About the Law of Definite Proportions

The Law of Definite Proportions is a scientific law discovered by Joseph Proust. It states that the composition of chemical compounds is proportionate regardless of the size of the sample. Though the principle has been found to be non-universal in the past 50 years due to increased testing capabilities, it still stands as a basic foundation of chemical composition.

Features

The Law of Definite Proportions, also called Proust's Law, states that a chemical compound has a set proportion of elements by volume regardless of the amount of the compound. For example, not matter what amount of water (H2O) you have, there will always be a ratio of 1/9 hydrogen to 8/9 oxygen, whether the sample size is a drop of water or a lake.

History

Joseph Proust, a French chemist, declared the law of definite proportions in 1806 after studying the principle for almost 10 years. It was a revolutionary concept among the scientific community and was opposed at first by other chemists. The adversaries of Proust's find believed that compounds could combine in any amount. It wasn't until John Dalton unveiled the atomic theory--that all compounds are made up of atoms--that credence was given to Proust's assertions.

Function

Proust's law helps chemists analyze and create various chemical compounds. If you know the basic ratio of the volume of each element in a compound, then you have the power both to extrapolate the amount in any given sample and also attempt to create the compound using the proper combination of elements. It is also helpful in identifying various compounds.

Misconceptions

The language in the law suggests that it is a universally true principle, but this is not the case. There are special instances of compounds whose composition of elements has been known to vary, such as ferrous oxide. These examples are called Non-Stoichiometric Compounds, and are usually found in transition metal oxides.

Benefits

While the Law of Definite Proportions is technically considered a chemical principle, it also translates to other areas like cooking. Using the Law of Definite Proportions, it is easy to modify a recipe based on the amount you want to produce. For example, if you have a recipe for a cake that uses eggs as 1/5 of the total ingredient volume and want to do a triple batch, you can set up a simple cross multiplication problem to find the specific amount of eggs needed, because no matter what size the cake, there will always be the same proportion of eggs.