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2 (a) Complete the electron configurations for Ni and Ni²⁺ - CIE - A-Level Chemistry - Question 2 - 2014 - Paper 1
Question 2
2 (a) Complete the electron configurations for Ni and Ni²⁺. Ni Ni²⁺ (b) The presence of electrons in d orbitals is responsible for the colours of transition eleme... show full transcript
Worked Solution & Example Answer:2 (a) Complete the electron configurations for Ni and Ni²⁺ - CIE - A-Level Chemistry - Question 2 - 2014 - Paper 1
Step 1
Step 2
Step 3
Complete the diagram to show the splitting of the d orbital energy levels in an octahedral complex ion.
Answer
In an octahedral complex, the five d orbitals split into two sets: the lower energy set comprising three orbitals (t₂g) and the higher energy set comprising two orbitals (e_g). Thus, the correct diagram should show three orbitals at the lower energy level and two at the higher energy level.
Step 4
On the axes below, sketch the shapes of one d orbital from the lower energy level and one d orbital from the higher energy level.
Answer
The lower energy d orbitals (t₂g) can be represented by the shapes of d_xy, d_xz, and d_yz, which are cloverleaf-shaped. The higher energy d orbitals (e_g) can be represented by d_x²-y² and d_z², which have different shapes. The sketches should indicate these distinct geometries.
Step 5
Explain the origin of the colour of the complex [Ni(H₂O)₆]²⁺.
Answer
The green colour of the complex [Ni(H₂O)₆]²⁺ arises from the d-d electronic transitions. Electrons in the lower energy d orbitals can absorb light energy (blue or red) to transition to higher energy d orbitals, resulting in the complementary colour being observed, which is green.
Step 6
Suggest formulae for A and B and write equations for the two reactions producing A and B.
Answer
The formula for the grey-green precipitate A formed when NH₃ is added is [Ni(OH)₂]. The formula for the blue-violet solution B after further addition of NH₃ is [Ni(NH₃)₆]²⁺. The reactions can be summarized as:
[ ext{[Ni(H₂O)₆]}^{2+} + 2 ext{NH₃} \rightarrow ext{[Ni(NH₃)₂(H₂O)₄]}^{2+} + 2 ext{H₂O} \ ext{(Formation of A)}]
[ ext{[Ni(H₂O)₆]}^{2+} + 6 ext{NH₃} \rightarrow ext{[Ni(NH₃)₆]}^{2+} + 6 ext{H₂O} \ ext{(Formation of B)}]