How much of `NH_4Cl` should be added to 1L 0.1(M) `NH_3` solution so that the pH of the mixed solution becomes 9.0? Assume that addition of `NH_4Cl` does not change the volume of the solution. lGiven: `pK_b(NH_3)= 4.74`]

Explanation

1mL of 10(M) HCl`=(10)/(100)=10^(-2)` mol of `H^+` ions .
`10^(-2)` mol of `H^+` ions combine with the same amount of `CH_3COONa` forming `10^(-2)` mol of `CH_3COOH`
After the addition of `10^(-2)` mol of `H^+` ions,
`[CH_3COOH]=0.1+10^(-2)=0.11(M)`
`[CH_3COONa]=0.1-10^(-2)=0.09(M)`
`:.pH=pK_a+log([CH_3COONa])/([CH_3COOH])`
`=4.74+log(0.09)/(0.11)=4.65`
change in pH=4.74-4.65=0.09 unit