Law of multiple proportions

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The Law of Multiple Proportions is a fundamental principle of chemistry that was first formulated by the English chemist John Dalton in 1803. This law states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers.

Historical Background

The Law of Multiple Proportions was a key component in the development of atomic theory. John Dalton's work on this law provided strong evidence for the existence of atoms and helped to establish the concept that chemical compounds are composed of atoms in specific ratios.

Explanation and Examples

According to the Law of Multiple Proportions, if element A combines with element B to form more than one compound, the different masses of B that combine with a fixed mass of A will be in simple whole number ratios. For example, consider the compounds formed by carbon and oxygen:

• Carbon monoxide (CO): 12 grams of carbon combine with 16 grams of oxygen.
• Carbon dioxide (CO₂): 12 grams of carbon combine with 32 grams of oxygen.

The ratio of the masses of oxygen that combine with a fixed mass of carbon (16:32) simplifies to a ratio of 1:2, which is a small whole number ratio.

Significance

The Law of Multiple Proportions is significant because it supports the idea that chemical compounds are composed of atoms in definite proportions. This law also reinforces the concept of stoichiometry in chemical reactions, which is the calculation of reactants and products in chemical reactions.

Related Concepts

• Law of Definite Proportions
• Atomic theory
• Stoichiometry
• Chemical compound
• Dalton's atomic theory

See Also

• John Dalton
• Chemical reaction
• Molecular formula
• Empirical formula