Question

If 6.00 g of the unknown compound contained 0.200 mol of C and 0.400 mol of H, how many moles of oxygen, O, were in the sample?

Answer 1

Convert moles to mass.

mass C = 0.2 mol * 12 g / mol = 2.4 g

mass H = 0.4 mol * 1 g / mol = 0.4 g

So mass left for O = 6 g – (2.4 g + 0.4 g) = 3.2 g

 

Calculating for moles O given mass:

moles O = 3.2 g / (16 g / mol) = 0.2 moles

 

Answer:

0.2 moles O

Answer 2

Answer : The moles of oxygen present in the sample is, 0.2 moles

Explanation : Given,

Moles of carbon = 0.200 mole

Moles of hydrogen = 0.400 mole

Mass of unknown compound = 6.00 g

Molar mass of carbon = 12 g/mole

Molar mass of hydrogen = 1 g/mole

Molar mass of oxygen = 16 g/mole

First we have to calculate the mass of carbon and hydrogen.

$\text{Mass of carbon}=\text{Moles of carbon}\times \text{Molar mass of carbon}=(0.200mole)\times (12g/mole)=2.4g$

$\text{Mass of hydrogen}=\text{Moles of hydrogen}\times \text{Molar mass of hydrogen}=(0.400mole)\times (1g/mole)=0.4g$

Now we have to calculate the mass of oxygen.

Total mass of unknown compound = Mass of carbon + Mass of hydrogen + Mass of oxygen

6.00 = 2.4 + 0.4 + Mass of oxygen

Mass of oxygen = 3.2 grams

Now we have tom calculate the moles of oxygen.

$\text{Moles of oxygen}=\frac{\text{Mass of oxygen}}{\text{Molar mass of oxygen}}=\frac{3.2g}{16g/mole}=0.2moles$

Therefore, the moles of oxygen present in the sample is, 0.2 moles