Chemical Effects of Electric Current
Overview
Electricity in water? Yes — some liquids allow current to pass through them and also cause chemical changes — this is how chrome and gold coatings are applied on objects (electroplating). Let us find out more.
Typed Notes
Which liquid conducts electricity
Liquids conduct electricity when they contain ions (charged particles): (1) Acids — lemon juice, vinegar; (2) Bases — lime water; (3) Salts — salt water, CuSO4. These are called electrolytes. Pure water (distilled) — poor conductor (no ions present) — add salt (not sugar — sugar forms molecules, not ions) — it will conduct. Seawater — contains salt — conducts. Oil and kerosene — do not conduct (molecules only, no ions). Test: connect an LED in a circuit — dip electrodes into the solution — if the LED glows, the liquid is a conductor. LED — glows even with very low current — and is safer (better than using a bulb).
Chemical effects — bubbles and deposits
When current passes through a liquid — chemical changes occur: (1) Bubbles appear at the electrodes (carbon or metal plates) — water undergoes electrolysis, releasing H2 and O2 gas (2 parts H2, 1 part O2); (2) Metal gets deposited — when current passes through a CuSO4 solution, copper is deposited on the cathode; (3) Colour of the solution changes. This means current does not only produce heat and light — it can also drive chemical reactions. This is called the 'chemical effect of electric current'.
Electroplating — giving a cheap object the look of an expensive one
Depositing a thin layer of one metal on another metal is called electroplating. Setup: electrolyte (a salt solution of the metal to be deposited) + anode (plate of that metal — connected to +ve terminal) + cathode (the object to be coated — connected to −ve terminal). When current flows — metal from the anode dissolves into ions — and gets deposited on the cathode. Example: copper plating on an iron key: CuSO4 solution, anode = copper plate, cathode = iron key — after 20–30 minutes — a golden-brown copper layer forms on the key. Chromium is plated on taps and bicycles (shine + rust-proof), tin on iron (tin can — safe for food — tin does not rust), gold/silver on cheap ornaments (expensive appearance at low cost), silver on cutlery.
Precautions — waste and safety
Electroplating involves chemicals (cyanides, acids) — the waste water is harmful — if it enters rivers and lakes it causes damage — treatment is necessary. Safety: (1) never touch water with wet hands when electricity is involved (wet hands — risk of electric shock); (2) In electroplating labs, acids are used — wear goggles and gloves; (3) Use an LED (safe), avoid high voltage. Also remember: the current test fails with pure water — so 'distilled water is not a conductor' is a favourite exam question.
Key Concepts
Revision ke liye ek nazar — exam se pehle yahi padhna hai.
- 01Liquids can also be conductors: solutions of acids, bases, and salts (lemon water, salt water, vinegar, soda) — conduct electricity; pure water — poor conductor; distilled water — does not conduct.
- 02Test: place the solution in a circuit with an LED or bulb — if it glows, the liquid is a conductor. LED — works even with very low current (safer to use).
- 03Chemical effects: current causes changes in the solution — bubbles appear at the electrodes (H2, O2), metal gets deposited, colour changes.
- 04Electrolysis: current breaks down a compound (water → H2 + O2). Electroplating: a thin layer of one metal is deposited on another — copper on iron (CuSO4 solution, copper anode, key as cathode).
- 05Uses: chromium on taps and bumpers (shine + rust-proof), tin on iron (tin can — for food), gold/silver on ornaments (expensive look at low cost), aluminium (anodising). Pure water — not a conductor — that is why the test fails with distilled water.
Questions & Solutions
Pehle khud try karo — phir solution kholo. Yahi tariqa topper banata hai.
Which liquids conduct electric current? Give two examples.
Why is testing with an LED better than using a bulb?
What is electrolysis of water? What is produced?
How does electroplating work? Give the example of copper plating on an iron key.
Why is tin plated on a tin can (food container)?
Why is the waste from an electroplating factory dangerous?
Solutions of acids, bases, and salts conduct electricity (electrolytes); pure/distilled water is a poor conductor; oil does not conduct. Test: LED circuit. Chemical effects: bubbles (H2/O2 — electrolysis), metal deposit (Cu on cathode). Electroplating: metal from anode → deposited on cathode object (chromium, tin, gold) — provides shine and rust-proofing. Proper waste treatment is essential.
Chapter-end quiz
4 MCQsOption tap karo — turant pata chalega sahi ya galat, explanation ke saath.
Q1.Pure (distilled) water — how does it behave with electric current?
Q2.What is the cathode in electroplating?
Q3.Which metal is coated on iron in a tin can?
Q4.What is produced at the cathode during electrolysis of water?
Mark karo — dashboard par progress dikhega.