Question

A compound that is composed of only carbon and hydrogen contains 80.0% c and 20.0% h by mass. What is the empirical formula of the compound?

Answer 1

Solution : Emperical Formula =  $CH_{3}$

Emperical Formula - A formula that gives the simplest whole number ratio of atom in a compound.

In the question percentages are given then assume that the total mass is 100grams so that the mass of each element is equal to the percentage given.

Given : 80.0g Carbon

            20.0g Hydrogen

First convert the given masses into moles.

$80.0g\text{ C} \times \frac{1 g/mole \text{ C}}{12.0 g/mole \text{ C}}= 6.66\text{mole of C}$

$20.0g\text{ H} \times \frac{1 g/mole \text{ H}}{1 g/mole \text{ H}}= 20.0\text{mole of H}$

Value of each mole divided by the smallest number of moles and then round off.

Moles ratio of the element are

$\frac{6.66}{6.66}\text{mole of C}= 1$

$\frac{20.0}{6.66}\text{mole of C}= 3$

This is the mole ratio of the elements and is repersented by the subscript in the emperical formula.

Emperical Formula =  $CH_{3}$