Nikita was having lunch in her new shiny lunchbox and notices that the bottom of the lunch box is coated with a shiny substance. She wears a gold bracelet everyday which looks shiny yellow. Upon taking a metal scraper and rubbing her bracelet, she notices that the yellow color weans off. She now realizes that the lunch box and her bracelet aren’t actually made of gold; they are just coatings. The process of coating of one metal over another metal is preferred when huge costs are incurred in making a substance. For instance, making a gold necklace is expensive compared to making a silver necklace. The latter can be coated with gold to give it an aesthetic appearance and not to mention, protect it against corrosion or other forms of degradation. A process known as electroplating is going to help us achieve this; as the name itself suggests, it makes use of electricity to facilitate coating of one metal over another. In this article, we will explore electroplating in detail.
Table of contents
Electroplating refers to the process of coating one metal onto the surface of another metal. In order to do so, the number of cations that are contained in the metal are reduced. Not only does electroplating protect metals against corrosion, but it is also done to enhance surface properties like lubricity and abrasion resistance.
The electroplating process consists of an anode and a cathode. The cathode is the terminal where electrons undergo reduction. The metal to be gold plated is made as the cathode. On the other hand, anode is a gold plate which is to be deposited on the cathode. Both the electrodes are kept immersed in an electrolytic solution, which is made from a salt of the metal taken. Reduction occurs on the cathode and oxidation occurs on the anode. Factors which affect the process of electroplating are—
1) The voltage applied by the external circuit.
2) The surrounding bath temperature and chemical composition of the electrolyte.
3) The duration of electroplating
4) The spacing between the anode and cathode
Let us take the example of copper plating. The anode is made of a block of pure copper metal which can be coated on the cathode. The latter is an impure copper plate which needs to be provided with a protective coating. The electrolyte is dilute copper sulphate solution When current is passed through the electrolyte, it dissociates into and The process goes on till the current is passed. The impurities get deposited as anode mud at the bottom of the vessel.
ions are reduced to metallic copper at the cathode. While at the anode, gets oxidized to
This process keeps on going on till the electric current is stopped.
at the cathode)
2)Machine parts- Since most heavy machinery are under constant stress or fatigue, electroplating them will protect against corrosion and abrasion.
3) Cellphones- Certain spare parts found in cell phones are coated with silver inorder to increase their conductivity
4)Jewelry- Gold being an expensive metal, it is not possible to make all jewelry with gold. Hence, jewelry is plated with gold.
5) Coins- Since coins change hands frequently, they are provided with protective coatings to reduce abrasion and improve their corrosion resistance.
Let us consider the following electrolytic reduction of
According to Faraday’s law of electrolysis, the charge required to reduce atoms
represents the Avogadro Number.
The mass of the substance deposited at the electrode is directly proportional to the charge passed through. I.e
the electrochemical equivalence.
represents current passed through.
Q1. Why is copper used in electroplating?
Answer: Owing to its conductivity, corrosion resistance and malleable properties, copper is an ideal material for electroplating.
Q2. Sodium sulphate solution is electrolysed using electrodes. The products at the anode and the cathode are?
Answer: At cathode, Cathode)
Q3. A current of is to be passed for minutes through a copper sulphate solution. If copper carries an electrochemical equivalent Calculate the mass of the copper that gets deposited?
Q4. Calculate the electrochemical equivalent of copper in the following reaction
(a) (b) (c)
Question 1. What is the principle behind electroplating?
Answer: It works on the principle of hydrolysis, i.e. when current is passed through an electrolytic solution, it splits into its constituent ions.
Question 2. What acids are used for electroplating?
Answer: Methanesulfonic acid and fluoroboric acid are used in electrolysis.
Question 3. Why is anode mud important?
Answer: Anode mud sometimes contains precious metals that can be recovered.
Question 4. Where is electroplating used?
Answer: It finds applications in decorative arts where surfaces of idols are to be protected against abrasion and corrosion.