Filter this.

Name: --

In "Drip, Dry?" (p. 12), you learned that pollutants are threatening the nation's freshwater supply. Now, complete this activity to learn how pollutants can be filtered from water.

PREDICT:

Do you think a paper towel can filter, or separate out, pollutants from water? Which substance do you expect to be best filtered from water: dish soap, vinegar, or dirt?

YOU NEED:

6 clear plastic cups (600 ml, or 20 oz) * measuring cup * water (354 ml, or 1.5 cups) * teaspoon * 2.5 ml, or 1/2 tsp of each: potting soil, vinegar, dish soap, and baking soda * marker * stack of books (stack should be 5 cm, or 2 in. high) * ruler * 3 paper towels * paper clip * paper and pencil

TO DO:

1. Pour 118 ml (1/2 cup) of water into each of three plastic cups.

2. Add 2.5 ml (1/2 tsp) of dirt to one cup, and stir the mixture with a teaspoon.

3. Using a marker, label the cup according to its contents.

4. Repeat Steps 2 and 3 using vinegar, and then dish soap, instead of dirt. (Note: The dirt, Vinegar, and soap represent "pollutants.")

5. Find a clean, flat surface. There, place a stack of books that is 5 cm, or 2 in., high.

6. Place the three pollutant-filled cups on top of the stack of books. Line the cups near the edge.

7. On the flat surface, line up three empty cups, placing each in front of a labeled cup.

8. Roll a paper towel into a tube shape. Then, bend the paper towel in half.

9. Place one end of the paper towel into the cup containing dirt, and place the dry end into the empty cup in front of it.

10. Repeat Steps 8 and 9 for the Vinegar and dish-soap cups.

11. Let the cups sit overnight. Then, observe and record where the water is--in the upper or lower cup--and if the water looks clean or dirty.

12. Test the water in the lower dish-soap cup for soap: Carefully set a paper clip on the surface of the water inside the dish-soap cup. Record whether the clip sinks or floats.

13. Test the water in the lower Vinegar cup for Vinegar: Pour 2.5 ml (1/2 tsp) of baking soda into the water inside the vinegar cup and stir. Record whether or not bubbles form.

CONCLUSIONS:

1. Did the paper towel separate the dish soap from the water? Note: If the paper clip sank, it means dish soap remains in the water.

2. Did the paper towel separate the vinegar from the water? Note: If bubbles formed after adding baking soda, it means vinegar remains in the water.

3. Which "pollutant" was best filtered from the water? why do you think this was the case?

ANSWER

1. The paper towel didn't separate the water and dish soap. That's because the soap mixed with the water and flowed through the paper towel. The paper clip sinks, because soap lowers water's surface tension, a property of some liquids whereby their surface acts like a thin film.

2. The paper towel didn't separate the water from the vinegar, because the vinegar flowed through the paper towel with the water. Bubbles of carbon dioxide formed because of a chemical reaction between the basic baking soda and the acidic vinegar.

3. The dirt was filtered out the best. That's because the dirt particles are large enough that the paper towel's tiny pores could block the dirt from flowing through with the water.