SHINCO OFF I.V POWER USE 2V 1.V The Effect of Voltage and Electrolyte Concentration on the Electroplating of Copper Introduction
Oxidation and Reduction (Redox) reactions are chemical reactions that involve the transfer of electrons between two species (molecule, atom or ion). Oxidation occurs when an atom loses its electrons, and its oxidation number is increased. Reduction occurs when an atom gains electrons, and the oxidation number decreases. The species which accepts electrons is called the oxidising agent; by accepting electrons, it oxidises, and the species which donates electrons is called the reducing agent, as by losing electrons, it reduces its counterpart[CITATION Che19 \l 3081 ]. The process of electrolysis refers to the decomposition of an element, through redox reactions, influenced by a direct electric current (DC). Electrolysis occurs in electrochemical cells; where two metal electrodes are placed in an aqueous salt solution, known as the electrolyte. An anode is the metal electrode which oxidises, and a cathode is the electrode which reduces during electrolysis, and the electrolyte is the salt solution of the corresponding anode metal. There are two types of cells; galvanic cells, which undergoes redox spontaneously and produces electricity, and electrolytic cells, which cannot occur spontaneously, therefore needing a power source (electric current) to force the reaction to occur[ CITATION Che191 |1 3081 ]. Electrolytic cells are cells where redox reactions do not occur spontaneously, therefore must be forced with an electric current. The anode and cathode of this cell as configured differently from the galvanic cell because the anode and cathode are connected to the positive and negative terminals respectively. In these cells, the current attracts the electrons from oxidised atoms in the anode into the positive terminals and supplies these electrons through the negative terminal of the power source into the cathode, which results in a negatively charged cathode(reduction) and a positively charged anode (oxidation) [ CITATION BBC191 \l 3081 ]. In this investigation, copper (Cu) metal and silver (Ag) metal were used as the anode and cathode respectively in CuSO4 electrolyte. This reaction can be expressed as: .,2+¿ Cu Cu =- 0.34 V -¿ E 2+¿ aq +2e oxidised species : Cu (s) - Cu2 2+¿(aq) Eºcell=0V<0.2V 2+i (aq +Cu (s) - Cu(s)+Cu2 overall : Cu' Cu Cu2+ -= 0.34 V -¿ - Cu(s) Eº2 2+¿ (aq) +2e reduced species : Cu2 . reaction is not spontaneous CITATION BCO19 \l 3081 (BC Open Textbooks, n.d.) (refer to the reduction table (see Appendix 1) for Eº values) This cell cannot undergo redox reactions spontaneously because the standard cell potential(Eº cell) (voltage), which is the potential difference between the cathode and anode is OV< 0.2V(see half equations above), therefore it is an electrolytic cell (requires current). Due to the low Eºcell, an electric current would need to be introduced to the circuit to force the non-spontaneous reaction to occur [ CITATION Che191 \l 3081 ]. In this electrolytic cell, the electric current pulls 2 electrons from Cu, oxidising it into Cu2+, which dissolves into the CuSO4 electrolyte.