- The conductivity apparatus is made up of a light bulb, a crucible, the connecting wires, and a bunsen burner.
Chemical Concept Demonstrated: Electrical conductivity under various conditions
Demonstration:
Determine the conductivity of the following samples:
| sample | conductivity? |
| 1. distilled water | No |
| 2. screw driver | Yes |
| 3. CH3OH | No |
| 4. CH3CH3OH | No |
| 5. HCl in toluene | No |
| 6. CCl4 | No |
| 7. solid NaCl | No |
| 8. NaOAC | No |
| 9. tap water | Yes |
| 10. aqueous solution of NaCl | Yes |
| 11. HCl in water | Yes |
|
|
Observations:
Some of the samples do not light the bulb, while others light the bulb to various levels of intensity. The video shows the conductivities of the samples in the order presented in the table.
Explanations:
Most solids don't conduct electricity, even ionic ones. The only solid that conducted was the metal screwdriver. Metals are generally good conductors because of their basic structure: crystalline solids surrounded by clouds of electrons. Because the cloud encompasses the entire metal structure, electrons have no trouble entering at one point and exiting at any other point, no matter how far it is from the point of entry.
Distilled water doesn't conduct electricity. Tap water, due to impurities, does.
Ionic solids (such as HCl and NaCl) dissolved in water conduct electricty due to the dissociation of the ionic components. For example, HCl dissociates into H+ and Cl- in water, making an environment of free-flowing electrons. Such an environment allows for extra electrons to be added at the anode as other electrons escape at the cathode, resulting in an electrical current and a completed circuit.
HCl does not dissociate in toluene. If the HCl can't break down into its ions, there is no electrical potential present.