2.1.10

Purity of Substances

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Melting and Boiling in Pure Substances

Pure substances melt or boil at sharp temperatures. Mixtures melt or boil over a range of temperatures. Graphs can be used to see this.

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Pure substances

  • Pure substances melt or boil at sharp temperatures.
    • E.g. Water boils at 100°C.
  • Graphs can be used to see that melting and boiling happens at sharp points.
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Mixtures

  • Mixtures melt or boil over a range of temperatures.
    • For example, salt in water (salt solution) boils between 90 and 110°C.
  • Graphs can be used to see that melting and boiling happen over a range of temperatures.
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Chemically pure

  • We describe things as being ‘pure’ in our everyday lives.
  • For example, you might buy ‘pure orange juice’. Here, pure means that nothing else was added to the orange juice when it was made.
  • But when we talk about pure substances in chemistry, we mean substances that contain only one element or compound.
  • If a substance contains 'impurities', it does not contain only one element or compound.

Jump to other topics

1Biology

1.1Cells, Tissues & Organs

1.2Reproduction & Variation

1.3Ecological Relationships & Classification

1.4Digestion & Nutrition

1.5Plants & Photosynthesis

1.6Biological Systems & Processes

2Chemistry

2.1Particles

2.2Chemical Reactions

2.3Atoms, Elements, Compounds

2.4The Periodic Table

2.5Materials & the Earth

2.6Reactivity

2.7Energetics

2.8Properties of Materials

3Physics

3.1Energy

3.2Forces & Motion

3.3Waves

3.4Electricity & Magnetism

3.5Matter

3.6Space Physics

4Thinking Scientifically

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