Chem Problem: density of a gas of unknown molar mass was measured as a function of pressure at 0,Determine a precise molar mass for the gas.?
The density of a gas of unknown molar mass was measured as a function of pressure at 0 ∘C, as in the table below.
1. Determine a precise molar mass for the gas. Hint: Graph d/P versus P.
2. Why is d/P not a constant as a function of pressure?
- Dr WLv 74 weeks ago
plot d/P vs P???
here's how I would do it
starting with these 2 equations
.. PV = nRT.. .. . ... ideal gas law
.. mw = mass / n.. . definition of molar mass (mw)
subbing and rearranging
.. PV = (mass / mw) RT
.. P = (RT/mw) * (mass / V)
since density (ρ) = mass / V
.. P = (RT/mw) * ρ
that's a linear equation if we plot P vs ρ slope = RT/mw
see the attached plot
and we know slope = RT/mw so that
.. RT/mw = 0.4354 atm/(g/L) = 0.4354 Latm / g
.. mw = RT * (1g / 0.4354 Latm)
.. mw = 0.08206 Latm/molK * 273.15K * (1g / 0.4354Latm) = 51.48g/mol