Question

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

• A. $50$ mole of $O_2$
• B. $100$ mole of $O_2$
• C. $125$ mole of $O_2$
• D. $200$ mole of $O_2$

Answer 1

The correct option is C $125$ mole of $O_2$

As we know that,

$\text{density}=\frac{\text{mass}}{\text{volume}}$

Density of octane $=0.8gm{L}^{-1}$

Volume of octane $=1.425L$

$\therefore 0.8=\frac{mass}{1.425}$

$\Rightarrow \text{given mass of octane}=0.8\times 1.425\times 1000=1140g$

Molecular mass of octane, $\left(C_8{H}_{18}\right)=114g$

No. of moles $=\frac{\text{Given mass}}{\text{Molecular mass}}=\frac{1140}{114}=10\text{mole}$

Combustion of octane-

$2C_8{H}_{18}+25O_2⟶16C{O}_2+18H_{2}O$

No. of moles of oxygen required for the combustion of 1 mole octane = 12.5 moles

$\therefore$ No. of moles of oxygen required for the combustion of 10 mole octane $=\frac{12.5}{1}\times 10=125\text{mole}$

Hence, 1.425 litres of octane will consume 125 moles of oxygen.

Hence, the correct option is $C$