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ChemWiki: The Dynamic Chemistry E-textbook > Development Details > Approaches > Demos > Additional Demos > Conductivity Apparatus--Ionic vs. Covalent Compounds

Conductivity Apparatus--Ionic vs. Covalent Compounds

 

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
  • The conductivity apparatus is made up of a light bulb, a crucible, the connecting wires, and a bunsen burner.

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.

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Last Modified
10:28, 2 Oct 2013

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