Electrical Conductivity of Aqueous Solutions:
This demonstration is an effective tool for investigating some properties of ionically and covalently bonded molecules.
Current flow, within aqueous solutions, is commonly and effectively demonstrated by the use of a simple, low-voltage electrical circuit connected either to a sensitive voltage meter and/or to a light bulb. Whether or not this experiment is used as a teacher only demonstration or a class experiment is dependant on whether you are using a low or high voltage electrical circuit.
- A simple electrical circuit with bulb and/or current meter.
- Solvents (deionized water and/or ethanol).
- A weak electrolyte solution (tap water).
- A strong electrolyte solution (salt water).
- non-electrolyte solution (either ethanol or a sugar solution).
- An appropriate number of beakers.
- A wash bottle containing deionized water.
1. Half-fill a clean beaker with deionized water, lower the electrodes a few cm into the
water, and record any evidence of electrical conductivity via the meter and light bulb.
If there is any evidence for conductivity on the ammeter it should be low. Light bulb should be extremely dim.
2. Repeat the experiment with a beaker of ethanol.
As ethanol does not ionise it will not conduct a current. Solutes:
3. To the beaker of deionized water mix in a teaspoon of glucose.
Although glucose does dissolve in water (to an extent) it does not ionize and
therefore does not conduct a current.
4. Half fill a beaker with tap water.
Depending on your local water supply electrical conductance will vary but should be noticeably greater than that of deionized water.
5. Empty and thoroughly rinse the beaker. Half fill with deionized water. Add up to one
teaspoon of sodium chloride.
As NaCl is a highly soluble ionic solid in water the electrical conductance of this aqueous solution is high.
6. Rinse the beaker thoroughly again and half fill it with deionized water. This time add
As calcium sulphate is sparingly soluble it’s conductance is weak.
If a high voltage circuit is to be used EXTREME caution should be used for this demonstration. It is obviously not recommended that students participate in this demonstration.
With low voltage circuits (batteries), students may carry out these experiments by themselves without any concern of electrocution. However, the lower voltage being passed through the solution lessens the visual impact.