Question

Determine the relative acid strengths of NH4 + and HCN by comparing their ionization constants. The ionization constant of HCN is given in Appendix H as 4.9 × 10−10. The ionization constant of NH4 + is not listed, but the ionization constant of its conjugate base, NH3, is listed as 1.8 × 10−5.

Answer 1

`NH_(4)^(+)` is stronger acid than HCN

Step-by-step explanation:

For a acid-conjugate base or base-conjugate acid pair-

`K_(a)* K_(b)=1* 10^(-14)`

Where,
`K_(a)` is acid dissociation constant of acid or conjugate acid and
`K_(b)` is base dissociation constant of base or conjugate base

So,
`K_(a)(NH_(4)^(+))=(1* 10^(-14))/(1.8* 10^(-5))=5.6* 10^(-10)`

As higher the
`K_(a)` value of an acid , higher will be the dissociation of the acid and hence more stronger will be the acid.

As
`K_(a)` value of
`NH_(4)^(+)` is higher than
`K_(a)` value of HCN therefore
`NH_(4)^(+)` is stronger acid than HCN