Question

A compound containing only carbon and hydrogen is found to have an empirical formula with molar mass of 13. 0 g/mol. The compound

	1.	cannot be either C2H2 or C6H6
	2.	could be C6H6 but no C2H2
	3.	could be C2H2 , but not C6H6
	4.	could be C2H2 or C6H6

A compound containing only carbon and hydrogen is found to have an empirical formula with molar mass of 13. 0 g/mol. The compound

	1.	cannot be either C2H2 or C6H6
	2.	could be C6H6 but no C2H2
	3.	could be C2H2 , but not C6H6
	4.	could be C2H2 or C6H6

Answer 1

The molar mass is the sum of the total mass in grams of all the atoms which makes a particular compound. It's depends only the atoms present in the compounds and their atomic mass. Atomic mass of carbon is around 12 grams per mole and atomic mass of hydrogen is around 1 gram per mole. In the above question it's stated that the molar mass of the compound is 13 grams per mole. so it's must contain one hydrogen and one carbon atom. So, the empirical formula should be CH. Whereas the molar mass of C₂H₂ is = (212)+(21) = 26 grams per mole and the molar mass of C₆H₆ = (612)+(61) =78 grams per mole. One thing you have to note carefully here is that the molar mass does not depends on the structure of the compound or any other properties. So, the empirical formula cann't be either C₂H₂ or C₆H_6.