Question

Assuming that petrol is octane $\left(C_8{H}_{18}\right)$ and has a density of $0.8gm{L}^{-1}$, 1.425 litre of petrol on combustion will consume:

• A. 100 mole of oxygen
• B. 125 mole of oxygen
• C. 150 mole of oxygen
• D. 175 mole of oxygen

Answer 1

The correct option is B 125 mole of oxygen

The equation looks like this $C_n{H}_{3n+2}+\left(\frac{3n+1}{2}\right)O_2⟶nC{O}_2+(n+1)H_{2}O$

For others,

$C_8{H}_{18}+\left(\frac{25}{2}\right)O_2⟶\left(8\right)C{O}_2+\left(9\right)H_{2}O1mol\frac{25}{2}mole$

Mass of octane $=PV=0.8\times 1425=1140g.$

No. of moles of octane $=\frac{1140}{114.23}=9.97$

Now, $1$ mol octane consumes $\frac{25}{2}$ mol of $O_2.$

$9.97$ mol octane consumes $\frac{25}{2}\times 9.97=124$ moles of $O_2$