a. Since you have a 100 g sample for all three gases, the percent C and H is the same as grams; i.e.,
ethane:
79.89% C
20.11% H
ethylene:
85.63% C
14.37% H
third hydrocarbon:
64.580% C
35.420% H
Look up the law of constant composition: it says that the amount of an element in a given compound doesn't change. You see that the percents are different for both C and H in all three compounds; therefore, they must be different substances.
b.
For ethane: C79.89H20.11.
Divide by 79.89 to make that C1H0.2517.
For ethylene: C85.63H14.37
Divide by 85.63 to make that
C1H0.1678.
The law of multiple proportions (look it up) says that when two elements form more than one compound that the mass of one element that combines with a fixed mass of the other will always be in the ratio of small whole numbers. So I divided to make the fixed mass 1g for C, now the ratio of H is 0.2517 to 0.1678 and that ratio is 0.2517/0.1678 =1.5 and 1:1.5 is the same as 2:3 and that is in the ratio of small whole numbers. That agrees with the Law of Multiple Proportions.
A 100.00g sample of the gaseous hydrocarbon ethane is a gaseous hydrocarbon, with 79.89g of carbon and
20.11g of hydrogen. Ethylene is a different gas phase hydrocarbon. A 100.00g sample of ethylene has 85.63g
of carbon with 14.37 of hydrogen. A sample of a hydrocarbon has 64.580g of carbon has 35.420g of hydrogen.
a. Use the mass percents and the law of constant composition to prove that all three compounds are different.
b. Prove that ethane and ethylene obey the law of multiple proportions.
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