1. Reaction first-order in A. (12)
Calculate: (a) Rate constant k
if 65.0% A remains after 6.00 min.
(b) Time needed for 75.0% of A to react. (c)
% A remaining after 25.0 min. (d) t½
2. A2(g) + B2(g)
2 AB(g)
(a) 10.0 mol A2 and 10.0 mol B2,
added to a 1.00 L container. At equilibrium 5.00 mol A2
(4)
and 5.00 mol B2
remain. Calculate equilibrium constant K.
(b) If 5.00 mole AB added to the system already
at equilibrium in part (a), (8)
determine [A2],
[B2], and [AB] when new equilibrium reached.
3. Calculate pH: (a) 0.100 M NaClO (b) 1.00 M NH4CN (12)
4. If 1.00 L of a buffer contains 1.00 mol HAc and 0.500 mol NaAc, calculate:
(15)
(a) pH of buffer.
(b) pH after adding 0.30 mol NaOH to the buffer
(assume volume remains 1.00L).
(c) pH after adding 0.30 mol HCl to the buffer (assume
volume remains 1.00L).
5. Calculate Ksp for Pb(OH)2 if 0.00100 g soluble in 1.00 L of water. (10)
6. Solution prepared from 95.3g MgCl2 and 450g H2O.
Calculate: (12)
(a) MgCl2 molality
(b) solution freezing point (c) solution vapor pressure (pure
water 600 torr)
7. SnCl4(g) + 2 H2O(g) ® SnO2(s) + 4 HCl(g) (15)
DHf
(-472) (-286)
(-581) (-92)
( kJ/mol)
DGf
(-432) (-237)
(-520) (-95)
( kJ/mol)
Determine: (a) DH°rxn (b) DG°rxn (c) DS°rxn (d) K (e) account for DS°
8. Design galvanic cell using Zn/Ni electrodes.
Indicate anode, cathode, direction of current, and cell (12)
solutions. Provide
balanced anode/cathode equations and calculate potential.
9. (a) Write balanced ox/red equations and determine overall E°
for CuCl2 ®
Cu + Cl2
(b) If CuCl2 subjected
to 8.0 amp for 5 hours, calculate grams of Cu obtained.
Answers
1. (a) ln(A0/A) = kt
ln 1.54 = 0.43
= k(6.00 min) k
= 0.072 min-1
(b) ln(A0/A) = kt
ln (100/25) = ln 4
= 1.39 = (0.072 min-1)t t
= 19.3 min
(c) ln(A0/A) = kt
ln(100/A) = (0.072 min-1)(25.0
min) = 1.80
100/A
= 6.05 A = 16.5 or 16.5%
(d) t½ = 0.693/.072min-1 = 9.63
min
2. (a) A2
+ B22AB
Eq: 5M
5M 10M
K = 102/52
= 4.0
(b) A2
+ B22AB
Eq: 5+x
5+x 15-2x K
= (15-2x)2/(5+x)2
= 4 or (15-2x)/(5+x) = 2
15-2x = 10+ 2x x = 1.25
[A2] = [B2]
= 6.15M [AB] = 12.5M
3. (a) ClO-1HClO
+ OH-1
Eq: 0.1-x
x
x Kb
= 4.0x10-8 = x2/0.1
x = [OH-1] = 2.0x10-4
pOH = 3.40 pH
= 10.60
(b) CN-1HCN
+ OH-1
Kb = 2.0x10-5
soluton basic (Kb > Ka)
NH4+1NH3
+ H+1
Ka = 5.6x10-10
CN-1HCN
+ OH-1
Eq: 1-x
x
x Kb
= 2.0x10-5 = x2/1
x = [OH-1] = 4.5x10-3
pOH = 11.650 pH = 2.35
4. (a) [H+1] = (Ka)([HAc])/[AC-1] = (1.8x10-5)(1.00M)/(0.500M) = 3.6x10-5 pH =4.44
In: 1.00M
0.50M
(b) HAc H+1
+ Ac-1
[H+1] = (Ka)([HAc])/[AC-1]
= (1.8x10-5)(0.70M)/(0.80M) = 1.6x10-5
Eq: 0.70M
0.80M
pH =4.80
(c) [H+1] = (Ka)([HAc])/[AC-1] = (1.8x10-5)(1.30M)/(0.20M) = 1.2x10-4 pH = 3.93
5. [Pb(OH)2]
= 0.00100/241 = 4.1x10-6 M
Pb(OH)2
Pb+2 + 2OH-1
4.1x10-6 M
4.1x10-6 M 8.2x10-6
M
Ksp = [Pb+2][OH-1]2
= (4.1x10-6 M)(8.2x10-6
M)2 = 2.8x10-16
6. (a) mol MgCl2 = 1.00
m = 1.00mol/0.450kg = 2.22m
(b) DTf
= imkf = (3)(2.22)(-1.86) = -12.4°C
(c) mol ions = 3.00 mol
H2O = 25.0 XH2O
= 25/28 = 0.89
P =(XH2O)(PH2O)=
(0.89)(600 torr) = 534 torr
7. (a) DH° = +85 kJ (b) DG° = +6 kJ (c) DS° = +265 J/K (d) K = 0.089 (e) 3 gas particles ® 4 gas particles
8.
9. (a) RED: Cu+2
+ 2e-1 ®
Cu° +0.34 V
OX: 2Cl-1®
Cl2 + 2e-1
-1.36 V E°
= -1.02 V
(b) Q = I x t = (8.0A)(5)(3600s) = 144,000
C = 1.5 F Cu+2
+ 2e-1®
Cu°
1.5F 0.75 mol 48g
Cu°