Question

LAW OF CONSTANT PROPORTIONS??​

Answer 1

Law of Constant Proportions ➔

Lavoisier, along with other scientists, noted

that many compounds were composed of two

or more elements and each such compound

had the same elements in the same

proportions, irrespective of where the

compound came from or who prepared it.

In a compound such as water, the ratio of

the mass of hydrogen to the mass of oxygen is

always , whatever the source of water. Thus,

if 9 g of water is decomposed, 1 g of hydrogen

and 8 g of oxygen are always obtained.

Similarly in ammonia, nitrogen and hydrogen

are always present in the ratio by mass,

whatever the method or the source from which

it is obtained.

This led to the law of constant proportions

which is also known as the law of definite

proportions. This law was stated by Proust as

“In a chemical substance the elements are

always present in definite proportions by

mass”.

The next problem faced by scientists was

to give appropriate explanations of these laws.

British chemist John Dalton provided the

basic theory about the nature of matter.

Dalton picked up the idea of divisibility of

matter, which was till then just a philosophy.

He took the name ‘atoms’ as given by the

Greeks and said that the smallest particles of

matter are atoms. His theory was based on the

laws of chemical combination. Dalton’s atomic

theory provided an explanation for the law of

conservation of mass and the law of definite

proportions.

According to Dalton’s atomic theory, all

matter, whether an element, a compound or

a mixture is composed of small particles called

atoms. The postulates of this theory may be

stated as follows:

(i) All matter is made of very tiny particles

called atoms, which participate in

chemical reactions.

(ii) Atoms are indivisible particles, which

cannot be created or destroyed in a

chemical reaction.

(iii) Atoms of a given element are identical

in mass and chemical properties.

(iv) Atoms of different elements have

different masses and chemical

properties.

(v) Atoms combine in the ratio of small

whole numbers to form compounds.

(vi) The relative number and kinds of

atoms are constant in a given

compound.

Answer 2

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The law of constant proportions states that chemical compounds are made up of elements that are present in a fixed ratio by mass. This implies that any pure sample of a compound, no matter the source, will always consist of the same elements that are present in the same ratio by mass. For example, pure water will always contain hydrogen and oxygen in a fixed mass ratio a gram of water consists of approximately 0. 11 grams of hydrogen and 0. 88 grams of oxygen, the ratio is 1: 8.