Question

The ionic compound formed by the ions ${\text{Fe}}^{3+}$ and $({\text{SO}}_4{)}^{2-}$ has the chemical formula ________.

• A. ${Fe}_{2}S{O}_4$
• B. ${Fe}_3(S{O}_4{)}_2$
• C. ${Fe}_2(S{O}_4{)}_3$
• D. ${Fe}_{3}S{O}_4$

Answer 1

The correct option is C

${Fe}_2(S{O}_4{)}_3$

An ionic compund consists of an anion and a cation. Here cation is ${\text{Fe}}^{3+}$ and anion is $({\text{SO}}_4{)}^{2-}$.

$$\begin{array}{cc}\text{Symbol}& \text{Charge}\\ \text{Fe}& \text{3}\\ {\text{SO}}_4& \text{2}\end{array}$$
In order to balance the overall charge, the short-cut method is to cross multiply the charges. Thus, the two ${\text{Fe}}^{3+}$ will combine with three $({\text{SO}}_4{)}^{2-}$. Hence, the formula is ${\text{Fe}}_2({\text{SO}}_4{)}_3$.