Group 2 (A Level Only) (CIE A Level Chemistry)

This question is about Group 2 nitrates. 

Strontium nitrate is is a Group 2 nitrate used to produce a colour in fireworks. 

[1]

The nitrate ion, NO₃ , contains a dative covalent bond.

Complete the following ‘dot-and-cross’ diagram of the bonding in the nitrate ion.

Use the following code for your electrons:

•  electrons from oxygen
x electrons from nitrogen
□ added electron(s) responsible for the overall negative charge

Describe and explain the trend in thermal stabilities of the nitrates of the Group 2 elements. 

Magnesium is a Group 2 metal. 

Write an equation, including state symbols for the reaction between:

[1]

Magnesium sulfate is soluble in water. 

Describe and explain how the solubilities of the sulfates of the Group II elements vary down the group.

The following table lists some enthalpy changes for magnesium and strontium compounds

Use the above data to calculate values of ΔH^θ_sol for Mg(OH)₂ and for Sr(OH)₂.

Mg(OH)₂    .....................................  kJ mol^-1 

Sr(OH)₂.     ....................................  kJ mol^-1 

Use your results from part (c) to suggest whether Sr(OH)₂ is more or less soluble in water than in Mg(OH)_2, assuming all other factors are the same.

This question is about Group 2 carbonates. 

Group 2 carbonates can react with acids.

[1]

Describe and explain the trend observed in the thermal stability of the carbonates of the Group II elements.

The ionic radii of three ions are shown in Table 4.1.

Suggest how the thermal stabilities of zinc carbonate and lead carbonate might compare to that of calcium carbonate. 

Zinc is found in d block of the Periodic table but is not a transition element. 

[1]

[3]

This question is about Group 2 hydroxides.

Samples of magnesium, calcium, strontium and barium are reacted with water to form their hydroxides. The resulting solutions are then filtered to collect the precipitates.

Explain the trend in the expected mass for the precipitates.

Table 4.1 shows the solubility data for the Group 2 metal hydroxides.

Table 4.1

A student determined that a 50 cm³ solution of an unknown Group 2 metal hydroxide contained 802 mg of the metal hydroxide.

Identify the metal hydroxide in the unknown sample.

Write an equation for the reaction between magnesium hydroxide and sulfuric acid. 

You should include state symbols. 

The solubility of Group 2 hydroxides increases going down the group because the enthalpy of solution, ΔH^θ_sol, gets more exothermic. 

[2]

[3]

This question is about magnesium. 

Magnesium forms a nitrate, Mg(NO₃)₂ which decomposes on heating as shown below:

2Mg(NO₃)₂ (s) →   2MgO (s) + 4NO₂ (g) + O₂ (g)

Using oxidation numbers, explain why the reaction involves both oxidation and reduction. 

Metal peroxides contain the ^–O–O^– ion.

The peroxides of the Group 2 elements, MO₂, decompose in a similar way to Group 2 metal carbonates. 

Table 2.1 below shows the solubility data for the Group 2 metal hydroxides.

Table 2.1

State and explain the factors responsible for the trend in the solubility of the Group 2 hydroxides.

Milk of magnesia, Mg(OH)₂ is used to neutralise stomach acid.

Explain why Mg(OH)₂ cannot be used to test for carbon dioxide but Ba(OH)₂ can. 

Use the data from Table 3.1 in part (a) to calculate the pH of a saturated solution of Mg(OH)₂ at 293 K. Show your working.

K_w at 293 K = 0.681 x 10^-14 mol² dm^-6

pH = ......................

Calcium carbonate can be thermally decomposed to make calcium oxide. 

CaCO₃ (s) → CaO (s) + CO₂ (g)   ΔH = + 178 kJ mol^-1

Table 3.1 below shows the standard entropies of each substance. 

Table 3.1

Describe and explain the trend that is observed in the thermal decomposition of the Group 2 carbonates. 

CaCO₃ has a solubility product, K_sp in water at 298 K of 5 x 10^-9 mol² dm^–6 

Calculate the solubility of CaCO₃ in water at 298 K, in g dm^–3

solubility of CaCO₃ = ............................. g dm^–3