Group 2: the alkaline earth metals

Barium is in Group 2 of the periodic table.

Which statement(s) about barium is / are correct?

1 Its outer shell electrons are in an s-orbital.

2 It reacts more vigorously with water than magnesium.

3 It has a higher first ionisation energy than magnesium.

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Which compounds of magnesium can be used as ‘antacids’?

A Chlorides

B Hydroxides

C Nitrates

D Sulfates

Your answer

This question is about redox reactions and electrode potentials.

The flowchart shows some reactions of barium and its compounds.

• Write balanced equations for Reaction 1 and Reaction 2.

• Identify the type of reaction in Reaction 3.

Reaction 1: equation........

Reaction 2: equation........

Reaction 3: type of reaction........

Potassium iodate tablets prevent the uptake of radioactive iodine in the human body following a nuclear accident.

The mass of potassium iodate(V), KIO₃, in a tablet can be determined by reaction with an aqueous solution of potassium iodide, K I, in the presence of acid.

A chemist finds that two KIO₃ tablets react with exactly 26.2 cm³ 0.150 mol dm^–3 KI.

Calculate the mass, in mg, of KIO₃ in one tablet.

Give your answer to the nearest whole number.

Standard electrode potentials are measured by comparison with a reference half-cell.

Draw a labelled diagram to show how the standard electrode potential could be measured for the redox system below.

Include details of the apparatus, solutions and the standard conditions needed when measuring this standard electrode potential.

Standard conditions........

Many electric vehicles are powered by lithium-ion cells.

Hydrogen-oxygen fuel cells can also be used to power vehicles.

Six redox systems are shown in the table. State symbols have been omitted.

Redox system	Half-equation	E / V
1	Li+ + e– Li	–3.04
2	2H2O + 2e– H2 + 2OH–	–0.83
3	2H+ + 2e– H2	0.00
4	O2 + 2H2O + 4e– 4OH–	+0.40
5	Li+ + CoO2 + e– LiCoO2	+1.16
6	O2 + 4H+ + 4e– 2H2O	+1.23

A lithium-ion cell involves redox systems 1 and 5.

Construct the overall cell equation for a lithium-ion cell.

Hydrogen-oxygen fuel cells can operate in acidic or in alkaline conditions.

Show that for acidic and alkaline hydrogen–oxygen fuel cells, the standard cell potentials, and the overall cell equations, are the same.

Acidic........

Alkaline........

This question is about acids and bases.

Table 20.1 shows the ionic product, K_w, of water at 25 °C and 40 °C.

Table 20.1

Temperature /°C	Kw / mol2 dm–6
25	1.00 10−14
40	2.92 10−14

Calculate the pH of water at 40 °C.

Give your answer to 2 decimal places.

Table 20.1 shows different K_w values at 25 °C and at 40 °C. A student suggests that water is neutral at these temperatures.

Explain why this student is correct.

A student reacts strontium metal with water to make a 250.0 cm³ solution of aqueous strontium hydroxide, Sr(OH)₂. The solution contains 0.145 g of strontium hydroxide.

• Write an equation for the reaction of strontium with water.

• Calculate the pH of this 250.0 cm³ solution of strontium hydroxide at 40 °C. You should refer back to Table 20.1 at the start of (a).

Give your answer to 2 decimal places.

Equation........

Calculation

A student reacts 1.00 g of strontium carbonate, SrCO₃, with an excess of dilute nitric acid, HNO₃. A gas is produced.

Construct the equation for this reaction.

The student then reacts 1.00 g of calcium carbonate, CaCO₃, with an excess of dilute nitric acid, HNO₃.

Explain why the student’s two reactions produce different volumes of gas.

A student reacts an excess of magnesium with 25.0 cm³ of 0.500 mol dm^–3 hydrochloric acid, HC l.

The student also reacts an excess of magnesium with 25.0 cm³ of 0.500 mol dm^–3 ethanoic acid, CH₃COOH.

Construct an ionic equation for the reaction of magnesium with an acid.

Explain why these two reactions of magnesium produce the same volume of gas but at different rates.

Butanoic acid, CH₃CH₂CH₂COOH, is a weak monobasic acid.

Explain what is meant by the term monobasic acid.

A buffer solution is prepared by dissolving 3.39 g of potassium hydroxide in 250 cm³ of 0.376 mol dm^–3 butanoic acid.

This buffer solution has a pH of 5.07 at 25 °C.

Calculate the acid dissociation constant, K_a, of butanoic acid at 25 °C.

Assume that the volume of the solution remains constant at 250 cm³ when the potassium hydroxide is dissolved.

K_a =........ mol dm^–3

A buffer solution has a pH of 4.50.

When a small volume of water is added to this buffer solution, the pH does not change.

Explain why the pH does not change.

This question is about the reactions of Group 2 metals and their compounds.

A student adds magnesium to dilute hydrochloric acid in one test tube. The student adds calcium to dilute hydrochloric acid in a second test tube.

A redox reaction takes place in each test tube.

Suggest two observations from the student’s experiment that would show that calcium is more reactive than magnesium.

Write half-equations for the reaction of magnesium with hydrochloric acid.

Oxidation half-equation:........

Reduction half-equation:........

A sample of barium oxide is added to distilled water at 25 °C. A colourless solution forms containing barium hydroxide, Ba(OH)₂.

The solution is made up to 250.0 cm³ with distilled water. The pH of this solution is 13.12.

Determine the mass of barium oxide that was used.

Give your answer to 3 significant figures.

10 cm³ of dilute sulfuric acid is added to 10 cm³ of the colourless solution of Ba(OH)₂

Write an ionic equation, including state symbols, for the reaction.

Limestone and huntite are two calcium minerals.

A typical sample of limestone contains 95.0% by mass of calcium carbonate, CaCO₃

Fertiliser Z, Ca₅NH₄(NO₃)₁₁•10H₂O (M_r = 1080.5 g mol^–1) can be made from limestone.

Calculate the mass, in g, of limestone needed to make 1.50 kg of fertiliser Z.

Give your answer to 3 significant figures.

Huntite is a carbonate mineral with the chemical formula Mg₃Ca(CO₃)₄.

Huntite reacts with dilute hydrochloric acid to produce bubbles of a gas and a colourless solution.

Construct the equation for the reaction. Include state symbols.

Which statement is not correct for Group 2 hydroxides?

A Mg(OH)₂ can be used to treat indigestion.

B Ca(OH)₂ is used in agriculture to neutralise alkaline soils.

C The anion in Sr(OH)₂ contains 10 electrons.

D Ba(OH)₂ is a product from the reaction of barium and water.

Your answer

Sir Humphry Davy discovered several elements including sodium, potassium, magnesium, calcium and strontium.

Explain which block in the Periodic Table sodium and magnesium belong to.

A sample of magnesium, A_r= 24.305, is found to consist of three isotopes. The accurate relative isotopic masses and % abundances of two of the isotopes are shown in the table.

Determine the relative isotopic mass of the third isotope of magnesium in the sample.

Give your answer to 5 significant figures.

A student adds an excess of calcium oxide to water in a test tube. In a separate test tube, the student adds an excess of strontium oxide to water.

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

State symbols are not required.

Suggest the approximate pH of the two solutions formed in the test tubes.

pH with calcium oxide........

pH with strontium oxide........

The table below shows enthalpy changes involving potassium, oxygen and potassium oxide,

The incomplete Born–Haber cycle below can be used to determine the lattice enthalpy of potassium oxide.

In the boxes, complete the species present in the cycle. Include state symbols for the species.

Calculate the lattice enthalpy of potassium oxide.

lattice enthalpy =........ kJ mol⁻¹

A similar Born–Haber cycle to potassium oxide in (d) can be constructed for sodium oxide.

The first ionisation energy of sodium is more endothermic than that of potassium.

Explain why.

The lattice enthalpy of sodium oxide is more exothermic than that of potassium oxide.

Explain why.