When `100mL` of `1.0M HCl` was mixed with `100 mL` of `1.0 M NaOH` in an insulated beaker at constant pressure, a temperature increase of `5.7^(@)C` was measured for the beaker and its contents (Expt.1). Because the enthalpy of neutralisation of a strong acid with a strong base is constant `(-57.0kJmol^(-1))` this experiment couldbe used to measure the calorimeter constant. In a second experiment (Expt.2), `100mL` of `2.0M` acetic acid `K_(a)=2.0xx10^(-5))` was mixed with `100mL` of `1.0M NaOH` (under identical conditions to Expt. 1) where a temperature rise of `5.6^(@)C` was measured.
The `pH` of the solution after Expt. 2 ils

Options

A. 2.8
B. 4.7
C. 5
D. 7

Answer

B

Explanation

Molarity of `CH_(3)COOH=(n)/(V)xx1000=(0.1xx1000)/(200)=0.5`
`pH=pK_(a)+log(["salt"])/(["acid"])`
`=-log(2xx10^(-5))+log[(0.5)/(0.5)]`
`=4.7`