Question

Compare the strength of HCN (Ka = 4.9×10^-10) with 0.01M aqueous solution of formic acid in which it is 14.5% dissociated.​

Answer 1

`{ \boxed{ \purple{ \tt{6.5 * {10}^(2) }}}}`

Explanation:-

Applying,

`{ \blue{ \tt{ (Strength \: of \: formic \: acid)/(Strength \: of \: HCN)} \: = }} \: \: \: { \green{ \tt{ \sqrt{ (K _(a)(formic \: acid))/(K _(a)(HCN)) }}}}`

Degree of dissociation of HCOOH
`{ \red{ \sf{( \alpha) = 14.5\%}}}`
`{ = \red{ \sf{ (14.5)/(100)}}}`
`{ = \red{ \sf{0.145}}}`

`{ \purple{ \tt{ K_(a)(HCOOH) = C { \alpha }^(2)}}}`

`{ \purple{ \tt{ K_(a)(HCOOH) = 0.01 * {(0.145)}^(2) }}}`

`{ \purple{ \tt{ K_(a)(HCOOH) = 2.1 * {10}^( - 4)}}}`

Thus,

`{ \blue{ \tt{ (Strength \: of \: formic \: acid)/(Strength \: of \: HCN)} \: = }}{ \green{ \tt{ \sqrt{ \frac{2.1 * {10}^( - 4) }{4.9 * {10}^( - 10) } }}}}`

`{ = \boxed{ { \red{ \sf{6.5 * {10}^(2)}}}}}`

i.e., formic acid is 6.5×10² times stronger than HCN or we can say that HCN is 6.5×10² times weaker than formic acid.