The ionization constant of nitrous acid is `4.5 xx 10^(-4)`. Calculate the pH of 0.04 M sodium nitrite solution and also its degree of hydrolysis.

Explanation

Sodium nitrite is a salt of a strong base and a weak acid . For such that,
` " " pH = (1)/(2) pK_w +(1)/(2) pK_a+ (1)/(2) log_(10) c `
`= (1)/(2) xx (- log_(10) 1.0 xx 10 ^(-14)) + `
` " "(1)/(2) xx (-log_(10) 4.5 xx 10 ^(-4) )+(1)/(2) xx log_(10) 0.04`
` " "= 7.0 + 1.673 - 0.698 = 7.975`
The degree of the hydrolysis of such a salt is given by
` h= sqrt((K_w)/(K_a. c))= sqrt((1.0 xx 10^(_14))/(4.5 xx 10 ^(-4) xx 0.04)) =2.36 xx 10^(-5)`