Question

When 2.00 g of a certain volatile liquid is heated, the volume of the resulting vapour is 821 mL at a temperature of 127°C at standard pressure. The molecular mass of this substance is:

• A. 20.0 g/mol
• B. 40.0 g/mol
• C. 80.0 g/mol
• D. 120.0 g/mol

Hint:

The molecular mass can be calculated using the Ideal Gas Law, remembering to convert the temperature to Kelvin and use appropriate units.

Answer 1

The Correct Option is C

We use the Ideal Gas Law to calculate the molecular mass: \[ PV = nRT \] Where: \[ n = \frac{m}{M} \] Using given values for P, V, and T, and applying the equation: \[ M = \frac{mRT}{PV} \] Substitute the known values: \[ M = \frac{2.00 \, {g} \times 0.0821 \, {L·atm/mol·K} \times (127 + 273) \, {K}}{1 \, {atm} \times 0.821 \, {L}} = 80.0 \, {g/mol} \]