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ICSE Class 10 Chemistry Question 6 of 25

Gay Lussac's Law — Avogadro's Law — Mole Concept — Question 6

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Question 6

On igniting a mixture of acetylene [C2H2] and oxygen, 200 cm3 of CO2 is collected at s.t.p. Calculate the volume of acetylene & O2 at s.t.p. in the original mixture.

Answer

[By Lussac's law]

2C2H2+5O2⟶4CO2+2H2O2 vol.:5 vol.⟶4 vol.:2 vol.\begin{matrix} \text{\scriptsize{2C}}_2 \text{\scriptsize{H}}_2 & \text{\scriptsize{+}} & \text{\scriptsize{5O}}_2 & \longrightarrow & \text{\scriptsize{4CO}}_2 & \text{\scriptsize{+}} & \text{\scriptsize{2H}}_2\text{\scriptsize{O}} \\ \text{\scriptsize{2 vol.}} & \text{\scriptsize{:}} & \text{\scriptsize{5 vol.}} & \longrightarrow & \text{\scriptsize{4 vol.}} & \text{\scriptsize{:}} & \text{\scriptsize{2 vol.}} \end{matrix}

To calculate the volume of acetylene :

CO2:C2H24:2200:x\begin{matrix} \text{CO}_2 & : & \text{C}_2 \text{H}_2 & \\ 4 & : & 2 \\ 200 & : & x \end{matrix}

Therefore,

24×200=x⇒x=100 cm3\dfrac{2}{4} \times 200 = x \\[0.5em] \Rightarrow x = 100 \text { cm}^3

Hence, volume of acetylene in the original mixture is 100 cm3.

To calculate the volume of oxygen :

CO2:O24:5200:x\begin{matrix} \text{CO}_2 & : & \text{O}_2 & \\ 4 & : & 5 \\ 200 & : & x \end{matrix}

Therefore,

54×200=x⇒x=250 cm3\dfrac{5}{4} \times 200 = x \\[0.5em] \Rightarrow x = 250 \text { cm}^3

Hence, volume of oxygen in the original mixture is 250 cm3.