the carbon in the

Question

The carbon (C) in the compound C3H3CI5 weighed 66g. How much did the hydrogen (H) weigh?

Answer 1

This is a problem using the Law of Definite Proportions = Law of Definite Composition  = Proust's Law.  This states that a given chemical compound (such as C3H3Cl5) always contains its elements in a fixed and definite ratio by mass.

Look at the total mass of one mole:

3C = 3x12 g = 36 g

3H = 3x1 g = 3 g

5Cl = 5x35.5 g = 178 g

 

NOTE that the mass ratio of H to C is 3g : 36g or mass of H is 1/12 the mass of C

1/12 x 66 g = 5.5 g of H would be present.