cation colour of hydroxide precipitate copper(II) light blue iron(II) green iron(III) red-brown calcium white The table shows the colour of the hydroxide pr...
Question 1 Report
| cation | colour of hydroxide precipitate |
|---|---|
| copper(II) | light blue |
| iron(II) | green |
| iron(III) | red-brown |
| calcium | white |
The table shows the colour of the hydroxide precipitate formed with aqueous sodium hydroxide for four cations. Which of these cations is NOT an ion of a transition element?
Answer Details
Adding aqueous sodium hydroxide to a solution of a metal ion precipitates the metal hydroxide, and the colour of that precipitate identifies the cation. Transition-metal hydroxides are coloured because these ions have a partly filled d sub-shell; main-group metal hydroxides are white.
In the table the light blue, green and red-brown precipitates belong to copper(II), iron(II) and iron(III), all transition-element ions. The white precipitate belongs to calcium, and calcium is a Group II metal, so it is the ion that is not from a transition element.
Note the question asks which is NOT a transition-element ion, so the odd one out is wanted. White precipitate means a main-group cation such as calcium, zinc or aluminium rather than a transition metal.
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