Page 116 - Basic physical chemistry for the atmospheric sciences

1 0 2 Basic physical chemistry

(h) The range of potential pH values for rain is greater over
the continents than over the ocean .
s
o
5 . 8 . What are the concentrations f H + (aq) and OH - (aq) i n an
aqueous solution to which 0.05 M of NaOH is added at
25°C? Is NaOH an acid or a base?
H
5 . 9. Calculate the concentrations of + (aq) and oH - (aq) in an
aqueous solution to which 1 . 0 M of acetic acid (CH3COOH)
is added at 25°C. Assume that the acetic \cid is 4% ionized.
5 . 1 0 . Identify the conjugate acid-base pairs for the forward reac­
tion (indicate by l ) and the reverse reaction (indicate by 2)
of the following reactions.
(a) HS0 4 (aq) + H20(l) � H3Q + ( aq) + So� - ( aq)
(b) H2P0 4 (aq) + HCl(l) � H 3POiaq) + cl - (aq)
(c) NH ! (aq) + CH3COO - (aq) � C H3COOH(aq) + NH3(aq)
5 . 1 . Determine the concentrations of oH - (aq) and H + (aq) ions
l
in a 0.50 M solution of ammonia that is 2% ionized. What is
the pH of the solution?
5 . 1 2 . The pH of a 0.200 M aqueous solution of hydrocyanic acid
(HCN) is 5 . 05 at 25°C. What is the value of the acid-dissoci­
ation constant for HCN at 25°C?
5 1 3 . What i s the concentration of protons i n a solution with an
.
initial concentration of nitrous acid (HN02) of 0.0050 M at
25°C? The acid-dissociation constant of HN0 2 at 25°C is
5 . 1 x 1 0 - 4 ·
+
5 . 14. Calculate the concentrations of H ( aq), H 2 P04(aq),
HPo� - ( aq), and Poi- ( aq) ions in a 0.020 M aqueous solu­
tion of phosphoric acid (H3P04) at 25°C. The successive
acid-dissociation constants at 25°C for phosphoric acid are
Ka1 = 5 . 9 x 1 0 - 3 • Ka2 = 6 . 2 x 1 0 - 8 , and Ka3 = 4 . 8 x 1 0 - 1 3 •
5 . 1 5 . What is the pH of a 0.0050 M solution of NH4C2H30 at
2
25° , and what fraction is hydrolyzed? The acid-dissocia­
C
tion constant for HC2H302 is l . 8 x 1 0 - 5 at 25°C and the
base-dissociation constant for NH3 is l . 8 x 1 0 - 5 at 25°C.
5 . 1 6 . A sample f water contai s 40 g L - 1 o f N a + ( aq), 5 . 2 g L - 1
o
n
2
-
of Ca + ( aq), 75 . 2 g L 1 of c1 - (aq), and 2 . 0 g L - 1 of
So� - ( aq). The only other ions present are Hp + ( aq) and
OH - ( aq). What is the pH of the solution?
5 . 1 7 . What s the H of a buffer solution that contains NH4Cl(aq)
i
p
and NH3(aq) if [NH4Cl(aq)] = 2.00[NHiaq)] ? The acid­
dissociation constant for NH ! (aq) is . 6 0 x 1 0 - 10•
5