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

Magnesium, calcium and barium are some of the Group 2 elements of the Periodic Table.

State and explain the trend in the atomic radius of the Group 2 elements from magnesium to barium.

Magnesium is frequently used in fireworks. It burns rapidly in oxygen, and it adds sparks which generally improves the appearance and brilliance of the firework.

Construct an equation to represent the reaction which takes place when a strip of magnesium is burned in oxygen and state an observation which would be made.

State symbols are not required.

Group 2 compounds, such as the hydroxides of magnesium and calcium, have a number of other uses.

i) Construct equations to show the formation of magnesium hydroxide and calcium hydroxide from their metals.

[2]

ii) Give an approximate pH value and a use for each of the hydroxides.

[3]

Group 2 elements will react with water.

A student added 20 cm³ of water to two boiling tubes. A small piece of calcium was added to one of the boiling tubes and a small piece of barium was added to the other.

State two observations that the student would make and how the observations would differ between the two boiling tubes.

Group 2 hydroxides, M(OH)₂, can be used to neutralise acids.

Construct an equation for the reaction of barium with cold water. State symbols are not required.

Explain why a saturated solution of barium hydroxide is more alkaline than a saturated solution of magnesium hydroxide.

An unknown solution of a group 2 metal salt was tested for the presence of carbonate ions.

Dilute hydrochloric acid was added to the solution and the gas given off was bubbled through limewater. A white precipitate formed.

i) Construct the ionic equation for the formation of the gas. State symbols are not required.

[1]

ii) Construct an equation for the formation of the precipitate. Include state symbols.

[2]

Magnesium hydroxide can be used as an indigestion remedy to neutralise hydrochloric acid in the stomach.

Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O

Calculate the minimum mass of magnesium hydroxide needed to neutralise 0.210 mol of hydrochloric acid. Give your answer to an appropriate number of significant figures. Show your working.

Group 2 metals and their compounds are used commercially in a variety of processes and applications.

Calcium carbonate is an insoluble solid that can be used to lower the acidity of lake water.

Explain why the rate of this reaction decreases when the water temperature falls.

Calcium carbonate reacts with lactic acid (Figure 3.1) to form calcium lactate, which is used to treat or prevent low blood calcium levels (hypocalcemia).

Figure 3.1

State the two other products of the reaction of calcium carbonate with lactic acid.

Magnesium can be used to extract titanium.

i) Construct an equation to show how magnesium is used as the reducing agent in the reaction of magnesium with titanium(IV) chloride. State symbols are not required.

[2]

ii) Explain, in terms of oxidation numbers, why magnesium is the reducing agent.

[1]

iii) The excess magnesium used in this extraction is removed by reacting it with dilute sulfuric acid to form magnesium sulfate.

Explain why the magnesium sulfate formed is easy to separate from the titanium.

[1]

Strontium metal is used in the manufacture of alloys.

Explain why strontium has a higher melting point than barium.

Calcium salts have a number of industrial, agricultural and medicinal uses.

Calcium carbonate is used as an antacid to relieve heartburn, acid indigestion, and upset stomach. Calcium oxide is used to make porcelain, glass, mortars and cement. Calcium hydroxide is used in agriculture when a rapid change in the pH of soil is required.

These three calcium salts are connected by the Lime cycle shown in Fig. 4.1.

Fig. 4.1

Construct three equations to demonstrate the reactions that occur in the Lime cycle. Include state symbols.

In agriculture, bulk lime spreaders are used to cover fields with solid calcium salts, including calcium carbonate, calcium oxide and calcium hydroxide.

i) Explain how solid calcium hydroxide increases the pH of acidic soil.

[3]

ii) Construct an ionic equation to show the reaction that causes the pH of the soil to increase. State symbols are not required.

[1]

When calcium carbonate is heated strongly it undergoes a process called calcination.

i) What is the chemical reaction that is described by calcination? 

[1]

 ii) Explain why strontium carbonate has greater thermal stability than calcium carbonate. 

[3]

A sample of hydrated calcium nitrate crystals was gently heated in a test tube. With further heating, a mixture of two gases was evolved. One of the gases was coloured and the other was colourless.

i) Identify the coloured gas and give its colour. 

[1]

 ii) Identify and describe a test, including the result, for the colourless gas. 

[1]

Explain why the first ionisation energy of calcium (590 kJ mol^-1) is greater than that of strontium (550 kJ mol^-1).

Strontium chloride is used in toothpaste for sensitive teeth.

i) Construct an equation for the formation of strontium chloride from strontium and hydrochloric acid. Include state symbols.

[2]

ii) Suggest why this reaction is not used to produce strontium chloride on an industrial scale.

[1]

Magnesium sulfate solution can be given as first aid to someone who has accidentally swallowed barium chloride.

Explain, with the help of an ionic equation, why drinking magnesium sulfate solution is an effective treatment for barium poisoning. State symbols are not required.

Milk of magnesia, Mg(OH)₂, and calcium carbonate can both be used in the effective relief of acid indigestion.

By comparing the chemical equations for their reactions with hydrochloric acid, justify which remedy might cause the person taking it to have wind.

Barium is silvery white but blackens when exposed to air.

This is due to the formation of barium nitride and one other compound.

Construct equations for the two separate reactions that occur. Include state symbols.

Barium can also react with water.

A student reacted 0.20 g of barium with 250 cm³ of water.

i) Calculate the volume of gas, in cm³, produced in this reaction at room conditions. Show your working.

[3]

ii) Calculate the concentration, in mol dm^-3, of the barium hydroxide solution produced.

[1]

Describe and explain the trend in the reactivity of Group 2 elements with water.

Explain why the reaction of calcium with water is a redox reaction.

Use oxidation numbers in your answer.

The trend in solubility and strength as a base can also be observed going down Group 2.

Explain how these two trends are connected.

Samples of 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 of the precipitates.

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

Table 2.1

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. Show your working.

Magnesium hydroxide reacts with sulfuric acid.

i) Construct an equation for the reaction between magnesium hydroxide and sulfuric acid. Include state symbols.

[2]

ii) Barium hydroxide also reacts with sulfuric acid. State and explain any differences in the observations between the two reactions.

[3]

i) Construct an equation for the thermal decomposition of calcium nitrate, Ca(NO₃)₂.

[1]

ii) State and explain how the thermal stabilities of the nitrates vary down Group 2.

[3]

iii) Predict what you would observe if a sample of lithium nitrate was heated.

[1]

The nitrates of calcium, strontium or barium are often added to firework mixtures to produce red or green flames. The equation for the decomposition of one such mixture is as follows.

Sr(NO₃)₂ (s) + 3C (s) → SrO (s) + N₂ (g) + 2CO₂ (g) + CO (g)

Calculate the volume of gas given off (measured at room temperature and pressure) when a 10.0 g sample of this mixture decomposes. Show your working.

[M_r: Sr(NO₃)₂ = 211.6]

One of the major ores of magnesium is the mixed carbonate called dolomite, CaMg(CO₃)₂.

Calculate the percentage loss in mass that would be observed when a sample of dolomite is heated at a high temperature until the reaction is complete. Show your working.