A hydrcarbon y contains 85.75% carbon and has a density of 2.5g/l at stpe

A hydrcarbon y contains 85.75% carbon and has a density of 2.5g/l at stpe

(A) Calculate the empirical formula of y
(B) Determine the molecular formular of y
(C) Write the structural formulae of the possible chain isomers of y

(A) Take a 100 g sample.

That gives you 85.75 g C and 14.25 g H.moles C = 85.75/12.01 = 7.14

moles H = 14.25/1.008 = 14.14


Find the ratio of the two with the smallest subscript being 1.0. To do this just divide both numbers by the smaller of the two like this:

moles C = 7.14/7.14 = 1.00

mols H = 14.14/7.14 = 1.98 which rounds to 2.0

To the empirical formula is CH2 with an empirical mass of 12 + 2 = 14.

(B) If the density is 2.5 g/L then 1 mole, which will occupy 22.4 L @ STP, will have a mass of 2.5 x 22.4 = 56.

Therefore, the molar mass is 56 and the empirical mass is 14, there must be 56/14 = 4

so the molecular formula is (CH2)4 or C4H8.