A blue colour salt becomes white on heating. Give reason for the above observation. Whathappens when we add water to the salt which is obtained after heating ? Also write its formula.

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Solution

According to the question, salt is obtained upon heating suggesting that blue colour salt has lost its water of crystallisation. There is no other reaction that has taken place. This salt is coloured due to the water of crystallisation. When it is heated, water is lost and anhydrous salt is obtained which is white in colour. Most probable salt is copper sulphate which become white when heated.
CuSO₄.5H₂O $\overset{h e a t}{\to}$ CuSO₄ + 5H₂O
Again when water is added to the anhydrous salt and is heated. Same blue colour salt is formed.

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Similar questions

When we heat a coloured salt, it turns into white coloured __________ salt.

_{A drop of water is poured over a white powdery substance. Then it is observed that the substance turns blue. Answer the following questions :}

_{(i) What is the white powdery substance?}

_{(ii) Why does the substance change to blue colour?}

_{(iii) Write the chemical formula of the blue substance .}

_{(iv) Is the blue substance an acidic salt or a basic salt?}

_{(v) Give a reason for your answer in (iv).}

Y C u {S O}_{4} \cdot X H_{2} O

= 500

= 320

X

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