Question

An unknown compound contains only carbon, hydrogen, and oxygen (cxhyoz). combustion of 5.00 g of this compound produced 7.33 g of carbon dioxide and 3.00 g of water. how many moles of carbon, c, were in the original sample?

Answer 1

Mass of carbon = 5.00 * 12.0 / (12.0 + 16.0*2)
= 1.36g
no. of moles of C = 1.36 * 12.0 = 16.3 moles

Answer 2

Answer : The number of moles of carbon in the original sample were 0.166 moles.

Explanation :

The chemical equation for the combustion of hydrocarbon having carbon, hydrogen and oxygen follows:

$C_xH_yO_z+O_2\rightarrow CO_2+H_2O$

where, 'x', 'y' and 'z' are the subscripts of Carbon, hydrogen and oxygen respectively.

We are given:

Mass of $CO_2=7.33g$

Mass of $H_2O=3.00g$

We know that:

Molar mass of carbon dioxide = 44 g/mol

For calculating the mass of carbon:

In 44 g of carbon dioxide, 12 g of carbon is contained.

So, in 7.33 g of carbon dioxide, $\frac{12}{44}\times 7.33=1.99g$ of carbon will be contained.

Now we have to calculate the moles of carbon.

Moles of Carbon =$\frac{\text{Given mass of Carbon}}{\text{Molar mass of Carbon}}=\frac{1.99g}{12g/mole}=0.166moles$

Therefore, the number of moles of carbon in the original sample were 0.166 moles.