Tips: It should be noted here that many of the same elements which contributed to water hardness also make it possible for water to conduct electric current. This is not however an exclusive statement. Salt dissolved in hard water continues to allow the water to conduct electricity, but lowers the total hardness. A stock solution of hard water made from conductive elements, along with suitable dilutions, might provide a convenient tie in with problems faced by certain manufacturing and power companies. The problems associated with hard water should be familiar to children who have completed the previous activity. It seems reasonable to connect hardness with conductivity in experimenting with a mystery sample, as long as the rough and inconclusive nature of the activity is explained. Students should understand that this test can not be used to determine the exact hardness or make up of a mystery sample but can only be used as a sort of guide. Conductivity of a water sample, in a laboratory would lead to further testing to determine the exact nature of the ionic material.
Students should be arranged in teams of 4 students. Each team should provide one sample of tap, rain, or pond water. Be sure to wash off the bare ends of the meter between samples to avoid contamination. The conductivity meter once constructed can be used for a wide range of additional activities.
Materials: TO CONSTRUCT THE METER - (part numbers from the 1991 Radio Shack catalogue)
LED assorted 276-1655
resistor 330ohm 271-1321
Alligator clips (no soider type) 270-374
18 gauge wir 278-1602
black electrical tape
craft sticks or tong depressors ( one per meter)
1.4 grams (1/4 tbs) Calcium or Calcium Chloride ice melt material
3 grams (1/2tbs) of Magnesium Chloride or Epsom Salts
4 empty two liter soda bottles
1 empty one liter soda bottles
100ml graduated cylinder
several empty baby food jars - 4 per...