Chemical Effects of Electric Current
This chapter shows that many liquids conduct electricity and that the current passing through a conducting solution drives chemical changes, the most useful of which is electroplating.
Basic-science chapters like this feed Prelims directly through statement-based and match-the-following questions on conductivity, electrolysis, electroplating and galvanization. For Mains it sits in GS-III Science & Technology fundamentals, and the disposal of polluting electroplating effluent links to GS-III environment (hazardous/industrial waste). The everyday-science framing (why wet hands + electricity is dangerous) also supports scientific-temper and safety arguments.
Understand the chapter
Do Liquids Conduct Electricity?
Conductivity is tested with a simple tester: a cell/battery, wires and a bulb forming a circuit completed by the test material. If the liquid lets current pass, the circuit completes and the bulb glows. Metals like copper and aluminium conduct in the solid state; the chapter extends the question to liquids and finds some do conduct.
- Good conductor: allows electric current to pass easily (bulb glows).
- Poor conductor: does not allow current to pass easily (bulb stays off).
- A weak current may complete the circuit yet be too feeble to heat the bulb's filament to glowing.
Detecting Weak Currents: LED and the Magnetic-Effect Tester
A bulb relies on the heating effect, so weak currents may not make it glow even when the liquid is conducting. Two fixes detect weak current: an LED (glows at very low current) and a tester using the magnetic effect, where a current-carrying wire deflects a nearby compass needle. The compass tester reveals conduction the bulb would miss.
- LED: longer lead to positive terminal, shorter lead to negative terminal.
- Magnetic-effect tester: even a small current deflects the compass needle.
- Lemon juice/vinegar may not glow the bulb but will deflect the needle.
Good vs Poor Conductors — Why the Reclassification
Distilled water is salt-free and is a poor conductor; dissolving common salt makes it conduct. Tap, well and pond water carry dissolved mineral salts naturally, making them good conductors — which is why wet hands or wet floors make electrical appliances dangerous. Because most materials conduct under some conditions (even air conducts during lightning), the chapter prefers 'good/poor conductor' over the absolute terms 'conductor/insulator'.
- Most conducting liquids are solutions of acids, bases and salts.
- Sugar solution does not conduct; salt/acid/base solutions do.
- Air is a poor conductor but conducts during lightning — 'poor' is conditional, not absolute.
Chemical Effects of Electric Current
When current flows through a conducting solution it triggers chemical reactions whose effects depend on the solution and electrodes used. In 1800 British chemist William Nicholson passed current through water and obtained gas bubbles: oxygen at the electrode joined to the positive terminal and hydrogen at the other. The potato experiment shows a greenish-blue spot forming only around the wire at the positive terminal — a way to identify a hidden cell's positive terminal.
- Possible effects: gas bubbles on electrodes, metal deposits, change of solution colour.
- Oxygen forms at the positive electrode; hydrogen at the negative.
- Greenish-blue mark on potato marks the positive terminal.
Electroplating — The Process
Electroplating is depositing a layer of a desired metal on another material using electricity — a key application of the chemical effect of current. Using copper sulphate solution (made more conducting with dilute sulphuric acid) and copper plates, the solution dissociates into copper and sulphate. Free copper is drawn to the negative electrode and deposits there, while an equal amount of copper dissolves from the other plate, so copper is effectively transferred electrode-to-electrode.
- Copper deposits on the electrode at the negative terminal (cathode).
- Copper dissolves from the positive plate, replenishing the solution.
- Dilute acid is added to make the solution more conducting.
Electroplating — Applications and Environmental Angle
Electroplating gives a cheap base metal a thin layer with a property it lacks. Chromium (shiny, corrosion- and scratch-resistant) plates car parts, taps and handlebars; gold/silver are plated onto cheaper metals for jewellery; tin (less reactive) is plated on iron for food cans; and zinc is coated on iron to resist rust (galvanization). The used conducting solution is a polluting waste with specific disposal guidelines to protect the environment.
- Chromium: appearance + corrosion/scratch resistance at low cost.
- Tin cans: tin less reactive than iron, keeps food from spoiling.
- Zinc on iron (galvanization): prevents corrosion and rust.
- Spent plating effluent is hazardous — regulated disposal required.
Key terms
- Good conductor
- A material that allows electric current to pass through it easily.
- Poor conductor
- A material that does not let electric current pass easily; conduction may still occur under certain conditions.
- Electrode
- A rod/plate (e.g., carbon or copper) through which current enters or leaves a conducting solution.
- Electroplating
- Depositing a layer of a desired metal onto another material by means of electric current.
- Electrolysis
- The chemical decomposition of a conducting solution caused by passing electric current through it.
- Conducting solution
- A liquid (usually an acid, base or salt solution) that conducts electricity due to dissolved ions.
- LED
- Light Emitting Diode; glows even at very weak current, with longer lead to the positive terminal.
- Galvanization
- Coating iron with a layer of zinc to protect it from rust and corrosion.
Must-know facts exam-ready
- Most liquids that conduct electricity are solutions of acids, bases and salts.
- Distilled water is a poor conductor (salt-free); tap water is a good conductor due to naturally dissolved mineral salts.
- Chemical effects of current: gas bubbles at electrodes, metal deposits, and colour change of the solution.
- William Nicholson (1800) passed current through water, producing oxygen at the positive electrode and hydrogen at the other.
- Potato test: a greenish-blue spot forms around the wire at the positive terminal, identifying the positive terminal.
- Electroplating is depositing a layer of a desired metal on another material using electricity.
- In copper sulphate electroplating, copper deposits on the negative electrode while equal copper dissolves from the positive plate.
- Chromium plating gives a shiny, corrosion-resistant, scratch-resistant surface (car parts, taps, handlebars).
- Tin cans = tin electroplated onto iron; tin is less reactive and protects food.
- Zinc coated on iron prevents rust and corrosion (galvanization).
- An LED glows even with weak current; its longer lead connects to the positive terminal.
- Used electroplating solution is a polluting waste subject to specific disposal guidelines.
Timeline
- 1800British chemist William Nicholson showed that passing current through water produces oxygen (at the positive electrode) and hydrogen (at the other) — an early demonstration of the chemical effect of c
Memory tricks remember it for good
Traps to avoid
- Distilled water vs tap water: distilled water is a POOR conductor; tap water conducts because of dissolved mineral salts — students often reverse this.
- Use 'good/poor conductor', not 'conductor/insulator' — because most materials (even air during lightning) conduct under certain conditions.
- Nicholson's gases: oxygen is at the POSITIVE electrode, hydrogen at the negative — easy to swap.
- Electroplating copper deposits on the NEGATIVE electrode (cathode); don't confuse with the potato/Nicholson effect noted at the positive terminal.
- Greenish-blue potato spot forms at the POSITIVE terminal, not the negative.
- Tin is LESS reactive than iron (that's why it protects food); the anti-rust coating that uses zinc is galvanization — don't mix the two metals/uses.
Exam focus
🧠 Prelims angles
- Chemical effects of current: identifying gas bubbles, metal deposition and colour change as the three effects.
- Match-the-following on electroplating metals and uses (chromium, tin, zinc/galvanization, gold/silver).
- Conductivity comparison: distilled water vs salt solution vs tap water vs sugar solution.
- Nicholson's electrolysis of water — which gas forms at which terminal.
- Galvanization defined as zinc coating to prevent rusting of iron.
- LED/tester basics: longer lead to positive terminal; weak-current detection.
✍️ Mains angles GS-III
- Electroplating is industrially indispensable yet its effluent is a serious pollutant — discuss.Balance utility (corrosion protection, cost-effective finishing) against heavy-metal/acid waste; tie to hazardous/industrial waste disposal norms and the precautionary principle.
- How do everyday chemical effects of electric current underpin modern industry and scientific temper?Use electrolysis, electroplating and corrosion protection as the base; link to public safety awareness (wet hands + electricity) and foundations for metallurgy and batteries.
Last-minute revision tick as you recall
- Acids, bases, salts solutions conduct; sugar solution and distilled water do not.
- Tap water conducts via dissolved mineral salts — never touch appliances with wet hands/floor.
- Prefer 'good/poor conductor'; most materials conduct under some conditions (air in lightning).
- Three chemical effects: gas bubbles, metal deposit, colour change.
- Nicholson 1800: water gives oxygen at positive, hydrogen at negative electrode.
- Potato test: greenish-blue at positive terminal identifies it.
- Electroplating = depositing a metal layer using electricity.
- Copper sulphate plating: copper deposits on the negative electrode, dissolves from the positive plate.
- Chromium = shine/anti-corrosion, tin = food cans, zinc = galvanization, gold/silver = jewellery; effluent needs regulated disposal.
Distilled from NCERT Class 8 · Science (Class 8) for UPSC. Always cross-check facts with the original NCERT.