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Electrochemistry - Electroplating

Grade 11IGCSEChemistry

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

🔑Concepts

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Electroplating is an electrolytic process used to coat the surface of one metal with a thin layer of another metal to improve appearance or provide corrosion resistance.

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The Cathode (negative electrode) is always the object to be plated (e.g., a steel spoon or a piece of jewelry).

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The Anode (positive electrode) is made of the pure metal that is intended to be the coating (e.g., a bar of pure silver or copper).

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The Electrolyte must be an aqueous solution of a soluble salt containing the ions of the plating metal (e.g., AgNO3AgNO_3 for silver plating or CuSO4CuSO_4 for copper plating).

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During the process, the concentration of the metal ions in the electrolyte remains constant because the rate of metal dissolving at the anode is equal to the rate of metal deposition at the cathode.

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At the cathode, reduction occurs as metal ions gain electrons to form a solid metal layer: Mn++ne−→M(s)M^{n+} + ne^- \rightarrow M_{(s)}.

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At the anode, oxidation occurs as the metal atoms lose electrons and enter the solution as ions: M(s)→Mn++ne−M_{(s)} \rightarrow M^{n+} + ne^-.

📐Formulae

M(aq)n++ne−→M(s)M^{n+}_{(aq)} + ne^- \rightarrow M_{(s)}

M(s)→M(aq)n++ne−M_{(s)} \rightarrow M^{n+}_{(aq)} + ne^-

Cu(aq)2++2e−→Cu(s)Cu^{2+}_{(aq)} + 2e^- \rightarrow Cu_{(s)}

Ag(s)→Ag(aq)++e−Ag_{(s)} \rightarrow Ag^+_{(aq)} + e^-

💡Examples

Problem 1:

Describe the setup and chemical reactions involved in plating a nickel keychain with copper.

Solution:

The keychain is placed at the cathode (negative electrode) and a strip of pure copper is placed at the anode (positive electrode). The electrolyte used is copper(II) sulfate solution (CuSO4CuSO_4). Anode reaction: Cu(s)→Cu(aq)2++2e−Cu_{(s)} \rightarrow Cu^{2+}_{(aq)} + 2e^-. Cathode reaction: Cu(aq)2++2e−→Cu(s)Cu^{2+}_{(aq)} + 2e^- \rightarrow Cu_{(s)}.

Explanation:

Copper atoms at the anode lose electrons (oxidation) and enter the CuSO4CuSO_4 solution as Cu2+Cu^{2+} ions. These ions are then attracted to the cathode, where they gain electrons (reduction) to form a solid copper layer on the nickel keychain.

Problem 2:

Explain why the blue color of the electrolyte does not fade during the electroplating of an object with copper using a copper anode.

Solution:

The intensity of the blue color depends on the concentration of Cu(aq)2+Cu^{2+}_{(aq)} ions. Since for every copper ion reduced to metal at the cathode, one copper atom is oxidized to an ion at the anode, the concentration of Cu2+Cu^{2+} ions remains constant.

Explanation:

In standard electrolysis with inert electrodes, ions are depleted. However, in electroplating with a reactive anode, the anode 'replenishes' the ions at the same rate they are removed at the cathode, maintaining a constant ion concentration.

Electroplating - Revision Notes & Key Formulas | IGCSE Grade 11 Chemistry