Chapter SH, Problem 18.3APP

To determine

To Establish: The formula for iron (III) oxide.

Answer to Problem 18.3APP

Foriron (III) oxidethe formula is ${\text{Fe}}_2{\text{O}}_3$ .

Explanation of Solution

Introduction:

The symbol and oxidation number of the positive ion:

Iron (III): ${\text{Fe}}^{3+}$

The symbol and oxidation number of the negative ion:

Oxygen: ${\text{O}}^{2-}$

First write the symbol of the element having positive charge followed by the symbol of the element having negative charge.

  ${\text{Fe}}^{3+}{\text{O}}^{2-}$

Without the sign, one ion’s charge forms the subscript of the other.

  ${\text{Fe}}_2{\text{O}}_3$

In this case, the subscripts already are the lowest whole numbers that maintain the ratio of the ions.

By determining whether the compound is neutral the formula obtained can be checked. The charge on two ferric ions is $(3+\times 2)=6+$ , and the charge on three oxygen is $(2-\times 3)=6-$ . The compound is neutral, so the formula is correct.

Conclusion:

For iron (III) oxidethe formula is ${\text{Fe}}_2{\text{O}}_3$ .