3.1.2.3 The ideal gas equation

Ideal gas equation

PV=nRT

Pressure

symbol: P
unit: Pa

Volume

symbol: V
unit: m³

Temperature

symbol: T
unit: K (kelvin)
value: C + 273

Moles

symbol: n
unit: none

Constant

symbol: R
unit: JK^-1 mol^-1
value: 8.31

Equation to find Mr of substance using ideal gas equation

n=PV/RT Mr=mass/moles

Volatile liquid

Liquid with a low boiling point and vapourises easily

Why would the experimental value of Mr using PV=nRT and Mr=mass/n be different?

Volume of gas would be less than expected
Fewer moles than expected
Leading to higher Mr
Since Mr is found by dividing mass/moles

Possible errors when finding Mr of volatile liquid

not all of the volatile liquid vapourised in the water bath
some liquid is lost through evaporation when weighing
temperature in the gas syringe isn’t the same as the water bath
room pressure isn’t exactly 100kPa