Science notes for Class 9 Atoms and Molecules

In this article of Atoms and Molecules we use the following terms frequently like Elements, Compounds, Reactants and Products.

ANTOINE LAVOISIER BIOGRAPHY :

Antoine Lavoisier (1743-1794) was a French nobleman. He made many important contributions to chemistry and some call him the Father of Modern Chemistry.

Lavoisier studied combustion reactions in detail. He was able to find the masses of reactants and products accurately irrespective of their physical states. Based on is observations he proposed the Law of Conservation of Mass.

LAW OF CONSERVATION OF MASS :

Earlier, it was thought that mass would be decrease in the burning of Charcoal. But Lavoisier, carried out the burning of Charcoal in a closed apparatus and found no change in mass.

ANTOINE LAVOISIER EXPERIMENT :

Antoine Lavoisier on the basis of this experiment he proposed the law of conservation of mass. It states that, “Matter is neither created nor destroyed during a chemical reaction. More simply, the mass of products is equal to the mass of the reactants in a chemical reaction.

Note : Though the Law of Conservation of Mass was proposed by Lavoisier, it was experimentally verified by Landolt.

LAW OF CONSTANT PROPORTION CLASS 9 :

Now let us look at the results of some experiments carried out by the Joseph L. Proust between 1798 and 1808.

Proust took two samples of copper carbonate- a compound of copper, carbon and oxygen. He took a sample from nature and another sample prepared in the lab and decomposed it chemically to find percentage of copper, carbon and oxygen in the two samples.

LAW OF CONSTANT PROPORTION EXAMPLES :

Similarly Proust took water from different sources and found that the percentage of oxygen and hydrogen was the same in all samples. There was no relation between the place from where the sample came and it’s composition.

LAW OF CONSTANT PROPORTION SIMPLE DEFINITION :

Based on his experiments, Proust put forward the law of constant (or definite) proportions. It states that, “a given chemical substances always contain the same elements combined in a fixed proportions by mass.” This means that the relative proportion of elements in a compound is independent of the source or method of preparation.

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