CHEM 1332
SPRING 2005
Test 3 Version 1
1.
Which of the following mixtures would NOT be described as a buffer solution?
(A)
(C)
(E)
0.15 M NH4Cl and 0.25 M NH3
0.25 M HNO2 and 0.15 M KNO2
0.30 M NH3 and 0.15 M HCl
2.
Given the values of Ka and Kb in the Table, which of the following systems would be most suitable to use to construct a buffer
of pH 9?
HCOOH
CH3COOH
H3AsO4
C5H5N
NH3
(B)
(D)
0.20 M NaOH and 0.40 M CH3COOH
0.25 M HNO3 and 0.15 M KNO3
Ka = 1.8 x 10-4
Ka = 1.8 x 10-5
Ka1 = 6.0 x 10-3, Ka2 = 1.1 x 10-7, Ka3 = 3 x 10-12
Kb = 1.7 x 10-9
Kb = 1.8 x 10-5
(A)
(D)
H3AsO4/NaH2AsO4
CH3COOH/KCH3COO
3.
Calculate the pH of a solution that is made by mixing 100.0 mL of a buffer solution comprised of 0.15 M NH4Cl and 0.15 M
NH3 and 50 mL of 0.15 M HCl. (Kb(NH3)= 1.8 x 10-5)
(A)
9.26
4.
Calculate the pH of the solution formed during the titration of 30.0 mL of 0.20 M HN3 (Ka = 1.9 x 10-5) with 0.10 M NaOH at
the stage at which 30.0 mL of NaOH was been added?
(A)
4.72
(B)
(B)
(B)
(E)
4.74
9.28
HCOOH/NaHCOO
NH4Cl/NH3
(C)
(C)
9.56
2.71
1
(C)
(D)
(D)
C5H5N/ C5H5NHCl
8.78
5.14
(E)
(E)
5.22
8.86
5.
Which indicator would be the best to use when titrating ammonia with nitric acid? Kb of NH3 is 1.8 x 10-5.
(A)
(C)
(E)
phenolphthalein (pH range 8-10)
alizarin yellow R (pH range 10-12)
methyl red (pH range 4.2-6.2)
6.
Given that the solubility of magnesium fluoride is 0.0729 g/L, calculate the value of Ksp for this salt?
(A)
(D)
6.40 x 10-9
3.87 x 10-4
7.
If the Ksp for aluminum hydroxide is 1.9 x 10-33, calculate the solubility (in mol/liter) of Al(OH)3 in a solution of 0.100 M
NaOH.
(A)
(D)
1.9 x 10-30
5.1 x 10-35
8.
Given that the Ksp for silver bromide is 3.3 x 10-13, which of the following solutions would NOT produce a precipitate of
AgBr?
(i)
(ii)
(iii)
0.20 M AgNO3 and 1.00 x 10-12 M CaBr2
2.00 x 10-8 Ag2SO4 and 1.0 x 10-5 M NaBr
0.20 M AgNO3 and 1.00 x 10-12 M NaBr
(A)
(D)
(i) and (ii)
(iii) only
9.
Which one of the following compounds would have an aqueous solubility that is dependent on the pH?
(A)
NaNO3
(B)
(D)
(B)
(E)
(B)
(E)
(B)
(E)
(B)
NaCl
bromothymol blue (pH range 6.5 -7.5)
thymol blue (pH range 1.2-2.8 and 8 to 9.2)
1.55 x 10-3
1.60 x 10-9
(C)
1.9 x 10-36
2.9 x 10-9
(C)
(i) and (iii)
all three of (i), (ii), (iii)
(C)
NaClO4
2
(C)
(D)
1.36 x 10-6
7.0 x 10-32
(ii) and (iii)
NaClO2
(E)
NaBr
10.
Which item (a, b or c) in each of the three groups below has the highest entropy?
I.
II.
III.
(i) 10 g ice
(ii) 10 g water vapor (iii) 10 g liquid water
(i) 1 mole NaCl solid (ii) 1 mol NaCl in 1 M aqueous solution (iii) 1 mol molten NaCl
(i) 1 mole C2H6(g), (ii) 1 mole CH4(g), (iii) 1 mol C3H8(g) all at 25 °C and 1 atm
(A)
i, i, ii
11.
Does the entropy of the system increase or decrease for the following reactions?
(i)
(ii)
(iii)
Ba2+(aq) + SO42-(aq) → BaSO4(s)
2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g)
2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(l)
(A)
(C)
(E)
(i) decreases, (ii) increases, (iii) increases
(i) decreases, (ii) decreases, (iii) increases
(i) increases, (ii) decreases, (iii) increases
12.
What is the standard entropy change and the standard free energy change for the reaction H2(g) + Cl2(g) → 2HCl(g) given the
following absolute entropies and free energies of formation: Sº(H2(g)) = 131 J/K.mol, Sº(Cl2(g)) = 223 J/K.mol, Sº(HCl(g)) =
187 J/K.mol, ∆Gfº(HCl(g)) = -95 kJ/mol.
(A)
(C)
(E)
∆Sº = -20 J/K.mol, ∆Gº = 190 kJ/mol
∆Sº = 167 J/K.mol, ∆Gº = 95 kJ/mol
∆Sº = 20 J/K.mol, ∆Gº = -190 kJ/mol
(B)
iii, ii, iii
(C)
ii, ii, iii
(B)
(D)
(B)
(D)
i, ii, iii
i, i, iii
(i) decreases, (ii) increases, (iii) decreases
(i) increases, (ii) increases, (iii) decreases
∆Sº = -167 J/K.mol, ∆Gº = -95 kJ/mol
(D)
∆Sº = -334 J/K.mol, ∆Gº = -190 kJ/mol
3
(E)
13.
The Gibbs free energy of formation of solid iron (III) oxide is the Gibbs free energy change for the reaction
(A)
(C)
(E)
4 Fe(s) + 3 O2(g) → 2 Fe2O3(s)
2 Fe(s) + 3/2 O2(g) → Fe2O3(s)
none of these
14.
A problem in combustion is the production of nitrogen oxides. Given that ∆Hº = -114 kJ and ∆Sº = -146.54 J/K for the
reaction, 2NO(g) + O2(g) <=> 2NO2(g), which nitrogen oxide is favored
i) at 50 ºC and ii) at 2500 ºC?
(A)
(D)
i) NO; ii) NO2
i) NO2; ii) NO2
15.
Consider the endothermic reaction: N2(g) + O2(g) → 2 NO(g), ∆Hº = 192.5 kJ/mol. At 200 K the equilibrium constant is 5.0 x
10-4. At 2500 K the value of the equilibrium constant:
(A)
(C)
(E)
is greater than 5.0 x 10-4.
is 10.0 x 10-4.
is less than 5.0 x 10-4.
16.
(B)
(D)
(B)
(E)
i) NO2; ii) NO
None is favored.
(B)
(D)
2 FeO(s) + 1/2 O2(g) → 2 Fe2O3(s)
2 Fe(s) + 3 O2(g) → Fe2O3(s)
(C)
i) NO; ii) NO
depends on the concentration of oxygen.
is 5.0 x 10-4.
For the reaction N2O3(g) → NO(g) +NO2(g) ∆Gº = -4.78 kJ. Calculate Keq at 25 ºC.
(A)
1.002
(B)
17.
Consider the skeleton reaction, Cr2O72- (aq) + Cl-(aq) → Cr3+(aq) + Cl2(g) (acidic solution).
balanced, using the lowest possible coefficients, what is the coefficient of water?
(A)
0
(B)
0.9981
2
(C)
(C)
2.33
3
4
(D)
(D)
1.21
7
(E)
6.88
When the equation is
(E)
14
18.
Balance the following equation in basic solution: MnO4-(aq) + Fe(OH)2(s) → MnO2(s) + Fe(OH)3.
of water?
(A)
0
19.
The following are some standard electrode potentials
Fe2+(aq) + 2e- → Fe
Fe3+(aq) + e- → Fe2+(aq)
(B)
1
(C)
-0.44 V
+0.77 V
2
(D)
What is the coefficient
3
Al3+(aq) + 3e- → Al
Mn2+ + 2e- → Mn
(E)
4
-1.66 V
–1.18 V
Which of the following statement is correct?
(A)
(C)
(E)
Fe2+ is a stronger oxidizing agent than Mn2+
Al3+ is a weaker oxidizing agent than Mn2+
None of the above
20.
A galvanic cell in which Al3+(aq) is reduced is made using Mg(s), Al(s), Mg2+(aq) and Al3+(aq). If the value of Eº for the cell
is +0.71 V and the reduction potential of Al3+ is -1.66 V, calculate the reduction potential of Mg2+.
(A)
(D)
-2.37 V
-0.95 V
(B)
(E)
(B)
(D)
+2.37 V
cannot be determined
5
Fe3+ is a stronger oxidizing agent than Fe2+
All of (A) through (C) are correct
(C)
0.95 V