Hard Chemistry Word Problem?

Question

Ethane and Ethylene are two gases containing only hydrogen and carbon atoms. In a certain sample of ethane, 4.53g of hydrogen is combined with 18g of carbon. In a sample of ethylene, 7.25g of hydrogen is combined with 43.2g of carbon.

a) show how the data illustrate the law of multiple proportions.

b) suggest reasonable formulas for the two compounds.

I have no idea how to do this..any help would be great!!

Answer 1

ethane:

4.53 g Hydrogen @ 1.01 g/mole = 4.49 moles H

18 g Carbon @ 12g/mole = 1.5 moles Carbon

ratio the moles:

4.5 moles / 1.5 = 3 moles Hydrogen

1.5 / 1.5 moles = 1 moles Carbon

your ratio is CH3

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ethene:

7.25 g Hydrogen @ 1.01 g/mol = 7.15 moles Hydrogen

43.2 grams carbon @ 12 g/mole = 3.6 moles Carbon

ratio the moles:

7.2 moles / 3.6 moles = 2 moles Hydrogen

3.6 moles / 3.6 = 1 mole Carbon

your formula is CH2

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a) show how the data illustrate the law of multiple proportions.

It states that when elements combine they do so in a ratio of small whole numbers. For example, carbon and oxygen react to form CO or CO2, but not CO1.8. Furthermore, it states that if two elements form more than one compound between them then the ratios of the masses of the second element combined with a fixed mass of the first element will also be in ratios of small whole numbers.

they did whole # ratios: CH2 & CH3

b) suggest reasonable formulas for the two compounds.

C2H4  & C2H6