In Search of Solutions: desert survival

The open-ended nature of this investigation makes it flexible enough to be used with different age groups (see below for how to use with primary learners). Explore separation techniques, distillation and states of matter and develop skills in scientific enquiry – and show learners that chemistry is fun. 

The investigation

Desert survival

Your aircraft has just crashed in the desert, and the last cupful of water has been spilled on the dry sand. You immediately scoop up the wet sand and put it into a plastic bag.

Learning objectives:

1 Use knowledge of solids, liquids, and gases to decide how mixtures might be separated, including through evaporating and condensing.

2 Observe that some materials change state when they are heated or cooled.

Your task

How can you get that vital water back? You have just 90 minutes before you die from dehydration…

Equipment & materials

General

The following items are available from the wrecked aircraft, or its occupants: plastic bags, yoghurt pots, aluminium foil, aluminium foil trays, beer cans, plastic lemonade bottles, rubber bands, wire, string, old pair of tights, blocks of expanded polystyrene or foam rubber. Pliers, craft knives.

Furthermore, the desert environment provides unlimited quantities of sand, and a source of radiant energy – a lamp with a 60 W bulb should be provided to simulate the desert sun (check that it is safely wired and earthed). A stage floodlight would be exciting if available!

Per group

A plastic bag containing 100 g sand mixed with 25 cm3 water, ie wet sand.

Curriculum links

Evaporation, condensation.

Planning

Time

90 minutes

Group size

2–3.

Possible approaches

Fits in well with classwork on evaporation and condensation. Some help on cooling steam may be necessary.

• A wide, clear plastic tube could be provided, so that the principle of extraction of water using centrifugal force could be explored, cf spin dryer.
• Plastic dish covered in foil, inside dish, porous pot (sealed) containing wet sand. Bottom of dish insulated. At the top a lamp is shone on the dish.
• A simple distillation set up using junk items:

 

 

 

 

 

 

 

 

 

 

Health & Safety notes

This is an open-ended problem solving activity, so the guidance given here is necessarily incomplete. Teachers need to be particularly vigilant, and a higher degree of supervision is needed than in activities which have more closed outcomes. Students must be encouraged to take a responsible attitude towards safety, both their own and that of others. In planning an activity students should always include safety as a factor to be considered. Plans should be checked by the teacher before implementing them.

Read our standard health & safety guidance and carry out a risk assessment before running any live practical. Refer to SSERC/CLEAPSS Hazcards and recipe sheets.

Please consider the dangers of using water near electric mains.

There should be no need for eye protection; unless the separation method chosen takes an unusual turn.

It is the responsibility of the teacher to carry out a suitable risk assessment.

Write-up and assessment

Suggested write-up

Taped interviews conducted with the ‘survivors’ of the plane crash on their return to the UK by science reporters. The novel water ‘extractors’ already making headline news need the students’ personalised explanations.

Evaluation of task

These are suggestions only:

1 Just before they are about to die, the ‘survivors’ (groups) present the judges with the water they have freed from the sand.

2 The judges will measure the volume of water collected. The winning group is that with the largest volume of water.

3 In the event of a tie, the group with the most appetising sample of water will be declared the winners.

Extension work

Cross-curricular possibilities with the geography department – ie water supply in desert regions.