Electrolysis of aquatic salt solution

The equation for the water splitting up is this.

H20 H+ + OH-

So the positive Hydrogen (H+) will also go to the cathode with a metal and the Hydroxide (OH-) will also to the anode with a non-metal. However only one will get out and that is what I am going to find out.

For help in my experiment I used the notes I made over this topic, The Chemistry for You Book, Britannica DVD and my Modular Science Revision Book.

I also had to test how to do my experiment. I decided that to collect gas it would be useful to have the electrodes sticking up.

To observe the metal appearing in my experiments, I decided that it would be easier to have the electrodes sticking down into a beaker of water.

I also used:

* Pipettes

* Goggles

* Various Salt Solutions

* Gloves

* Bunsen Burner

* Test Tubes

* Litmus Paper

I decided that I would do the experiment with the electrodes sticking up, as that would be the only way to collect the gas.

I did my experiment like so.

. I set up my experiment like in Figure. 1.

2. I chose a solution and put it in the yoghurt pot.

3. I turned on the power pack.

4. I watched the anode and cathode and noted what happened.

5. I then filled a test tube with water and put it over the anode.

6. I waited until the water had been replaced with a gas then tested the gas.

7. If there wasn't a metal forming at the cathode I filled another test tube with water a tested the gas.

8. I then washed the electrodes and the beaker out and did the same with another solution.

I read the safety cards for the chemicals we had to use. I wore goggles and protective gloves when handling the compounds

I found out the tests for the gases like:

* Chlorine - a green gas that bleaches litmus paper

* Hydrogen - a colourless gas that pops if heated up.

* Oxygen - a colourless gas that will relight a glowing splint.

* Bromine - a brown gas.

* Iodine - A purple gas.

My Results:

After doing the electrolysis of the solutions I notice at the cathode the element produce was either Hydrogen or a metal. The metals were low down in the reactivity series. At the anode it was a gas. Either Oxygen or a gas from group 7 in the Periodic Table e.g. Bromine (Br).

My results support my prediction. This is because I thought that negatively charged ions (either the Hydroxide atoms or the non-metal atoms) would go to the anode, which they did. And that positively charged ions (either the Hydrogen atoms or the metal atoms) would go to the cathode, which they did. However I couldn't predict which atoms of the two would escape.

Starting with the cathode, either the Hydrogen ion (H+) or the metal ion (e.g. cooper Cu2+) would escape and the other would be left in the solution. The question is, which one. After looking carefully at my results I saw that the only metals that would escape the solution were the ones that were below Hydrogen. I concluded that since Hydrogen was higher up than the metal it was stronger and was able to stay in the solution while the weaker metal would grab the electrode and go from being an ion to an atom.

Since non-metals aren't on the reactivity series (apart from Hydrogen because it has a plus charge.) they can't be judged on their placing in it. This means there is another series called The Series of Displacement. The series of displacement is used to find out whether the negative ion of the solution or the negative Hydroxide (OH-) ion will escape.

This is the series of displacement:

The negative ions below Hydroxide in the displacement table will escape from the solution leaving the Hydroxide behind to combine with the other, positive ion in the solution. This is because the weaker ion is less stable than Hydroxide and since the ions prefer to stay ions and not combine with each other to become atoms (2Cl- - 2e- Cl2) the lower ion is kicked out by the hydroxide. If the negative ion is higher than Hydroxide then that is kicked out by the stronger ion because it is more stable than the Hydroxide. The series of displacement agrees with my results.

One of the problems with the experiment was collecting the gases and the metals. It was very hard to collect the elements as to collect gases the electrodes had to be up but to collect a metal the electrodes were better to be sticking down. The testing of the gases was sometimes hard as they didn't always work, the oxygen gas test (to relight a splint) test especially.

Although this was a successful experiment, there were some factors of the experiment, which could have been improved to make it even more successful. One of these factors could have been the electrodes, which, even after a good clean were still quite dirty and obviously still had irremovable substances from previous experiments still attached to them. If this experiment were to be repeated for a second time, in need of greater accuracy, it would be imperative to have a new pair of electrodes, which have never been used before.

Another factor which may have affected the overall outcome of the investigation, may have been the fact that the practical work of the investigation was carried over from lesson to lesson, meaning that variables such as the concentration or the amount of the aquatic salt solution could have changed between lessons. To overcome this problem, the same electrodes and equipment should have been used throughout.

To further this investigation I should investigate more of the variables in this experiment, which may or may not affect the different elments deposited onto the cathode and anode, such as changing the Current or Temperature variable.

To carry on with this experiment I decided to see how the rate of electrolysis was affected by amount of electricity flowing around the electrodes. For this experiment I did the electrolysis of Sulphuric acid (HSO4). I think if you increase the flow of electricity the volume of Hydrogen will increase. This is because the flow of electrons go to the cathode, the hydrogen ions collects the electrons and become hydrogen. The faster the electrons flow, the greater volume of Hydrogen will be made. I tested the electrolysis of HSO4 every five minutes at 0.6 Amps, 0.8 Amps and 1.4 Amps. These are the results I got:

My results support my prediction; the faster the electrons flow the greater the increase of Hydrogen is.

2H+ + 2e- H2

Overall my experiment went well. Even though the gases and metals were hard to collect, the results hold up to my prediction.