Question

Chloroform is a volatile liquid once commonly used in the laboratory but now being phased out due to its ozone depletion potential. If the pressure of gaseous chloroform in a flask is 195 mm Hg at 25°C and its density is 1.25 g/L, what is the molar mass of chloroform? A) 10.0 g/mol B) 76.3 g/mol C) 119 g/mol D) None of these

Answer 1

Answer : The correct option is, (C) 119 g/mol

Explanation :

To calculate the molar mass of chloroform we are using ideal gas equation:

$PV=nRT\\\\PV=\frac{w}{M}RT\\\\M=\frac{w}{V}\times \frac{RT}{P}\\\\M=\rho \times \frac{RT}{P}$

where,

P = pressure of gas = 195 mmHg = 0.256 atm    (1 atm = 760 mmHg)

V = volume of argon gas

T = temperature of gas = $25^oC=273+25=298K$

R = gas constant = 0.0821 L.atm/mole.K

w = mass of gas

$\rho$ = density of gas = 1.25 g/L

M = molar mass of chloroform = ?

Now put all the given values in the ideal gas equation, we get:

$M=1.25g/L\times \frac{(0.0821L.atm/mole.K)\times (298K)}{0.256atm}$

$M=119.4g/mol\approx 119g/mol$

Therefore, the molar mass of chloroform is, 119 g/mol.