Question

Air contains nearly 20% oxygen by volume. The volume of air needed for complete combustion of 100 ml of acetylene will be :

• A. 500 ml
• B. 100 ml
• C. 250 ml
• D. 1250 ml

Answer 1

The correct option is D 1250 ml

$2C_2{H}_2+5O_2⟶4C{O}_2+2H_{2}O$

2 moles of $C_2{H}_2$ react with 5 moles of $O_2$

1 moles of $C_2{H}_2=22400ml$

100 ml of $C_2{H}_2=\frac{100}{22400}=4.46\times {10}^{-3}mole$

2 moles of $C_2{H}_2$ react with 5 moles of $O_2$

4.46$\times {10}^{-3}$ moles of $C_2{H}_2$ will react with $\frac{4.46\times {10}^{-3}\times 5}{2}$ = 0.0112 moles of $O_2$

$0.0112\times 22400$ = 250 ml of $O_2$

Since air contains nearly 20% oxygen by volume.

The volume of air needed for complete combustion of 100 ml of acetylene =$\frac{250\times 100}{20}=1250ml$.

Hence,option D is correct.