Some Basic Concepts of Chemistry — Chemistry STD 11 Science — Question
Gujarat BoardEnglish MediumSTD 11 ScienceChemistrySome Basic Concepts of Chemistry5 Marks
Question
Define the law of multiple proportions. Explain it with two examples. How does this law point to the existance of atoms?
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Answer
Law of multiple proportions: When two elements combine to form two or more chemical compounds, then the masses of one of the elements which combine with a fixed mass of the other, bear a simple ratio to one another, e.g., carbon combines with oxygen to form two compounds, namely, carbon dioxide and carbon monoxide. The masses of oxygen which combine with a fixed mass of carbon in $\mathrm{CO}_2$ and CO are 32 and 16 respectively. These masses of oxygen bear a simple ratio of $32: 16$ or $2: 1$ to each other. For example, sulphur combines with oxygen to form two compounds, namely, sulphur trioxide and sulphur dioxide.
The masses of oxygen which combine with a fixed mass of sulphur in $\mathrm{SO}_3$ and $\mathrm{SO}_2$ are 48 and 32 respectively. These masses of oxygen bear a simple ratio of $48: 32$ or $3: 2$ to each other. This law shows that there are constituents whom combine in a definite proportion. These constituents may be atoms. Thus, the law of multiple proportions shows the existence of atoms which combine to form molecules.
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