Question

Two non - reactive gases A and B are present in a container with partial pressures 200 and 180 mm of Hg. When a third non - reactive gas C is added then total pressure becomes 1 atm then mole fraction of C will be:

• A. 0.225
• B. 0.75
• C. 0.5
• D. none of these

Answer 1

The correct option is C 0.5

According to Dalton's law of partial pressures, 'Total pressure is the sum of partial pressures of the gases present in the container.'

Total pressure = partial pressure of A + partial pressure B + partial pressure of C

Partial pressure of C = total pressure -(partial pressure of A + partial pressure of B)

Note: (1 atm = 760 mmHg)

Let's plug in the values:

partial pressure of C = 760 mmHg -(200 mmHg + 180 mmHg)

partial pressure of C = 760 mmHg - 380 mmHg = 380 mmHg

Also, partial pressure = total pressure$\times$(mole fraction)

So, partial pressure of C = total pressure$\times$(mole fraction of C)

mole fraction of C = $\frac{380}{760}$

mole fraction of C = 0.5

So, the mole fraction of C is 0.5.