30. WATER WATER EVERYWHERE BUT NOT A DROP TO DRINK

SUBJECT: Science
GRADE: 7,8,9
GROUP SIZE: Small or Large
TIME: Several short periods
TYPE OF ACTIVITY: Student Investigation
TEACHING STRATEGY: Expository Guided Discovery
CONCEPTS: Filtration Bacteria Culture Water Purification
SKILLS: Experimentation Collecting Data Interpreting Data

Objectives: To understand that pure water must be carried or manufactured on board a space craft; to understand that there are ways of purifying water through filtration and distillation making it possible to use waste water.

Materials:

  • (Activity 1) 2 liter jug and water;
  • (Activity 2) flask, one hole stopper, glass tube, rubber tubing, tray of ice cubes, beaker;
  • (Activity 3) sand, lamp chimney, cloth, rubber band, dirty water;
  • (Activity 4) aquarium, water, aquarium charcoal filter;
  • (Activity 5) filter paper, funnel and support, 20 grams of aluminum chloride (AlCl3), dilute sodium hydroxide [NaOH] solution, beaker.

Teacher Background Information: There are a number of reasons that water is a vital consideration while traveling in space. Water is needed most urgently for drinking. It is also needed for reconstituting some of the food carried on board, for hygiene, and for cooling. Because of the duration of flights and because the equipment through which water passes must be kept free of residue, the water used must be free of bacteria and precipitates. Clogged equipment or a culture of bacteria in the drinking water could spell disaster for the astronauts.
Procedure: (Activity 1)

Fill a CLEAN jug with tap water and let it stand for several weeks. Observe, taste and discuss the problems associated with storage of water over extended periods of time.

(Activity 2) Distill water by boiling it in a flask fitted with a one hole stopper containing a glass tube and a length of rubber tubing. Lay the tubing across a tray of ice cubes and collect drops of water from the end of the tubing. Discuss the physical changes that water goes through during the distillation process (evaporation and condensation). Examine the residue in the flask from which the water was distilled. Why might it be a good idea to use distilled water in a steam iron or in a storage battery? Why might a space vehicle need to use distilled water? Where on earth might it be necessary to be able to distill water for drinking purposes? (Anywhere materials need to be removed from the water which would make the water undrinkable, ie., on a ship in order to use sea water.)

(Activity 3) Demonstrate the filtration of water by placing about 5 centimeters of fine sand in a lamp chimney which has a piece of cloth fastened across the larger end. Pour dirty water on top of the sand. Collect the water as it drips through. What do you observe about the water compared to its original condition? How effective is the sand? What other materials might be used in place of sand? Try some.

(Activity 4) Put tap water into an aquarium and let it stand for several weeks without the filtration system being turned on. Observe the water and note any changes in color or smell. After several weeks, turn on the filtration system and observe the results.

(Activity 5) Moisten a piece of filter paper with water and place it in a funnel on a support stand. Dissolve 20g of aluminum chloride in 100ml of water in a beaker. Slowly add 10ml of dilute sodium hydroxide solution. Pour the solution through the filter paper. Observe the material left behind (aluminum hydroxide, an insoluble precipitate). This chemical and filtration system is another way to remove materials from a liquid which may damage equipment it passes through.
Extensions: Have the students find out about other substances which are used in aerospace which may have to be distilled or filtered to avoid potentially harmful residue, ie., fuel.

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