The concentration of acetic acid `(K_(a)=1.8 xx 10^(-5))` required to give `3.5 xx 10^(-4) ` moles `//` litres of `H_(3)O^(+)` ions is

Options

A. `6.8 xx 10^(-3) mol L^(-1)`
B. `6.8 mol L^(-1)`
C. `1.94 mol L^(-1)`
D. `0.194 mol L^(-1)`

Answer

A

Explanation

`K_(a)=([CH_(3)COO^(-)][H_(3)O^(+)])/([CH_(3)COOH])`
`1.8 xx 10^(-5)[CH_(3)COOH]=[H_(3)O^(+)]^(2)`
`[CH_(3)COOH]=((3.5xx10^(-4))^(2))/(1.8 xx10^(-5))`
`=(12.25 xx 10^(-8))/(1.8 xx 10^(-5))=6.80 xx 10^(-3) mol L^(-1)`