1.

When 100 mL of 1.0 M HCl was mixed with 100 mL of 1.0 M NaOH in an insulated beaker at constant pressure, a temerature increase of `0.7^(@)`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 kJ `"mol"^(-1)`), the experiment could be used to measure the calorimeter constant. In a second experiment (Expt. 2), 100 mL of 2.0 M acetic acid `(K_(a)=2.0xx10^(-5))` was mixed with 100 mL of 1.0 M NaOH . (under identical conditions of Expt.1) where hte temperature rise of `5.6^(@)C` was measured. (Consider heat capacity of all solutions as `4.2 J g^(-1) K^(-1)` and density of all solutions as 1.0 m `mL^(-1)`) The pH of the solution after Expt. 2 isA. 2.8B. 4.7C. `5.0`D. `7.0`

Answer» Correct Answer - B
`CH_(3)CO OH ` present in 100 mL of 2.0 M the solution = 0.2 mole
NaOH present in 100 mL of 1.0 M solution = 0.1 mole
0.1 mole of NaOH neutralizes 0.1 mole of NaOH to form 0.1 mole of `CH_(3)CO ON a`
`:. ` In the final solution, `CH_(3)CO OH` = 0.1 mole,
`CH_(3)CO ONa`= 0.1 mole, i.e., it is a buffer solution
`pH = pK_(a) + log. (["Salt"])/(["Acid"])=-log(2xx10^(-5))+log.(0.1)/(0.1)`
`=-log(2xx10^(-5))`
`=5-0.301=4.699~= 4.7`


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