Atoms and Molecules - Dalton’s Atomic Theory

In a reaction, $5.3\text{ g}$ of sodium carbonate reacted with $6.0\text{ g}$ of ethanoic acid. The products were $8.2\text{ g}$ of sodium ethanoate, $2.2\text{ g}$ of $CO_2$ and $0.9\text{ g}$ of $H_2O$. Show that these observations are in agreement with the law of conservation of mass.

Mass of reactants: $5.3\text{ g} + 6.0\text{ g} = 11.3\text{ g}$. Mass of products: $8.2\text{ g} + 2.2\text{ g} + 0.9\text{ g} = 11.3\text{ g}$. Since $11.3\text{ g} = 11.3\text{ g}$, the law is verified.

According to the Law of Conservation of Mass, the total mass before and after a chemical reaction must be equal. Calculation of reactants: $\begin{array}{r} 5.3 \\ + 6.0 \\ \hline 11.3 \end{array}$ Calculation of products: $\begin{array}{r} 8.2 \\ 2.2 \\ + 0.9 \\ \hline 11.3 \end{array}$

Hydrogen and oxygen combine in the ratio of $1:8$ by mass to form water. What mass of oxygen gas would be required to react completely with $3\text{ g}$ of hydrogen gas?

Mass of oxygen = $3 \times 8 = 24\text{ g}$.

Dalton's theory states atoms combine in fixed ratios. Given the ratio of $H:O$ is $1:8$: $\frac{\text{Mass of H}}{\text{Mass of O}} = \frac{1}{8}$ $\frac{3\text{ g}}{\text{Mass of O}} = \frac{1}{8}$ $\text{Mass of O} = 3 \times 8 = 24\text{ g}$