Preliminary
I am going to use voltages 5,6,7,8,9 and10 because for voltages lower than five there was not a lot of gas produced this made it extremely difficult to measure the amount of gas. For voltages over 10 there was too much gas produced and it went out of both sized measuring tubes. I decided to do it for 2 minutes as this figure seemed to be the one where the results were at their best, they were easily measurable unlike the results for one and three minutes.
Method
Equipment list Diagram:
- Lab pack
- Brine
- Electrolysis cell
- 25ml measuring cylinder
- 10ml measuring cylinder
- Clamp stand
- Boss
- Clamp
- 2 plug to crock wires
- 1plug to plug wire
- Ammeter
- Sand paper
- Stop watch
Instructions
- Set up the equipment as shown in the diagram.
- Make sure the negative terminal on the lab pack is connected to the longest electrode and the positive terminal to the shortest electrode.
- Fill the electrolysis cell and the measuring cylinder with brine put finger over the top and turn upside down over the negative electrode ensuring there is no air in the top of the cylinder
- Turn the lab pack on to 5v
- Check the electrode is collecting the gas
- Wait for 2 minutes
- Turn of the lab pack
- Measure the amount of hydrogen gas in the measuring cylinder
- Wash out the electrolysis cell and measuring cylinder
- Fill with brine again and repeat the last 6 steps for voltages 6,7,8,9 and 10
- Record in table and repeat all results and take averages
Fair test points
- Temperature- has to stay the same so it doesn’t speed up the process of electrolysis
- Time- the amount of gas produced could be increased or decreased depending on whether the experiment is done for a different period of time.
- Molarity- if the solution of brine is stronger or weaker the rate of electrolysis could become faster or slower
- Amount of solution- if there is more solution then there is more room for the electrons to flow across the solution as ions and more gas can be produced
- The size of the electrodes-this has to stay the same because if there was a really short electrode this would produce less gas compared to a longer one.
- Surface area of electrodes-It has to have the same surface area to stop more gas being able to be produced
- The distance between the electrodes also has to stay the same as the ions would have to travel further and it would take a longer time than if they were really close together.
- Between each experiment the electrodes need to be sanded down, there then won’t be any substances on the electrode to make it harder for the ions to get through.
Safety points
- Wear goggles incase of an accidental splash of brine into the eyes
- Tie hair back, so it doesn’t get into the brine.
- Make sure that the brine of any other liquid doesn’t come into contact with any of the electrical equipment.
Results
I think these results were good the only one that I think was a bit wrong was the 9 volts where we got 11ml of hydrogen gas produced, I thought that this value was a bit too high so I did it again:
This result was far better so I included this in my graphs.
Conclusion
From my graph I can see that as the voltage increased the amount of hydrogen gas produced at the negative electrode also increased. This means that my prediction was correct, and that if the voltage is increased the current then is increased, this is because of ohms law, V=IxR, where the voltage is proportional to the current, if the current is increased the charge then increases because Q=IxT. The number of moles of electrons=charge -:- 96500, this is Faradays constant from his 2nd law. The relationship between the amount of substance deposited at an electrode and the number of electrons that are passed around a circuit (current) can be used to calculate the expected volume of substance produced at the electrode. This means that as the voltage increased the current increased, if the current is increased the charge is increased, because the charge is directly proportional to the number of moles of electrons the amount of substance increases. I think that my results would support my conclusion to a high extent, the higher the voltage the steeper the graph got, I think this pattern would hold true at the extremes of the range.
Evaluation
This experiment was overall very accurate and the evidence obtained was very reliable. I repeated my results and took 6 measurements. When I did repeat my results I got similar ones that were very close to the line of best fit. I had one anomalous result which may have been because I used a different bottle of brine this could have been a different concentration or the change from a plastic measuring cylinder to a glass one could have upset the experiment. To improve this experiment I would use a 25 volt lab pack with bigger measuring cylinders this would allow me to see if the pattern was still the same at the higher extremes of the range. Instead of using the measuring cylinder I could use a gas syringe this would be a lot more accurate. Another factor 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, I would get a new electrolysis cell, with clean electrodes which have never been used before.