What are the equilibrium concentrations of H2SO3, H+, HSO3−, and SO32−in a
0.050 M solution of sulfurous acid H2SO3 at 25 oC? For H2SO3 at 25 oC, Ka1 =
1.5×10−2 and Ka2 = 1.0×10−7.
Solution:
H2SO3↔H++HSO3[H ][HSO3  ]
Ka1=
[H2SO3 ]
From this equation [H ][HSO3 ]  Ka1  [H2SO3 ]  1.5  102  0.050  7.5  104 .
The concentration of H+= HSO3- = 7.5  104  2.738  102 M.
HSO3- ↔H++SO32Ka2=
[H ][SO32 ]
.
[HSO3  ]
So, [H ][SO32 ]  Ka2  [HSO3 ]  1.0  102  2.738  102  2.738  109
The concentration of H+= SO32- = 2.738  109  5.23  105 M.
Answer:
The equilibrium concentrations in 0.050 M solution are:
[H2SO3]= 5·10-2-2.738·10-2=2.262·10-2 M;
[H+]=2.738·10-2+5.23·10-5=2.743·10-2 M,
[HSO3−]=2.738·10-2-5.23·10-5= 2.733·10-2 M, and
[SO32−]=5.23·10-5 M.