Question

Which of the following sets of compounds correctly illustrate the law of reciprocal proportion ?

• A. $N_{2}O,N{H}_3,S{O}_2$
• B. $P_2{O}_5,P{H}_3,H_{2}O$
• C. $N{O}_2,N{H}_3,S{O}_3$
• D. None of these

Answer 1

Answer: (B)

$P_2{O}_5,P{H}_3,H_{2}O$

The law of reciprocal proportions is one of the basic laws of stoichiometry. It relates the proportions in which elements combine across a number of different elements. A simple statement of the law is:

Element A combines with element B and also with C, then, if B and C combine together, the proportion by weight in which they do so will be simply related to the weights of B and C which separately combine with a constant weight of A.

Hydrogen combines with Oxygen to form $H_{2}O$

$2:161:8$

Phosphorous combines with Oxygen to form $P_2{O}_5$

$62:8031:40$

Phosphorous combines with Hydrogen to form $P{H}_5$

$31:5\frac{31}{40}\times \frac{8}{1}=\frac{31}{5}$