CAIE IGCSE Chemistry 6.3.2 Changing the Conditions Can Change the Questions

Explain how heating hydrated salts removes water and how adding water restores the hydrated form, using characteristic colour changes as evidence.

Exam points

use heating to remove water from a hydrated salt and form its anhydrous colour
add water to an anhydrous salt to restore the hydrated form and reverse the change
identify blue-to-white copper sulfate and pink-to-blue cobalt chloride changes
complete equations for reversible hydration and dehydration of salts

[Maximum number: 2]

Complete the equation for the thermal decomposition of hydrated cobalt(II) nitrate.

2 \mathrm{Co}\left(\mathrm{NO}_{3}\right)_{2} \bullet 4 \mathrm{H}_{2} \mathrm{O} \rightarrow \ldots . \mathrm{CoO}+\ldots . \mathrm{NO}_{2}+\mathrm{O}_{2}+\ldots . \mathrm{H}_{2} \mathrm{O}

$\text { M1 2CoO + 4 } \mathrm{NO}_{2}(1)$

M2 $8 \mathrm{H}_{2} \mathrm{O}$ (1)

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