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Chemical Effects of Electric Current - Process and Applications of Electroplating

Grade 8CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Electroplating is the process of depositing a layer of any desired metal on another material by means of electricity.

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It is one of the most common applications of the chemical effects of electric current.

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The object to be electroplated is made the negative electrode (cathode).

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The metal that is to be deposited is made the positive electrode (anode).

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The electrolyte must be a soluble salt of the metal that is to be deposited (e.g., using CuSO4CuSO_4 solution for copper plating).

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When current passes through the electrolyte, the salt dissociates into ions. For example, CuSO4CuSO_4 dissociates into copper ions (Cu2+Cu^{2+}) and sulphate ions (SO42−SO_4^{2-}).

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The free copper ions (Cu2+Cu^{2+}) are drawn to the cathode, where they gain electrons and get deposited as a layer of copper metal.

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Common applications include: Chromium (CrCr) plating on car parts and taps for a shiny look and scratch resistance; Gold (AuAu) or Silver (AgAg) plating on less expensive metals for jewelry; and Zinc (ZnZn) coating on Iron (FeFe) to prevent corrosion (Galvanization).

📐Formulae

ightleftharpoons Cu^{2+} + SO_4^{2-}$$

At Cathode (Reduction): Cu2++2e−→Cu\text{At Cathode (Reduction): } Cu^{2+} + 2e^- \rightarrow Cu

At Anode (Oxidation): Cu→Cu2++2e−\text{At Anode (Oxidation): } Cu \rightarrow Cu^{2+} + 2e^-

💡Examples

Problem 1:

During the electroplating of a copper plate onto an iron key, what happens to the concentration of the CuSO4CuSO_4 solution over time?

Solution:

The concentration of the copper sulphate (CuSO4CuSO_4) solution remains constant.

Explanation:

As copper ions (Cu2+Cu^{2+}) from the solution are deposited on the iron key (cathode), an equal amount of copper dissolves into the solution from the copper plate (anode). Thus, the loss of copper from the electrolyte is restored, keeping the concentration of CuSO4CuSO_4 unchanged.

Problem 2:

Explain the chemical reaction that occurs at the cathode when silver plating a brass spoon using silver nitrate (AgNO3AgNO_3).

Solution:

Ag++e−→AgAg^+ + e^- \rightarrow Ag

Explanation:

In a silver nitrate solution, the salt dissociates into Ag+Ag^+ and NO3−NO_3^- ions. The silver ions (Ag+Ag^+) move toward the negative electrode (the brass spoon), where they gain one electron (e−e^-) each to become neutral silver atoms (AgAg) that stick to the spoon.