DP Chemistry (first assessment 2025)

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Question 23M.2.HL.TZ2.8

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Date May 2023 Marks available [Maximum mark: 10] Reference code 23M.2.HL.TZ2.8
Level HL Paper 2 Time zone TZ2
Command term Annotate, Calculate, Describe, Explain, State Question number 8 Adapted from N/A
8.
[Maximum mark: 10]
23M.2.HL.TZ2.8

Solid ionic compounds form crystal lattices.

(a)

Enthalpy of solution, enthalpy of hydration and lattice enthalpy are related in an energy cycle.

(a.i)

Annotate the energy cycle for the enthalpy of solution of solid magnesium chloride, MgCl2 (s), by naming the processes A, B and C and completing the boxes. Include state symbols.

 

[2]

Markscheme

correct boxes ✓
A: enthalpy of solution / ΔHsolution / ΔHsol
AND
B: lattice enthalpy / ΔHlattice
AND
C: enthalpy of hydration / ΔHhydration ✓

(a.ii)

Calculate the enthalpy of solution for magnesium chloride, MgCl2. Use sections 18 and 20 of the data booklet.

[1]

Markscheme

«ΔHsolution = ΔHlattice + ΔHhydration

= 2540 + (−1963) + 2(−359) =»
−141 «kJ mol−1» ✓

(b)

Explain why the lattice enthalpy of barium chloride, BaCl2, is lower than that of magnesium chloride. 

[2]

Markscheme

ionic radius Ba2+ is greater than that of Mg2+ ✓
weaker attraction between «Ba2+ and Cl− » ions ✓

(c)

Cobalt also forms chlorides with the formula CoCl2.

(c.i)

State the full electron configuration of the cobalt (II) ion, Co2+.

[1]

Markscheme

1s2 2s22p6 3s23p63d7 ✓

(c.ii)

Hydrated cobalt (II) ions, Co(H2O)62+, are pink. Describe the interaction between the cobalt ion and a water molecule in terms of the type of bond and how this bond is formed.

 

Type of bond: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

How the bond forms:  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

[2]

Markscheme

Type of bond:
coordinate/dative/covalent ✓

How the bond forms:
oxygen/water molecule /ligand donates e− pair to cobalt«(II) ion» ✓

CoCl42− ions are blue.

(c.iii)

Explain why the different ligands cause different coloured complexes.

[2]

Markscheme

magnitude of ΔE/energy gap between split d-orbitals differs «according to ligand» ✓
ΔE/energy gap determines the wavelength of light absorbed/colour «of complex»
OR
energy absorbed by electrons «to transition/to be promoted to higher levels»
corresponds to different wavelengths of light/colour ✓

 

Reference to different energy gap/splitting of d-orbitals needed for M1.