how can i do this problem?

Question

Consider 100.0-g samples of two different compounds consisting only of carbon and oxygen.Once compound contains 27.2 g of carbon and the other has 42.9 g of carbon. How can these data support the law of multiple proportions if 42.9 is not a multiple of 27.2?

Answer 1

The law of multiple proportions states that if two elements form more than one compound between them , then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers
First compound :
27.2 g of C and 72.8 g of O
72.8 / 27.2 = 2.67

Second compound
42.9 g of C and 57.1 g of O
57.1 / 42.9 = 1.33

2.67 / 1.33 = 2 this is the whole number

Answer 2

Instead of actual mass we have to consider the gram atoms of the elements :

I compound Carbon : 27.2/12 =2.27;
Oxygen : 72.8/16 =4.55
Carbon: oxygen : 1: 2.
II compound carbon : 42.9/12 = 3.57
oxygen : 57.1/16 = 3.57

Carbon : oxygen : 1:1

Thus the data clearly supports the law of ultiple proportions.

Answer 3

Convert the figures so that the mass of oxygen is the same, and not the total mass, and the law will be seen to be obeyed.