Question

If 6.50 g of the unknown compound contained 0.217 mol of C and 0.433 mol of H , how many moles of oxygen, O , were in the sample?

Answer 1

First, you should find the mass of carbon and hydrogen in the 6.5g of the unknown compound.
mass of carbon and hydrogen in the compound
=(0.217×12)+(0.433×1)
=3.037g
mass of oxygen in the compound
=6.5-3.037
=3.463g
no of mol of oxygen
=3.463÷16
=0.216 mol

Answer 2

Answer : The moles of oxygen in the sample was 0.216 mole.

Explanation : Given,

Moles of C = 0.217 mol

Moles of H = 0.433 mol

Mass of unknown compound = 6.50 g

Molar mass of C = 12 g/mol

Molar mass of H = 1 g/mol

Molar mass of O = 16 g/mol

First we have to calculate the mass of C and H.

$\text{Mass of C}=\text{Moles of C}\times \text{Molar mass of C}$

$\text{Mass of C}=0.217mol\times 12g/mol=2.604g$

$\text{Mass of H}=\text{Moles of H}\times \text{Molar mass of H}$

$\text{Mass of H}=0.433mol\times 1g/mol=0.433g$

Now we have to calculate the mass of oxygen.

Mass of oxygen = Mass of unknown compound - [Mass of C + Mass of H]

Mass of oxygen = 6.50 - [2.604 + 0.433]

Mass of oxygen = 3.463 g

Now we have to calculate the moles of oxygen.

$\text{Moles of O}=\frac{\text{Mass of O}}{\text{Molar mass of O}}$

$\text{Moles of O}=\frac{3.463g}{16g/mol}=0.216mol$

Therefore, the moles of oxygen in the sample was 0.216 mole.