClO4   e)  HCl

 

      7.   The pKa for HF is 3.45. This expression refers to which of the following reactions?

 

      a)   HF(aq) + H2O(l) « F–(aq) + H3O+(aq)         d)   F–(aq) + H2O(l) « HF(aq) + OH–(aq)

      b)   HF(aq) + OH–(aq) « F–(aq) + H2O(l)          e)   F–(aq) + H3O+(aq) « HF(aq) + H2O(l)

      c)   H3O+(aq) + OH–(aq) « 2H2O(l)

 

      8.   The equation for which one could write a Ka2 expression for sulfurous acid is ________.

 

      a)   HSO3–(aq) + H2O(l) « SO32–(aq) + H3O+(aq)

      b)   HSO3–(aq) + H2O(l) « H2SO3(aq) + OH–(aq)

      c)   H2SO3(aq) + H2O(l) « HSO3–(aq) + H3O+(aq)

      d)   SO32–(aq) + H2O(l) « HSO3–(aq) + OH–(aq)

      e)   H2SO3(aq) + 2H2O(l) « SO32–(aq) + 2H3O+(aq)

 

      9.   What is the pH of 1.0 M HCNO(aq) (Ka = 2.2  ΄ 10–4)?

 

      a)   7.32   b)  7.00    c)  1.83    d)  4.70    e)  3.66

 

    10.   If a small amount of HCl(aq) is added to 0.10 M CH3COOH(aq),

 

      a)   Ka becomes larger.

      b)   the equilibrium concentration of CH3COO–(aq) is decreased.

      c)   the equilibrium concentration of acetic acid decreases.

      d)   the equilibrium concentration of the acetate ion is increased.

      e)   no change occurs.

 

    11.   Calculate [H+] for a solution labeled "0.0500 M H2SO3(aq)" (pKa1 = 1.81, pKa2 = 6.91).

 

      a)   0.021 M    b)  0.025 M    c)  0.029 M    d)  0.050 M    e)  0.015 M

 

    12.   The conjugate acid of HPO42– is

 

      a)   H3O+   b)  PO43–   c)  HPO42–   d)  H3PO4   e)  H2PO4–

 

    13.   Which one of the following salts gives an acidic aqueous solution?

 

      a)   NaH2PO4   b)  KBr    c)  KCN    d)  KNO3   e)  Na3PO4

 

    14.   Which one of the following salts gives a basic aqueous solution?

 

      a)   NaCH3CO2   b)  KI    c)  NH4Cl    d)  Fe(ClO4)2   e)  RbNO3

 

    15.   Which one of the following gives a neutral aqueous solution?

 

      a)   Cu(ClO4)2   b)  LiClO4   c)  NaNO2   d)  KF    e)  C5H5NH(ClO4)

 

    16.   Which of the following pairs of ions can exist in large concentrations simultaneously in aqueous solution?

 

      a)   NH4+ and OH–                                              d)   H3O+ and CN–

      b)   CH3NH3+ and OH–                                        e)   NH4+ and F–

      c)   H3O+ and CH3CO2–

 

    17.   Calculate the pH of a 0.136 M solution of aqueous sodium fluoride. The value of Ka for HF is 3.5 ΄ 10–4.

 

      a)   8.29    b)  5.71    c)  8.73    d)  2.16    e)  11.84

 

    18.   What is the pH at the stoichiometric point in the titration of 0.018 M CH3COOH(aq) with 0.036 M NaOH(aq) at room temperature? For acetic acid, Ka = 1.8 ΄ 10–5.

 

      a)   less than 7.0    b)  greater than 7.0    c)  equal to 7.0    d)  need more information to predict

 

    19.   The curve below corresponds to the titration of __________.

             

      a)   0.010 M HClO4(aq) with 0.10 M KOH(aq).

      b)   0.10 M HClO2(aq) (pKa = 2.0) with 0.10 M KOH(aq).

      c)   0.010 M HClO(aq) (pKa = 7.5) with 0.10 M KOH(aq).

      d)   0.10 M HCl(aq) with 0.10 M KOH(aq).

      e)   0.010 M H2SO4(aq) (pKa2 = 1.9) with 0.10 M KOH(aq)

 

    20.   For HF, pKa = 3.45. What is the pH of an aqueous buffer solution that is 0.100 M HF(aq) and 0.300 M KF(aq)?

 

      a)   11.03   b)  2.97    c)  3.93    d)  10.07    e)  3.45

 

    21.   What is the Ksp expression for lead(II) chloride?

 

      a)   [Pb2+][Cl–]2                                                   d)   [Pb+][Cl–]2/[PbCl2]

      b)   [Pb+][Cl–]                                                     e)   [Pb2+]2[Cl–]

      c)   [Pb22+][Cl–]2

 

    22.   If the value of the solubility product for AgBr is 5.0 ΄ 10–13 at 25oC, calculate the solubility of AgBr(s) in water.

 

      a)   5.0 ΄ 10–7   b)  7.1 ΄ 10–7   c)  2.5 ΄ 10–13   d)  2.5 ΄ 10–6   e)  1.4 ΄ 10–6

 

    23.   The relationship between the molar solubility in water, s, and Ksp for the ionic solid Fe(OH)2 is

 

      a)   Ksp = s3   b)  Ksp = 4s3   c)  Ksp = 2s2   d)  Ksp = s   e)  Ksp = s2

 

    24.   Which of the following water–insoluble salts is much more soluble in 1.0 M HClO4(aq)?

 

      a)   PbI2   b)  Hg2Br2   c)  PbCO3   d)  AgI    e)  AgCl

 

    25.   The combined equilibrium reaction from the reactions shown below, for carbonic acid in water and carbon dioxide in water, provide a buffering system for blood in our bodies.  What pH range will these combined equilibria provide an effective buffer?

                        H2CO3(aq)  +  H2O(l)  ίΰ  HCO3-(aq)  +  H3O+(aq)                     Ka = 1.53 ΄ 10–4.

                        CO2(aq)  +  H2O(l)  ίΰ  H2CO3(aq)                                          Keq = 3.1 ΄ 10–3.

 

 

            a)         2.0 – 4.0                                              d)         7.4 – 9.4

            b)         1.5 -3 1                                                e)         5.3 – 7.3

            c)         3.7 – 5.7

 

Show all work clearly for the following work-out problems.

 

26.      (5 pts.)  What condition is required for an aqueous solution to be considered neutral regardless of the temperature?

 

 

 

27.  (10 pts.)  What happens when 200.0 mL of 1.0 x10-4M AgNO3(aq) and
900.0 mL of 1.0 x 10-6 M KCl(aq) are mixed together to make a solution with a total volume of 1.100 L.  What are the final concentrations of all ions present in solution (ignoring hydronium and hydroxide ions)?  Show all work to receive credit. 
(Note:  Ksp of silver chloride is 1.6 x 10-10.)

 

 

 

28.  (10 pts.)  For the titration of 50.0 mL of 0.020 M hypochlorous acid (aqueous) with 0.020 M KOH(aq), calculate the pH:

(i)                  before addition of the strong base.

(ii)                after the addition of 30.0 mL of the strong base.

                 The Ka for HClO(aq) is 3.0 x 10-8.

 

                        (i)

 

 

 

                        (ii)

 

 

 

Answer Key -- MT3F99

 

      1.   d         

      2.   a         

      3.   a         

      4.   b         

      5.   e         

      6.   a         

      7.   a         

      8.   a         

      9.   c         

    10.   b         

    11.   a         

    12.   e         

    13.   a         

    14.   a         

    15.   b         

    16.   e         

    17.   a         

    18.   b         

    19.   a         

    20.   c         

    21.   a         

    22.   b         

    23.   b         

    24.   c         

    25.   e         

    26.   [hydronium ion] = [hydroxide ion]

    27.   no precipitation occurs, [Ag+] = [NO3-] = 1.8 x 10-5, [Cl-] = [K+] = 8.2 x 10-7

    28.   (i)  pH = 4.61   (ii)  pH = 7.70