3.1 - Determination of the Relative Molecular Mass of a Volatile Liquid (Leaving Cert Chemistry): Flashcards

$PV = nRT$ (ideal gas equation)

Estimate relative molecular mass ($M_r$)

Propanone

Approximately 95°C

$3-4$ cm³

Difference in mass before and after vaporisation

Fill with water, transfer to graduated cylinder

Barometer

$n = \frac{PV}{RT}$

$M_r = \frac{m}{n}$

Highly flammable

So ideal gas law can be applied accurately

Mass spectrometry

Volume measurement

Gives smaller calculated $M_r$