Is calcium hydroxide an alkali or an insoluble base? The book says it's an alkali (soluble in water) but when NaOH reacts with Calcium Nitrate, we get insoluble ppt. of Calcium hydroxide (insoluble in water). What is correct?

An alkali is a basic hydroxide or ionic salt of an alkali metal or alkaline earth metal element,which is soluble in water.
Only few alkalis are known, examples, sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2).

Calcium hydroxide, Ca(OH)₂, is sparsely soluble in water. Limewater is the common name for a diluted solution of calcium hydroxide . Pure limewater is clear and colorless, with a slight earthy smell and an alkaline bitter taste of calcium hydroxide. When excess calcium hydroxide is added to limewater, a suspension of calcium hydroxide particles results, giving it a milky aspect.

if more calcium hydroxide are added or present , then it will be precipitated and present as insolube in water. this is the reason why in the above case .

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