Question
Solid ionic compounds form crystal lattices.
(a) Enthalpy of solution, enthalpy of hydration and lattice enthalpy are related in an energy cycle.
(i) Annotate the energy cycle for the enthalpy of solution of solid magnesium chloride, \(MgCl_2\) (s), by naming the processes A, B and C and completing the boxes. Include state symbols.
(ii) Calculate the enthalpy of solution for magnesium chloride, \(MgCl_2\). Use sections 18 and 20 of the data booklet.
(b) Explain why the lattice enthalpy of barium chloride, \(BaCl_2\), is lower than that of magnesium chloride.
(c) Cobalt also forms chlorides with the formula \(CoCl_2\).
(i) State the full electron configuration of the cobalt(II) ion, \(Co^{2+}\).
(ii) Hydrated cobalt(II) ions, \(Co(H_2O)_6^{2+}\), 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:
\(CoCl_4^{2−}\) ions are blue.
(iii) Explain why the different ligands cause different coloured complexes.
Answer/Explanation
Answer:
(a) (i) 
correct boxes
A: enthalpy of solution / \(\delta \)Hsolution / \(\delta \)Hsol
AND
B: lattice enthalpy / \(delta \)Hlattice
AND
C: enthalpy of hydration / \(\delta \)Hhydration
(ii) «\(\delta\)Hsolution = \(\delta \)Hlattice + \(\delta \)Hhydration
= 2540 + (−1963) + 2(−359) =»
−141 «kJ \(mol^{−1}\) »ü
(b) ionic radius \(Ba^{2+}\) is greater than that of \(Mg^{2+}\)
weaker attraction between «\(Ba^{2+}\) and \(Cl^−\) » ions
(c) (i) \(1s^2\) \(2s^2\) \(2p^6\) \(3s^2\) \(3p^6\) \(3d^7\)
(ii) Type of bond:
coordinate/dative/covalent
How the bond forms:
oxygen/water molecule /ligand donates e− pair to cobalt«(II) ion»
(iii) magnitude of ∆E/energy gap between split d-orbitals differs «according to ligand»
∆E/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
Question
The periodic table provides information about electron configuration, and physical and
chemical properties of elements.
(a) Bismuth has atomic number 83. Deduce two pieces of information about the electron configuration of bismuth from its position on the periodic table.
(b) Outline why aluminium is malleable.
(c) An 11.98g block of pure aluminium was heated. Calculate the heat energy absorbed, in J, to increase its temperature from 18.0°C to 40.0°C. The specific heat capacity of aluminium is 0.902J \(g^{−1} K^{−1}\).
(d) Argon has three naturally occurring isotopes, \(^{36}Ar\), \(^{38}Ar\) and \(^{40}Ar\).
(i) Identify the technique used to determine the relative proportions of the isotopes of argon.
The isotopic composition of a sample of argon is 0.34% of \(^{36}Ar\), 0.06% of \(^{38}Ar\) and 99.6% of \(^{40}Ar\).
(ii) Calculate the relative atomic mass of this sample, giving your answer to two decimal places.
Answer/Explanation
Answer:
(a) Any two ofthe following:
«group 15 so Bi has» 5 valence electrons
«period 6 so Bi has» 6 «occupied» electron shells/energy levels
«in p-block so» p orbitals are highest occupied
occupied d/f orbitals
has unpaired electrons
has incomplete shell(s)/subshell(s)
(b) «layers of» cations slide over each other without disrupting bonding
OR
attraction between metal ions and delocalized electrons/metallic bonding is not
disrupted by changing position of metal ions
OR
metallic bonds are non-directional
OR
changing the shape does not disrupt the bonding
(c) «heat energy = 11.98 g x 0.902 J \(g^{−1} K^{−1}\) x 22.0 K =» 238 «J»
(d) (i) mass spectrometry
OR
mass spectroscopy
OR
mass spectrum
OR
MS
(ii) (0.0034 x 36) + (0.0006 x 38) + (0.996 x 40)
39.99