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UPPCS Chemistry Gap Sheet: Water, Mixtures and Cleaning.

UPPCS has asked 16 of these. 3 have not been asked yet. Lock the first list, then read the second: it holds what UPPCS has not used yet.

First, the concept

Solutions have molecular-sized dissolved particles. Colloids have larger dispersed particles that scatter light; suspensions have still larger particles that can settle. Milk is an emulsion of fat dispersed in water.

Hard water contains calcium and magnesium ions that interfere with soap. Boiling removes temporary hardness, not every type. Detergents work by lowering surface tension and surrounding oily dirt with micelles.

✅ Already asked (16)

Changes and mixtures

  • Physical change · No new chemical substance; water becoming vapour is an example.
  • Chemical change · New substances form; iron rusting is an example.
  • Sublimation · Direct solid-to-gas change; examples include dry ice and naphthalene.
  • Homogeneous solution · Uniform composition throughout; dissolved salt in water is an example.
  • Milk emulsion · Liquid fat droplets dispersed in a water-based phase.
  • Osmosis · Solvent moves through a semipermeable membrane toward lower solvent activity.
  • Diffusion · Particles spread from higher toward lower concentration.
  • Catalyst · Speeds approach to equilibrium without changing the equilibrium position; not consumed overall.

Hardness and treatment

  • Temporary hardness · Mainly calcium and magnesium bicarbonates; removable by boiling.
  • Permanent hardness · Often calcium and magnesium sulphates or chlorides; boiling alone does not remove it.
  • Distillation · Evaporation followed by condensation separates water from non-volatile dissolved salts.
  • Reverse osmosis · Applied pressure drives water through a membrane for desalination.
  • Dissolved oxygen · Low dissolved oxygen can signal poor water quality.

Cleaning chemistry

  • Soap · Sodium or potassium salts of long-chain fatty acids.
  • Soap scum · Insoluble calcium and magnesium salts of fatty acids in hard water.
  • Detergent action · Lowers surface tension; many detergents work in hard water.

❌ Not asked yet (3)

Items marked 'asked in other exams' have come in UPSC or other state exams, not yet in UPPCS.

🔒 3 items not asked yet

Changes and mixtures: 1 · Hardness and treatment: 1 · Cleaning chemistry: 1

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⚠️ Ordinary filtration does not remove dissolved salts; detergent lowers, rather than raises, surface tension.

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