The law states that in a chemical compound

Two or more elements are always present in same ratio by mass

It does not matter where the compound came from or who prepared it.

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Example

Water (H 2 O) is a chemical compound. 

It contains 2 elements; Hydrogen and Oxygen

 

These 2 elements are present in constant proportion by mass which is of 1 :8  

(Since Mass of H 2 = 2g and O=16g, therefore H 2 :O = 2:16 = 1:8)

It means that in 9 grams of Water

There will always be 1 gram of Hydrogen and 8 Grams of Oxygen

It does not matter what the source of water is (rain water/tap water/sea water) or how the water was prepared (melting of ice/cooling of water vapour)

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SAMPLE PROBLEM 2,3,4 LS

 

Example -

In text Question - Page 33 Q2

NCERT Question - Q2

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Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo