Question

When 3.0 g of carbon is burnt in 8.0 g of oxygen, 11.0 g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.0 g of carbon is burnt in 50.0 g of oxygen? Which law of chemical combination will govern the answer?

Answer 1

The laws of chemical combinations are the laws that explain the combination of elements to form compounds. There are several laws in chemistry like – the law of conservation of mass, the law of definite proportion, the law of multiple proportions, gay lussac’s law, Avogadro’s law, the law of reciprocal proportion, etc.

Complete answer:
Let us study 2 laws in detail before answering the question-
(A)Law of conservation of mass-
This law was given by Antoine Lavoisier. According to this law, Mass can neither be created nor be destroyed or in other words, the mass of reactants is equal to the mass of products.
For example- Suppose we take 12 g of Carbon and 32 g of Oxygen, it will produce 44 g of carbon dioxide.
$C + {O_2} \to C{O_2}$
$12g + 32g = 44g$ (Since the mass of reactants and products must be the same).
(B)Law of constant or definite proportion-
This law was given by Joseph Proust. As per this law, a chemical compound no matter from which source it is obtained will contain the same elements combined in the same fixed proportion by mass.
For example-Water no matter from what source it is obtained will have the mass ratio of H: O as 1:8 since the mass of 2 atoms of hydrogen is 2 and that of oxygen is 16 so 2:16 or 1:8.
In the question we are given 3.0 g of carbon is burnt with 8.0 g of oxygen to form 11 g of Carbon dioxide-
$C + {O_2} \to C{O_2}$
$3g + 8g \to 11g$
Here the law of conservation of mass is obeyed since the mass of reactants is equal to the mass of the product.
In the second part of the question, we are given 3.0 g of carbon combining with 50.0 g of oxygen, since we know that 3.0 g of carbon will be combined with only 8.0 g of oxygen i.e. in a fixed proportion, the remaining 50-8=42.0 g of oxygen will remain unreacted. Hence there is a production of 11.0 g of carbon dioxide only.
Here the law of constant or definite proportion is obeyed.

Note:
It is important to note that the law of conservation of mass has limitations during nuclear reactions in which some of the mass is lost in the form of energy. The law of definite proportion fails when isotopes of elements are involved in the reaction or the combination of elements in the same ratio produces different compounds.