Question

Consider the sequence of oxides: $N{a}_{2}O$, $Si{O}_2$, $P_4{O}_{10}$. Which factor decreases from $N{a}_{2}O$ to $Si{O}_2$ to $P_4{O}_{10}$?

• A. Covalent character
• B. Solubility in aqueous alkali.
• C. pH when mixed with water
• D. Melting point

Answer 1

The correct option is C pH when mixed with water

pH decreases from $N{a}_{2}O$ to $Si{O}_2$ and then from $Si{O}_2$ to $P_4{O}_{10}$ when these oxides are mixed with water. This is because $N{a}_{2}O$ is a basic oxide which reacts with water to give a strong base NaOH so that the pH of the solution is higher than both $Si{O}_2$ and $P_4{O}_{10}$. Both $Si{O}_2$ and $P_4{O}_{10}$ are acidic oxides but $Si{O}_2$ is insoluble in while $P_4{O}_{10}$ reacts with water to give acid, $H_{3}P{O}_4$ and the pH of the solution is lower than that of $Si{O}_2$ .