Question

Determine the molar mass of a compound that has a density of 0.1633 g/L at STP.
(show work)

Answer 1

M.Mass = 3.66 g/mol

Data Given:

M.Mass = M = ??

Density = d = 0.1633 g/L

Temperature = T = 273.15 K (Standard)

Pressure = P = 1 atm (standard)

Solution:

Let us suppose that the gas is an ideal gas. Therefore, we will apply Ideal Gas equation i.e.

P V = n R T ---- (1)

Also, we know that;

Moles = n = mass / M.Mass

Or, n = m / M

Substituting n in Eq. 1.

P V = m/M R T --- (2)

Rearranging Eq.2 i.e.

P M = m/V R T --- (3)

As,

Mass / Volume = m/V = Density = d

So, Eq. 3 can be written as,

P M = d R T

Solving for M.Mass i.e.

M = d R T / P

Putting values,

M = 0.1633 g/L × 0.08205 L.atm.K⁻¹.mol⁻¹ × 273.15 K / 1 atm

M = 3.66 g/mol