What is a Displacement Reaction with Electricity?

S6-SA4-0323

Grade Level:

Class 10

AI/ML, Physics, Biotechnology, Space Technology, Chemistry, Engineering, Medicine

Definition

What is it?

A displacement reaction with electricity, also known as electrolysis, is a process where electrical energy is used to break down a compound into simpler substances. In this reaction, a more reactive element or ion is replaced by a less reactive one using an electric current. It's like using electricity to force a chemical change that wouldn't happen on its own.

Simple Example

Quick Example

Imagine you have a solution of copper chloride (CuCl2), which is blue. If you pass electricity through it using two carbon rods (electrodes), something magical happens. Copper metal starts depositing on one rod, and chlorine gas bubbles out from the other. Here, electricity is 'displacing' copper from its chloride compound.

Worked Example

Step-by-Step

Let's purify impure copper using electrolysis.

1. **Setup:** We need an electrolytic cell. This includes a container, an electrolyte (copper sulfate solution, CuSO4), an impure copper block (anode), and a thin sheet of pure copper (cathode).
---
2. **Power Source:** Connect the impure copper to the positive terminal of a battery and the pure copper sheet to the negative terminal.
---
3. **Reaction at Anode (Impure Copper):** When electricity flows, the impure copper (anode) starts to dissolve. Copper atoms (Cu) from the impure block lose two electrons and become copper ions (Cu2+), which go into the copper sulfate solution. Impurities like zinc or iron also dissolve, while less reactive impurities like silver or gold settle down as 'anode mud'.
*Equation: Cu(s) -> Cu2+(aq) + 2e-*
---
4. **Reaction at Cathode (Pure Copper):** At the pure copper cathode, the copper ions (Cu2+) from the solution gain two electrons and turn back into pure copper metal, which deposits onto the cathode.
*Equation: Cu2+(aq) + 2e- -> Cu(s)*
---
5. **Overall Result:** Over time, the impure copper anode gets smaller, and the pure copper cathode gets thicker with deposited pure copper. The copper is 'displaced' from its ionic form in the solution to its metallic form on the cathode, all thanks to electricity.
---
**Answer:** Pure copper is obtained at the cathode, and impurities are separated.

Why It Matters

Understanding displacement reactions with electricity is crucial for many industries. It's used in electroplating (making jewellery shiny), extracting metals like aluminium from their ores, and purifying metals like copper. This concept is fundamental for careers in chemical engineering, materials science, and even in developing new battery technologies.

Common Mistakes

MISTAKE: Thinking that electrolysis is always about breaking down water into hydrogen and oxygen. | CORRECTION: While water electrolysis is a common example, electrolysis can be used to break down many different compounds, like molten salts or aqueous solutions of various compounds, not just water.

MISTAKE: Confusing the anode and cathode, or their charges. | CORRECTION: Remember 'AN OX, RED CAT'. Anode is where Oxidation (loss of electrons) happens, and it's connected to the positive terminal. Cathode is where Reduction (gain of electrons) happens, and it's connected to the negative terminal.

MISTAKE: Believing that any two metals will displace each other in a solution just by touching. | CORRECTION: Displacement reactions with electricity require an external electrical energy source to force the reaction. Without electricity, only a more reactive metal will displace a less reactive metal from its salt solution naturally.

Practice Questions

Try It Yourself

QUESTION: What is the main purpose of using electricity in a displacement reaction like electrolysis? | ANSWER: The main purpose is to provide the energy needed to force a non-spontaneous chemical reaction to occur, breaking down a compound or purifying a substance.

QUESTION: If you perform electrolysis on molten sodium chloride (NaCl), what substances would you expect to form at the anode and cathode respectively? | ANSWER: At the anode, chlorine gas (Cl2) would form. At the cathode, sodium metal (Na) would form.

QUESTION: Why is aluminium metal extracted from its ore (bauxite) using electrolysis, even though it's an energy-intensive process? Explain in terms of reactivity. | ANSWER: Aluminium is a highly reactive metal, meaning it has a strong tendency to remain in its compound form (like aluminium oxide in bauxite). Chemical reduction methods using other metals are not effective or practical for such a reactive metal. Electrolysis provides the necessary electrical energy to overcome this strong bonding and displace aluminium from its oxide, making it the most viable method for its extraction on an industrial scale.

MCQ

Quick Quiz

Which of the following is an application of a displacement reaction with electricity?

Burning of wood

Rusting of iron

Electroplating a silver spoon with gold

Digestion of food

The Correct Answer Is:

Electroplating uses electricity to deposit a layer of one metal onto another, which is a type of displacement reaction where ions in solution are reduced to metal using electrical energy. The other options are not examples of electrolysis.

Real World Connection

In the Real World

In India, companies involved in metal refining and manufacturing, like Hindalco or Vedanta, heavily use electrolysis for purifying metals like copper and extracting aluminium. Even the shiny chrome plating on bicycle parts or car bumpers, and the gold plating on imitation jewellery you see in local markets, are all done using this very principle of displacement with electricity.

Key Vocabulary

Key Terms

ELECTROLYSIS: The process of using electrical energy to cause a non-spontaneous chemical reaction. | ANODE: The positive electrode where oxidation occurs. | CATHODE: The negative electrode where reduction occurs. | ELECTROLYTE: A substance (liquid or solution) that conducts electricity due to the presence of mobile ions. | ELECTROPLATING: The process of coating an object with a thin layer of metal using electrolysis.

What's Next

What to Learn Next

Great job understanding electrolysis! Next, you should explore 'Faraday's Laws of Electrolysis'. This will teach you how to calculate exactly how much substance is produced or consumed during these electrical displacement reactions, giving you a deeper understanding of the quantities involved.