Question

Calculate the equivalent weight of ${H_3}P{O_4}$ in following reaction
$Ca{(OH)_2} + {H_3}P{O_4} = CaHP{O_4} + 2{H_2}O$

Answer 1

Equivalent weight, is the quantity of a substance that exactly reacts with, or is equal to the combining value of, an arbitrarily fixed quantity of another substance in a particular reaction. The equivalent weight of an element is its gram atomic weight divided by its valence.

Complete Step By Step Answer:
Equivalent weight is the mass of one equivalent mass of a given substance which will combine with or displace a fixed quantity of another substance. Equivalent weight has the dimensions and units of mass, unlike atomic weight, which is dimensionless.
The formula to calculate the equivalent weight is given as:
Equivalent weight $= \dfrac{{molecular\;weight}}{{valency}}$
The given reaction is:
$Ca{(OH)_2} + {H_3}P{O_4} = CaHP{O_4} + 2{H_2}O$
In this reaction ${H_3}P{O_4} \to HP{O_2}^{ - 4} + 2{H^ + }$
Orthophosphoric acid leaves $2$ hydrogen ions.
Hence, its valency factor is $2$
Equivalent weight $= \dfrac{{molecular\;weight}}{2}$
Molecular weight $= 1.3 + 31 + 4.16 = 98$
Therefore,
The equivalent weight is $\dfrac{{98}}{2} = 49$ .

Additional Information:
Phosphoric acid appears as a clear colorless liquid or transparent crystalline solid. The pure solid melts at ${42.35^ \circ }C$ and has a density of $1.834\dfrac{g}{{c{m^3}}}$ . Liquid is usually an $85$ aqueous solution. Shipped as both a solid and liquid. Corrosive to metals and tissue. Used in making fertilizers and detergents and in food processing.

Note:
Equivalent weight has the dimensions and units of mass, unlike atomic weight, which is dimensionless. Equivalent weights were originally determined by experiment, but insofar as they are still used are now derived from molar masses. Additionally, the equivalent weight of a compound can be calculated by dividing the molecular mass by the number of positive or negative electrical charges that result from the dissolution of the compound.