Chemistry 9701 · AS & A Level · Group 2

Group 2 — practice question

Magnesium nitrate, $\text{Mg(NO}_3)_2$, dissolves very readily in water. If a hot saturated solution of magnesium nitrate is allowed to cool, crystals of the hydrate, $\text{Mg(NO}_3)_2\cdot6\text{H}_2\text{O}$, are produced. Inside the crystals, six water molecules are attached to each $\text{Mg}^{2+}$ ion, and some of these water molecules are also linked to the nitrate ions.
(a(i))[2]

Suggest the type of bonding present between $\text{H}_2\text{O}$ and $\text{Mg}^{2+}$, and also between $\text{H}_2\text{O}$ and $\text{NO}_3^-$.

(a(ii))[1]

Describe how the water molecules are positioned around the $\text{Mg}^{2+}$ ion.

(a(iii))[4]

Describe in detail what you would observe when crystals of $\text{Mg(NO}_3)_2\cdot6\text{H}_2\text{O}$ are heated in a boiling tube, first gently and then more strongly. Write equations for any reactions that take place.

(a(iv))[2]

Calculate the percentage decrease in mass when $\text{Mg(NO}_3)_2\cdot6\text{H}_2\text{O}$ is heated strongly to constant mass.

(b)[2]

Explain why the Group 2 nitrates become more thermally stable down the group.

(c)[1]

Magnesium nitrate and silver nitrate, $\text{AgNO}_3$, break down on heating to give the same gases. Silver nitrate also forms silver metal during decomposition. Write an equation for the decomposition of $\text{AgNO}_3$.

Worked solution & mark scheme

This 12-mark question has a full step-by-step worked solution and mark scheme. One marking point: Coordinate bond or dative (covalent) bond

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