Conductivity of Solutions

A series of free IGCSE Chemistry Activities and Experiments (Cambridge IGCSE Chemistry).

Activity:
Investigate the electrical conductivity of several solutions.
Substances include tap water, distilled water, sodium chloride, hydrochloric acid, sodium hydroxide, sugar, vinegar, ethanol, and barium sulfate. The solutions are mixed to approximately the same ratios.
The tester is a pair of stripped copper wires in series with a bulb. The probe is rinsed in distilled water between each test.

Electrolysis
Electrolysis is the passage of an electrical current through a molten salt or an aqueous solution of the salt.

This experiment tests whether a liquid or a solution is an electrolyte (conduct electricity) or a non-electrolyte. Electrolysis is brought about by the movement of ions. Ions must be present in solution for electrical conductivity. Salt, acid and alkali solutions containing ions are called electrolytes. As the current flows, the ions move to the electrodes placed in the solution. If a light bulb in the circuit lights up, a current is flowing in the circuit. Electrolysis brings about chemical decomposition. Ions are attracted to the electrode with the opposite charge. Ions are discharged at the electrodes when the current flows, and new products are formed at the electrodes.

The term electrolyte is a term used when talking about solutions with water as the solvent. We demonstrate the property of being an electrolyte with an electrical conductivity tester.

Pure water does not conduct electricity. When electrodes are put into a beaker of pure water, there is no light coming from the light bulb. If a material is dissolved in this water and the light lights brightly, the dissolved material is called a strong electrolyte.

As an example, sodium chloride is added to the water. The sodium chloride dissolves by breaking into charged particles, the ions of sodium and chlorine, which now allow the solution to conduct electricity. So the ionic substance, sodium chloride, is a strong electrolyte.

The term non-electrolyte refers to a substance which dissolves in water but does not allow electrical conductivity. Add some sugar to the water. As the sugar dissolves, the light does NOT light up. So sugar is a non-electrolyte.

Some acids and bases are also strong electrolytes. For example, a small amount of hydrochloric acid in the water allows the light to light up very brightly. So the acid is also a strong electrolyte and is called a strong acid.

Acetic acid, on the other hand, dissolves but allows very little electricity to go through the water. The light bulb gives off much less light. Acetic acid a weak electrolyte and a weak acid.

Note that electrolytes are either acids, bases or salts.

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Questions

1. Write down which of the solutions tested conduct electricity and which did not.
2. What do all the liquids and solutions that conduct electricity in this state have in common? Use the example of sodium chloride solution in your explanation.
3. Give an example of a strong electrolyte, a weak electrolyte and a non-electrolyte.
4. What are the 3 types of electrolytes?

Answers

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  1. Conduct: Tap water, NaCl, HCl, NaOH, Vinegar
     Did not conduct: Distilled water, sugar, ethanol, BaSO₄
  2. There are positive and negative ions present that can move to the electrodes carrying the current. Sodium Chloride solution will contain Na⁺ ions and Cl^- ions.
  3. HCl, Acetic acid, sugar.
  4. Acid, base, salt.

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