Question

Sodium hydroxide is an ionic compound and contain hydroxide ions , then why it does not change the colour of red litmus paper to blue in solid state ?

Answer 1

in solid state it is neutral state and do not react with litmus paper

Answer 2

Because it does not hydroxide ions in solid state. It is a neutral compound in solid state therefore does not change the colour of red litmus in to blue. But in sodium hydroxide dissociates into sodium ion and hydroxide ion therefore it acts as base andturns red litmus blue in aqueous state.