Colour in transition metal complexesEdexcel A-Level Chemistry: Mind map

Exam questions on Colour in transition metal complexes

1. 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
2. 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
3. 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