Question

Calcium phosphate is present in tooth enamel, its nature is

• A. Acidic
• B. Basic
• C. Neutral
• D. Amphoteric

Answer 1

The correct option is B

Basic

Concept

Salts of strong acid and weak base are acidic in nature.

Salts of a strong base and weak acid are basic in nature.

The explanation for the correct option.

$$\begin{gathered} \mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_3{\mathrm{PO}}_4\left(\mathrm{aq}\right)\to {\mathrm{Ca}}_3{\left({\mathrm{PO}}_4\right)}_2\left(\mathrm{aq}\right) \\ \mathrm{Calcium}\mathrm{Phosphoric}\mathrm{Calcium} \\ \mathrm{hydroxide}\mathrm{acid}\mathrm{phosphate} \end{gathered}$$

1. From the above reaction calcium phosphate is a salt of phosphoric acid (${\mathrm{H}}_3{\mathrm{PO}}_4$) and calcium hydroxide $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$.
2. Since phosphoric acid H₃PO₄ is a weak acid and calcium hydroxide $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$ is a strong base,
3. hence calcium phosphate is basic in nature.

The explanation for the incorrect option.

1. Since calcium phosphate is the salt of a strong base and weak acid, therefore it is basic in nature, hence it cannot be neutral or amphoteric.
2. Amphoteric substances are those substances which can show both the character acidic and basic, for example ${\mathrm{Al}}_2{\mathrm{O}}_3$.
3. Therefore, options a) and d) both are incorrect.

Therefore, calcium phosphate ${\mathrm{Ca}}_3{\left({\mathrm{PO}}_4\right)}_2$ is basic in nature, hence option (b) is correct.