Chapter 9.5, Problem 49SP

Interpretation Introduction

Interpretation: Whether the given sample is iron (III) oxide or not is to be explained.

Concept Introduction : According to the law of multiple proportions, the two elements form more compound, then the ratios of the second element’s masses, which combines with the fixed first’s element mass will always be ratios of small whole numbers.

Answer to Problem 49SP

The given sample is not iron (III) oxide as the ratio is not observed as 7:3.

Explanation of Solution

It is given that the mass ratio of iron to oxygen is 7:3. It means that 7 g of Fe will combine with 3 g of oxygen to form iron (III) oxide.

The sample of the compound contains 33 g of iron and 10 g of oxygen. The ratio for the given grams is calculated as follows:

  $\frac{\text{Mass}\text{of}\text{Fe}}{\text{Mass}\text{of}\text{O}}=\frac{33\text{g}}{10\text{g}}\ne 7:3$

So, the given sample is not iron (III) oxide. If the ratio is multiplied by 3, then:

  $\begin{array}{c}\frac{\text{Mass}\text{of}\text{Fe}}{\text{Mass}\text{of}\text{O}}=7:3\\ \frac{7}{3}\times \frac{3}{3}=\frac{21\text{g}}{9\text{g}}\end{array}$

Therefore, when the grams should be 21 g of Fe and 9 g of O then it will be iron (III) oxide.