How many molecules of water of crystallisation (per formula unit) are present in (a) copper sulphate crystals (b) washing soda (c) gypsum ? [3 marks]

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Solution

(a) Copper Sulphate ( $C u S O_{4} .5 H_{2} O$ ): 5 molecules of water of crystallisation. [1 mark]

(b) Washing soda ( $N a_{2} C O_{3} .10 H_{2} O$ ): 10 molecules of water of crystallisation. [1 mark]

(c) Gypsum ( $C a S O_{4} .2 H_{2} O$ ): 2 molecules of water of crystallisation. [1 mark]

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The number of molecules of water of crystallisation present in washing soda crystals is :

(a) five

(b) two

(d) seven

Q. What is meant by water of crystallisation in a substance? How would you show that blue copper sulphate crystals contain water of crystallisation?

Q. How many molecules of water of crystallisation (per formula unit) are present in:
(a) copper sulphate crystals?
(b) washing soda?
(c) gypsum?

Water of crystallization is the fixed number of water molecules present in the crystal of that salt. The chemical formula of hydrated copper sulphate is CuSO₄.5H₂O i.e., there are five water molecules present in one formula unit of copper sulphate. Therefore, water of crystallization of copper sulphate is 5.

Similarly, there are two water molecules present in one formula unit of gypsum (CaSO₄.2H₂O). Hence, water of crystallization of gypsum is 2.

however in hemihydrated Caso4 is known as POP it has half water of crystalization. Pl explain

Q. The number of molecules of water of crystallisation present in washing soda crystals is:

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How many molecules of water of crystallisation (per formula unit) are present in (a) copper sulphate crystals (b) washing soda (c) gypsum ? [3 marks]

(a) Copper Sulphate (CuSO4.5H2O ): 5 molecules of water of crystallisation. [1 mark] (b) Washing soda (Na2CO3.10H2O ): 10 molecules of water of crystallisation. [1 mark] (c) Gypsum (CaSO4.2H2O): 2 molecules of water of crystallisation. [1 mark]

(a) Copper Sulphate ( $C u S O_{4} .5 H_{2} O$ ): 5 molecules of water of crystallisation. [1 mark]

(b) Washing soda ( $N a_{2} C O_{3} .10 H_{2} O$ ): 10 molecules of water of crystallisation. [1 mark]

(c) Gypsum ( $C a S O_{4} .2 H_{2} O$ ): 2 molecules of water of crystallisation. [1 mark]