Amount of Substances: Mr of Gases & Volatile Liquids

Question 1

Determining the Mr of Gases

Answer 1

• Record mass of cylinder of gas
• Sample of gas is released into a gas syringe - gas will be at same pressure as surrounding air
• Cylinder of gas is reweighed, so mass of gas in syringe can be calculated
• Volume of gas in the syringe is recorded, along with room temperature and pressure
• Number of moles can be calculated using the ideal gas equation
• Calculate Mr: - Moles = Mass / Mr
  - Mr = Mass / Moles

Question 2

Determining the Mr of Volatile Liquids

Answer 2

• Gas syringe is heated using a steam jacket. A known mass of the volatile liquid is added
• Volatile liquid is injected into gas syringe, where it evaporates. Volume of gas, temperature inside steam jacket and atmospheric pressure are all recorded
• Calculate no. of moles with PV=nRT
• Mr = Mass / Moles

Question 3

Avogadro’s Law

Answer 3

• Equal volumes of different gases at the same temperature and pressure will contain equal numbers of particles
• One mole of any gas occupies 24dm^3 at standard conditions of temperature and pressure (298K and 100kPa)