Law Of Multiple Proportions

Compounds are one of the fundamentals of chemistry. When two or more atoms merge, they become a compound. These are specifically known as chemical compounds. Around these chemical compounds, several laws and theories have been proposed. These laws revolve around the compositions and elements in compounds.

The law of multiple proportions is one such law that revolves around compounds and their compositions. The law of multiple proportions lays the fundamentals for the chemical formulas in chemistry. This law is one of the basic rules in stoichiometry, a subdivision of chemistry. 

Let us begin by drawing the history of the law of multiple proportions. Further, we will also learn more about the law of the multiple proportions’ formula.

Know The Law Of Multiple Proportions

The pioneer of the law of multiple proportions is John Dalton. He initiated this law of multiple proportions in 1804. This law was mentioned in his work “A New System Of Chemical Philosophy”.

As per the law of multiple proportions, the proportions of the elements in a compound are expressible in small whole numbers. This means that compounds are formed by combining the elements. And the weight of these combining elements is considered expressible in whole numbers. This law is also termed Dalton’s law. 

Dalton pioneered this law of multiple proportions after he observed the atmospheric gases. This law of multiple proportions is an integral part of atomic theory by Dalton. It is one of the important postulates of his atomic theory that explains atomic structuring. This law emphasises that when we combine a fixed mass element with the same mass of another element, the ratios come in whole numbers. 

Dalton’s law of multiple proportions has revolutionised the world of modern chemistry. This law of multiple proportions is a significant basis in stoichiometry. Proust’s law of definite proportions and Lavisoier’s law of conservation mass also contribute. These three laws are considered to be the pathways for framing modern chemistry. 

Examples Of Law Of Multiple Proportions. 

The examples of the law of multiple proportions emphasise the practical side of Dalton’s theory. Understanding the examples of the law of multiple proportions brings in the idea of applying the law. 

When one mole of hydrogen reacts with one mole of chlorine, it results in the formation of one mole of hydrochloric acid. The ratio of hydrogen to chlorine is 1:1, which is a ratio expressed in small whole numbers. 

For example, Nitrogen combines with oxygen to form oxides of five types. These are NO, NO2, NO3, NO4, NO5. The weight of nitrogen is the same across all these oxides. It is 14g. The weight of oxygen in the increasing order is 8,16,24,32,64. All these weights are in the ratio 1:2:3:4:5. This implies the law of multiple proportions, as the ratios are in small whole numbers. 

Hydrogen combines with oxygen. This forms two kinds of oxides. These are water and hydrogen peroxide. The weight of hydrogen in both these oxides is 1. The weight of oxygen is 8 and 16, respectively. The ratio of the weight is 1:2. This implies that the ratio is a small whole number. Thus, indicating what the law of multiple proportions advocates. 

Limitations Of Law Of Multiple Proportions

While Dalton has given us a very strong law that bounds the compound in our nature, it is not the only side. The law of multiple proportions has limitations to it. These are in terms of compounds and the element masses. 

The law of multiple proportions is efficiently applicable to simple compounds. These simple compounds include hydrogen, oxygen, etc. Using it for complex compounds such as undecane would give a huge number of ratios. 

The law of multiple proportions cannot be applicable to non-stoichiometric compounds. These are compounds whose element positioning cannot be represented through any rations. Further, this law of multiple proportions is inefficient for polymers and oligomers. 

Polymers are chemical substances having various subunits. This makes it difficult for them to be calculated in small whole numbers and ratios. Oligomers are molecules that have repeating units, and hence cannot be represented through ratios. 

Parting Note

The field of chemistry had a modern shift with various laws and theories proposed. One such law is the law of multiple proportions. This law was proposed by an English chemist, John Dalton. Dalton derived the law after observing the atmospheric gases. 

As per the law, the proportions of elements that are combined to make the compound can be expressed in whole numbers. This means that when an element with a fixed ratio is combined with the ratio of other elements, it can be expressed in whole numbers. To be specific, the ratios are expressed in small whole numbers. 

There is no specific law of multiple proportions’ formula to execute. These are based on the weightage of the elements that are combined. The above article has several examples which impose on the law of multiple proportions. The examples also bring in the practical application of the law of multiple proportions. 

There are some limitations to the law of multiple proportions proposed by Dalton. This law is inapplicable for complex compounds. If this law is applied to complex compounds, it turns out to be contradictory. The ratios of the elements of a complex compound are larger and not small whole numbers. 

Further, the law of multiple proportions does not apply to non-stoichiometric compounds. These compounds have no representable ratios. Also, this law is not applicable for polymers and oligomers.