Conductivity of water
Initial Publication Date: September 26, 2008
Summary
It this exercise the students will discover that pure water does not conduct electricity and that dissolving different substances in water may or may not cause it to conduct electricity. Through this demonstration there should be constant discussion between students on whether or not the mixture will conduct electricity.
CollapseLearning Goals
Students should understand these concepts following the demonstration.
1. Pure water does not conduct electricity
2. Water with dissolved ions in it does conduct electricity.
3. The amount of conduction is directly related to the amount of dissolved ions is the mixture.
1. Pure water does not conduct electricity
2. Water with dissolved ions in it does conduct electricity.
3. The amount of conduction is directly related to the amount of dissolved ions is the mixture.
Context for Use
I have used this activity in physical science, chemistry, and physics. It is important for students to know that it is not the water that conducts electricity but what is in the water that makes it happen. It is also helpful when discussing corrosion, electrical shorts and strong and weak acids.
Description and Teaching Materials
In this activity the teacher will facilitate a discussion on water conducting electricity, following a demonstration of pure water (DI water) not conducting electricity, and then demonstrate how dissolving sodium chloride into the water will cause the mixture to then conduct electricity. The teacher then can use many other types of mixtures as class experimentation (sugar and water, ethanol and water, strong acids, weak acids, iron nails in water, etc). I will often have the students vote on which will conduct electricity and then discuss which will conduct electricity, and finally we test which will conduct electricity. The conductivity tester we use is a 15 watt light bulb, a 60 watt light bulb and a 100 watt light bulb wired with switches plugged into a wall outlet and two open leads to be placed in a beaker. This apparatus works wonderfully but is not appropriate for someone who is not comfortable with electricity and circuits. I recommend using a 9 volt conductivity tester with a diode for safe results and if you would like the students to complete the experiments this way is much safer.
Teaching Notes and Tips
If you use a 110volt conductivity tester be very careful that the leads never cross or that you do not touch them. If you are concerned use a 9voly conductivity tester.
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Assessment
For assessment on the next day I have the students predict whether or not a substance placed in the water will conduct electricity (eg KI mixed with water, or copper shot placed in water)
Standards
9-12.II.C.4 Transmission of electricity