Why is calcium hydroxide used in excess in the lab preparation of ammonia?

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NH3 i.e, ammonia has high affinity towards water and is soluble in water. Calcium hydroxide gets converted to calcium oxide which absorbs moisture and helps in extracting ammonia in its dried form.
 
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It is possible because it may produce hydrogen gas
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NH3 gas has high affinity to react with water to dissolve.
CaO(calcium oxide) is used to absorb water from the laboratory.
CaO+H2O -> Ca(OH)2
Ca(OH)2 (Calcium hydroxide) is the by-product of the reaction, not Ca(OH)2 is used.
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Sodium hydroxide is a soluble hydroxide, so it is not preferably used in the preparation of ammonia, as it will get dissolved in the reacting mixture itself and not form the required product.
Calcium hydroxide being insoluble, reacts with ammonium chloride to form ammonia according to the reaction.
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