The fuel used in many disposable lighters is liquid butane, C4H10. Butane has a molecular weight of 58.1 grams in one mole. How many carbon atoms are in 2.50 g of butane?

The exact molecular mass for butane (C4H10) is

12.0096*4+1.0079*10=58.1174 which is 58.1 to 3 significant figures.

Proportion of carbon in the compound

12.0096*4: 58.1174

=>

48.0384 : 58.1174

The mass of carbon in 2.50 grams of butane can be obtained by proportion, namely

Mass of carbon

= 2.50 * (48.0384/58.1174)

= 2.0664

= 2.07 g (approximated to 3 significant figures)