# What is percent composition of ethanol ( C_2H_5OH )?

Apr 26, 2016

The percentage composition of ethanol (${C}_{2} {H}_{5} O H$) is:
52.2% of Carbon, 13.0% of Hydrogen, and 34.8% of Oxygen.

#### Explanation:

First step, find out what is the molar mass of ${C}_{2} {H}_{5} O H$.
Break up the formula to see what elements are involved.

If you look closely, you can see that Carbon, Hydrogen and Oxygen are involved.

If you look into your periodic table, you can find out what is the molar mass of each element.
Carbon = 12.0 g/mol
Hydrogen = 1.0 g/mol
Oxygen = 16.0 g/mol

Now you can calculate what is the molar mass of ${C}_{2} {H}_{5} O H$.

[$2 \times 12.0 + 6 \times 1.0 + 1 \times 16.0$] = 46.0 g/mol is the molar mass of ethanol.

The next step is to find out what are the percentages of each element.

To find out the percentage of Carbon,
$\left(\text{molar mass of carbon") / ("molar mass of ethanol}\right) \times 100$

The percentage of Carbon is:
24.0 g/mol $\div$ 46.0 g/mol $\times$ 100 = 52.2 % of Carbon
Note: The molar mass of carbon adds up to 24.0 because if you look back at the formula, you can see that there are two carbons.

Next step:
Find the percentage of Hydrogen
Note: Look carefully at the formula! You can see that there are 6 hydrogens, not 5!

The percentage of Hydrogen is:
6.0 g/mol $\div$ 46.0 g/mol $\times$100 = 13.0 % of Hydrogen.

Final step:
Find the percentage of Oxygen.

The percentage of Oxygen is:
16.0 g/mol $\div$ 46.0 g/mol $\times$ 100 = 34.8 % of Oxygen.

Therefore, the percentage composition of ethanol (${C}_{2} {H}_{5} O H$) is:
52.2% of Carbon, 13.0% of Hydrogen, and 34.8% of Oxygen.

Reminder: In the future, please check that every element has been calculated. Don't miss out any otherwise you won't get the right final answer.

Note: Percentages are rounded to 1 decimal place.