Introduction
Electrolysis is when an electric current pass through a chemical solution to create a non-spontaneous chemical reaction (Britannica, 1998). Electrolysis can be used to separate compounds into its original elements (libretexts, 2019). In electrolysis, the reduction - or the gain of electrons - and the oxidation - or the loss of electrons occurs. This is referred to as Redox reactions. When a battery’s positive and negative terminals is connected to the electrodes it can alter the charge of the neutral atoms in the electrode. Both electrodes are placed in an aqueous or molten solution called an electrolyte. Electroplating is an example of electrolysis. Electroplating is depositing a thin coat of one metal (or metal onto a plastic) onto another, thus allowing the metal to resist rust, build in thickness, become more aesthetically pleasing for consumers and it provides protection against external surfaces (SPC, 2019). The speed in which electroplating occurs depends of multiple factors including the concentration of the solution.
For the electroplating process to occur, an electrolytic cell must be used. Two electrodes (normally metal) are connected two the positive and negative terminals of the battery via leads. The metal to be plated must be connect to the anode of the circuit while the metal to be coated must be in the cathode to allow attraction. Both electrodes must be placed into an aqueous solution consisting of dilute salt solution of the anode metal. This is referred to as electrolyte. With no electric current, both metals have a neutral charge thus inhibiting any chemical reactions to occur. However, when the battery is turned on, the battery terminals force the charges anode to change and cause the free-floating positively charged atoms in the aqueous solution to be attracted to the cathode. Within the anode, the electrons (consists of a negative charge) are attracted to the positively charged terminal thus forcing the electrons to be pulled out of the atoms. The loss of electrons is referred to as oxidation. The electrons follow the electric circuit to the cathode. In the anode, the atoms become positively charged and break free from the neutrally charged solid metal. Positively charged atoms are attracted to the cathode terminal. In the cathode terminal, the electrons bond to the positively charged metal as opposed to the neutrally charged metal connected to the cathode. The charge of the metal becomes neutral as the number of protons and electrons become balanced. Therefore, the anode loses pieces of the metal to be attracted to the coating of the cathode.
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Typically, there are 3 major factors that can affect an electrolysis reaction. The following increase the rate of electrolysis as per faraday’s law: an increased current, an increased voltage (increased current), an increased concentration in electrolyte, an increase in the surface area of the electrodes which allows for more atoms to lose their electron within the surface and detach from the electrode and a decrease in the distance between eh electrode and the cathode (easychem, n.d) the Faraday’s Law of electrolysis states that 1) the mass of the substance being deposited is proportional to the electrical currents passing through the solutions, 2) for the given quantity of electricity (electric charge), the mass of an element altered at an electrode is directly proportional to the element’s equivalent weight (sciencedirect, n.d). Essentially, if voltage or concentration is increased, the change of mass should positively correlate as more atoms allow for an increased rate of electrolysis.
Discussion and Evaluation
As per the electrolysis theory, as concentration increases, the change in mass must increase due to the increase in the atoms available to be transferred from the copper in the anode and in the copper sulphate solution. However, as shown in figure 1, there was a weak negative correlation between concentration and change in mass providing a R2 value of 0.2591 when the anomalies are removed. This may be due to systemic errors brought on by extraneous variables such as different experimenters conduct each sample. Experimenter variability will increase the chances of the methodology not equal in each trial therefore making the results unreliable. A methodology error may be been when air drying the nail as a general 2 minutes air dry may not allow the nail to fully dry. Since the mass change of the copper deposit would be small (see table 1), the mass of any excess water would be significant which would theorise as to why there are fluctuations within the experimental results in comparison to the theoretical results. To reduce such errors, one group of experimenters should conduct the experiment which will reduce experimenter variability. This will allow all conditions to be conducted similarly and will not contribute to the introduction of any other extraneous variables. As a limitation, the duration of the electrolysis should be extended to observe any significant changes from 7 minutes from 10 minutes. However due to time constraints, this could not occur. To improve, more time must be allocated to complete this experiment for the adequate observations. In addition to this, each condition was only tested once therefore making each test unreliable as it was not a fair test as a result may be considered an anomaly. The methodology allows for precise measurements to be used allowing for more accurate results as evident within table 2 where the average mass change was indicated within three decimal places as opposed to the standard 2 decimal places scales. Due to the miniscule mass change, it was empirical that a precise mode of measurement must be used.
To extend upon this experiment, the effect of increasing the voltage should be experiment. Increasing the voltage and solution follow Faraday’s theory – an increase in the voltage was directly proportional to the amount of the substance being deposited. More specifically, when voltage increased, more collisions should occur due to the higher energy input within the solution resulting to an increase in the atoms plated due to a faster rate of oxidation from the anode and reduction from the cathode. This should occur in 2 voltage increments (4,6,8,10) which will allow for a steady increase in deposit which allows for an easy comparison between each condition.
Conclusion
Overall, the effect of CuSO4 solution concentration (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 was observed to decrease and oppose the theoretical results. It was expected that when the concentration increased, the rate of electrolysis should increase. In addition to this, the experimental results fluctuated, with the average deposit of copper resulting to 0.086 in a 0.2 mol solution and a 0.030 in a 1 mol copper sulphate solution. The results showed the opposite whereas when the concentration increased, the mass change decreased. This may be due to experimental errors and systemic errors such as limited duration of electrolysis and experimenter variability.
References
- Encyclopedia Britannica. (2019). Electrolysis | chemical reaction. [online] Available at: https://www.britannica.com/science/electrolysis [Accessed 3 Nov. 2019]. https://www.britannica.com/science/electrolysis
- Libretexts. (2019, June 5). Electrolysis. Retrieved from: https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Analytical_Chemistry)/Electrochemistry/Electrolytic_Cells/Electrolysis
- What Is Electroplating? (n.d.). Retrieved from: https://www.sharrettsplating.com/about/what-electroplating
- Faraday's Law. (n.d.). Retrieved from: https://www.sciencedirect.com/topics/chemistry/faradays-law
- Factors that affect an electrolysis reaction. (n.d.). Retrieved from: https://easychem.com.au/shipwrecks-and-salvage/3-electrolytic-cells/factors-that-affect-an-electrolysis-reaction/
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