Competition for oxygen

Magnesium, iron, lead, zinc and copper will fight it out in this practical to show students who is the winner in the race for oxygen.

Introduction

There are many reactions between gases and solids which illustrate chemical principles. Heating a solid in an atmosphere of the required gas can be carried out in a modified boiling tube or test tube.

Heating a Pyrex test tube or boiling tube fitted with a bung, causes the pressure to rise inside and the glass to soften. Eventually the tube fails, and a hole is made.

Although this practical is not part of any Awarding Body specification, and although the purpose of making reaction tubes is for the reaction they will contain, the overall experience is so beneficial to students that most teachers say it is a practical worth doing in its own right.

Equipment

Apparatus

• Eye protection
• Bunsen burner
• Tripod
• Pipe clay triangle
• Crucible or cleaned beer bottle tops
• Tongs 

Chemicals

• Magnesium oxide, 0.5 g
• Iron, 0.5 g
• Lead(lI) oxide, 0.5 g
• Zinc, 0.5 g
• Copper(II) oxide, 0.5 g

Health, safety and technical notes

• Read our standard health and safety guidance.
• Always wear eye protection.
• Magnesium oxide is of low hazard (see CLEAPSS Hazcard HC059b).
• Lead(ll) oxide is a reproductive toxin, harmful if swallowed or inhaled, Specific Target Organ Toxin and dangerous for the environment (see CLEAPSS Hazcard HC056).
• Copper(ll) oxide is harmful if swallowed and dangerous for the environment (see CLEAPSS Hazcard HC026).
• Zinc is highly flammable and dangerous for the environment (see CLEAPSS Hazcard HC108b).
• Iron is of low hazard, if iron powder is used it will be highly flammable (see CLEAPSS Hazcard HC055A).
• Under no circumstances should a mixture of copper oxide and magnesium be heated by students.
• In the reaction of copper(ll) oxide and zinc, students should be told not to stir the mixture with a metal spatula.

Procedure

1. Set up the apparatus as shown in the diagram provided on the student sheet.
2. Place one spatula measure of one of the reaction mixtures into the crucible.
3. Heat the mixture gently at first and then more strongly. Watch carefully to see what happens, but do not lean over the crucible.
4. Allow the mixture to cool. Look for evidence that a reaction has taken place.
5. Use your observations to decide which of the two metals has ‘won’ the competition for oxygen - which is more reactive?
6. Choose another mixture and repeat the experiment.

Questions

1. Complete the table below:
2. Write word equations for reactions that occur.

Answers

1. Lead oxide + iron → iron oxide + lead
2. Lead oxide + zinc → zinc oxide + lead
3. Copper oxide + zinc → zinc oxide + copper

Notes

• This experiment uses lots of crucibles, which a school may not have. An alternative is to use beer bottle tops. The plastic insert of the tops should first be removed by heating them strongly in a fume cupboard.
• Some teachers recommend using ceramic paper rather than crucibles, as some products are difficult to remove from the crucible after reaction.
• One consideration is that using ceramic paper causes more mess and the Bunsen burners become clogged from spilt powders.
• Some teachers like to heat the mixture directly from above. Care is needed not to let powder be sprayed by the flame.
• Students must wear eye protection.
• Students must not lean over the reaction mixture.
• Some of the reactions may be unexpectedly violent.
• Ensure the room is well ventilated.
• If the mixtures are not given to the students pre-mixed, then students should be told to place the chemicals on a piece of paper and pass them back and forth to another piece of paper until they are well mixed. The mixture can then be placed in the crucible, or on the beer bottle top.