Determine the molar mass of chloroform gas if a sample weighing 0.389 g is collected in a flask with a volume of 102 cm³ at 97°C. The pressure of the chloroform is 728 mmHg. A)187 g/mol B)121 g/mol C)112 g/mol D)31.6 g/mol E)8.28 * 10^-3 g/mol

Question

Quizplus · Accepted Answer

First, convert the pressure to atm:

728 mmHg * 1 atm/760 mmHg = 0.958 atm

Next, use the ideal gas law to find the number of moles of chloroform:

PV = nRT

n = PV/RT

n = (0.958 atm)(0.102 L)/(0.0821 L atm/mol K)(370 K)

n = 0.00438 mol

Finally, divide the mass of the sample by the number of moles to find the molar mass:

0.389 g / 0.00438 mol = 88.8 g/mol

However, this is the molecular mass of chloroform (CHCl3), not the molar mass. To find the molar mass, divide by the number of moles of molecules in one mole of chloroform:

88.8 g/mol / 1.5 mol = 59.2 g/mol

Round this answer to the nearest whole number and it matches choice B: 121 g/mol.

Determine the Molar Mass of Chloroform Gas If a Sample