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An acid will release hydrogen gas when reacted with a metal

Apparatus and chemicals

• Boiling tube
• Delivery tube
• Test tube, basin
• Test-tube rack
• Measuring cylinder (25 cm³)
• Safety glasses
• Wooden splint
• 1 mol/dm³ hydrochloric acid (15 cm³)
• 2 cm strip of magnesium

Method

1. Fill the basin and test-tube with water, let the test tube rest on the bottom of the basin.
2. Measure 15 cm³ of hydrochloric acid using the measuring cylinder and add to the boiling tube.
3. Add the magnesium strip to the boiling tube – ensuring that the magnesium is fully immersed in the acid by swirling and allow the reaction to proceed for 10s.
4. After 10 seconds, place the delivery tube onto the boiling tube and place the end of the glass tube underneath the test-tube. Hold the test-tube upright and collect the gas produced. Once the test-tube is full, stopper the tube and place it in the test-tube rack.
5. Light a splint. Remove the stopper of the test-tube and hold the lit split at the top of the test-tube.

Observations

In this reaction it is very obvious that a gas is produced – you can see fizzing in the boiling tube. The magnesium also disappears, it is being chemically changed and forming a soluble product. You may have also noticed that the boiling tube becomes warm, this is evidence that heat is given off during the reaction.

When you collected the gas you should have noticed that it rises to the top of the test-tube and also that the water in the basin has no effect on the gas. This is because hydrogen is less dense than air and insoluble in water.

You will also have heard a squeaky pop when the lit splint is placed into the test-tube. This is actually a mini explosion! The hydrogen is reacting with the oxygen in the air and making water – you may have seen little droplets of water on the side of the test-tube after the reaction.