Question

In first experiment, 1.288g of Copper oxide was obtained from 1.03g of copper. In second experiment, 3.672g of Copper oxide gave 2.938g of copper. Show that the data is in accordance with the law of constant proportion.

Answer 1

Step 1: Definition of law of constant proportions

The chemical compounds contain elements in a fixed ratio by mass. This implies that any pure sample of a compound, no matter the source, will always consist of the same elements that are present in the same ratio by mass.

Step 2: Identify the given data

Mass of Copper oxide $\left({\mathrm{Cu}}_2\mathrm{O}\right)$ obtained in the first experiment = 1.288g

Mass of copper in the first experiment = 1.03g

Mass of Copper oxide $\left({\mathrm{Cu}}_2\mathrm{O}\right)$ obtained in the second experiment = 3.672g

Mass of copper in the second experiment = 2.938g

Step 3: Estimating the ratio of mass in the first experiment

From the first experiment,

Weight of oxygen $\left({\mathrm{O}}_2\right)$ = Weight of Copper oxide $\left({\mathrm{Cu}}_2\mathrm{O}\right)$ - Weight of copper $\left(\mathrm{Cu}\right)$

Weight of oxygen $=1.288\mathrm{g}-1.03\mathrm{g}=0.258\mathrm{g}$

Ratio of mass in the first experiment = $\frac{\mathrm{Weight}\mathrm{of}\mathrm{copper}}{\mathrm{Weight}\mathrm{of}\mathrm{oxygen}}=$ $\frac{1.03}{0.258}\approx \frac{4}{1}$

Step 3: Estimating the ratio of mass in the second experiment

From the second experiment,

Weight of oxygen $\left({\mathrm{O}}_2\right)$ = Weight of Copper oxide $\left({\mathrm{Cu}}_2\mathrm{O}\right)$ - Weight of copper $\left(\mathrm{Cu}\right)$

Weight of oxygen $=3.672-2.938=0.734\mathrm{g}$

Ratio of mass in the second experiment = $\frac{\mathrm{Weight}\mathrm{of}\mathrm{copper}}{\mathrm{Weight}\mathrm{of}\mathrm{oxygen}}=$ $\frac{2.938}{0.734}\approx \frac{4}{1}$

Conclusion:

1. The proportion of copper to oxygen in both experiments is the same.
2. Hence, the results are in accordance with the law of constant proportion here.