Alyn G McFarland Nora Henry CCEA A2 CHEMISTRY EXAM ...

Alyn G McFarland

Nora Henry

CCEA A2

CHEMISTRY

EXAM PRACTICE

MARK SCHEME

This mark scheme is for use in conjunction with

the book Chemistry Exam Practice for CCEA A2,

ISBN: 978 1 78073 254 1

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Unit A2 1:

Further Physical

and Inorganic Chemistry

Answers

2

4.1 LATTICE ENTHALPY

4.1 Lattice Enthalpy

1 C

[1]

2 B

[1]

Enthalpy of solution = lattice enthalpy + hydration enthalpy of calcium ion + 2 ¡Á hydration enthalpy of

chloride ion = + 2237 + (¨C1650) + 2(¨C364) = ¨C141 kJ mol¨C1. Most common error would be forgetting the

2 ¡Á for the enthalpy of hydration of the chloride ion. This would give answer C.

3 (a) the energy required to convert one mole of gaseous atoms into gaseous ions with a single

positive charge.

(b) enthalpy change when one mole of a compound is formed from its elements under standard

conditions.

(c) enthalpy change when one mole of gaseous atoms is formed from the element in its standard

state.

(d) enthalpy change when one mole of an ionic compound is converted to gaseous ions.

4 (a) (i)

(ii)

(iii)

(iv)

(b) (i)

Cs(g) ? Cs+(g) + e¨C

Cs(s) + ?Cl2(g) ? CsCl(s)

Cl(g) + e¨C ? Cl¨C(g)

CsCl(s) ? Cs+(g) + Cl¨C(g)

[2]

[2]

[2]

[2]

[1]

[1]

[1]

[1]

Cs+(g) + Cl(g) + e¨C

Cs+(g) + Cl¨C(g)

Cs+(g) + ?Cl2(g) + e¨C

Cs(g) + ?Cl2(g)

Cs(s) + ?Cl2(g)

CsCl(s)

[1] for each correct level with state symbols

(ii) lattice enthalpy = ¨C (¨C433) + (+78) + (+380) + (+122) + (¨C364)

= + 649 kJ mol¨C1

(c) Cs+ ion larger ionic radius than other Group I metal ions [1]

weaker ionic bonding as ions not as close packed [1]

5 (a) A, D, B, E, C, F

all correct [2]; one error [1]

(b) lattice enthalpy

= ¨C (¨C642) + (+150) + (+736) + (+1450) + (+242) + 2(¨C364)

= + 2492 kJ mol¨C1

1

[3]

[2]

[2]

[2]

[3]

4.1 LATTICE ENTHALPY

(c) ¨C165 = + (+2492) + (¨C1891) + (2x)

2x = ¨C766

x = ¨C383 kJ mol¨C1

(d)

O

¦Ä¨C

O

H

O

¦Ä¨C

Cl ¨C

¦Ä¨C

H

¦Ä+H

¦Ä+

H ¦Ä+

¦Ä¨C

¦Ä¨C

O

¦Ä+

H

Mg2+

H¦Ä+

H

¦Ä¨C

O

H ¦Ä+

¦Ä+

¦Ä+

¦Ä+

¦Ä+

¦Ä+

H

H

H

H

H¦Ä+

O

¦Ä+

H

¦Ä+ H

[3]

¦Ä+

O

O¦Ä¨C

H

¦Ä+

¦Ä¨C

[1] for each diagram with partial charges and bonds to ions

bonds form between water molecules and ions [1]

bond formation is exothermic [1]

[4]

6 (a)

Ag+(g) + F(g) + e¨C

Ag+(g) + ?F2(g) + e¨C

Ag+(g) + F¨C(g)

Ag(g) + ?F2(g)

Ag(s) + ?F2(g)

AgF(s)

(b) first electron affinity = ¨C (+79) ¨C (+730) ¨C (+286) + (¨C203) + (+943)

= ¨C355 kJ mol¨C1

(c) (i) 1 = lattice enthalpy of silver(I) fluoride [1]

2 = hydration enthalpy of silver(I) ions [1]

3 = hydration enthalpy of fluoride ions [1]

4 = enthalpy of solution of silver(I) fluoride [1]

(ii) + (+943) + (¨C464) + (¨C457) = + 22 kJ mol¨C1

2

[2]

[4]

[2]

4.1 LATTICE ENTHALPY

7 (a)

2K+(g) + O2¨C(g)

+844

2K+(g) + O(g) + 2e¨C

+248

2K+(g) + ?O2(g) + 2e¨C

¨C142

2K+(g) + O¨C(g) + e¨C

2K(g) + ?O2(g)

+2531

+180

2K(s) + ?O2(g)

¨C561

K2O(s)

[1] for each correct value

(b) 2 ¡Á first ionisation energy

= ¨C (+180) + (¨C561) + (+2531) ¨C (+844) ¨C (¨C142) ¨C (+248) = +840

first ionisation energy = 840 ¡Â 2 = +420 kJ mol¨C1

(c) (i) sodium smaller ions in metallic lattice [1]

stronger metallic bonding [1]

(ii) atomic radius smaller for sodium [1]

less shielding by inner electrons [1]

(iii) lattice enthalpy

= ¨C (¨C416) + 2(+108) + 2(+500) + ?(+496) + (¨C142) + (+844)

= +2582 kJ mol¨C1

3

[5]

[3]

[2]

[2]

[3]

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