Question

True or False? EXPLAIN

For a titration of C5H5N with HNO3 the half equivalence point occurs when the molar concentrations of C5H5N and C5H5NH are equal.

Answer 1

yes its true.

Reaction is : C₅H₅N + HNO₃ ----------> C₅H₅NH⁺ + NO₃^-

now at equlivalence point, equlivalent of  C₅H₅N = equivalent of HNO₃

but at half equivalence point, 1 /2 of equlivalent of  C₅H₅N used =  equivalent of HNO₃ used

now equlivalent of  C₅H₅NH⁺ formed = equivalent of HNO₃ used = 1 /2 of equlivalent of  C₅H₅N

so at half equivalence point so at half equivalence point

equivalent of C₅H₅NH⁺ formed = remaining equlivalent of  C₅H₅N

At, half equivalence point P^H = P^K_a  .

it is possible only when Concentration of C₅H₅NH⁺ is equal to concentration of C₅H₅N. because at this point for buffer solution P^H is given by P^H = P^K_a + log ([C₅H₅NH⁺] / [  C₅H₅N].