Formation of coloured ionsAQA A-Level Chemistry: Mind map

Exam questions on Formation of coloured ions

1. Aqueous copper(II) sulfate is blue and aqueous zinc sulfate is colourless. The copper(II) ion has the electron configuration [Ar]3d⁹ and the zinc ion has the configuration [Ar]3d¹⁰.
   Explain why aqueous copper(II) sulfate is coloured but aqueous zinc sulfate is colourless.2 marks
2. A solution of [Ti(H₂O)₆]³⁺ is purple. A student is investigating how the colour of a complex ion is related to the light it absorbs. Use h = 6.63 × 10⁻³⁴ J s and c = 3.00 × 10⁸ m s⁻¹.
   The purple solution absorbs green light with a wavelength of 510 nm. Calculate the energy difference, ΔE, in J for one ion.2 marks
3. A student uses a colorimeter to find the concentration of copper(II) ions in a waste solution. Standard solutions of copper(II) sulfate with concentrations of 0.020, 0.040, 0.060 and 0.080 mol dm⁻³ are each treated with excess ammonia solution, and their absorbances at the chosen wavelength are 0.14, 0.28, 0.42 and 0.56 respectively.
   Explain why the student adds excess ammonia solution to each solution, and why a coloured filter is used in the colorimeter.3 marks