(a(i))[2]
Fill in Table 4.1 with the formula of the cobalt-containing species formed in each of the three reactions described.
(a(ii))[1]
Describe the colour change observed in reaction 3. State the original colour of $[\text{Co(H}_2\text{O)}_6]^{2+}(aq)$ and the final colour after excess concentrated $\text{HCl}(aq)$ is added.
(b(i))[1]
Write an equation for the thermal decomposition of $\text{Ca(NO}_3)_2$.
(b(ii))[3]
Suggest temperatures at which $\text{Mg(NO}_3)_2$ and $\text{Ba(NO}_3)_2$ start to decompose. Explain your answer.