Question

The following phosphorus sulfides are known: P4S3, P4S7, and P4SIO. Do these compounds obey the law of multiple proportions?

Answer 1

Answer: The given compounds obeys Law of multiple proportions.

Explanation:

Law of multiple proportions states that when two elements combine to form two or more compounds in more than one proportion. The mass of one element that combine with a given mass of the other element are present in the ratios of small whole number. For Example: $Cu_2O\text{ and }CuO$

We are given:

Three compounds having chemical formulas of $P_4S_3,P_4S_7\text{ and }P_4S_{10}$

In the given compounds, mass ratio of phosphorus and sulfur are:

• Ratios of mass of elements in $P_4S_3$

Mass of phosphorus = (4 × 31) = 124 g/mol

Mass of sulfur = (3 × 32) = 96 g/mol

Mass ratio of phosphorus and sulfur in $P_4S_3$ is 124 : 96

• Ratios of mass of elements in $P_4S_7$

Mass of phosphorus = (4 × 31) = 124 g/mol

Mass of sulfur = (7 × 32) = 224 g/mol

Mass ratio of phosphorus and sulfur in $P_4S_7$ is 124 : 224

• Ratios of mass of elements in $P_4S_{10}$

Mass of phosphorus = (4 × 31) = 124 g/mol

Mass of sulfur = (10 × 32) = 320 g/mol

Mass ratio of phosphorus and sulfur in $P_4S_3$ is 124 : 320

As, the mass of phosphorus is fixed, so the mass ratio of sulfur in both the compounds must be in whole number ratio.

Mass ratio of sulfur in both the compounds =  96 : 224 : 320 = 3 : 7 : 10

Hence, the given compounds obeys Law of multiple proportions.