Question

With excess of water, both ${P_2}{O_5}$ and $PC{l_5}$ are:
a.) ${H_3}P{O_3}$
b.) ${H_3}P{O_2}$
c.) ${H_3}P{O_4}$
d.) ${H_4}{P_2}{O_7}$

Answer 1

Hint: To solve this question, we will see the chemical reaction of ${P_2}{O_5}$ and $PC{l_5}$ with excess of water. The phosphorus pentoxide is a white crystalline solid and it is a potent dehydrating agent. The phosphorus pentachloride is a colorless and moisture sensitive solid.

Complete step by step solution: Now we will see the reaction of ${P_2}{O_5}$ with the excess of water. When peroxide react with excess water, the product formed is orthophosphoric acid
${P_2}{O_5} + 3{H_2}O\xrightarrow{{}}2{H_3}P{O_4}$
While the reaction of pentachloride with water gives phosphorus pentoxide and if excess water is provided the product formed is orthophosphoric acid.
$PC{l_5} + 4{H_2}O\xrightarrow{{}}{H_3}P{O_4} + 5HCl$

Hence, the correct option is C.

Additional Information- acidic hydrogen- the necessary condition for a hydrogen atom to be acidic is that it must be connected to the electronegative atoms like oxygen or fluorine.
In case of orthophosphoric acid, we will see a number of hydrogen atoms connected to the oxygen for calculating its basicity.
\[\begin{array}{*{20}{c}}
  {}&{\begin{array}{*{20}{c}}
  O \\
  {||}
\end{array}}&{} \\
  {H - O - }&{P - }&{O - H} \\
  {}&{\begin{array}{*{20}{c}}
  | \\
  H
\end{array}}&{}
\end{array}\]
The above compound is the orthophosphorous acid. The number of H atoms bonded to the oxygen atoms in the above compound is equal to 2.

Therefore, the basicity of the orthophosphorous acid is 2.

Note: The orthophosphorous acid is also known as phosphorous acid. It is used as a reducing agent in the chemical analysis because they are easily oxidized to phosphoric acid and phosphate salts. It is a colourless and crystalline substance. It is one of the oxyacids of the phosphorus and the other oxyacids of the phosphorus are phosphoric acid and the basicity of this acid is 3 because it contains 3 acidic hydrogen atoms. The chemical formula for orthophosphoric acid is ${H_3}P{O_4}$