EDEXCEL IGCSE CHEMISTRY: DOUBLE SCIENCE 复习笔记:2.7.5 Tests for Water

EDEXCEL IGCSE CHEMISTRY: DOUBLE SCIENCE 复习笔记:2.7.5 Tests for Water

Tests for Water

 

  • Water can be identified using a chemical test and/or a physical test

 

Chemical test for water

  • Anhydrous copper(II) sulfate turns from white to blue on the addition of water
  • The equation is:

 

CuSO(s) + 5H2O (l) → CuSO4.5H2O (s)

Copper-Sulfate-Crystals

Copper sulfate turns a light blue colour in the presence of water

Physical test for water

  • A physical test to see if a sample of water is pure is to check its boiling point
  • A sample of the liquid is placed in a suitable container such as a boiling tube and gently heated
  • Using a thermometer, you can check if the boiling point is exactly 100 oC
  • Any impurities present will usually tend to raise the boiling point and depress the melting point of pure substance

 

Exam Tip

A lot of students are tempted to say you can identify water because it has no taste or smell. While this may be true, it would be extremely hazardous to taste anything in the lab and water is not the only colourless liquid to have no taste or smell!

转载自savemyexams

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