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Crystals of Salts

what is water...

Question

what is water of crystallization? write the common name and chemical formula of a commercially important compound which has ten water molecules a s water of crystallization. how is this compound obtained? write the chemical equation also. list any two uses of this compound.

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Solution

Water of crystallisation is the number of water molecules that are bound to the crystalline form of the salt in stoichiometric proportion.
Compound with 10 water molecules as water of crystallisation:
Common names- Washing soda, soda ash, soda crystals.
Chemical formula: Na₂CO₃.10H₂O
Chemical name- Sodium carbonate decahydrate

It is obtained commercially by Solvay process-
Chemical equation:
2NaCl + CaCO₃ $\to$ Na₂CO₃ + CaCl₂

Uses:
It is used for softening of hard water.
It is used for washing purposes in laundry.
It is used for paints and dye stuffs.
It is used for metal refining.

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Q. A compound which is prepared from gypsum has the property of hardening when mixed with a proper quantity of water. Identify the compound and write its chemical formula. Write the chemical equation for its preparation. Mention any one use of the compound.

Q. Copper sulphate crystals which seem to be dry contain water of crystallization. When we heat the crystals, this water is removed and the salt turns white. If you moisten the crystals again with water, you will find that blue colour of the crystals reappears.

The water of crystallization is the fixed number of water molecules present in one formula unit of a salt. Five water molecules are present in one formula unit of copper sulphate. The chemical formula for hydrated copper sulphate is

C u {S O}_{4}

5 H_{2} O

. Now you would be able to answer the question whether the molecule of

{N a}_{2} {C O}_{3}

10 H_{2} O

is wet. One other salt, which possesses water of crystallization is gypsum. It has two water molecules as a water of crystallization. It has the formula

C a {S O}_{4}

2 H_{2} O

What are the uses of this salt?

Q. An organic compound 'A' is widely used as a preservative in pickles and has a molecular formula C₂H₄O₂. This compound reacts with ethanol to form a sweet smelling compound 'B'.
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(ii) Write the chemical equation for its reaction with ethanol to form compound 'B'.
(iii) How can we get compound 'A' back from 'B'?
(iv) Name the process and write corresponding chemical equation.
(v) Which gas is produced when compound 'A' reacts with washing soda? Write the chemical equation.

Q. (a) The blue colour of crystals of a substance changed on heating in a closed test tube but the colour was regained after sometime on cooling. Name the substance and write its chemical formula. Explain the phenomenon involved.

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Q. (a) Name the compound which is obtained from baking soda and is used to remove permanent hardness of water.
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