Specification Point 3.18:
Describe reversible reactions such as the dehydration of Hydrated Copper (ii) Sulfate and the effect of heat on Ammonium Chloride

Dehydration of Hydrated Copper (II) Sulfate

Dehydration of Hydrated Copper (II) Sulfate, CIE IGCSE Chemistry

The dehydration of Hydrated Copper (II) Sulfate


When anhydrous copper (II) sulfate crystals are added with water they turn blue and heat is given off, this reaction is reversible:

When Copper (II) Sulfate crystals are heated in a test tube, the blue crystals turn into a white powder and a clear, colourless liquid (water) collects at the top of the test tube.

The form of Copper (II) Sulfate in the crystals is known as Hydrated Copper (II) Sulfate because it contains water of crystallisation.

When Hydrated Copper (II) Sulfate is heated, it loses its water of crystallisation and turns into anhydrous Copper (II) Sulfate:

CuSO4.5H2O (s)             CuSO4 (s)      +      5H2O (l)

Effect of heat on Ammonium Chloride

Thermal decomposition of Ammonium Chloride, Edexcel IGCSE Chemistry

The thermal decomposition of Ammonium Chloride


If Ammonium Chloride is heated in a test tube, the white crystals disappear from the bottom of the tube and reappear further up. In between there is a colourless gas.

Heating Ammonium Chloride decomposes it into the colourless gases Ammonia, NH3, and Hydrogen Chloride, HCl:

CNH4Cl (s)                  NH3 (g)      +      HCl (g)

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Author: Jamie

Jamie got a First class degree in Chemistry from Oxford University before going on to teach chemistry full time as a professional tutor. He’s put together these handy revision notes to match the Edexcel IGCSE Chemistry specification so you can learn exactly what you need to know for your exams.