Introduction
In our modern society, a plethora of chemical processes and reactions are commonly found in our everyday environment and are significant parts of the products we use. One such process is a redox equation, which consists of oxidation and reduction.
Originally, oxidation and reduction were viewed in terms of adding or removing oxygen. Now, they are defined in three different ways; the loss or gain of oxygen, the loss or gain of hydrogen, and the loss or gain of electrons, oxidation being the loss, and reduction being the gain (Oxidation-reduction (redox) reactions, n.d). A simple example of a redox reaction consisting of oxidation and reduction is as below; CuO+Mg →Cu+MgO
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Copper (II) oxide and Magnesium oxide are ionic compounds, and if the equation is rewritten as an ionic equation by omitting the oxygen, the oxidation and reduction are clear. Cu^(2+) + Mg → Cu + Mg^(2+)
The magnesium reduces the copper by transferring its electrons, so copper gained two, and the copper oxidises the magnesium by losing two electrons, so magnesium lost two electrons. Overall, the equation is balanced, and the overall charges are neutral, but the loss and gain of electrons is clearly shown. More reactive metals are prone to lose electrons then less reactive metals.
Electrolysis is defined as ‘use of an electric current through an electrolyte to create a non-spontaneous chemical reaction’ (Song, 2019). It can be used to separate a substance into its original components or elements, but one common application of electrolysis in the modern world is electroplating.
According to the Australian Institute of Surface Finishing, ‘Electroplating is the process of depositing a metallic coating upon a negatively charged electrode by the passage of an electric current. The purpose of electroplating is to obtain a metallic coating having different properties or dimensions than those of the basis metal.’ (AISF, n.d). It involves a closed circuit consisting of a direct source of current (eg. Power supply), a container containing the electrolyte (the plating solution with a dissolved salt of the metal that will be plated), an anode (positive electrode), and a cathode which is being plated (negative electrode), as shown in Figure. 2 (AISF, n.d).
In this investigation, the aim was to explore how changing the concentration of an electrolyte would affect the rate of electrolysis. The rate of electrolysis is affected by the current which passes through the electrolysis, the higher the current, the faster the rate of electrolysis is (Mark Gould, 2006). The factors that affect the current are the voltage used and the electrical conductance of an electrolysis cell. The electrical conductance of an electrolysis cell are affected by the surface are of the electrodes used, the distance between the electrodes, and the concentration of ions in the solution (Mark Gould, 2006). Therefore, it is assumed that by increasing the concentration of the Copper Sulphate solution [CuSO4] (the electrolyte) (independent variable), the rate of electrolysis (dependent variable) of copper on the iron nail (cathode) will increase.
The initial colour change of the nails after sanding was due to the removal of rust gathered on the nail, however, the second colour change, during the experiment, can be attributed to the nail being coated or plated with the copper, which has a brownish-red colour. The fact that the beaker had what looked like copper at the bottom of the beaker suggests that some of the copper meant to be plated on the iron nail fell off the nail after the experiment.
Data Analysis
When hypothesising about this experiment, it was assumed that as the concentration of the Copper Sulphate solution increased, so would the rate of reaction of electroplating to the nail. This would result in a trend of high positive correlation between the amount of copper deposited on the nail and the concentration of the Copper Sulphate solution. The average of each concentration’s amount of copper deposited is widely different, as seen in Figure. 3. The results the experiment bore, however, have an extremely low correlation and while being given a linear line of best fit, does not have a linear relationship. There was an outlier in Trial 2 of the 0.2 mol dm-3 and Trial 2 of 0.8 mol dm-3, the difference in mass being, respectively, 0.130g and 0.103g. These weights were much higher than majority of the differences in mass, being 0. 29 to 0.110 above the other data. As is evident in Figure. 3 itself, the incredibly low r2 value, which shows how close the data is to the line of best fit, the data has barely any correlation.
Discussion and Evaluation
The data didn’t display any distinguishable trends that correlate with the general assumption made about the experiment. It is commonly known that by increasing the number of ions in the solution, the conductance of the electrolysis cell is increased as the electrical resistance is lowered. This should ultimately result in the current to be higher, which would increase the rate of production of the plating (Mark Gould, 2006). If the experiment had been carried out accurately, the results would have shown a high positive correlation between the increase in concentration and the rate of electrolysis or the mass of copper deposited on the nail. The only possible reasons for the results to have such extreme and drastic deviation from the predicted results have to be due to errors in the experiment. There weren’t any strengths of the experiment that outweigh the drastic difference between the theoretical and experimental data.
There are two types of errors, excluding human error, in an experiment; Systematic and random errors. In this particular experiment, the table below shows the systematic and random errors of this experiment. These are the many limitations to the experiment, as proven by our skewed data.
Type of Error Error How can it be minimised?
Systematic The time of 7 minutes (420 s) may not have been long enough to see clear impact of CuSO4. Increase the amount time spent electroplating to 10 minutes.
Each variation of the concentration of CuSO4 in the experiment was performed by a different group of people which can affect the validity and how methodically the procedure was carried out (For example; Not many groups let the nail air dry for 2 minutes despite it being written in the method, and one group only completed two trials, while others completed three.) Either minimise the differences in every group and uphold them to the same standards, or make each singular group performs every variation of the independent variable.
The mass of the copper plating on the nail was most likely very small, so the mass of residual water/CuSO4 on the nail instead could have increased or skewed the overall mass of deposit. Enforce step number 8 in the method and ensure that the nails are allowed to air dry for 2 minutes before being measured.
There are variables the affect the rate of electrolysis, such as increasing the voltage of the power supply, and those factors weren’t explored. Introduce two, or more, different independent variables; The concentration of the CuSO4 and the voltage of the power supply.
Random The measurement of the difference in mass of the nail before and after the electroplating. Choosing equipment with a sufficient level of precision for the experiment being conducted.
Apart from the minimisations of errors stated in Table. 4, some ways the experiment could be extended to generate more data is to conduct more trials for each concentration of CuSO4. This not only provides more data to analyse, it also increases the validity of those results.
Conclusion
In summary, the aim of this experiment was to explore how changing the concentration of an electrolyte would affect the rate of electrolysis and it was hypothesised that by increasing the concentration of the Copper Sulphate solution [CuSO4], the rate of electrolysis of copper on the iron nail will increase. However, due to many systematic and random errors in the methodology, experimental design and the execution of said methodology, the results were extremely different then the assumption. There was no correlation between the amount of copper deposited on the nail and the concentrations of CuSO¬4, not even a negative one, as the data had an incredibly low r2 value.
The original research question was; What is the effect of different concentrations of the solution CuSO4, Copper Sulphate, (0.2, 0.4, 0.6, 0.8, and 1 mol dm-3) on the mass of copper deposited on a nail after 7 minutes (420s), in a copper and nail electrolysis experiment?
Though, the results suggest that the different concentrations have no effect on the mass of copped deposited on a nail, logically, and with understanding of the factors that increase the rate of electrolysis, it can be concluded that the results are invalid because of their significant deviation from predicted results.
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