Determine the hydrolysis constant and pH of an aqueous 1.0(M) ammonium format solution Given : `pK_a(HCOOH)=3.8 and pK_b(NH_3)=4.74`

Explanation

Ammonium fo rmate is a salt of weak acid (HCOOH) and weak base `(NH_3)` . In the aqueous solution of such salts,
`h=sqrt((k_w)/(K_axxK_b))` & pH of the solution `=7+1/2pK_a-1/2pK_b`
As given in the question, `pK_a(HCOOH)=3.8`
`:.K_a(HCOOH)=10^(-3.8)=1.58xx10^(-4)`
`pK_b(NH_3)=4.74`
`:.K_b(NH_3)=10^(-4.74)=1.82xx10^(-5)`
`:.h=sqrt((10^(-14))/(1.58xx10^(-4)xx1.82xx10^-5))=1.86xx10^(-3)` and
`pH=7+1/2pK_a-1/2pK_b`
`=7+1/2xx3.8-1/2xx4.74=6.53`