Question

34. 45 ml of phosphorus vapour weighs 0.0625 gram at 546 degree Celsius and 1 bar pressure. what is the molar mass of phosphorus.

Answer 1

Given,

p = 0.1 bar

V = 34.05 ml = 34.05 × 0.001 L = 34.05 × 0.001dm3

R = 0.083 bar dm3/K mol

T = 546°C = (546 + 273) K = 819 K

The number of moles (n) can be calculated using the ideal gas equation as:

PV = nRT

Where, P - Pressure of gas

V - Volume of gas

n - Number of moles of gas

R- Gas constant

T -Temperature of gas

n = 5.01×10-5 mol

Therefore, molar mass of phosphorus = mass/moles

⇒ M = 1247.5 g/mol

Hence, the molar mass of phosphorus is 1247.5 g/mol.