Question

Define the law of conservation of mass and law of constant proportion?

Answer 1

The law of conservation of mass and law of constant proportion both come under the law of chemical combination.
Law of chemical combination governs the chemical reaction which converts product into product. This law is further made up of four different types of laws.

Complete answer:
During any chemical reaction the mass of its reactant and product are governed by the law of conservation of mass.
Law of conservation of mass is defined as “when two or more reactants undergo physical or chemical change then the mass of the product is always equal to the sum of masses of reactants”.
According to this law matter is not destructed nor created during any physical or chemical reaction which means that the amount of matter remains the same as in the beginning of reaction.
For example, when we treat $50g$ of potassium nitrate with $40g$ of sodium chloride. At the end of reaction, we get two compounds potassium chloride and sodium nitrate.
$KN{O_3} + NaCl \to KCl + NaN{O_3}$
As we see that the total mass of reactant in the beginning is $100g$ then the weight of compounds at the end must also be equal to $100g$.
If at the end of reaction total weight of reactant remains $60g$ then $40g$ of product is formed in the reaction.
law of constant proportion defined as “elements always combine together in the same definite proportion by weight in a pure chemical compound”.
This law basically governed the composition of various elements which combined together to form a particular compound.
According to this law on varying the source of compound, the proportion of its constituents’ elements should not change.
For example, there are a number of sources which produce carbon dioxide gas but no matter what is the source of it, carbon dioxide is always made up of one atom of carbon and two atoms of oxygen.
Carbon dioxide generated during fossils burning-
$C + {O_2} \to C{O_2}$
Decomposition of limestone on heating produces carbon dioxide-
$CaC{O_3}\underrightarrow \Delta CaO + C{O_2}$
Similarly, Decomposition of copper powder produces carbon dioxide with the same chemical formula.
All these reactions show that one atom of carbon is combined with two atoms of oxygen to produce carbon dioxide.
As we know, the atomic mass of carbon is $12$ and atomic mass of oxygen is $16$.
$\dfrac{C}{O} = \dfrac{{12}}{{2 \times 16}}$
$\dfrac{C}{O} = \dfrac{{12}}{{32}}$
On solving the above equation, we get
$\dfrac{C}{O} = \dfrac{3}{8}$
Hence, each sample of carbon dioxide contains carbon and oxygen elements in the ratio of $3:8$ by weight.

Note:
Law of chemical combination also includes the law of multiple proportions and law of reciprocal proportion and law of combining volume.
Out of these five laws of chemical combination only the law of combining volume deals with volume of reaction while rest deals with the concept of mass relationship.