There are two laws of Chemical Combination which we are studying in class 9.
1. Law of conservation of mass
2. Law of constant proportion
Law of conservation of mass
Law of conservation of mass was given by Lavoisier in 1774. According to this law, a matter is neither be created nor be destroyed in a chemical reaction which means that in a chemical reaction the total mass of the product is equal to the total mass of reactants there is no change in mass during a chemical reaction
In a reaction, 5.3 gram of sodium carbonate reacted with ethanoic acid. The product word 2.2 gram of carbon dioxide, 0.9 gram of water 12 gram of sodium ethanoic. These observations are in agreement with the law of conservation of mass.
Sodium carbonate + ethanoic acid ⇒ sodium ethanoate + carbon dioxide + water
Sodium carbonate + ethanoic acid ⇒ sodium ethanoate + carbon
5.3 gram + 6 grams ⇒ 8.2 gram + dioxide + water + 2.2 grams + 0.9 grams
11.3 grams ⇒ 11.3 grams
The mass of reactants is equal to the mass of products which proves the law of conservation of mass.
Law of constant proportion
The law of constant proportion was given by Proust 1779 according to this law a chemical compound always consist of same elements combined together in the same proportion by mass
For example – hydrogen and oxygen combine in the ratio of 1:8 by mass to form water.
If hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. What mass of Oxygen gas would be required to react completely with 3 gram of hydrogen gas?
One gram of hydrogen reacts with 8 gram of oxygen to form water.
So, 3 gram of hydrogen will react with 8 x 3 = 24 gram of oxygen to form water.