Question

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Q.47. In which of the following reaction, equivalent weight of acid is equal to its molar mass?
(1) $H_{3}P{O}_4+NaOH\to Na{H}_{2}P{O}_4+H_{2}O$
(2) $H_{3}P{O}_4+2NaOH\to N{a}_{2}HP{O}_4+2H_{2}O$
(3) $H_{3}P{O}_4+3NaOH\to N{a}_{3}P{O}_4+3H_{2}O$
(4) $H_{2}S{O}_4+2NaOH\to N{a}_{2}S{O}_4+2H_{2}O$

Answer 1

For acids,
Equivalent is molar mass divided by number of replacable hydrogen atoms. For an acid reaction, equivalent mass of acid reactant is equal to its molar mass divided by number of H+ removed from one acid molecule.
Here ,
In 1st reaction, 1 H+ is removed from acid , as it reacts with 1 NaOH. Hence,
Equivalent mass = Molar mass /1 = molar mass.
In 2nd reaction, 2 H+ is removed. Hence, equivalent mass = molar mass /2
The same is true for 4.
In 3rd reaction, 3 H+ is removed. Hence , equivalent mass = molar mass/ 3 .
Hence answer is 1