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Identifying Common Electrolytes and Comparing their Strengths

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Author: Janice VanCleave

Electricity is fundamental to nature. It is utilized in the form of electric currents. Electrolytes are chemicals that conduct an electric current in a water solution. Not all solutions conduct electricity.

In this project, you will identify common electrolytes and compare their strengths. The electrolysis of water and brine will be studied. You will also look at the history of electrolytic cells and construct a simple electrolytic cell.

Getting Started

Purpose: To determine whether table salt is an electrolyte.

Materials

  • duct tape
  • 3 "D" cell batteries
  • 2 teaspoons (10 ml) of table salt (sodium chloride)
  • 1/2 cup (125 ml) of distilled water
  • cereal bowl
  • spoon
  • ruler
  • scissors
  • aluminum foil
  • flashlight bulb

Procedure

CAUTION: Do not use batteries other than "D" cell batteries and do not use more than three "D" cell batteries. Electricity can be dangerous.

  1. Tape the three batteries together with the positive end of one touching the negative end of the other.
  2. Combine the salt and water in the bowl. Stir well.
  3. Measure and cut a strip of aluminum foil 4 inches (10 cm) wide × 12 inches (30 cm) long.
  4. Fold the foil strip lengthwise four times so that the strip is 1/4 inch (0.64 cm) wide and 12 inches (30 cm) long.
  5. Stand the flat, negative end of the connected batteries in the bowl of salty water.
  6. Wrap one end of the foil strip around the metal base of the flashlight bulb.
  7. Hold the foil strip tightly around the base and press it against the raised, positive end of the connected batteries.
  8. Lay the free end of the foil strip under the surface of the salty water in the bowl so that it is near, but not touching, the connected batteries (see Figure 15.1).

Result

The bulb glows.

Why?

An electric current is produced by a flow of electric charges. In metals, the current is due to a flow of electrons and is called metallic conduction. In a solution, the current is due to movement of ions (positive and negative particles) and is called ionic conduction. In this experiment, the electric current is carried by electrons in the aluminum foil and in metals in the battery as well as by ions in the salt solution. The bulb glows because as the electric current passes through the filament of the bulb, the filament heats up and gives off light.

The electrons do not flow spontaneously. They must be caused to flow by an electric force from the battery. The negative end of the battery repels electrons, and the positive end of the battery draws electrons toward it. Electrons do not flow out the cathode (negative terminal) of the battery and swim through the solution to the aluminum foil strip attached to the anode (positive terminal). Instead, at the negative terminal, cations (positive particles) in the solution accept electrons; at the positive terminal, anions (negative particles) give up electrons. The space between the foil strip and the battery is "bridged" as the ions in solution remove electrons from one side and add electrons to the opposite side of the gap.

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