By Allan Robinson Updated Mar 24, 2022

Helmut Feil/iStock/GettyImages

Potassium (K), atomic number 19, is a highly reactive alkali metal. In its pure form it is a soft, silvery‑white metal that reacts violently with water. Because of its reactivity, elemental potassium is rarely handled outside of specialized laboratories; most industrial uses involve potassium compounds, such as potassium chloride, in fertilizers and other applications.

In 1807, Sir Humphry Davy demonstrated the first successful isolation of potassium by electrolyzing molten potash derived from wood ashes. This classic laboratory technique is still performed today as a demonstration of electrolysis, but it requires stringent safety precautions.

Step 1 – Reaction Overview

The electrolysis of potassium hydroxide (KOH) proceeds according to the following equation:

KOH → K⁺ + OH⁻

When an electric current is applied, potassium ions (K⁺) migrate to the cathode, where they are reduced to metallic potassium. Hydroxide ions (OH⁻) remain in the solution.

Step 2 – Setup the Electrodes

Attach insulated metal wires to the terminals of a 9‑V battery. Connect the wire to the positive terminal (anode) and the other to the negative terminal (cathode). The metallic potassium will deposit on the cathode.

Step 3 – Prepare the Potash

Place raw wood ash into a heat‑resistant metal dish. Using a Bunsen burner, gently heat the ash until it turns white and melts into a viscous liquid. This molten material is rich in potassium hydroxide and is commonly referred to as potash.

Step 4 – Initiate Electrolysis

Carefully remove the burner and immediately immerse the battery leads into the molten potash, positioning the anode and cathode at opposite ends. Allow the current to flow until the molten material begins to sputter and the metallic potassium visibly collects at the cathode. Once the reaction ceases, disconnect the battery.

Step 5 – Collection and Cooling

Transfer the collected metal to a second metal dish and allow it to cool to room temperature. The result is a small quantity of highly pure metallic potassium.

Materials Required

• 2 heat‑resistant metal dishes
• 2 insulated metal wires
• 9‑V battery
• Bunsen burner
• Wood ash (preferably from hardwood)

Safety Notice

Potassium is extremely hazardous. Store the metal in a container of mineral oil or a sealed dry environment to prevent accidental contact with moisture. Always conduct the experiment behind a blast shield and with a fire extinguisher rated for metal fires. This procedure is only suitable for experienced chemists working in a properly equipped laboratory.