Chemistry Reference
In-Depth Information
Solution
Since the solution is buffered, the acidity does not change despite addition of
hydronium ion from the ionization of the acid.
H
3
O
HS
H
2
S
H
2
O
E
10
5
Initial
0.100
1.0
0.000
Change
Final
x
x
x
10
5
0.100
x
0.100
1.0
x
[H
3
O
][HS
]
[H
2
S]
10
5
)
x
0.100
(1.0
10
8
K
1
9.1
10
4
x
9.1
[H
3
O
][S
2
]
[HS
]
10
5
)[S
2
]
(1.0
10
12
K
2
1.1
10
4
9.1
[S
2
]
10
10
1.0
In the less acidic solution, both equilibria are shifted right, giving a greater sulfide
ion concentration than the unbuffered
H
2
S
solution (see Example 19.21).
Buffer solutions can be prepared with polyprotic acids, just as with mono-
protic acids. If any acid and its conjugate, which differs by
one
proton, are
together in the same solution, they form a buffer solution. Instead, if an acid
and its salt are combined, they will react to produce one or more acid salt(s).
EXAMPLE 19.23
What is the hydronium ion concentration of a solution containing 0.100 M malic
acid and 0.100 M sodium hydrogen malate?
Solution
HC
4
H
4
O
5
H
3
O
H
2
C
4
H
4
O
5
H
2
O
E
Initial
0.100
0.100
0.000
Change
Final
x
x
x
0.100
x
0.100
x
x
[HC
4
H
4
O
5
][H
3
O
]
[H
2
C
4
H
4
O
5
]
10
4
K
1
3.9
[H
3
O
]
10
4
3.9
Practice Problem 19.23
What is the major product after equal vol-
umes of 0.100 M
H
2
SO
3
and 0.100 M
Na
2
SO
3
are combined?
It must be noted that we cannot calculate the pH of an acid salt alone in
solution by the methods that we have been using. The problem is that the anion
