LECTURE - 2 : CLASS VIII : SCIENCE : CHAPTER 14 : CHEMICAL EFFECTS OF ELECTRIC CURRENT

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Chemical Effects of Electric Current Explained
Electrolysis and its applications
Science | Class 8 | CBSE & SEBA Board

Introductions of Electrolysis

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BOARD: CBSE | CLASS: 8 | SCIENCE | Chapter 14:
📌 CHEMICAL EFFECTS OF ELECTRIC CURRENT

⚡ The Case of Distilled Water, Tap Water, Sea Water & Rainwater

💡 Core Idea: Electricity flows through water only when ions (charged particles) are present.

1️⃣ Distilled Water

Observation: Distilled water does not conduct electricity.

Think WHY:
Distilled water is pure. No dissolved salts → no ions → no charge flow.

Q. How can we make distilled water a conductor of electricity?

By adding:

1. Salts
2. Acids
3. Bases

🧠 Memory Hook:
PURE water = NO current
ADD ions = SWITCH ON current

2️⃣ Tap Water

Tap water contains small amounts of dissolved salts, so it conducts electricity.

Think Safety:
Since tap water conducts electricity, touching electrical appliances with wet hands can cause electric shock.

🚫 Never operate heaters, irons, mixers, grinders, or switches with wet hands.

🧠 Wet hands + electricity = DANGER

3️⃣ Drinking Water

Drinking water also contains dissolved salts, hence it is a conductor of electricity.

Compare:
Distilled water (no salts) ❌
Drinking water (some salts) ✔️

4️⃣ Sea Water

Sea water contains a large amount of salts, making it a very good conductor of electricity.

Which is a better conductor: drinking water or sea water? Why?

Sea water is a better conductor because it contains more dissolved salts than drinking water.

🧠 More salts → more ions → more current

5️⃣ Rain Water

Rain water contains small amounts of acids, so it also conducts electricity.

Is it safe to carry out electric repairs during a rainy day?

No. Rain water conducts electricity, so it is unsafe for electricians to work during rain.

🧠 Rain + electricity = RISK

🧪 Chemical Effects of Electric Current

When electric current passes through a conducting liquid, it can cause chemical reactions.

When electric current is passed through acidified water using carbon electrodes:

1. Water decomposes
2. Hydrogen gas is released
3. Oxygen gas is released

🧠 Electricity doesn’t just flow — it can CHANGE substances

🔬 Electrolysis

Electrolysis: The chemical decomposition of a conducting liquid caused by the passage of electric current.

Example: Electrolysis of acidified water produces:

1. Hydrogen at the cathode
2. Oxygen at the anode

🧠 Break it to remember it:
Electro = electricity
Lysis = breaking

🧠 Activity: Demonstration of Chemical Effect of Electric Current

Describe an activity to demonstrate the chemical effect of electric current.

1. Take a beaker filled with water.
2. Add a few drops of dilute sulphuric acid.
3. Insert two carbon electrodes into the water.
4. Connect the electrodes to a battery.
5. Pass electric current through the solution.
6. Observe gas bubbles forming at both electrodes.

Think Observation → Conclusion:
Gas bubbles = chemical reaction → proves chemical effect of current.

🧠 See bubbles? ✔️ Electricity is doing chemistry!

Describe an activity to demonstrate the change in colour caused by the chemical effect of electric current.

🧪 Chemical Effect of Electric Current: Change in Colour

💡 Key Thinking Idea: Electric current flowing through a conducting material can trigger chemical reactions that may cause a visible colour change.

🔬 Activity: Colour Change Using a Potato

Describe an activity to demonstrate the change in colour caused by the chemical effect of electric current.

1. Cut a potato into two halves.
2. Take one half and insert two iron nails into it, keeping some distance between them.
3. The iron nails act as electrodes.
4. Connect the nails to a battery using wires, a switch, and a compass.
5. Close the switch to allow electric current to pass.
6. Keep the current flowing for about 30 minutes.

Observation:
The compass needle shows deflection, proving that the potato conducts electricity. After some time, a greenish-blue spot appears around the iron nail connected to the positive terminal.

Think Like a Scientist:
✔ Deflection of compass → current is flowing ✔ Colour change → chemical reaction is taking place ✔ Reaction occurs near positive electrode (anode)

🧠 Memory Hook: No reaction → no colour
Current + conductor → chemistry + colour

🧠 Conclusion from the Activity

The formation of a greenish-blue spot near the positive electrode proves that the chemical effect of electric current can cause a change in colour in a conducting medium.

⚙️ Applications of Chemical Effect of Electric Current

1. Electroplating of metals
2. Purification of metals
3. Production of metals from their ores
4. Production of chemical compounds
5. Decomposition of chemical compounds

🧠 Think Big Picture: Electricity is not only energy — it is a chemical tool.

🔩 Electroplating of Metals

Electroplating: The process of depositing a thin layer of one metal over another metal using electric current.

Commonly electroplated objects:

1. Taps
2. Utensils
3. Jewellery
4. Machine parts

Metals used include chromium, nickel, tin, copper, silver, and gold.

Why Electroplate?
✔ Prevent corrosion ✔ Improve appearance ✔ Increase durability ✔ Reduce cost (thin layer, expensive metal)

🧠 Shiny outside, strong inside — that’s electroplating!

🧲 Activity: Electroplating Copper on Iron

How can copper be electroplated on the surface of an iron object?

1. Take copper sulphate solution in a beaker.
2. Clean the iron object thoroughly.
3. Connect the iron object to the negative terminal of the battery.
4. Connect a copper plate to the positive terminal.
5. Dip both electrodes in the solution.
6. Allow current to pass for some time.

Observation:
A thin layer of copper gets deposited on the iron object.

Think Mechanism:
Copper ions move towards the negative electrode (iron) and get deposited as metal.

🧠 Negative attracts metal — remember this for electroplating!

⚙️ Purification of Metals by Chemical Effect of Electric Current

The chemical effect of electric current is widely used to purify impure metals. This process is called electrolytic refining.

🔩 Electrolytic Refining of Copper

1. A thick rod of impure copper is made the positive electrode (anode).
2. A thin strip of pure copper is made the negative electrode (cathode).
3. A water-soluble salt of copper (copper sulphate) is used as the electrolyte.

Experimental Setup:
• Take 250 ml distilled water in a beaker. • Dissolve two teaspoons of copper sulphate in it. • Add a few drops of dilute sulphuric acid. • Connect the impure copper rod to the positive terminal. • Connect the pure copper plate to the negative terminal. • Switch on the current and allow it to pass for about 30 minutes.

Think Process Flow:
Anode dissolves → Copper ions move → Cathode gains copper

Observation:
✔ The impure copper rod becomes thinner. ✔ The pure copper plate becomes thicker. ✔ Impurities settle at the bottom of the beaker.

🧠 Anode loses, cathode gains — remember this golden rule!

🏭 Production of Metals

The chemical effect of electric current is used to extract certain metals from their ores.

Think Why:
Some metals are too reactive to be extracted by heating — electricity does the job.

🧠 Electricity replaces fire for reactive metals.

🧫 Production of Chemical Compounds

Electrolysis is used to produce chemical compounds such as:

1. Sodium hydroxide from aqueous sodium chloride

Think Conversion:
Electricity → Chemical factory

🔬 Decomposition of Chemical Compounds

The chemical effect of electric current is used to decompose compounds into their elements.

Example: Water → Hydrogen + Oxygen (by electrolysis)

🧠 Electricity doesn’t just move — it breaks matter.

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