Question

In a $0.250{\text{M}}$ solution of ${\text{N}}{{\text{a}}_3}{\text{P}}{{\text{O}}_4}$ the concentration of the sodium ions would be:
A. $0.250{\text{M}}$
B. $0.750{\text{M}}$
C. $0.0833{\text{M}}$
D. $1.99{\text{M}}$

Answer 1

Stoichiometry can be used to predict concentration of entities if concentration of one entity is given in a balanced chemical equation. . Generally salts dissociate completely into its respective ions in aqueous solution.

Complete step by step answer:
Stoichiometry is for the determination of quantities of reactant and products involved in balanced chemical reaction.
For example: ${{\text{H}}_2} + {\text{C}}{{\text{l}}_2} \to 2{\text{HCl}}$ , in this one mole of hydrogen reacts with one mole of chlorine to produce 2 mole of hydrochloric acid. Hence $2{\text{g}}$ of hydrogen reacts with $71{\text{g}}$ of chlorine to produce $73{\text{g}}$ of hydrochloric acid. For a given balanced chemical equation, information of reactant or product can be determined if information of one of the species is given either in terms of moles, molecules, weight or atoms.
${\text{N}}{{\text{a}}_3}{\text{P}}{{\text{O}}_4}$ is known as trisodium phosphate. It is used to control the pH of water hardness precipitation and control agent in mildly acidic solution. ${\text{N}}{{\text{a}}_3}{\text{P}}{{\text{O}}_4}$ is readily dissolved in water and produces sodium ions and phosphate ion.
The dissociation of trisodium phosphate in water will be as follow: ${\text{N}}{{\text{a}}_3}{\text{P}}{{\text{O}}_4} \rightleftarrows 3{\text{N}}{{\text{a}}^ + } + {\text{PO}}_4^{ - 3}$ as we can see one mole of trisodium phosphate on dissociation produces 3 moles of sodium ions and one mole of phosphate ion. Now as given in question that $0.250{\text{M}}$ solution of ${\text{N}}{{\text{a}}_3}{\text{P}}{{\text{O}}_4}$ is taken. Thereby concentration of sodium ion produce will be: $3 \times 0.250 = 0.75{\text{M}}$ and similarly we can say that concentration of phosphate ion produced will be: $0.250{\text{M}}$ .

Thus, the correct option is B.

Note:
Generally concentration of a compound or a molecule represents in terms of molarity. Molarity is defined as the number of moles of a substance present in per Litre of a solution. On the other hand, concentration of gases is represented in terms of their partial pressure. Partial pressure of a gas is defined as pressure exerted by that gas in the mixture of gases.