Molar Volume of a Gas – Measure It and Use pV = nRT

What it shows

One mole of any ideal gas fills the same volume at a given temperature and pressure: about 24 dm³ at 20 °C and 1 atm, 24.8 dm³ at 25 °C and 100 kPa, and 22.7 dm³ at 0 °C and 100 kPa. Here the student measures it. A weighed sample gives one mole of gas per mole of solid. The balance, the plunger and the time of reading all add real errors. The model treats the gas as ideal and the syringe gas as dry, saturates gas over water with vapour, and uses illustrative values for how much CO₂ dissolves.

How to use

Choose the Reaction, Collect gas in and Sample mass, then press Start reaction. Wait for a steady reading, press Record reading and start a New sample with another mass. On the Graph screen, read the gradient of V against n and answer the tasks. Use Conditions to change temperature and pressure. The pV = nRT screen compares the standard conditions, and the Converter screen links V, n, m and N for two gases.

Parameters you can change

• Screen Bench, Graph, pV = nRT, Converter
• Reaction Magnesium + excess hydrochloric acid, Calcium carbonate + excess hydrochloric acid, Heating copper(II) carbonate
• Collect gas in Gas syringe, Over water
• Sample mass 0.02–0.6 g
• Ribbon cleaned with emery paper
• Conditions RTP (20 °C, 1 atm), SLC (25 °C, 100 kPa), STP (0 °C, 100 kPa), 0 °C, 1 atm (older STP), Custom
• Temperature 0–40 °C
• Pressure 90–110 kPa
• Gas A Hydrogen, H₂, Methane, CH₄, Nitrogen, N₂, Oxygen, O₂, Carbon dioxide, CO₂, Chlorine, Cl₂
• Gas B Hydrogen, H₂, Methane, CH₄, Nitrogen, N₂, Oxygen, O₂, Carbon dioxide, CO₂, Chlorine, Cl₂
• Volume in the converter 0.001–1000 dm³

Questions to explore

1. What happens to the gas volume at RTP when you double the mass of magnesium?
2. Why does calcium carbonate give a smaller molar volume over water than in the gas syringe?
3. Which of the listed standard conditions gives the largest molar volume, and what does pV = nRT say about why?