Question

In water $\left( {{H_2}O} \right)$ and hydrogen peroxide $\left( {{H_2}{O_2}} \right)$, the masses of oxygen which combine with fixed mass of hydrogen bear simple whole number ratio, i.e., $1:2$. This is an illustration of:
A.Law of definite proportions
B.Law of multiple proportions
C.Gay Lussac’s law
D.Avogadro’s law

Answer 1

Stoichiometry of a substance is based upon the very basic laws of chemistry that help us in the better understanding of the concept, namely, the law of conservation of mass, the law of reciprocal proportions, the law of definite proportions (also known as the law of constant composition) and the law of multiple proportions . Chemicals generally combine in fixed ratios in chemical reactions to form a chemical compound.

Complete answer:
The given example of the compositions of water and hydrogen peroxide molecules is explained on the basis of the law of multiple proportions. The law of multiple proportions was given by John Dalton and is thus, also known as Dalton’s Law. The law states that when two elements combine to form more than one compound, given the mass of one element constant, the masses of the other element in the compounds are in a simple whole number ratio.
Now, considering the reaction occurring between hydrogen and oxygen. We know they can form either water or hydrogen peroxide depending upon the conditions of the reaction. The two reactions occurring can be written as,
${H_2} + {O_2} \to {H_2}{O_2}$
${H_2} + \dfrac{1}{2}{O_2} \to {H_2}O$
The mass of hydrogen required in both the reactions is the same, i.e., one mole or 2 grams. So the mass of hydrogen is fixed. The masses of oxygen required in the reactions are 32 gram and 16 grams respectively. The ratio of these masses is $32:16 = 2:1$, which is a whole number ratio.

Hence, the correct answer is B.

Note:
It should be taken care that the law of multiple proportions is not confused with law of definite proportions. The latter states that a chemical compound always contains fixed proportions of its constituent elements.