Chapter 14: Chemical Effects of Electric Current
विद्युत धारा के रासायनिक प्रभाव (विद्युत लेपन, एलईडी, इलेक्ट्रोलाइट, आसुत जल बनाम नल का जल)
Don't Let a 20-Minute Bubbling Delay Cost You CTET Qualification
In offline CTET exams, bubbling 150 bubbles takes 18 to 22 minutes of mechanical time. A single misaligned row can trigger an 8-question domino error. Practice bubble-filling this chapter's solved MCQs inside Mentora's official OMR simulator.
- Electrical Conductivity in Liquids:
- - Good Conductors: Liquids that contain free mobile ions — Tap water (contains dissolved mineral salts), Lemon juice, Vinegar, Salt solution, dilute Hydrochloric acid, Sodium hydroxide solution.
- - Poor Conductors / Insulators: Liquids lacking free ions — Pure Distilled Water, Sugar solution, Honey, Vegetable cooking oil, Kerosene, Alcohol.
- Testing Weak Currents: Ordinary torch bulb filament may not glow with weak current because heat is insufficient to make filament white hot. A Light Emitting Diode (LED) glows even with minute electric currents. An LED has two lead wires: the LONGER lead is connected to positive terminal (+), the SHORTER lead to negative terminal (-). A magnetic compass needle wrapped with wire also detects minute current via magnetic deflection.
- Chemical Effects of Electric Current (Electrolysis):
- - In 1800, British chemist William Nicholson demonstrated that passing electric current through water produces gas bubbles at electrodes:
- * OXYGEN gas bubbles form at the POSITIVE electrode (Anode).
- * HYDROGEN gas bubbles form at the NEGATIVE electrode (Cathode).
- Electroplating (विद्युत लेपन): The deposition of a thin protective layer of a desired metal over another conducting material using electrolysis.
- - Industrial Applications of Electroplating:
- * Chromium plating: Applied to bicycle handlebars, car bumpers, bathroom taps, wheel rims for shiny lustre, corrosion resistance, and scratch resistance (Chromium is expensive, so core is cheap iron).
- * Zinc plating (Galvanization): Coated on iron sheets and bridges to shield against rust.
- * Gold/Silver electroplating: Thin film electroplated onto cheap base metals (copper, brass) to produce inexpensive artificial jewelry.
- * Tin plating: Coated onto iron cans used for storing food, because tin is significantly less reactive than iron, preventing food spoilage.
- Trap: Does pure distilled water conduct electricity? Correct: NO. Pure distilled water is a POOR CONDUCTOR. It becomes conducting only when common salt, acid, or base is added to it.
- Trap: In water electrolysis, which gas collects at the positive electrode (anode)? Correct: OXYGEN ($O_2$), while Hydrogen ($H_2$) collects at negative cathode.
- Trap: Which terminal of an LED is connected to the positive battery terminal? Correct: THE LONGER LEAD is positive (+).
NCERT Core Facts: Electrolysis & Industrial Electroplating
Liquid conductivity and electroplating mechanisms are frequent CTET Paper 2 questions:
1. Liquid Electrical Conductivity Spectrum
| Liquid Tested | Conductivity Status | Underlying Biochemical Reason |
|---|---|---|
| Pure Distilled Water | Poor Conductor (Insulator) | Complete absence of free dissociated mineral ions |
| Tap / Well / River Water | Good Conductor | Contains natural dissolved mineral salts (Na^+, Cl^-, Ca^2+) |
| Lemon Juice / Vinegar | Good Conductor | Organic acids release free hydronium (H^+) ions |
| Sugar Solution | Poor Conductor | Molecular covalent solute; zero ion dissociation |
| Mustard Oil / Alcohol | Poor Conductor | Non-polar covalent organic liquids; no mobile charges |
2. High-Yield Industrial Electroplating Applications
[ Electroplating Objectives & Coatings ]
│
├──> Chromium (क्रोमियम) ── Shiny, scratch-resistant; taps, bicycle rims
├──> Tin (टिन) ── Less reactive than iron; food storage cans
├──> Zinc (जिंक) ── Prevents rusting; automobile chassis & bridges
└──> Gold / Silver ── Decorative artificial jewelry on copper/brassTest Your Mastery: Chemical Effects of Electric Current
Authentic CBSE exam questions tested directly from this NCERT chapter.
When electric current is passed through acidified water using carbon electrodes, gas bubbles evolve at both terminals. Which gas forms at the positive electrode (anode)?
जब कार्बन इलेक्ट्रोड का उपयोग करके अम्लीय जल से विद्युत धारा प्रवाहित की जाती है, तो दोनों टर्मिनलों पर गैस के बुलबुले निकलते हैं। धन इलेक्ट्रोड (एनोड) पर कौन-सी गैस बनती है?
Which of the following liquids will NOT conduct electricity when tested with a standard LED conduction tester?
निम्नलिखित में से कौन-सा द्रव मानक एलईडी चालकता परीक्षक से परीक्षण करने पर विद्युत का संचालन नहीं करेगा?
How can pure distilled water be made electrically conductive in a laboratory?
By adding a pinch of common salt (NaCl), a few drops of lemon juice/acid, or a small amount of caustic soda (base), which release free ions into the water.
Why is tin plated on iron cans used for storing cooking oil and food items?
Tin is much less chemically reactive than iron. Plating prevents food from coming into direct contact with iron, preventing contamination and spoilage.