For example, take the redox displacement reaction of a strip of magnesium metal (silver color) and a solution of copper nitrate (blue color). The reaction is obviously able to progress due to the strength of copper as an oxidising agent; it will be reduced out of solution to form a layer of copper metal on the magnesium strip.

However, the Chemistry Data Booklet which is currently used in our state (and, I hope, is up to date) states that the precipitate, in this case, copper, should be salmon pink in colour (come on, who knows what salmon pink looks like?). This was certainly not the case; my observations for this reaction state: "Silver metal dissolves into light blue solution. Black precipitate formed."

I apologise for the lack of pictures of the experimental setup, but I was wondering if there is an explanation for the mismatch of colours. I have noticed this black precipitate in other reactions, notably zinc metal in a copper nitrate solution, and zinc metal in a lead nitrate solution. This is the data booklet currently authorised for use in our assessments.


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