Question

A bulb of unknown volume contained an ideal gas at 650mm pressure. A certain amount of the gas was withdrawn and found to occupy 1.5 cc at 700 mm pressure. The pressure of the gas remaining in the bulb was found to be 600 mm. If all measurements are made at the same temperature, the volume of the bulb is ?

• A. 21 cc
• B. 42 cc
• C. 105 cc
• D. 63 cc

Answer 1

Answer: (A)

21 cc

The number of moles of gas withdrawn, $n_1=\frac{RT}{PV}=\frac{RT}{1.5cc\times 700mm}=\frac{RT}{1050}$

If the total volume of bulb is $x$ cc

The number of moles of gas remaining in the bulb, $n_2=\frac{RT}{x\times 600}$

Again, before withdrawal of gas

$n_1+n_2=\frac{RT}{x\times 650}$

$\Rightarrow RT(\frac{1}{1050}+\frac{1}{600\times x})=\frac{RT}{x\times 650}$

$\Rightarrow \frac{1}{1050}=\frac{1}{x}(\frac{1}{650}-\frac{1}{600})\Rightarrow x=21$ cc