A definite volume of a N/20 `CH _(3) COOH (pK _(a) =4.7447)` is titrated with a strong base (NaOH). It is found that 80 equal sized drops of NaOH, added from a burette effects the complete neutralisation. Find the pH, when the acid solution is neutralised to the extent of 20%

Options

A. `4.14`
B. `9.86`
C. `5.34`
D. `8.68`

Answer

A

Explanation

`W _(A) (CH _(3) COOH) ` is titrated with `S _(B) ` (NaOH) and `20%` of the `W _(A)` is neutralised, so `20%` of the salt of `W _(A) // S _(B) (CH _(3) COONa)` is formed and `80%` of the `W _(A) (CH _(3) COOH)` is left so an acidic buffer is formed.
`therefore ["Acid"]= 80, ["Salt"] = 20`
`pH = pKa + log ""[("Salt")/("Acis")] = 4.447 + log [("Salt")/("Acid")] = 4.447 + log "" (1)/(4)`
`=4.7447-2 log 2 = 4.7447- 2 xx 0.30 10 = 4.14`