Electrolysis of water

Concept:

Electrolysis is the chemical decomposition produced by passing a current through a solution containing ions.

Etymology

‘lysis’ means to break down. Therefore electrolysis means “to break down using electricity.”

Experiment

We will perform electrolysis of water and decompose it into hydrogen and oxygen.

Materials needed

  • A container to store the electrolyte.
  • Thick cardboard strip (~8x4 cms)
  • Test tubes with stopper - 2 nos.
  • Graphite rod.
  • Stainless steel material like a spoon or screw.
  • Insulated copper wire.
  • Teflon tape.
  • Alligator clips - 2nos.
  • 9v power supply.
  • Epsom salt
  • Matchbox
  • Thin wooden stick, about 6 inches long.

Details of each of the above items can be found in the electrochemistry-kit-01.

Safety guidelines

  • The final solution after the electrolysis can be highly basic due to the presence of hydroxyl ions. To dispose of it safely, add some vinegar to make the overall solution neutral before throwing it away.
  • Be careful when popping the hydrogen gas - use a lighter to keep the hands away. If you collect a lot of hydrogen, then it can be a small explosion.

Steps

Assemble graphite electrode (cathode)

  • Take a strip of wire about 12 cms long, and strip three cms on both ends.
  • Use the Teflon tape to attach one side of the wire to the graphite rod.
  • Ensure there is no exposed copper wire. Exposed copper in the electrolyte solution will immediately react and start a secondary reaction, and that’s not what you want.
  • Teflon is pretty awesome. Pull and tear off - no need for scissors.

Assemble the stainless steel electrode (anode)

Connect a wire to the stainless steel spoon or screw. Make sure the wire is stripped on both ends. Secure the end connected to the stainless steel electrode with Teflon tape.

Setup the tube stand

To keep the tubes vertical and upside down in the water:

  • Use the box cutter knife to cut two holes in the cardboard.
  • The diameter of the holes should be slightly less than the diameter of the test tubes.
  • Test the tube stand by ensuring the tubes stay firm when inserted through the holes.

If you have a burette stand, you can clamp the two test tubes and insert them into the water, as shown below.

500

Create the electrolytic solution

Drop-in 4 spoons of Epsom salt and mix it up thoroughly.

Insert the tubes

Insert the test tubes in the solution and fill them up, by keeping them slightly horizontal.

  • When you see no bubbles in the tube, bring it up, making sure the open face is down in the solution.
  • Insert the test tube through one of the holes in the cardboard, and then lay the cardboard flat across the container.
  • Repeat for the other test tube.

Take one of the electrodes, submerge it in the water and then insert it into the test tube, ensuring that no air enters the tube.

  • Repeat using the other electrode.
  • Connect the electrodes to a 9v battery using alligator clips.

At this point, electrolysis should begin.

Observations

Test of hydrogen

  • At the cathode, i.e. the graphite rod that is connected to the negative terminal, you should see more bubbling of gas. Is this hydrogen?
    • Carefully take the test tube out of the water, making sure that you always keep the tube vertical (why?).
    • Bring a lit match near the mouth of the tube. It should create a popping sound, proving that it is hydrogen.

Test of oxygen

At the anode, there will also be bubbling of gas, but lesser. Is this oxygen? - Bring a glowing wooden flint into the tube. - If it immediately gets snuffed out, it is carbon dioxide. - If it re-ignites or glows more strongly, then it is oxygen.

We have successfully proved that water is indeed a mixture of hydrogen and oxygen. Also, the amount of hydrogen created is more than oxygen. In fact, there is exactly twice more hydrogen than there is oxygen. Hence water is also called H2O.

Investigate further

Why did the solution around the anode turn pink?

The science behind this

The history behind this

Stay Qurious.