GCSE C2 Science

C2 - Chemisty, Science.

OCR Gateway B.

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Paints and Pigments

Paint contains:

  • Pigment - gives the paint its colour
  • Binding medium - liquid that carries the pigment bites and holds them together. When it turns to solid, it sticks the pigments to the surface you've painted.
  • Solvent - keeps the binding medium and the pigment runny - as a liquid in a tin or paste in a tube.

Paints are colloids:- a colloid consists of really small particles of one kind dispersed into a another kind.

The particles can be bits of solid, droplets of liquid or bubbles of gas.

Colloids don't separate because the particles are so small.

Emulsion paints > water based. The solvent is water, binding medium is a polymer such as acrylic.

Gloss paints > oil based. Binding material is oil, the solvent is an organic compound such as turpentine.

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Paints and Pigments

Some solvents in oil based paints produce fumes that can be harmful so there has to be plenty of ventilation.

Water based emulsion > solvent evaporates leaving behind the binder and pigment. It dries quite quickly.

Oil based > take longer to dry because the oil has to be oxidised by oxygen in the air before it turns solid.

To paint the outside part of a door:

  • Waterproof
  • Hard wearing
  • So it would be oil-based gloss.

To paint bedroom walls:

  • Goes on easily
  • Dries quickly
  • Doesn't produce harmful fumes
  • So it would be water-based emulsion
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Dyes and Special Pigments


  • Used to colour fabrics
  • Originally, people made dyes from plants by grinding the plant with water or another solvent and draining the liquid. Example, indigo dye comes from a plant.
  • Over the past hundred years, people have invented a lot of synthetic dyes.

Thermochromic Pigments.

  • Change colour or become transparent when heated or cooled.
  • Different pigments change colour at different temperature.
  • Used in novelty drinking mugs, safety signs, clothing.

Phosphorescent Pigments.

  • Glow in the dark.
  • Absorb light/artificial light and store the energy in molecules. This energy is released as light over a period of time.
  • Used in clocks, novelty decorations.
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Construction Materials

Aluminium and Iron are extracted from ores in rocks.

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Paints and Pigments is now in C1, not in C2

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