Question

Sodium pyrophosphate is represented by which of the following formula?

• A. $N{a}_2{P}_2{O}_4$
• B. $N{a}_4{P}_2{O}_5$
• C. $N{a}_4{P}_2{O}_7$
• D. $N{a}_2{P}_2{O}_5$

Answer 1

Answer: (C)

Sodium pyrophosphate is represented by $N{a}_4{P}_2{O}_7.$ It is sodium salt of pyrophosphoric acid $\left(H_4{P}_2{O}_7\right)$, which may be considered to be made up by two molecules of ortho phosphoric acid $\left(H_{3}P{O}_4\right)$, eleminating one molecule of $H_{2}O$.
$2H_{3}P{O}_4\stackrel{-\mathrm{H}{}_2\mathrm{O}}{\to }\underset{\text{Pyrophosphoric acid}}{H_4{P}_2{O}_7}$