This is too hard Help me!!

Question

how do you calculate mass?

like what is the mass of hydrogen in 50.0g of propane C3H8

Answer 1

I hope someone has told you about the unit factor method and conversion factors, because that is the preferred way to solve problems.

50.0 g C3H8 x (1 mol C3H8 / 44.0 g C3H8) x (8 mol H / 1 mol C3H8) x (1.01 g H / 1 mol H) = 9.18 grams H

A conversion factor is a ratio of two quantities in different units which are equal to each other.  By setting up the conversion factors so that the units you don't want cancel out, leaving the units you do want, you know that the problem has been set up correctly.   Using this system it's pretty difficult to get the wrong answer.

Oh yes, one of the conversion factors is based on the ratio of H to C3H8 as given by the subscripts.

Answer 2

C3H8 = 44 g  (In 1 mole)              50 g

H8 = 8 g (in 1 mole)                        ?

Simple proportion:

8/44*50=9.09 g of Hydrogen in 50 g of Propane (C3H8)