The Law of Constant Composition Essay Sample

The Law of Constant Composition Essay Sample The law of constant composition is one of the most fundamental laws, a true cornerstone of quantitative chemistry. Together with another basic law the law of multiple proportions developed by Dalton, the law of constant composition makes the basis of stoichiometry. This fundamental chemistry law is also sometimes called as Prousts law, or the law of definite proportions, or the law of definite composition. The Law of Constant Composition Definition What is the law of constant composition? In chemical science, the law of constant composition states that any chemical compound always contains exactly the same (fixed) proportion of chemical elements by mass whatever its source or method of preparation are. In other words, if we take any unique chemical compound, the composition of its elements is always the same for all pure samples that exist in the Universe. For example, 18 g of H2O contain 16 g of oxygen and 2 g of hydrogen 54 g H2O contain 48 g oxygen and 6 g of hydrogen 72 g H2O contain 64 g oxygen and 8 g of hydrogen In any case, the proportion by mass of oxygen to mass of hydrogen is 8 to 1. This ratio is fixed and it will never change no matter whether we take river water, sea water, lake water or water from a well or a spring. Similarly, we can use different methods to obtain carbon dioxide (CO2), for example, heating a lime stone or burning carbon, and each sample of pure carbon dioxide that we get is made of carbon and oxygen in 3:8 ratio. The History of the Law of Constant Composition The law of constant compositions is also referred as Proust’s law because it was first observed by a French chemist Joseph Proust. His observation was based on series of experiments that he conducted between 1798 and 1804. He studied inorganic binary compounds such as metallic oxides, sulfates, and sulfites. First, the law was published in a paper discussing iron oxides. He summarized the results of his observations in 1806 in his law hat stated that all chemical compounds are made of definite and fixed ratios of elements by mass. Nowadays, this fundamental law seems obvious to modern chemists because it is a basic part of the very definition of a chemical compound. But at that time it was completely a new idea, and Proust’s theory was considered controversial. It was disputed by a number of his contemporaries. The most noted of scientists who opposed Proust’s theory was a well-known French chemist Claude Louis Berthollet. He was a supporter of the concept that elements could mix at any proportion. This debate showed that at that time scientists did not understand the difference between mixtures and pure chemical compounds. The conflict lasted until an English chemist John Dalton formulated his atomic theory in 1803. He explained that the matter consisted of discrete atoms for each element and that compound chemicals consisted of certain combinations of different types of atoms in a constant proportion. The theory supported Proust’s law. Dalton’s law of multiple proportions developed the law of definite composition and stated that if certain elements could make multiple combinations, the proportion with which elements combined to make these compounds can be expressed in small whole numbers. Swedish chemist John Jacob Berzelius explained the relation between Dalton’s atomic theory and Proust’s law in 1811. Exceptions to the Law of Constant Compositions The law of constant composition laid the foundation for many outstanding breakthroughs in chemistry. It won’t be an exaggeration to say that the entire quantitative chemistry is based on his essential law. But the law of constant composition is not universally true. There are exceptions â€" non-stoichiometric compounds which can differ in elemental composition from sample to sample, for example, iron oxide wüstite, which can have between 0.83 and 0.95 iron atoms for every atom of oxygen, and so contain something between 23% and 25% oxygen by mass. Proust had only basic instruments at his disposal so he couldn’t detect such variations. The existence of isotopic variations has a lot of advantages and they are used in geochemical dating because oceanic, atmospheric, astronomic, crustal, and deep Earth process may contain lighter or heavier isotopes. These variations are rather small, except in hydrogen, but they could be measured with modern instrumentation.