Question

When $C{{O}_{2}}$(g)is passed over red-hot coke it partially gets reduced to $CO$(g). Upon passing 0.5 litre of $C{{O}_{2}}$(g) over red hot coke, the total volume of the gases increased to 700 mL . The composition of the gaseous mixture at STP is:
A. $C{{O}_{2}}$ = 200 mL; $CO$ = 500 mL
B. $C{{O}_{2}}$ = 350 mL; $CO$ = 350 mL
C. $C{{O}_{2}}$ = 0.0 mL; $CO$ = 700 mL
D. $C{{O}_{2}}$ = 300 mL; $CO$ = 400 mL

Answer 1

The equation for the red hot coke is $C{{O}_{2}}+C\to 2CO$. The constant value to convert gas at STP is 22.4. By dividing the gas volume by this constant find the volume of gas at STP.

Complete step by step answer:
Let us assume that ‘x’ liter of $C{{O}_{2}}$is consumed in the reaction.
We know,

22.4L of $C{{O}_{2}}$ = 1mole of $C{{O}_{2}}$ so

X L of $C{{O}_{2}}$ = $\dfrac{x}{22.4}$moles of $C{{O}_{2}}$ is consumed.

The moles of $C{{O}_{2}}$ left after the reaction will be moles of$(\dfrac{0.5-x}{22.4})$

From the equation we get to know that 1 mole of $C{{O}_{2}}$ forms 2 moles of $CO$ so,

$\dfrac{x}{22.4}$moles of $C{{O}_{2}}$will form= $2(\dfrac{x}{22.4})$ moles of $CO$

We have to find the composition of gaseous mixture at STP. So, the composition at STP will be the amount of $C{{O}_{2}}$ left and the amount of $CO$ formed.
The total volume increased is =700mL (0.7L)
The total volume increased in moles will be

22.4L of volume = 1 mole of the substance so,

0.7L of volume = $\dfrac{0.7}{22.4}$moles of the substance

The composition of mixture will be = left amount of $C{{O}_{2}}$ moles + $CO$formed moles

$\dfrac{0.7}{22.4}$ moles = $(\dfrac{0.5-x}{22.4})$ + $2(\dfrac{x}{22.4})$

22.4 in the denominator will get cancel and we will get

0.7= 0.5-x +2x

x = 0.2L (200mL)

So the volume of $C{{O}_{2}}$ consumed is 200mL and $CO$ formed is 400mL (2x of $C{{O}_{2}}$ consumed)

Now the $C{{O}_{2}}$left = given volume-consumed volume

= 500mL-200mL

=300mL

The left $C{{O}_{2}}$is 300mL and formed $CO$ is 400mL.

So, the correct answer is Option D.

Note: The students generally do not convert the given volumes in moles and get confused while solving them. They also find the left $C{{O}_{2}}$by taking a variable and making the question. So students must read the question thoroughly and understand it.