(a) What is meant by “water of crystallisation” in a substance? Explain with an example.
(b) How would you show that blue copper sulphate crystals contain water of crystallisation?
(c) Explain how anhydrous copper sulphate can be used to detect the presence of moisture (water) in a liquid.
(a) The water molecules that form part of the structure of a crystal of salt is known as the water of crystallisation. For example, washing soda crystals contains 10 molecules of water of crystallisation (Na2CO3.10H2O).
(b) Copper sulphate crystals (CuSO4.5H2O) are blue in colour. On heating, it loses water of crystallization and becomes white in colour. Thus, we can conclude that the blue colour of copper sulphate crystals is due to the water of crystallization
(c) Anhydrous copper sulphate can be used to detect the presence of moisture (water) in a liquid by taking a drop of the liquid which to be tested and add it to white anhydrous copper sulphate powder. The blue colour indicates the presence of moisture.
Related Articles
- (a) What happens when copper sulphate crystals are heated strongly? Explain with the help of an example.(b) What happens when a few drops of water are added to anhydrous copper sulphate? Explain with the help of an equation.
- How many molecules of water of crystallisation (per formula unit) are present in :(a) copper sulphate crystals ? (b) washing soda? (c) gypsum ?
- State whether the following statement is true or false:Copper sulphate crystals are always wet due to the presence of water of crystallisation in them.
- Pure copper sulphate can be obtained from an impure sample by the process of :(a) evaporation (b) fractional distillation(c) centrifugation (d) crystallisation
- Explain how, impure copper sulphate can be purified by crystallization.
- When a crystal of copper sulphate is placed at the bottom of a beaker containing water, the water slowly turns blue. Why?
- Write the name and formula of one salt each which contains:(a)Two molecules of water of crystallisation (b)Five molecules of water of crystallisation (c)Ten molecules of water of crystallisation.
- Describe how crystals of copper sulphate are prepared?
- Which of the following salts does not contain water of crystallisation?Blue vitriolBaking sodaWashing sodaGypsum
- The number of molecules of water of crystallisation present in washing soda crystals is:(a) Five (b) Two (c) Ten (d) Seven
- Which single term is used to describe the mixing of copper sulphate and water kept in a beaker, on its own?
- Write word equations for two chemical reactions with the help of materials given in the box.[ Air, copper sulphate, iron, vinegar, iron oxide, carbon dioxide, iron sulphate, copper, lime water, water ]
- Which of the following reactions will not occur? Why not?(a) Zinc Sulphate + Copper âž Copper Sulphate + Zinc(b) Copper Sulphate + Iron âž Iron Sulphate + Copper
- (a) Define solubility of a substance. How does it vary with temperature?(b) What do you understand by the statement the solubility of copper sulphate in water at 20°C is 20.7 g"?(c) What is the effect of temperature on the solubility of solids in liquids?"
- How many molecules of water are present in hydrated copper sulphate? What color change can we observe upon its heating?
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