Similarities & Trends in the Properties of the Group 2 Metals, Magnesium to Barium, & Their Compounds (Cambridge (CIE) A Level Chemistry): Exam Questions

This question is about Group 2 nitrates. 

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

i) Give the formula of strontium nitrate. 

[1]

ii) Give the colour that strontium nitrate will give in fireworks. 

[1]

i) Write an equation for the reaction that occurs when strontium nitrate is heated.

You should include state symbols. 

[2]

ii) Give one observation of this reaction. 

[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:

i) magnesium and steam

[1]

ii) magnesium and sulfuric acid

[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.

i) Compare the reaction of calcium carbonate with hydrochloric acid and sulfuric acid.

[2]

ii) Write an equation for the reaction between calcium carbonate and sulfuric acid, including state symbols. 

[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 3.1.

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

Table 3.1 

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

i) Explain why zinc is not classed as a transition element. 

[1]

ii) Describe three characteristic chemical properties of transition elements that are not shown by Group 2 elements. 

[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. 

i) Define the term enthalpy of solution, ΔH^θ_sol.  

[2]

ii) Explain why going down Group 2 the enthalpy of solution, ΔH^θ_sol  gets more exothermic. 

[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. 

The values for the first, second and third ionisation energies of magnesium are shown in Table 1.1.

Table 1.1

i) Write an equation for the second ionisation energy of magnesium. 

[2]

 ii) Explain the trend in the first three ionisation energies of magnesium. 

[3]

 iii) Explain why magnesium has a greater second ionisation energy than barium. 

[3]

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. 

i) Write an equation for the thermal decomposition of strontium peroxide, SrO₂. 

[1]

 ii) Suggest how the temperature at which thermal decomposition of MO₂ occurs varies down Group 2. Explain your answer. 

[3]

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. 

i) Write an expression for the solubility product of Sr(OH)₂  

K_sp = 

[1]

ii) Use the data from Table 3.1 in part (a) to calculate the value of K_sp at 293 K. Include units in your answer and show your working. 

K_sp = ................................................ units = ..............................

[2]

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

i) Use the information in Table 3.1 to show that calcium carbonate is stable at room temperature (25 ^oC). 

[4]

 ii) Calculate the minimum temperature needed to decompose calcium carbonate 

[2]

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

i) Write an equation to show the equilibrium for the solubility product for CaCO₃. Include state symbols.

[1]

ii) With reference to your equation in part (c)(i), suggest what is observed when a few cm³ of concentrated K₂CO₃ (aq) are added to a saturated solution of CaCO₃. Explain your answer.

[2]

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