How many carbon atoms are in 10g of CH4 and 20g of C3H8?

There are ##3.8 × 10^23" C atoms"## in 10 g of ##"CH₄"## and ##8.2 × 10^23" C atoms"## in 20 g of ##"C"_3"H"_8##.

##"C"## atoms in ##"CH"_4##

You must convert

##"grams of CH"_4 → "moles of CH"_4 → "molecules of CH"_4 → "atoms of C"##

The molar mass of ##"CH"_4"## is 16.04 g/mol.

You use this to convert grams to moles.

##10 cancel("g CH"_4) × (1 cancel("mol CH₄"))/(16.04 cancel("g CH₄")) × (6.022 × 10^23 cancel("molecules CH₄"))/(1 cancel("mol CH₄")) × "1 atom C"/(1 cancel("molecule CH₄")) = 3.8 × 10^23"atoms C"##

C atoms in ##"C"_3"H"_8##

The molar mass of ##"C"_3"H"_8## is 44.10 g/mol.

Can you show there are ##8.2 × 10^23" C"## atoms in 20 g of ##"C"_3"H"_8##?