Q3.119CP - Chemistry: Molecular Nature Of Matter And Change

Question

Isobutylene is a hydrocarbon used in the manufacture of synthetic rubber. When 0.847 g of isobutylene was analyzed by combustion analysis (see Figure 3.5), the gain in mass of the CO₂ absorber was 2.657 g and that of the H₂O absorber was 1.089 g. What is the empirical formula of isobutylene?

Step-by-Step Solution

Answer

The empirical formula of isobutylene is CH₂.

Step 1: Finding the moles of C and H

The chemical equation can be written as:

$isobutylene\left(g\right)+O_2\left(g\right)\to C{O}_2\left(g\right)+H_{2}O\left(g\right).$

The moles of carbon and hydrogen can be denoted as:

$\begin{array}{rcl}Moles of C& =& 2.657 g C{O}_2\left(\frac{mol C{O}_2}{44.01 g C{O}_2}\right)\left(\frac{1 mol C}{1 mol C{O}_2}\right)\\ & =& 0.0604 mol C.\\ Moles of H& =& 1.089 g H_{2}O\left(\frac{mol H_{2}O}{18.02 g H_{2}O}\right)\left(\frac{2 mol H}{1 mol H_{2}O}\right)\\ & =& 0.1209 mol H.\end{array}$

Step 2: Finding the empirical formula

The empirical formula can be denoted as:

$C_{\frac{0.0604}{0.0604}}{H}_{\frac{0.1209}{0.0604}}\to C{H}_2.$