JEE Main 2016 · Chemistry · s-Block, p-Block Elements and Hydrogen · easy

10 mL each of 0.10 M H3PO2, 0.10 M H3PO3 and 0.10 M H4P2O7 are mixed. The volume of 0.10 M NaOH required for complete neutralisation of the mixture is

Single correct option

10\ \mathrm{mL}

each of

0.10\ \mathrm{M}

\mathrm{H_3PO_2}

0.10\ \mathrm{M}

\mathrm{H_3PO_3}

and

0.10\ \mathrm{M}

\mathrm{H_4P_2O_7}

are mixed. The volume of

0.10\ \mathrm{M}

\mathrm{NaOH}

required for complete neutralisation of the mixture is

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Answer: (B) $70\ \mathrm{mL}$

Only P-OH hydrogens are ionisable.

\mathrm{H_3PO_2}

(hypophosphorous acid) has one P-OH, so it is monobasic.

\mathrm{H_3PO_3}

has two P-OH groups (the third H is on P), so it is dibasic. Pyrophosphoric acid

\mathrm{H_4P_2O_7}

has four P-OH groups, so it is tetrabasic. Millimoles of

\mathrm{H^+}

1(1)+1(2)+1(4)=7

mmol (each acid is

1.0

mmol). NaOH volume

=7/0.10=70

mL. Counting all hydrogens as acidic gives

3+3+4=10

mmol i.e. 100 mL.

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