4.1 Analysis of results
After testing each independent variable (Copper, Aluminium and Brass) twice and recording the average reading of the difference in mass of each wire mesh and anode, we have concluded that brass is the best anode.
The rate of electrolysis is directly proportionate to the amount of CaCO3 formed on the wire mesh. Therefore, the greater the difference between the mass of the cathode and anode respectively at the start of the experiment to the end of the experiment, the faster electrolysis have reacted to that particular circuit. When Brass was used as the anode, there were a greater change in both the cathode and anode, showing that it was the best material for the anode.
After testing each independent variable (temperature at 15˚C , 20 ˚C and 25˚C) twice and recording the average reading of the difference in mass of each cathode and anode, we have concluded that the best temperature for electrolysis is 20˚C.
The temperature is not proportionate in any sense to the rate of electrolysis but 20˚C is the best temperature for that growth (lower & higher temperature and it’s affect on the weight of cathode).
4.2 Key findings
The greatest increase in the cathode mass was recorded for brass anode.
Since the brass anode was the best in experiment 1, we used brass as the material for anode in the 2nd experiment. We found out that 20℃ was the temperature that results in the greatest increase in the cathode mass.
4.3 Explanation of key findings
During electrolysis, the anode loses mass as it dissolves, and the cathode gains mass as calcium carbonate is deposited on it therefore, we can conclude that the cathode mass increase is directly proportioned to that of the anode mass decrease.
At the cathode, copper ions become atom and formed on it:
At the anode, the copper decompose forming copper ions:
Therefore the result is that anode wears away while cathode gains mass. Therefore, we can conclude that the rate of electrolysis is directly proportional to that of the amount of mass loss for the anode during the experiment. Though some iron is dissolved into the water, the amount of SiO2, CaCO3 and Mg(OH)2 produced will still be more. Therefore, we can conclude that the rate of electrolysis is directly proportional to that of the amount of mass gain for the wire mesh through the experiment.
The copper results and the metal reactivity series shows that copper is not a very good material for the anode as it is not very reactive.
Brass is made of 62% copper, 35.5% zinc and 2.5% lead. Since the reactivity of copper is not very good, we can infer that the reactivity of zinc caused the brass to react better than the anode made of copper only.
Photo 1: The Metal Activity Series
Though in this table it shows that Aluminium is more reactive than Zinc, after the Aluminium is taken out of the hydrochloric acid and is placed the water bath, oxide would form on the aluminium when it comes with contact with air almost immediately. Oxide would deter electrolysis therefore, Aluminium isn’t a good material for the anode as we wouldn’t be able to get all the oxide off it and it is very time consuming to try to have as little oxide forming on the aluminium .
For the temperature , we have found out that 20 degrees is the most suitable temperature for electrolysis to take place. At 15 degrees the water temperature is too cold, resulting in solubility of the calcium carbonate being very little and slow to attach onto the cathode, making the rate of electrolysis slower. At 25 degrees the water temperature is too warm, resulting in solubility of the calcium carbonate being too much and too fast to attach onto the cathode, making the rate of electrolysis slower. Hence we chose to try out the temperatures in the middle range and finally evaluating from the many experiments done that approximately in the middle , 20 degrees is the best for stimulating the highest rate of electrolysis .
During the process electrolysis, SiO2, CaCO3 and Mg(OH)2 is produced and formed on the wire mesh. But, CaCO3 produced in larger amount when compared to the rest. Also, SiO2 and Mg(OH)2 is more soluble than CaCO3. Thus, more CaCO3 is formed on the wire mesh and therefore, CaCO3 is more visibly seen on the cathodes when compared to SiO2 or Mg(OH)2.
Explanation of the atoms movement
4.4 Evaluation of Hypothesis
Our hypotheses have been both proved wrong by our results of our experiments.
For experiment 1:
We actually thought in the start that aluminium would react the fastest as it was one of the materials people commonly use in their circuits in daily life but electrolysis proved to be different as brass made electrolysis react the fastest. In the real world, zinc is actually the fastest material as used as anode. Since Brass is made up of Zinc and Copper, it has proved to be the material to increase the rate of electrolysis the fasted out of the 3 materials.
For experiment 2:
In the start, before the experiment, we predicted that the temperature was directly proportional to the rate of electrolysis. After the experiment, we then found out that it was wrong. Out of the three temperatures, 20˚C proved to be the best temperature for our experiment, followed by 25˚C and 15˚C being the worst.
4.5 Areas for improvement
We could have made all the cathodes and anodes of the same mass so that there would not be a different amount of exposed surface area for the anode and cathode for each experiment, which affected the results a little.
Another area for improvement is that we left the water in the fish tank overnight for a whole week. This resulted in the water in our salt solution, made to imitate the sea , evaporating away into the surroundings. We continued our 2nd experiment using that solution, which had a different concentration of salt in it compared to the first experiment, after the water evaporated. This would have affected the results of our 2nd experiment slightly.
The anode and cathode could not be spaced equally throughout all the 6 temperature experiments and that may result in the inaccuracy of the results.
Everyday, the salt always falls to the bottom of the tank so we had to stir the tank to let the salt ‘float’ in the tank. We stirred the tank a different amount of time and the strength used was different so some salt on some days may have still stayed at the bottom of the tank. This may have affected the results too.