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Whenthe carbon-containing compound is heated in presence of a limited amount of oxygen, it gives carbon dioxide and carbon monoxide. The combustion equation of carbon-containing compound is:

$Compound\left(s\right)+O_2\left(g\right)→C{O}_2\left(g\right)+CO\left(g\right)$

The number of moles is calculated by the mass and Molar mass. The relationship between the number of moles, mass, and molar mass is given below.

$Number of moles=\frac{mass}{Molar mass}$

Consider 100 g of carbon-containing compound is burned and forms 35 mass %$CO$ and 65 mass % $C{O}_2.$ This states that 100 g of carbon-containing compound produces 35 g of CO and 65 g ofCO₂

The mass ofCO = 35 g

The molar mass ofCO = 28.01 g/mol

The number of moles of CO is calculated as

$\begin{array}{rcl}moles of CO& =& \frac{mass of CO}{Molar mass of CO}\\ & =& \frac{35 g}{28.01 g/mol}\\ & =& 1.2496 mol\end{array}$

Since 1 mol of theC atom is present in 1 mol of CO

So, the number of moles ofC is:

$\begin{array}{rcl}1 mol of CO& =& 1 mol of C\\ 1.2496 mol of CO& =& 1.2496 mol of C\end{array}$

The molar mass ofCarbon = 12.01 g/mol

Thus, themassof Carbon is:

$\begin{array}{rcl}mass of C& =& moles of C×molar mass of C\\ & =& 1.2496 mol×12.01 g/mol\\ & =& 15.01 g\end{array}$

The mass ofCO₂ = 65 g

The molar mass ofCO₂ = 44.01 g/mol

The number of moles CO₂ is calculated as

$\begin{array}{rcl}Moles of C{O}_2& =& \frac{mass of C{O}_2}{Molar mass of C{O}_2}\\ & =& \frac{65 g}{44.01 g/mol}\\ & =& 1.4769 mol\end{array}$

Since 1 mol of thecarbon atom is present in 1 mol of$C{O}_2.$

So, the number of moles of C is:

$$\begin{gathered} \text{1} \text{mol} \text{of} {\text{CO}}_{\text{2}}\text{=1} \text{mol} \text{of} \text{C} \\ \text{1.4769} \text{mol} \text{of} {\text{CO}}_{\text{2}}\text{=1.4769} \text{mol} \text{of} \text{C} \end{gathered}$$

The molar mass ofcarbon = 12.01 g/mol

Thus, themassof carbon is:

$\begin{array}{rcl}Mass of C& =& moles of C×molar mass of C\\ & =& 1.4769 mol×12.01 g/mol\\ & =& 17.74 g\\ & & \\ & & \end{array}$

The total mass ofC is the sum of the mass ofC present inCO andCO₂Therefore,

The mass % of theCarbonis calculated as

$\begin{array}{rcl}mass \% of C& =& \frac{mass of C}{mass of carbon containing compound}×100\%\\ & =& \frac{32.75 g}{100 g}×100\%\\ & =& 32.75\%\end{array}$