One mole of any gas occupies the same volume when measured under the same conditions of temperature and pressure
In this experiment, the volume of one mole of hydrogen is calculated at room temperature and pressure.
This experiment should take 40 minutes.
- Eye protection
- Burette stand
- Water bath
- Hydrochloric acid, 2 mol dm–3
- Magnesium ribbon 0.02–0.04 g
Health, safety and technical notes
- Read our standard health and safety guidelines.
- Wear eye protection.
- Hydrochloric acid is an irritant, see CLEAPSS Hazcard HC047a.
- Magnesium is water reactive, see CLEAPSS Hazcard HC059a.
- Clean a piece of magnesium ribbon about 3.5 cm long and weigh accurately. (This should weigh between 0.02 and 0.04 g; if not, adjust the amount used.)
- Measure 25 cm3 of dilute hydrochloric acid into the burette. Carefully add 25 cm3 of water on top of this.
- Push the magnesium into the end of the burette so it will stay in position with its own tension.
- Add 50 cm3 of water to a 250 cm3 beaker.
- Quickly invert the burette into the water. If this is done quickly and carefully, very little is lost. It is important that the liquid level in the burette starts on the graduated scale. If it is not on the scale; momentarily open the tap, this allows the level to drop. Clamp the burette vertically.
- Take the burette reading (care: it is upside down!)
- Observe the magnesium react as the acid diffuses downwards, wait until all the magnesium has reacted.
- Note the new volume on the burette (care: it is upside down).
- Record your results.
You should demonstrate the procedure beforehand.
The inversion is not difficult. Rest the end of the burette on the lip of the beaker and swing the tap end round and upward to a vertical position.
It is important that the liquid level starts on the graduated scale of the burette. If the liquid level is not on the scale, opening the tap momentarily allows the liquid to drop onto the scale.
Volume of one mole of gas at standard temperature and pressure, stp, (0 °C, 101,500 N m–2) is 22.4 dm3.
At room temperature and average pressure, rtp, the students can expect an answer of approximately 24 dm3.
Students that are more able may be able to use the equation P1V1/T1 = P2V2/T2 to find the volume at stp.
The temperature and pressure in the laboratory need to be measured.
The equation for the reaction is:
Mg +2HCl → MgCl2 + H2
The relative atomic mass of magnesium is 24.
- Copy out and fill in the gaps:
____ g Magnesium has produced ____cm3 hydrogen
____ /24 moles magnesium produces _____ cm3 hydrogen
1 mole magnesium produces ________cm3 hydrogen which is the volume of one mole of hydrogen gas.
- Expect rtp molar volume to be approximately 24 dm3.
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This practical is part of our Classic chemistry experiments collection.