Both HCOOH and `CH_(3)COOH` solutions have equal pH. If `K_(1) // K_(2)` ( ration of acid ionisation constants ) of these acids is 4, their molar concentration ratio will be

Options

A. 2
B. 0.5
C. 0.05
D. 0.25

Answer

D

Explanation

As pH of HCOOH sol. `= pH` of `CH_(3)COOH` sol.
`:. [H^(+)] ` in HCOOH sol.
`=[H^(+)]` in `CH_(3)COOH` sol.
`K_(1)=([HCOO^(-)][H^(+)])/([HOOH])=([H^(+)]^(2))/([HCOOH])`
`K_(2)=([CH_(3)COO^(-)][H^(+)])/([CH_(3)COOH])=([H^(+)]^(2))/([CH_(3)COOH])`
`K_(1)[HCOOH]=K_(2)[CH_(3)COOH]`
`([HCOOH])/([CH_(3)COOH])=(K_(2))/(K_(1))=(1)/(4)=0.25`