How to Make a Pure Sample of Potassium

Potassium (K) is a chemical element with the atomic number 19. Pure potassium is a white metal that is very soft and burns in water. It has few uses in elemental form since it's so reactive with water, but potassium compounds have a wide range of applications, especially as fertilizer. Potassium was first isolated by Sir Humphry Davy in 1807 by subjecting melted wood ashes to electricity in a process called electrolysis. This method is still performed today as a simple chemistry experiment.

Things You'll Need

• 2 Metal dishes
• 2 Metal wires
• 9 Volt battery
• Bunsen burner
• Wood ash

Instructions

1. Examine the reaction that will be demonstrated by this experiment. This is given by the following equation: KOH + electricity -> K+ + OH- where potassium hydroxide (KOH) is split into its components of potassium metal (K+) and the hydroxide ion (OH-).

2. Attach a wire to each electrode of the battery. The wire on the positive terminal will be the anode and the wire on the negative terminal will be the cathode. The potassium metal will collect on the anode.

3. Place the wood ash into a metal dish and heat the ash with the Bunsen burner, so that the ash turns completely white and melts. This material is called potash and should be extremely high in postassium hydroxide.

4. Remove the heat and immediately place the battery leads on opposite ends of the molten ash. Keep them there until the molten ash becomes a molten metal. Remove the leads once the reaction is complete.

5. Pour the metal from Step 4 into the second pan and allow the metal to cool. This metal should be highly concentrated potassium.

Tips & Warnings

• Store potassium metal in mineral oil for maximum safety. Potassium is extremely reactive with water and must be stored in a completely dry environment.

References

• British Colombia Institute of Technology