You will need the Ka for sulfurous acid to calculate the pH as it is a weak acid. Were you given a figure in the question?
H2SO3<> HSO3- + H+
Ka = 1.54×10−2 mol L^-1
(from a data book)
at start
H2SO3 HSO3- H+
0.250M 0M 0M
at equilibrium
0.250-x x x
Ka=[HSO3-][H+]/[H2SO3]
1.54×10−2 mol L^-1 = x^2/(0.250-x)
you can either solve the quadratic or assume that x is small with respect to 0.250 hence
1.54×10−2 mol L^-1 = x^2/(0.250 mol L^-1)
x^2=0.00385 mol^2 L^-2
hence find x
and pH=-log(x)
Calculate the pH of a 0.250M solution of Sulfurous acid, H2SO3.
2 answers
1.207