Question

Find the ratio by mass of the combining elements in the following compound: $Ca(OH{)}_2$ .

Answer 1

Hint :This question is based on the concept of law of constant proportions. It defines each compound as a combination of different elements in a fixed proportion and this is universal, that is whatever be the source of the compound, the elements present in the compound will be in the exact same proportion.

Complete Step By Step Answer:
Chemical compounds are formed up of elements that are present in a fixed mass ratio, according to the law of constant proportions. This means that each pure sample of a compound, regardless of its source, will always contain the same elements in the same mass ratio. Pure water, for example, will always have a constant mass ratio of hydrogen and oxygen (a gram of water consists of approximately 0.11 gram of hydrogen and 0.88 gram of oxygen, the ratio is 1:8).
In non-stoichiometric compounds, the element ratio fluctuates from sample to sample. As a result, the law of constant proportions does not apply to these compounds. Because the masses of two different isotopes of an element differ, samples of elements with varying isotopic compositions can likewise defy the law of definite proportions. Natural polymers have also been shown to defy the proportional law.
In $Ca(OH{)}_2$ , calcium, oxygen and hydrogen are present as:
(molar mass of calcium = 40g, oxygen = 16, hydrogen = 1)
 $$\begin{gathered} Ca:O:H \\ 40:2\times 16:2\times 1 \\ 40:32:2 \\ 20:16:1 \end{gathered}$$
Thus, the ratio by mass of combining elements in $Ca(OH{)}_2$ is 20:16:1.

Note :
The hydrogen and oxygen atoms in water molecules are arranged in a 2:1 ratio. Water molecules follow the law of constant proportions because they have a set mass ratio. Methane is another chemical molecule that follows the law of constant proportions. Four hydrogen atoms join with one carbon atom to produce a methane molecule.