Question

Which of the following is the best example to demonstrate the law of conservation of mass?

• A. 12 gm of carbon combines with 32 gm of oxygen to form 44 gm of $C{O}_2$.
• B. When 72 gm of carbon is heated in a vacuum and no change in its mass takes place.
• C. The weight of a piece of platinum is the same before and after heating in air.
• D. None of these

Answer 1

Answer: (A)

12 gm of carbon combines with 32 gm of oxygen to form 44 gm of $C{O}_2$.

According to the law of conservation of mass:

The total mass of the reactant = the total mass of the product.

Mass of reactants $=12+32=44$ i.e w(C)+ w(oxygen)

Mass of products $=44$ i.e. w(carbon dioxide)
Both B and C do not represent a chemical reaction, but only heating of elements, hence they are not the best examples to demonstrate the law of conservation of mass.