Alchemy

Before we had Chemistry and other sciences as we now know them, we had Alchemy, a sort of tradition which spread throughout the world, from Europe to Africa and Asia. The practitioners of this tradition worked on converting base metals (such as copper and iron) to more precious metals like Silver or Gold. They also worked on a cure that would eliminate all kinds of diseases and a medication that would serve as an elixir of mortality.. Okay, now relax. I did not say they succeeded, only that they worked on these things. Unfortunately, they did not succeed. However, even though we may not be able to convert one metal to another, we can achieve the next best thing - coat one metal with another, making the coated metal look like the real thing. The process described above is called Electroplating.

^{Wikipedia Creative Commons: Gold-plated electrical connectors}

All that is gold does not glitter, not all those who wander are lost; the old that is strong does not wither, deep roots are not reached by the frost. J. R. R. Tolkien^[1]

Electroplating

Electroplating is the process of passing electric current through a solution or molten substance called an electrolyte which is usually a salt. Two conductors called electrodes are dipped in the electrolyte and connected up to a source of direct current such that when electric current is passed through the electrolyte , it is decomposed into a metal and another substance and some of the metal atoms are deposited on one of the electrodes. The above explanation is very crude but we have to do with it for now.

Whenever you set out to do something, something else must be done first.^[3] - An extension of Murphy's Law

Electrolysis

Electroplating is similar to electrolysis so it would be worth our while first to familiarise ourselves with Electrolysis. Even though other scientists, starting from 1785 had worked on the process of electrolysis and used it to achieve their various aims, it was Michael Faraday who coined the word from two Greek words.

Just as earlier described, electrolysis involves the passing of a direct current (DC) through a molten salt or salt solution (electrolyte) and producing chemical reactions at the electrodes which are made of conducting materials. Electrolysis is set up using the following components:

• Two Electrodes: these are electrical conductors that provide the physical interface between the electrolyte and the electric circuit that provides the energy. One is called the anode(connected to the positive terminal of the direct current voltage source). The other electrode is the cathode (connected to the negative terminal of the direct current source). The electrodes are usually metals, semiconductors or graphite.

• Electrolyte: this is a substance, usually a soluble salt or a polymer that is capable of producing mobile ions that can conduct electric current, thereby completing the circuit.

• Direct Current (DC) Supply: this is usually a battery which is capable of creating a potential difference between the electrodes and providing the energy required to ionise the electrolyte to enable the freeing of electrons that will carry current to the external circuit.

Why go through all this trouble? Well, electrolysis is vital in the separation of elements such as the process of separating a metal from its ores.The process of electrolysis merely is the interchange of atoms and ions by the removal or addition of electrons from the external circuit. In other words, when the circuit is closed, current flows because electrons from the battery cell flow into the electrolyte through the anode (positive terminal). This is where oxidation takes place.

For instance, in the electrolysis of copper (II) sulphate (CuSO₄) using a copper anode and a graphite cathode, the following reduction reaction happens at the cathode:

Cu²⁺(aq) + 2e^- → Cu(s)

whereas, at the anode, there is an oxidation reaction as follows:

2H₂O(l) → O₂(g) + 4H⁺(aq) + 4e^-

By the way, in Chemistry, reduction means that the atom or ion has gained electrons whereas oxidation means that the ion or atom has lost electrons. Each electrode as described above attracts ions that are of the opposite charge. In this case, the positively charged copper ions (cations) would migrate towards the electron-providing negatively charged cathode where it would be deposited as a thin film of copper. The negatively charged sulphate ions, SO₄^2- (anions) move towards the electron-extracting, positively charged anode. At the anode, they will contribute electrons to the copper used in the electrode, forming CuSO₄ which enters the electrolyte ensuring that the solution remains of the same concentration at the end of the process.

When a positively charged ion gains electrons and becomes neutral, it is said to have been discharged. In this process, when the positively charged copper ion receives electrons at the graphite cathode, it becomes a neutral copper atom which must leave the electrolyte and be deposited on the graphite cathode. The process now described is called Electroplating or Electrowinning. It is also applied in the refining of metals, in which case, the process is called Electrorefining.

Electroplating Plastics or Non-Conductors

You may have seen some plastics with a metallic finish. Those are probably electroplated plastics. The thing is that plastic is cheap and quite commonplace. Because of these two properties, it is unsuitable for luxury goods unless someone figured out a way to make the plastics look like something else, perhaps silver or gold. This is what is achieved through electroplating plastics.

Ordinarily, because plastics are non-conductors, it is easy to conclude that they cannot be electroplated. However, if they undergo specific treatment, they can be electroplated just like metals. The prerequisite treatment for plastic before electroplating are cleaning thoroughly and removing any rough surfaces, etched with an acid solution and treating it with a catalyst to help speed up the chemical reaction. Finally, the plastic is dipped in a copper or nickel solution such that the plastic is covered by a fragile layer of the conducting material to enable it to conduct electricity.

Conclusion

Electroplating is a redox reaction which means reduction-oxidation reaction. Reduction happens at the cathode where a cation gains electrons and oxidation happens at the anode where anions give up or lose electrons to form the electrolyte, thereby restoring the concentration of the electrolyte to its original level. A naturally occurring slow oxidation reaction is rusting or corrosion.

Base metals (usually cheaper) can be protected from corrosion or made more beautiful by coating them with precious metals (which are at the same time more inert and more expensive), through the process of electroplating. In other words, two main reasons for electroplating are 1. to beautify and 2. to protect the base metal from corrosion. Plastics can also be electroplated to make it appear more luxurious and beautiful than ordinary plastic. The non-conductivity problem that electroplating plastics presents is bypassed by cleaning and dipping the plastic material in a conductive liquid before electroplating.

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References

1. Brainy Quote | J. R. R. Tolkien
2. Wikipedia | Salt(Chemistry)
3. Google User Content | Murphy's Law
4. RSC.org | Learn Chemistry - Electrolysis of Copper (II) Sulphate
5. Wikipedia | Electroplating
6. Britannica | Electroplating