Question

An unknown organic compound composed of carbon, hydrogen, and oxygen was analyzed and found to be 50.84% C, 8.53% H, and the rest oxygen. What is the empirical formula

Answer 1

In every 100g of that compund there is 50.84 g of C, 8.53 g H and (100-59.37) g = 40.63 g of O.

Step 1: Convert each element's mass in moles. To do that we need to divide each element's mass by their respective molar mass.

For Carbon.

$C = \frac{50.84}{12} = 4.24 mol$

For Hydrogen.

$H = \frac{8.53}{1} = 8.53 mol$

For Oxygen.

$O = \frac{40.63}{16} = 2.54 mol$

Step 2: Divide each of the numbers by the smallest number.

For Carbon.

$C = \frac{4.24}{2.54} = 1.7$

For Hydrogen.

$H = \frac{8.53}{2.54} = 3.36$

For Oxygen.

$O = \frac{2.54}{2.54} = 1$

Step 3: So the empirical formula will be.

$C_{1.7} H_{3.36} O_1$

But using decimal will be messy. So we multiply the numbers by 3. The right empirical formula will be.

$C_{5} H_{10} O_3$