Question

$P_4{O}_{10}$ dissolves in water to give

• A. phosphorous acid
• B. orthophosphoric acid
• C. hypophosphorus add
• D. pyrophosphoric add

Answer 1

Answer: (B)

Phosphorus pentoxide, $P_4{O}_{10}$ has great affinity for water and gives orthophosphoric acid as final product.
It is therefore named phosphoric anhydride.
$P_4{O}_{14}\stackrel{2H_{2}O}{\to }\underset{\stackrel{\text{metaphosphoric}}{\mathrm{acid}}}{4HP{O}_3}\stackrel{2H_{2}O}{\to }$
$\underset{\stackrel{\text{pyrophosphoric }}{\mathrm{acid}}}{2H_4{P}_2{O}_7}\stackrel{2H_{2}O}{\to }\underset{\text{orthophosphoric acid}}{4H_{3}P{O}_4}$