Question

# Assuming that petrol is octane $$({ C }_{ 8 }{ H }_{ 18 })$$ and has density $$0.8 g { mL }^{ -1 }, 1.425$$ litre of petrol on complete combustion will consume:

A
50 mole of O2
B
100 mole of O2
C
125 mole of O2
D
200 mole of O2

Solution

## The correct option is C $$125$$ mole of $${ O }_{ 2 }$$As we know that,$$\text{density} = \cfrac{\text{mass}}{\text{volume}}$$Density of octane $$= 0.8 g\ m {L}^{-1}$$Volume of octane $$= 1.425 L$$$$\therefore \; 0.8 = \cfrac{mass}{1.425}$$$$\Rightarrow \text{ given mass of octane} = 0.8 \times 1.425\times 1000 = 1140 g$$Molecular mass of octane, $$\left( {C}_{8}{H}_{18} \right) = 114 g$$No. of moles $$= \cfrac{\text{Given mass}}{\text{Molecular mass}} = \cfrac{1140}{114} = 10\text{ mole}$$Combustion of octane-$$2{C}_{8}{H}_{18} + 25 {O}_{2} \longrightarrow 16 C{O}_{2} + 18 {H}_{2}O$$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 $$= \cfrac{12.5}{1} \times 10 = 125\text{ mole}$$Hence, 1.425 litres of octane will consume 125 moles of oxygen.Hence, the correct option is $$C$$Chemistry

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