An unknown solid gives water droplets and changes colour on heating. Its colour returns after adding water. This indicates the presence of what?
Answer and explanation
Correct answer: Water of crystallisation
Water of crystallisation is a definite number of water molecules incorporated into the crystal structure of some salts. Heating can remove this water, producing a colour change and sometimes visible moisture; adding water may restore the hydrated form and its original colour. Hydrated copper sulphate is a standard example. Common salt does not explain this reversible colour change, and oxygen or chlorine gas are not crystal water. Hence A is correct.
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What is the correct answer to this question?
Water of crystallisation
Why is this the correct answer?
Water of crystallisation is a definite number of water molecules incorporated into the crystal structure of some salts. Heating can remove this water, producing a colour change and sometimes visible moisture; adding water may restore the hydrated form and its original colour. Hydrated copper sulphate is a standard example. Common salt does not explain this reversible colour change, and oxygen or chlorine gas are not crystal water. Hence A is correct.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
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