Electrolysis of Water

Electrolysis of water decomposes water (H2O) into oxygen (O2) and hydrogen (H2), thus their extraction.

Pure water conducts current poorly. Electrolysis of pure water proceeds very slowly because of its poor conductivity.

If a water-soluble electrolyte is added, the conductivity of the water rises.

Sodium and lithium are frequently used, as they form inexpensive, soluble salts.

Strong acids such as sulfuric acid (H2SO4), and strong bases such as potassium hydroxide (KOH), and sodium hydroxide (NaOH) are frequently used as electrolytes.

A solid polymer electrolyte can also be used such as NAFION and when applied with a special catalyst on each side of the membrane can efficiently split the water molecule with as little as 1.8 Volts.

Two leads, running from the terminals of a battery, are placed in a cup of water with a quantity of electrolyte. Oxygen will collect at the anode and hydrogen will collect at the cathode.

The Hofmann voltameter is often used as a small-scale electrolytic cell. It consists of three joined upright cylinders. The inner cylinder is open at the top to allow the addition of water and the electrolyte. A platinum electrode is placed at the bottom of each of the two side cylinders, connected to the positive and negative terminals of a source of electricity. When current is run through the Hofmann voltameter, gaseous oxygen forms at the anode and gaseous hydrogen at the cathode. Each gas displaces water and collects at the top of the two outer tubes, where it can be drawn off with a stopcock.

Electrolysis of Water

Simple Demo:

Get: 1. A 9 volt battery 2. 2 pencils (remove erasers and metal parts) 3. Salt 4. Thin cardboard 5. Electrical wire 6. A small glass 7. Warm water

Do this: 1. Sharpen each pencil at both ends. 2. Cut the cardboard to fit over the glass. 3. Push the two pencils into the cardboard, about 3 cm apart. 4. Dissolve some salt into the warm water. 5. Using one piece of the electrical wire, connect one side of the positive side of the battery to the black lead of the pencil. Do the same on the negative side connecting to the second pencil lead. 6. Place the other two ends of the pencil into the salted water.

Chemical changes are caused by the passage of electrical current in water. The current breaks up the water, bubbles can be observed.