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Edexcel A-Level Chemistry A2 17.7 Aqueous Solutions of Transition Metal Ions Are Usually Coloured Questions

Use the ion and its d-electron count: Ni2+, Cu2+, Cr3+, Fe2+ or vanadium complexes can be coloured, while d0 or d10 ions are common traps.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
A2

Exam points

  • Identify ions such as Ni2+ that form coloured transition-metal complexes.
  • Use known colours or formulae to suggest cations responsible for green or blue solutions.

Edexcel A-Level Chemistry A2 17.7 Aqueous Solutions of Transition Metal Ions Are Usually Coloured Questions question 1

[Maximum number: 3]

Solution A and solution B are aqueous solutions.
The compound in each solution contains one cation and one anion.
The cations are different but the anions are the same.
Both solutions are green.

Question (a)

(a)

Give the formulae of three cations which could be responsible for the green colour.

[ 2 ]

Question (b)

(b)

A student added dilute aqueous sodium hydroxide, drop by drop, to samples of each solution.
Initially a green precipitate formed in both solutions.
More aqueous sodium hydroxide was added until the sodium hydroxide was present in excess.
The precipitate produced from solution A was insoluble and turned brown on standing.
The precipitate produced from solution B dissolved to give a dark green solution C.

[ 1 ]

Question (i)

(i)

Give the formula of the species responsible for the dark green colour in solution C.

[ 1 ]
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