Question

You have a sample of Methane $\left( {C{H_4}} \right)$ with a mass of $32g$ . How much of that sample is Hydrogen?

Answer 1

Number of moles can be calculated from the mass of that compound or atom to the molar mass of that compound or atom. The mass of methane was given, from the molar mass and mass of methane number of moles of methane will be calculated which can be used to calculate the moles of hydrogen atom, giving the mass of hydrogen in the sample.

Complete answer:
Methane is a saturated hydrocarbon consisting of carbon and hydrogen atoms only. It consists of single bonds only. Methane is an alkane with the molecular formula of $C{H_4}$
Given that the mass of methane is $32g$
The molar mass of methane is $1\left( {12} \right) + 4\left( 1 \right) = 16gmo{l^{ - 1}}$
Thus, the number of moles will be obtained by dividing the mass of methane with molar mass of methane
${n_{C{H_4}}} = \dfrac{{32}}{{16}} = 2moles$
The number of moles of hydrogen will also be $2moles$ as the hydrogen is present in methane.
Methane consists of four hydrogen atoms, each hydrogen atoms has $1gmo{l^{ - 1}}$ , thus the four hydrogen atoms will have the molar mass of $4gmo{l^{ - 1}}$
Multiply the moles of hydrogen and molar mass of hydrogen to obtain the mass of hydrogen in sample.
$4gmo{l^{ - 1}} \times 2mol = 8g$
$32g$ sample of methane has $8g$ of hydrogen.

Note:
The number of moles is the ratio of the mass of an atom to the molar mass of the atom. The molar mass of atoms should be considered from the periodic table in grams per moles only. While calculating the mass of hydrogen in a sample, the molar mass of all the hydrogen atoms must be considered which can be obtained by the sum of four hydrogen atoms.