A-LevelChemistryChemical bonding9701/41 · Oct/Nov 2025 · Q514 Marks

Copper shows typical properties of transition elements, including its behaviour as a catalyst.

(a)Complete Table 5.1 to show the total number of unpaired electrons in the 3d and 4s orbitals of an isolated gaseous Cu atom and a Cu2+ ion. Table 5.1 number of unpaired electrons species 3d 4s Cu Cu2+ [1][1]
(b)The 3d orbitals in an isolated Cu2+ ion are degenerate. Complete the diagram to show the relative energies of the 3d orbitals in an isolated Cu2+ ion and in Cu2+ in a tetrahedral complex. [Figure for 5(b)] [2][2]
(c)Explain why transition elements behave as catalysts.[2]
(d)CN- is a monodentate ligand. Table 5.2 shows information about two complex ions that contain only CN- ions as ligands. Complete Table 5.2. Table 5.2 metal ion coordination number formula of complex ion charge of complex ion Ag+ 2 4- Fe2+ [2][2]
(e)The complex ion [Au(CN)2Br2]- displays geometrical (cis/trans) isomerism. Draw the structure of trans-[Au(CN)2Br2]-. State its shape and the Br-Au-Br bond angle. shape _________________________ Br-Au-Br bond angle = _________________________ [2][2]
(f)(i)An impure sample of a vanadium(V) compound of mass 0.250 g is dissolved in aqueous acid. This solution contains VO3¯ ions. An excess of zinc is added to this solution. All the VO3¯ ions are reduced to V2+ ions and Zn atoms are oxidised to Zn2+ ions. The unreacted zinc is removed and the resulting solution is titrated with acidified MnO4¯. The end-point is reached when 22.5 cm3 of 0.0750 mol dm-3MnO4¯ is added. A redox reaction takes place and all the V2+ reacts forming VO3¯. 3MnO4¯ + 5V2+ + 3H2O → 3Mn2+ + 5VO3¯ + 6H+ Calculate the percentage by mass of vanadium in the 0.250 g of impure sample. Assume the impurities do not contain any vanadium ions. Show your working. percentage of vanadium = _________________________ [3][3]
(f)(ii)Complete the equation for the reaction between acidified VO3¯ ions and Zn metal. ...... VO3¯ + ...... Zn + _________________________ → ...... V2+ + ...... Zn2+ + _________________________ [2][2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.

[1] Cu 0 1
[1] Cu2+ 1 0
[1] five 3d orbitals (lines, boxes) in the isolated Cu2+ ion of the same energy
[1] splitting: three higher and two lower d orbitals
[1] energy of all five d orbitals in complex higher than all d orbitals in isolated ion
[any two [1], all three [2]]
[1] M1: more than one (stable) oxidation state / exist in variable oxidation states
[1] M2: vacant/empty (d) orbitals are energetically accessible OR vacant / empty (d) orbitals can form dative bonds with ligands
[1] Ag+ 2 Ag(CN)2- 1-
[1] Fe2+ 6 Fe(CN)64-
[each row [1]]
[1] M1: (structure of trans-[Au(CN)2Br2]-)
[1] M2: (shape) square planar AND (bond angle) 180°
[1] M1: moles MnO4 = 0.075 × 0.0225 = 1.6875 × 10-3
[1] M2: moles V2+ = 5 / 3 × 1.6875 × 10-3 = 2.8125 × 10-3
[1] M3: mass V = 50.9 × 2.8125 × 10–3 = 0.143 g % of V = 0.143 / 0.250 × 100 = 57.3 min 2sf
[1] M1: 2: 3 ratio on both sides
[1] M2: rest of the equation correct 2VO3- + 3Zn + 12H+ -> 2V2+ + 3Zn2+ + 6H2O