This activity demonstrates how water is recycled from the earth into the atmosphere and back to the earth again, and how this process actually cleans or improves the quality of water. It also shows how pollutants are sometimes transported by this system and continue to pose a threat to water quality if not effectively removed.

Water Cycle

1. Water evaporates from lakes and ocean surfaces. The evaporated water forms clouds that may travel over vast distances.

2. Precipitation as mist, rain, snow or ice falls over the land and the sea.

3. Some groundwater may emerge as a spring or may enter lakes and oceans.
4. Some water sinks into the ground, becoming part of the groundwater.
5. Plants and animals use water and return it to the environment through transpiration, perspiration, or urination.
6. Surface water runoff enters streams, rivers, lakes and oceans.

Objectives

You will create a small model that demonstrates how the water cycle is constantly renewing itself on earth. You can experiment by adding different pollutants to the water cycle and observing how they move through the system.

Materials Needed
A clear plastic box with a clear lid (about the size of a shoe box) If you cannot find a clear plastic box use a large Tupperware container with a clear lid or use plastic wrap secured with a rubber band. 100 ml of water Heat lamp Plastic bag of ice Wide range pH strips or a pH testing kit Food coloring Vinegar and ammonia

Procedure

1. Prop the box up at a 30 degree angle.
2. Pour 100 ml of water into the box and replace the lid.
3. Focus the heat lamp on the lower portion of the box to heat the water.
4. Lay the ice pack over the top corner of the box as shown.
5. Observe for the box for about 5 minutes. The water cycle starts when the droplets forming on the lid form drops that drip back into the puddle. Once the water cycle is initiated add food coloring to the water (pollutant to the system).

Questions

1. In terms of evaporation, condensation, and precipitation, describe the following:
• What process takes place when the heat lamp is turned on?
• What process takes place when you apply ice to the lid of the box?
2. What happens to the food coloring in the water cycle? Does the water cycle help purify the water? If so, in what part?
3. Let's do this experiment again, except this time we will explore how acid rain travels throughout the water cycle.

Acid Rain

	Sulphur dioxide (SO2) and nitrogen oxides (NOx) enter our atmosphere from the burning of fossil fuels such as coal and oil in power stations, motor vehicles, and industry.
These gasses mix with water vapor, sunlight and oxygen in the atmosphere to form dilute sulfuric acid (H2SO4) nitric acid (HNO3). These acid droplets are carried in clouds sometimes thousands of miles. When it rains these droplets fall to the earth as acid rain or snow. Acid rain or snow has a pH below 6.
	A healthy lake has a pH between 6-8. Continual acid rain can lower the pH below 6 which can kill fish and plants. In some cases such as lakes in Sweden, Canada and the northern United States, the water has become so acidic that most of the life is gone. Acidic rain can also damage buildings and lower the pH of soil, making it difficult for some plants to grow.

Acid Rain Procedure

1. Add vinegar (a weak acid) to the water and measure its pH. You have now created an example of an acidic lake. (See next activity for more information on acidic lakes.)
2. How do you think the pH of water is effected by the water cycle?
3. Start up the water cycle by closing the lid, turn on the heat lamp and place the bag of ice on the upper edge.
4. Once the cycle of evaporation, condensation and precipitation is established, test the pH of the water that condenses on the lid and compare it to the pH of the water at the bottom of the box.
5. What would happen if we created a new water cycle model and added ammonia or salt?

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