Question

A compound is 80.0% carbon and 20.0% hydrogen by mass. Assume you have a 100.-g sample of this compound.

Answer 1

The empirical formula is:
`CH_3`

Step-by-step explanation:

In a sample of 100 g:

`m_C=100g *0.8= 80g`

`m_H=100g *0.2= 20g`

To determine the molecular formula you need to calculate the moles of each element. To do that the atomic weights are needed:

`M_C=12g/mol`

`M_H=1g/mol`

So, the moles of each one:

`n_C=(80g)/(12g/mol)=6.66mol`

`n_H=(20g)/(1g/mol)=20mol`

Now, you need to take this values to non-fractional numbers (keeping the ratio):

`n_C=(6.66mol)/(6.66mol)=1`

`n_H=(20mol)/(16.66mol)=3`

Therefore the empirical formula is:
`CH_3`

The molecular formula probably is a multiple of the empirical due to the carbon's valence.