(a) Successive ionisation energies for the elements magnesium to barium are given in the table. element 1st ionisation energy / kJ mol⁻¹ 2nd ionisation energy / kJ mol⁻¹ 3rd ionisation energy / kJ mol⁻¹ --- --- --- --- Mg 736 1450 7740 Ca 590 1150 4940 Sr 548 1060 4120 Ba 502 966 3390 (i) Explain why the first ionisation energies decrease down the group. (ii) Explain why, for each element, there is a large increase between the 2nd and 3rd ionisation energies. (b) A sample of…

Chemistry 9701/22 — October/November 2014

Cambridge AS Level · AS Level Structured Questions · worked solutions for every part, with the mark scheme

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Topics Atoms, Molecules and Stoichiometry · Atomic Structure · Electrochemistry · Group 2 · Chemical Energetics · Nitrogen and Sulfur · +7 more

Q1Atomic StructureAtoms, Molecules and StoichiometryElectrochemistryGroup 2Free sample

(a)

Successive ionisation energies for the elements magnesium to barium are given in the table.

element	1st ionisation energy / kJ mol⁻¹	2nd ionisation energy / kJ mol⁻¹	3rd ionisation energy / kJ mol⁻¹
Mg	736	1450	7740
Ca	590	1150	4940
Sr	548	1060	4120
Ba	502	966	3390

(i)

Explain why the first ionisation energies decrease down the group.

(ii)

Explain why, for each element, there is a large increase between the 2nd and 3rd ionisation energies.

(b)

A sample of strontium, atomic number 38, gave the mass spectrum shown. The percentage abundances are given above each peak.

Fig. 1.1

(i)

Complete the full electronic configuration of strontium.

1s² 2s² 2p⁶ ...................................................................................................................

(ii)

Explain why there are four different peaks in the mass spectrum of strontium.

(iii)

Calculate the atomic mass, $A_r$ , of this sample of strontium.
Give your answer to three significant figures.

$A_r$ = .............................

(c)

A compound of barium, A, is used in fireworks as an oxidising agent and to produce a green colour.

(i)

Explain, in terms of electron transfer, what is meant by the term oxidising agent.

(ii)

A has the following percentage composition by mass: Ba, 45.1; Cl, 23.4; O, 31.5.

Calculate the empirical formula of A.

empirical formula of A = ...........................................

(d)

Some reactions involving magnesium and its compounds are shown in the reaction scheme below.

Fig. 1.2

(i)

Give the formulae of the compounds X, Y and Z.

X .........................................................................................................................................

Y .........................................................................................................................................

Z .........................................................................................................................................

(ii)

Name the reagent needed to convert Y(s) into Z(aq) in reaction 1 and write an equation for the reaction.

reagent ...............................................................................................................................

equation ..............................................................................................................................

(iii)

How would you convert a sample of Z(s) into Y(s) in reaction 2?

(iv)

Give equations for the conversions of Mg into X, and Z(s) into Y.

Mg to X ...............................................................................................................................

Z to Y ..................................................................................................................................

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