Question

The ${H_3}P{O_4}$ is a tribasic acid and one of its salt is $Na{H_2}P{O_4}$ . What volume in ml of $1M$ $NaOH$ solution should be added to $12g$ of $Na{H_2}P{O_4}$ to convert into $N{a_3}P{O_4}$ ?

Answer 1

For solving the question numerically first we should know and write the chemical reaction which is required for the formation of $N{a_3}P{O_4}$ from $Na{H_2}P{O_4}$ . Quantify the amount of reactant required for the reaction to complete and then quantify them with the amount of reactant we are given to find the required volume of $1M$ $NaOH$ .

Complete step by step answer:
As it is given in the question that ${H_3}P{O_4}$ is a tribasic acid which means it can replace its three hydrogen atoms. Phosphoric acid acts as an oxidizing agent. It is also called orthophosphoric acid mainly to distinguish it from other phosphoric acids. The oxidation state of phosphoric acid is $+ 5$ . So first let us write down the reaction which is required for formation of $N{a_3}P{O_4}$ .
$Na{H_2}P{O_4} + 2NaOH \to N{a_3}P{O_4} + {H_2}O$
If we look at the above reaction we can observe that $1M$ of $Na{H_2}P{O_4}$ is required for $2M$ of $NaOH$ .
First let us write the molar mass of $Na{H_2}P{O_4}$ which is $120g/mol$ . So the number of moles in $12g$ of $Na{H_2}P{O_4}$ will be $0.1mol$.
Therefore the number of moles of $NaOH$ required for the reaction $= 2 \times 0.1mol = 0.2mol$ .
As we know the molarity of $NaOH$ is $1mol/L$ , so volume of $1mol$ $NaOH = 1L$ .
Therefore volume of $0.2mol$ $NaOH = 1 \times 0.2L = 0.2L = 0.2 \times 1000mL = 200mL$
So $200mL$ of $1M$ $NaOH$ is to be added to $12g$ of $Na{H_2}P{O_4}$ to convert into $N{a_3}P{O_4}$ .

Note:
Phosphoric acid is soluble in alcohol as well as in water. It forms orthophosphate salts by replacing its hydrogen atoms with other positive ions. It is used for making fertilizers by forming phosphate salts. It is also used in the textile industry, dental cements and sugar industry. It is formed by the reaction of sulfuric acid with natural phosphate rock. This reaction also gives calcium sulfate also known as gypsum.