[Maximum number: 5]

A Group 2 metal combines with bromine to form a crystalline solid, $\mathrm{MBr}_{2}$ .
Excess aqueous $\mathrm{AgNO}_{3}$ is added to a solution of $\mathrm{MBr}_{2}$ and a precipitate forms. The mixture is filtered. The precipitate is dried and the mass of the precipitate is recorded.

(a)

Separate 1.0 g samples of three different magnesium salts are tested in order to identify the anion present in each sample.

[ 3 ]

(i)

Explain how the action of heat is used to identify which sample is:
- $\mathrm{MgCO}_{3}$
- $\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}$
- MgO .

[ 3 ]

(b)

A sample of $\mathrm{MgCO}_{3}(\mathrm{~s})$ is distinguished from a sample of $\mathrm{Mg}(\mathrm{OH})_{2}(\mathrm{~s})$ by adding a small amount of each solid to HCl(aq).

State one similarity and one difference in these two reactions.
similarity
difference

[ 2 ]

(a)

(i)

State how the solubilities of the hydroxides of the Group 2 elements vary down the group.

[ 1 ]

(b)

Metal peroxides contain the $-\mathrm{O}-\mathrm{O}^{-}$ ion.

The peroxides of the Group 2 elements, $\mathrm{MO}_{2}$ , decompose on heating to produce a single gas and the solid oxide, MO, only.

[ 1 ]

(i)

Write an equation for the thermal decomposition of strontium peroxide, $\mathrm{SrO}_{2}$ .

[ 1 ]

(c)

(i)

The ethanedioates of the Group 2 elements, $\mathrm{MC}_{2} \mathrm{O}_{4}$ , decompose on heating to produce a mixture of two different gases and the solid oxide, MO, only.

Complete the equation for the thermal decomposition of barium ethanedioate.

\mathrm{BaC}_{2} \mathrm{O}_{4} \rightarrow \ldots \ldots \ldots \ldots \ldots \ldots . .+\ldots \ldots \ldots \ldots \ldots \ldots \ldots . .+\ldots \ldots \ldots \ldots \ldots \ldots . .

[ 1 ]

(a)

Hydrated cobalt(II) nitrate, $\mathrm{Co}\left(\mathrm{NO}_{3}\right)_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}$ , is a red solid that behaves like hydrated magnesium nitrate, $\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}$ , when heated.

Describe in detail what you would expect to observe when crystals of $\mathrm{Co}\left(\mathrm{NO}_{3}\right)_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}$ are heated in a boiling tube, gently at first and then more strongly.

[ 2 ]

(a)

Describe what is observed when magnesium and barium are reacted separately with an excess of dilute sulfuric acid.
magnesium
barium

[ 1 ]

(a)

$\mathrm{Zn}\left(\mathrm{NO}_{3}\right)_{2}$ undergoes thermal decomposition when heated. The reaction is similar to the thermal decomposition of Group 2 nitrates.

[ 1 ]

(i)

Construct an equation for the thermal decomposition of $\mathrm{Zn}\left(\mathrm{NO}_{3}\right)_{2}$ .

[ 1 ]

(a)

Group 2 carbonates decompose when heated to form the metal oxide and carbon dioxide.

[ 3 ]

(i)

Describe the variation in the thermal stability of Group 2 carbonates. Explain your answer.

[ 3 ]

(a)

Describe the trend in the solubility of the sulfates of magnesium, calcium and strontium.
Explain your answer. > >
most soluble
least soluble

[ 4 ]

(a)

Group 2 elements share common chemical properties.

[ 7 ]

(i)

Calcium reacts in cold water more quickly than magnesium because more energy is required to remove the outer electrons in magnesium. This occurs even though calcium atoms have a greater nuclear charge.

Explain why more energy is required to remove the outer electrons in magnesium than in calcium.

[ 2 ]

(ii)

0.001 mol of strontium reacts with an excess of cold water. When the reaction is complete a colourless solution is seen.

Construct the equation for the reaction of strontium with cold water. Include state symbols.

[ 2 ]

(iii)

0.005 mol of calcium and 0.005 mol of strontium are added separately to two beakers. Each beaker contains $100 \mathrm{~cm}^{3}$ of cold water.
At the end of each reaction a white solid and a colourless solution are seen in both beakers.

Predict which element, calcium or strontium, produces the more alkaline solution. Explain your answer.

[ 2 ]

(iv)

Describe one observation when magnesium carbonate is added to excess dilute sulfuric acid.

[ 1 ]

(b)

Element X is a metal. X reacts with oxygen to form a black solid oxide. The oxidation state of X in this oxide is +2 . The carbonate of $\mathbf{X}, \mathbf{X C O}_{3}$ , is a green solid. It decomposes on heating to form the oxide and a colourless gas.

[ 5 ]

(i)

From the information given, state two similarities and one difference that metal X and its compounds have with Group 2 metals and their compounds.
similarity 1
similarity 2
difference 1

[ 3 ]

(ii)

Write the formula of the oxide of X.

[ 1 ]

(iii)

Write an equation for the reaction of $\mathrm{XCO}_{3}$ when it is heated.

[ 1 ]

(a)

The oxide of silicon reacts with calcium oxide in an addition reaction to produce calcium silicate, $\mathrm{CaSiO}_{3}$ . The oxidation number of calcium in $\mathrm{CaSiO}_{3}$ is +II .

[ 1 ]

(i)

Calcium oxide can be made from calcium carbonate in a single-step reaction.

Identify the type of reaction that occurs.

[ 1 ]

[Maximum number: 2]

Group 2 metals form alkaline solutions in water.

(a)

(i)

Write the equation for the reaction of calcium oxide with water.

[ 1 ]

(b)

Oxygen reacts readily with some metals, but each Group 2 metal requires strong heating to start the reaction with oxygen.

Suggest why strong heating is required to start these reactions.

[ 1 ]

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