Question

An unknown compound contains only carbon, hydrogen, and oxygen (CxHyOz). Combustion of 5.50 g of this compound produced 8.07 g of carbon dioxide and 3.30 g of water.

Required:
a. How many moles of carbon, C, were in the original sample?
b. How many moles of hydrogen, H, were in the original sample?

Answer 1

a. 0.183 mol C

b. 0.366 mol H

Step-by-step explanation:

Assuming total combustion, all of the carbon in the unknown compound turned into carbon dioxide, CO₂.

So first we calculate the CO₂ moles produced, using its molecular weight:

• 8.07 g CO₂ ÷ 44 g/mol = 0.183 mol CO₂

This means in the unknown compound there were 0.183 moles of carbon, C.

Conversely, all of the hydrogen in the unknown compound turned into water, H₂O.

Calculating the H₂O moles:

• 3.30 g ÷ 18 g/mol = 0.183 mol H₂O

We multiply the water moles by two, as there are 2 H moles per H₂O mol:

• 0.183 * 2 = 0.366 mol H.