How to Use Electrolysis to Change Water pH

A battery with anode and cathode terminals can be used for electrolysis.

Electrolysis, the process of electrically splitting water molecules, can only be efficiently done using distilled water. It is often done to extract pure samples of hydrogen and oxygen gas. Besides producing oxygen and hydrogen gas, waste ionized water is created. Electrolysis can change the pH of distilled water by creating water ionized with hydronium and hydroxide ions. Hydronium makes water acidic and hydroxide makes water basic. The pH of the resulting solutions will be more and less than seven, respectively.

Things You'll Need

• Electrolysis equipment

Instructions

1. Set up your equipment for electrolysis. The bulbous reservoir should be at the top while the open ends of the two glass tubes should be the closest to the ground. Plug the open ends of the glass tubes by inserting rubber stoppers with electrodes. If done properly, the rubber tubes' electrodes should extend into the glass tubes. You can hold your electrolysis equipment upright by using a ring stand and clamp. Attach the clamp near the middle. The electrodes you inserted into the glass tubes should be connected to a wire. Attach the other end of this wire to a battery with cathode and anode terminals.

2. 

   Pure water has a pH of seven.

   Put distilled water into the bulbous reservoir. By doing this, your water does not have the chance of containing impurities that could alter pH or potentially interfere with reactions. The pH of pure water is exactly seven, meaning it is a neutral substance. Hydronium (H3O+), hydroxide ions (OH-) and water molecules (H2O) are the only molecules present in pure water. Because distilled water is neutral, there will be an equal number of hydronium and hydroxide molecules in your sample. An acidic solution will have more hydronium ions, while a basic solution with have more hydroxide ions.

3. Turn on the battery. This will start electrolysis. The chamber associated with the anode receiver will have water dominated with hydronium ions, while the cathode tube will be primarily water with hydroxide ions. This will provide two new samples of water with a pH different than seven. The tube with hydroxide ions will be more basic while the tube with hydronium ions will be more acidic. Their pH will be higher and lower, respectively.

4. Turn off the battery when the reaction appears to be complete. Extract the ionized water that has gathered in the two glass tubes. Run checks to make sure electrolysis took place. Start by verifying that gas was created. You should notice a gap between the stopcocks and the ionized water samples (near the stopcocks). This area is filled with gas. The anode side is filled with pure diatomic oxygen, while the cathode is filled with hydrogen gas. There should appear to be twice as much hydrogen as oxygen. You can next test the samples of ionized water themselves. The best acid-base indicator is Universal Indicator. When you use it, a more basic solution will turn blue-green and an acidic sample will turn pink. If your colors are similar or are not distinct, the reaction did not properly occur.

Tips & Warnings

• The following reactions occur during electrolysis:

• 2H_2_O ---> O_2 + 4H^+ + 4e^-

• 4H_2_O + 4e^- ---> 2H_2 + 4OH^-

References

• University of Illinois, Department of Chemistry: Electrolysis of Water Using an Electrical Current
• The City University of New York, John Jay College of Criminal Justice: Acids, Bases, and pH