Question

The formula of iron (III) sulphate is

• A. ${\mathrm{FeSO}}_4$
• B. ${\mathrm{Fe}}_2{\left({\mathrm{SO}}_4\right)}_3$
• C. $\mathrm{Fe}{\left({\mathrm{SO}}_4\right)}_3$
• D. ${\mathrm{Fe}}_3{\mathrm{SO}}_4$

Answer 1

The correct option is B

${\mathrm{Fe}}_2{\left({\mathrm{SO}}_4\right)}_3$

Explanation for correct option:

Option B

Chemical formula:

• The formula of a substance is the symbolic representation of a chemical substance.
• To write the formula of a chemical substance, the valency and the symbol of the various atoms or radicals present in it must be known.
• For example, the chemical formula of sulphuric acid is ${\mathrm{H}}_2{\mathrm{SO}}_4$.

The formula of iron (III) sulphate is ${\mathrm{Fe}}_2{\left({\mathrm{SO}}_4\right)}_3$.

• As Iron ($\mathrm{Fe}$) has +3 oxidation state (III), and sulfate (${{\mathrm{SO}}_4}^{2-}$) has always −2 charge.
• So to neutralize both cation and anion, the total charge must be equal= $$\begin{gathered} 2\times (+3)=3\times (-2) \\ 6=-6 \end{gathered}$$
• Hence there must be 2 atoms of Iron ($\mathrm{Fe}$) and 3 ${{\mathrm{SO}}_4}^{2-}$units in the formula.

Therefore, Option B is the correct option.