Colour in transition metal complexesEdexcel A-Level Chemistry: Flashcards
What these 12 flashcards ask
- Why are transition metal ions in solution often coloured?
- What causes the d orbitals to split in a complex?
- Write the equation linking ΔE and light absorbed.
- What colour is seen when a complex absorbs one colour?
- What is a d–d transition?
- Why is Sc³⁺(aq) colourless?
- Why is Zn²⁺(aq) colourless?
- Name three changes that can change the colour of a complex.
- Why is [Cu(NH₃)₄(H₂O)₂]²⁺ a different colour from [Cu(H₂O)₆]²⁺?
- How does coordination number change in [Co(H₂O)₆]²⁺ → [CoCl₄]²⁻?
- What colour is [Cu(H₂O)₆]²⁺?
- Does a larger ΔE mean absorption of longer or shorter wavelength?
Exam questions on Colour in transition metal complexes
- A solution containing the complex ion [Ti(H₂O)₆]³⁺ is purple. It absorbs visible light most strongly at a wavelength of 500 nm. Planck constant, h = 6.63 × 10⁻³⁴ J s; speed of light, c = 3.00 × 10⁸ m s⁻¹; Avogadro constant, L = 6.02 × 10²³ mol⁻¹.Explain why the solution appears purple.2 marks
- A student compares the aqueous ions of several d-block elements. The ions are Sc³⁺, Ti³⁺, Fe²⁺, Cu²⁺ and Zn²⁺, each in the form of a hexaaqua complex.Explain why the aqueous Sc³⁺ ion is colourless.2 marks
- A student adds reagents to a pale blue solution of copper(II) sulfate, which contains [Cu(H₂O)₆]²⁺. Adding an excess of aqueous ammonia gives a deep blue solution containing [Cu(NH₃)₄(H₂O)₂]²⁺. Adding concentrated hydrochloric acid to a fresh sample gives a yellow-green solution containing [CuCl₄]²⁻.Explain why [Cu(NH₃)₄(H₂O)₂]²⁺ is a different colour from [Cu(H₂O)₆]²⁺, even though copper is in the +2 oxidation state in both.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).