The Medical College - Page 66
105.
C.
The work done in accelerating the cart is
equal
to the gain in kinetic energy:
Fnetx = 1/2
mv
2, or (100
N)(10 m) = (1/2) 80v
2 and then v = 5
m/sec.
106.
C.
Both [H
+] and
[OH–] =
1.0
10
–7. The pH
=
7.0.
107.
B.
Ka =
= 6.6
10
–5 =
[H
+]2 = 6.6
10
–9 =
66
10
–10
Because the square root of 66 is about 8,
[H
+] = 8
10
–5 or between
1
10
–4 and
1
10
–5 pH
=
– log [H
+ ] and is between 4
and 5. Although
water itself contributes [H
+] = 1
10
–7, this
is
negligibly small in comparison to the
H
+ from
benzoic acid. Thus, in this example, the
H
+
from water may be neglected.
108.
D.
pH + pOH = 14
Although in pure water pH = pOH, that is not
the
case here. Because pH is between 4 and 5,
how-
ever, this pOH will be between 9 and
10.
109.
B.
Ka =
1
[H
1
+]
0
2
–12 =
6.6
10
–5
[H
+]2 = 6.6
10
–17 =
66
10
–18
[H
+] = about
8
10
–9 or
0.08
10
–7.
This is very small compared with the
[H
+] of
1.0
10
–7 supplied by
ionization of water. Thus
the pH approximates 7.
110.
A.
Henderson-Hasselbalch formula
pH = pKa
+ log
When the concentrations of salt and acid are
equal,
pH = pKa. By inspection of
Ka =
6.6
10
–5, its
neg-
ative log would be between 4 and 5. Thus the
pKa
and the resulting pH are between 4 and
5.
111.
D.
Ksp
= 9
10
–12 =
[Ag+]2 [CrO=
4]
= (1
10
–6)2 [CrO=
4] = 9
10
–12
[CrO
=
4] = 9 or
approximately 1
10
1
112.
C.
Addition of Cl
– ions will bring
about precip-
itation of AgCl when its Ksp is exceeded.
113.
B.
The Ksp
is given for a particular
temperature
and will change with temperature. It may
speed
the reaction but will not likely bring about
more
complete precipitation.
[salt]
[acid]
[H ]
0.0001
2
+
[H ][B ]
[HB]
±
+
114.
C.
The Ksp
with the smallest number represents
the one with the lowest
solubility.
115.
D.
The Ksp's are independent of each other.
If
the Ksp
of one is not reached, no precipitation
will
occur.
116.
A.
Phosphorus, a nonmetal, will react with
oxy-
gen to form an oxide. This oxide will react
with
water to form an acidic solution.
117.
A.
Nitrogen, a nonmetal, will react with
oxygen
to form an oxide. This oxide will react with
water
to form an acidic solution.
118.
B.
One mole of Ca will form one mole of
CaO
by oxidation. This will form one mole of
Ca(OH)2
by reaction with water.
119.
C.
One mole of Ca(OH)2 will require two
moles of HCl for neutralization.
120.
A.
Oxides of sulfur are produced during
burn-
ing of coal. These acid anhydrides react
with
water to form acids. Carbon dioxide can
react
with water to form the weak acid, carbonic
acid.
There is already a substantial amount of
carbon
dioxide in the atmosphere. Although carbon
diox-
ide above the earth may contribute to other
prob-
lems, it has not been suggested to contribute
to
acid rain.
121.
C.
One mole of each would exert the
same
effect, but only if they are ionized. NaCl
produces
2 ions per molecule, and Na2SO4
produces 3 ions
per molecule. Colligative properties depend
on
the number of particles.
122.
B.
Molality (moles of solute per 1000 g of
sol-
vent) is used in calculations of colligative
proper-
ties. Further calculations are required if
there is
ionization.
123.
D.
All of these are colligative
properties.
124.
A.
Without knowing the identity of the
solute,
we know that twice the amount will lower
the
freezing point twice as much.
125.
C.
If the weight is the same, the
nonionizing
solute with the lowest molecular weight will
have
the largest number of dissolved
molecules.
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