6B CHEM PRACTICE FINAL EXAM (Prof. Crowell)
March 14, 2012
FILL IN YOUR STUDENT ID NUMBER, NAME, and TEST FORM = A
1. For the following four salts, determine whether water solutions of each salt would be acidic, basic, or
neutral? The salts are:
1. KNO2 , 2. NH4Cl , 3. CsI , 4. CH3COONa
a) 1. acidic, 2. basic, 3. neutral, 4. acidic
b) 1. acidic, 2. basic, 3. basic, 4. acidic
c) 1. neutral, 2. acidic, 3. basic, 4. neutral
d) 1. neutral, 2. acidic, 3. neutral, 4. basic
e) 1. basic, 2. acidic, 3. neutral, 4. basic
2. Consider the titration of 100.0 mL of 0.500 M NH3 (Kb = 1.8 x 10-5) with 0.500 M HCl. At the
stoichiometric point of this titration, the [H+] is:
a) 1.0 x 10-7 M b) 1.8 x 10-5 M
c) 1.2 x 10-5 M d) 5.6 x 10-10 M e) none of these.
3. For ammonia, NH3, Kb is 1.8 x 10-5. To make a buffered solution of pH = 10.0 at 298K, the ratio of NH4Cl to
NH3 must be:
a) 1.8 : 1
b) 1 : 1.8
c) 0.18 : 1
d) 1 : 0.18
e) 1.8 x 105 : 1
4. 50.0 mL of 1.50 M NaOH solution is being titrated at 298K with a 2.00 M HCl solution. What will the pH be after
the addition of 35.0 mL of HCl?
a) 1.23
b) 11.70
c) 12.77
d) 2.30
e) 10.56
5. 180 mL of an unknown concentration of propionic acid, (CH3CH2COOH, Ka = 1.35 x 10-5 M) is titrated with 1.5
M KOH at 298 K. The equivalence point is reached after the addition of 31.2 mL of KOH, resulting in a pH = 9.15.
What is the initial concentration of propionic acid?
a) 7.0 M
b) 0.26 M
c) 8.5 M
d) 0.32 M
e) 0.03 M
6. Ethylamine, C2H5NH2, is a weak base with Kb = 4.3 x 10-4 M at 298 K. What is the value of the equilibrium
constant at 298 K for the following reaction: C2H5NH3+ + OH C2H5NH2 + H2O
d) 2.3 x 10-11
e) 2.1 x 105
a) 4.3 x 1010
b) 2.3 x 103
c) 4.3 x 10-4
7. Rank the following 0.1 M solutions in order of INCREASING pH (i.e. increasing base strength):
RbOOCCH3
CH3NH3Cl
Na2O
HBr
KClO4
a) KClO4 < RbOOCCH3 < Na2O < HBr < CH3NH3Cl
b) HBr < CH3NH3Cl < KClO4 < RbOOCCH3 < Na2O
c) Na2O < HBr < KClO4 < RbOOCCH3 < CH3NH3Cl d) HBr < CH3NH3Cl < RbOOCCH3 < Na2O < KClO4
e) HBr < KClO4 < CH3NH3Cl < Na2O < RbOOCCH3
8. What is the pH after 120 mL of 4.0 M HClO4 is added to 150 mL of 3.0 M KOH at 298 K?
a) 0.60
b) 13.05
c) 0.95
d) 13.89
e) 13.40
9. Suspose you titrate 200 mL of 0.45 M solution of NaNO2 with 6 M HCl at 298 K (Ka for HNO2 is 5.1 x 10-4 M at
298 K). What is the pH at the stoichiometric point?
a) 3.29
b) 5.54
c) 7.00
d) 8.46
e) 1.84
10. Calculate the pH of a solution prepared by dissolving 0.040 moles of sodium nitrite (NaNO2) in 200 mL of 0.10
M nitrous acid, HNO2 at 298 K. The acidity constant at 298 K for HNO2 is Ka = 5.1 x 10-4.
a) 3.59
b) 2.99
c) 2.59
d) 0.59
e) 5.99
11. For the hypothetical reactions 1 and 2 below, K1 = 103 and K2 = 10-5.
1).
3).
A + 2B AB2
AB2 AB + B
a) K3 = 102
2).
A + B AB
The value of K for reaction 3 (i.e. K3) is:
b) K3 = 108
c) K3 = 10-2
d) K3 = 10-8
e) K3 = 10-11
-3
-8
12. What is the pH of a 3.2 M solution of H3PO4 at 298K? ( Ka1 = 7.2 x 10 , Ka2 = 6.3 x 10 ,
-13
Ka3 = 4.2 x 10
)
a) 3.35
b) 1.07
c) 0.82
d) 1.41
e) 1.64
Chem 6B Practice Final
1A
Prof. Please Crowell
13. rank the following acids in order of decreasing acidity: HClO, HIO, HBrO, HI, HClO2
a) HIO > HBrO > HClO2 > HClO > HI
b) HI > HClO2 > HClO > HBrO > HIO
c) HClO2 > HClO > HI > HIO > HBrO
d) HClO2 > HI > HClO > HBrO > HIO
e) HI > HClO > HBrO > HIO > HClO2
14. If an aqueous solution containing a non-dissociating molecular (non-electrolyte) solute boils at 101.10C, at
what temperature does it freeze? The proportionality constants (in units of degrees C - kg/mol ) for water are
Kf = 1.86 C/m and Kb = 0.515 C/m.
a) 3.97C
b) 0.87C
c) + 2.14C
d) 0.30C
e) 5.42C
15. What is the boiling point (in C) under normal pressure conditions of a 0.33 m aqueous solution of sodium
phosphate, Na3PO4? The proportionality constants (in units of degrees C - kg/mol ) for water are Kf = 1.86 C/m
and Kb = 0.515 C/m.
a) 100.17
b) 100.68
c) 102.46
d) 99.32
e) 102.06
16. For the dissolution of PbCl2 in water, Ksp = 1.90 x 10
this temperature?
a) 2.67 x 10
2
b) 2.18 x 10
3
5
at 25 C. What is the solubility of PbCl2 in water at
c) 1.68 x 10
2
d) 4.36 x 10
3
e) 3.08 x 10
3
17. What is the vapor pressure of H2O at 65.0 C? The heat of vaporization, Hvap = 40.7 kJ/mol for H2O.
a) 125 torr
b) 77 torr
c) 250 torr
d) 195 torr
e) 760 torr
18. A solution is prepared by adding 20 mL of 0.035 M nitric acid, HNO3, to 200 mL of 0.1 M hydrocyanic acid,
HCN (Ka = 6.2 x 10-10 for HCN at 298 K). What is the pH of this solution?
a) 2.50
b) 7.75
c) 0.15
d) 2.45
e) 11.50
19. Which of the following is the strongest base?
a) ClO2 -
b) ClO3 -
c) BrO -
d) IO -
e) ClO -
20. Calculate the vapor pressure in torr at 25C of a solution containing 26.9 g of the nonvolatile, non-electrolyte (i.e.
non-dissociating) solute: urea, CO(NH2)2, in 712 g H2O. The vapor pressure of water at 25C is 23.8 torr.
a) 10.7
b) 0.27
c) 23.5
d) 0.60
e) 22.9
21. Commercial laundry bleach is an aqueous solution containing sodium hypochlorite, NaOCl. The concentration of
NaOCl in bleach is typically 0.67 M. Given that pKb for OCl- is 6.48 at 298 K, calculate the pH of commercial
laundry bleach at 298 K.
a) 3.33
b) 13.83
c) 13.33
d) 10.67
e) 7.35
22. Using molecular orbital theory, estimate which of the following molecules would be expected to have the largest
bond order?
b) NO
c) AlSi
d) O2e) SeBr+
a) CN+
23. Which of the following liquids would be expected to have the highest vapor pressure at a given temperature?
a) CH4
b) PH3
c) H2O
d) H2Se
e) H2Te
24. A solution is prepared by mixing 100 ml of 0.05 M Pb(NO3)2 and 200 ml of 0.10 M NaI. Calculate the
concentration of the lead ion (i.e. [Pb2+]) in solution at equilibrium, given that the Ksp for solid PbI2 at 298 K is
Ksp = 1.4 x 10-8.
a) 1.3 x 10-5
b) 3.33 x 10-2
c) 1.5 x 10-3
d) 1.7 x 10-2
e) 6.7 x 10-2
25. Calculate the solubility of Al(OH)3 in moles per liter in a solution buffered at pH = 9.31 at a temperature of
298 K. [Al(OH)3 has a Ksp = 1.3 x 10-33 at 298 K].
a) 1.1 x 10-5
Chem 6B Practice Final
b) 1.5 x 10-19
c) 5.7 x 10-21
2A
d) 2.7 x 10-24
e) 6.4 x 10-29
Prof. Crowell