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. `5.0`
D. `7.0`

Answer

B

Explanation

Final solution contain `0.1` mole of `CH_(3)COOh` and `CH_(3)COONa` each.
hence it is a buffer solution.
`pH = pK_(a) + log([CH_(3)COO^(-)])/([CH_(3)COOH])`
`=5-log2 + "log"(0.1)/(0.1) = 4.7`