Prediction
I predict that, as the current increases the mass of the deposit also increases. I predict, as the current doubles so will the deposit. This is because
Charge = time x current
If I increase the current across the solution the charge at the cathode will be greater therefore giving me more deposit.
Equipment list
I need the following to carry out a successful experiment…
Lab pack, beaker of copper sulphate solution, copper anode, copper cathode, covered wires, an ammeter, timer, scales
Recording results
I will use a table and a line graph to show my results, as they are the most appropriate for my discovered information.
Risk assessment
To make my experiment safe I will wear goggles, be sure not to spill any copper sulphate and check for bare wires. I will also wash my hands after the experiment.
Diagram of how equipment is set up
Preliminary trials
The highest current I could reach was 3.0 amps without the solution becoming too hot. Therefore I have decided to have a range of 0.5 –3.0 amps. Even so, with the current flowing for 10 minutes the solution did get quite warm so I have decided to allow the current to flow for 5 minutes instead of 10 minutes as the increase will still be noticeable.
Step by step procedure
1, Set up the experiment as shown in the diagram above.
2, Record the mass of the cathode
3, Set a timer for 5 minutes and start the current flowing. I decided on 5 minutes because after preliminary experiments I discovered that 5 minutes was long enough to discover a big enough increase in the mass of the cathode.
4, Dry the cathode with a hair dryer after 5 minutes and record the mass of the cathode. By deducting the mass of the cathode from instruction 2 the increase in mass can be discovered.
5, Repeat the procedure increasing the current by 0.5 amperes for each result until you reach 3 amps. I discovered that 0.5 amps is the best measurement of current because it is big enough to measure efficiently but small enough to give accurate results. I have discovered that over 3.0 amps the components will begin to overheat after preliminary tests.
6, Repeat the readings three times and take averages of the three readings. Record in a table the results and plot the average readings on a line graph.
This is a table to show the amount (in grams) of copper deposited on the cathode during electrolysis
I am confident with my recorded results because I have taken enough accurate, repeated trials and used the equipment accurately to make reliable evidence of my experiment. I have taken extra observations of my experiment at various stages to improve my experiment results.
Analysing evidence & drawing conclusions
My graph is a straight-line graph and it is positive, it goes through the points I have plotted in a line of best fit. I was able to plot the points on my graph by calculating the average amounts of copper deposited at the cathode, by finding an average of two different sets of results I am able to discover the best results.
My graph tells me the higher the current running through the solution of copper sulphate, the average mass of the copper deposited at the cathode also increases.
My graph matches up to my prediction. I initially predicted that as the current increases the mass of the deposit would also. Therefore I predicted a graph to be straight lined and positive however I would have expected it to bisect the origin. The positively charged ions in the copper sulphate solution are attracted to the negatively charged cathode and deposited when the combine with +2 electrons. This produces a deposit, like I predicted.
I recorded my experiments in a table and as I noticed notable observations I recorded the observation next to the amount of amps which were flowing through the solution at that time. All of my observations are in the tables above. I tried my best to record all of my results and observations using the equipment I have stated.
To make my results better I did my experiment three times. This made my experiment results more reliable because the averages are taken from three different tests. To make my experiment results better I would have done it more times, perhaps four and then taken an average.
Conclusion of my graph
My graph is a straight-line graph and it is positive, it goes through the points I have plotted in a line of best fit. I was able to plot the points on my graph by calculating the average amounts of copper deposited at the cathode, by finding an average of three different sets of results I am able to discover the best results.
My graph tells me the higher the current running through the solution of copper sulphate, the average mass of copper deposited at the cathode also increases. My results don’t match up to my prediction. I predicted that as the current increases the mass of the deposit would also increase. However this is true but I actually predicted that, as the current doubles so will the deposit. My prediction is incorrect because I expected the line of best fit to bisect the origin but it began much higher. If the line of best fit had bisected the origin, then yes my prediction would have been true however lenient rounding would be needed… For example on my line of best fit at 0.5 amps 0.1 grams of copper is deposited and at 0.1 amp 0.157 grams of copper is deposited. It is obviously not doubled, however if the line of best fit bisected the origin at 1.5 amps 0.11 grams is deposited and at 3.0 amps 0.225 grams is deposited. Here doubling is evident.
Evaluating evidence
I am confident that I have used the equipment correctly. I set up the equipment as my plan showed me. Each time I used the timer I made sure that I reset it to 0 so that my experiment would be fair. I also took time to zero the scales so the measurements would be more accurate. I checked the wires to make sure they were covered, I wore goggles throughout the experiment and I washed my hands before and after the experiment. I have made some observations as I was carrying out my experiment, during both trials, excess copper was deposited on the bottom of the flask of solution therefore the results varied greatly between the trials because the amount of copper deposited on the bottom varied between the two experiments. Also obtaining the results for the experiment spanned over a couple of one hour lessons, even though I was very careful when putting the equipment away while putting away the cathode small amounts of deposited copper rubbed off therefore our results do not look quite right.
As I have commented before, I feel my results are very accurate as I carried out my experiment methodically and recorded my results in a clear way. We took readings spanning from 0.5 amps to 3.0 amps. At each point I repeated it three times. Because points on my graph show good correlation there isn’t an ‘odd’ point. I took many results, which were repeated, so I am confident that there are enough results to support my conclusion. To improve my experiment I would use, instead of a paper cathode, a small cylinder cathode so I could collected more deposit, which would make better more varied results. Other than that I feel my experiment was successful.