JEE Advanced 2015 Paper 2 Chemistry Q20

Chemistry · Titrations: Acid-Base, Complexometric, Redox, Precipitation · Reactions in Aqueous Solution

Problem

PARAGRAPH 2 When

100\,\mathrm{mL}

1.0\,\mathrm{M}

\ce{HCl}

was mixed with

100\,\mathrm{mL}

1.0\,\mathrm{M}

\ce{NaOH}

in an insulated beaker at constant pressure, a temperature increase of

5.7^\circ\mathrm{C}

was measured for the beaker and its contents (Expt. 1). Because the enthalpy of neutralization of a strong acid with a strong base is a constant (

-57.0\,\mathrm{kJ\,mol^{-1}}

), this experiment could be used to measure the calorimeter constant. In a second experiment (Expt. 2),

100\,\mathrm{mL}

2.0\,\mathrm{M}

acetic acid (

K_a=2.0\times10^{-5}

) was mixed with

100\,\mathrm{mL}

1.0\,\mathrm{M}

\ce{NaOH}

(under identical conditions to Expt. 1) where a temperature rise of

5.6^\circ\mathrm{C}

was measured. (Consider heat capacity of all solutions as

4.2\,\mathrm{J\,g^{-1}\,K^{-1}}

and density of all solutions as

1.0\,\mathrm{g\,mL^{-1}}

.) The pH of the solution after Expt. 2 is