The concentration of hydrogen ions in the solution with PH2.2 is 10-2.2 mol/L,

The concentration of hydrogen ions in the solution with PH6.9 is 10-6.9 mol/L,

Suppose that v ml is needed, that is, acid-base neutralization, and hydrogen ions are neutralized.

[2 1× 10^-2.2-(2 1+v)× 10^-6.9]÷ 1= 10^-6.9÷(2 1+v]

If we simply calculate how much is needed, both V and 10-6.9 mol/L can be ignored first, and about 0.0063 1mL 1mol/l of potassium hydroxide will be needed. If accurate calculation is needed, just solve the equation.