64.(E) This problem can be done using the factor-label method.

..

./

.

liter vinegar

gram equiv HC H O

gram equiv HC H O liter of vinegar

gC H O

1

10

1

(^232) 60 00
232
232

65.(D) This problem can be solved using the factor-label method.
wt.% solution %
parts HC H O
100
232
= #
../
.
mL solution g mL %.%
gHC H O
1000 1 0
60
100 6 0
232
==: #
66.(A) Heat needs to be absorbed when a solid melts; therefore, the reaction is endothermic,
∆H> 0. When a solid melts and becomes a liquid, it is becoming more disordered, ∆S> 0.

67. (C) The question concerns the effect of changing standard conditions of a cell to nonstan-
    dard conditions. To calculate the voltage of a cell under nonstandard conditions, use the
    Nernst equation
    
    
    • EE ..log log
      n QE Ag
    
    
    
    

0 0591 Zn

2

0 0591

2

2

=-% =-% +

7

7

A

A

where E°represents the cell voltage under standard conditions, E represents the cell volt-

age under nonstandard conditions, nrepresents the number of moles of electrons passing

through the cell, and Qrepresents the reaction quotient.

Choices (D) and (E) would have the effect of increasing the cell voltage. Choices (A) and

(B) would have no effect on the cell voltage.

68.(C) To solve this problem, use the equation

logx.

xkt

230

(^0) = :
with the corresponding half-life t 1 /2= 0.693/k, where x 0 is the number of original radioac-
tive nuclei and xrepresents the number of radioactive nuclei at time t. krepresents the
first-order rate constant. Substituting into the equation yields
.
./..
logxx.
years years
230
0 693 6 93 11 5
(^0) == 05
``jj
x
x (^0). 3
xx 0 .. 31 #^100 %%^33 that remain unreacted
69.(D) Begin by writing the equations which define the equilibrium constants.
() () ().
() () ().
AgCl s Ag aq Cl aq K mol L
AgI s Ag aq I aq K mol L
16 10
80 10
sp
sp
10 2 2
17 2 2
1
2
"
"
#:
#:
+=
+=
+- - -
+- - -
Part IV: AP Chemistry Practice Test