11. Class 8 Science Chapter 11 Chemical Effects of Electric Current

Notes on Chemical Effects of Electric Current:

Introduction:

• Safety First: 
  • Wet hands conduct electricity, posing a safety hazard.
  • Emphasize caution when handling electrical appliances with wet hands.

Materials and Electricity:

• Conductors: Metals like copper, silver, and aluminum readily allow the flow of electrons (electric current). Think of them as highways for charged particles!
• Insulators: Non-metals like rubber, plastic, and wood have tightly bound electrons, hindering current flow. Imagine them as roadblocks!
• Conductivity Tester: This handy tool uses the “bulb glow” principle to identify conductors (bulb lights up) and insulators (no glow). Think of it as a traffic light for electricity!

Testing Liquids for Conductivity:

• Electrolytes: Liquids that conduct electricity are called electrolytes. They contain dissolved ions (charged atoms or molecules) that act like charged vehicles on the highway.
• Non-electrolytes: Pure water lacks electrolytes and is a poor conductor, like a deserted road. Tap water, with its dissolved minerals, becomes a bustling highway thanks to the ions.
• Safe Power: Always use small, safe electric cells, not mains or generators! Think of them as safe, low-traffic zones instead of high-voltage racetracks.
• Tester Check: Before diving into experiments, test the tester! A glowing bulb signifies it’s ready to roll. If not, troubleshoot connections, bulb, or cells.

Activities:

• 11.1: Touch Tester: Briefly connect the tester ends. Bulb glow? You’re good to go! No glow? Time to investigate!
• 11.2: Liquid Conductors: Test liquids like lemon juice or vinegar. Remember, glowing bulb = good conductor (highway open!), no glow = poor conductor (road closed).

Beyond Bulb Glows:

• Weak Currents: Don’t be fooled by a dim bulb! Even good conductors can have weak currents that struggle to light it up. Imagine a slow-moving traffic jam.
• Magnetic Needle Tester: This nifty tool detects even weak currents by deflecting a compass needle. Think of it as a current detector that senses the faintest rumble on the highway.
• Activity 11.3: Join Wires, Observe Needle: Connect the wires and watch the needle dance! Repeat Activity 11.2 with this tester to identify conductors even with weak currents.
• LEDs: Super Sensitive Glow: For the faintest electric whispers, use LEDs! They glow even with minimal flow, like fireflies flitting through the darkness.

Distilled Water and Chemical Effects:

• Pure and Poor: Pure, distilled water lacks electrolytes and is a poor conductor, like a lonely, empty highway.
• Adding Salt, Triggering Changes: Adding salt creates a traffic jam of ions, making distilled water conductive. This unlocks the door to exciting chemical reactions caused by electricity!

Chemical Effects of Electric Current:

• Beyond Heating: Remember the heating effect from Class VII? Now, explore the magic of:
  • Gas Bubbles: Watch for bubbly activity near the electrodes, like tiny cars popping up on the highway.
  • Metal Deposits: Witness new metal layers forming on the electrodes, like fresh paint on the road.
  • Solution Color Changes: The solution might change color, like adding a splash of paint to the highway scenery.
• Activity 11.6: Salted Water Bubbles: Pass current through salty water with carbon rod electrodes. Be patient, the bubbly traffic jam takes 3-4 minutes to build!

Electroplating: The Magic of Coating Metals:

• Shiny Reimagined: Electroplating coats metals with other metals for a dazzling makeover! Think of it as adding a new layer of paint to your bike that’s also super protective.
• Real-world Wonders: From the chrome shine of your bike to the gold on your jewelry, electroplating is everywhere! It even coats food cans and protects bridges from rust.
• Activity 11.7: Copper Transformation: Immerse copper plates in copper sulphate solution and connect them to a battery. Watch in awe as new copper deposits magically appear on the negative plate!

Benefits and Concerns of Electroplating:

• A Boon for Industries: Electroplating revolutionizes various industries by adding functionality, beauty, and protection to metals. Imagine a world without shiny car parts or rust-proof bridges!
• Environmental Responsibility: Remember, used solutions can harm the environment. Dispose of them carefully, like responsible drivers on the highway of sustainability!

Bonus Points:

• Air can conduct electricity under special circumstances, like during lightning strikes. Imagine a temporary highway formed by charged particles in the air!
• Most liquids can conduct electricity to some degree, not just “conductors”

“The passage of an electric current through a solution can cause a variety of chemical changes, known as electrolysis. These changes can include the decomposition of the solution into its constituent ions, the formation of new compounds, and the deposition of metals onto electrodes.”