An environmental chemist collects a water sample near an abandoned mine. On adding a few drops of sodium hydroxide solution to the sample, a dirty green precipitate is formed. After leaving the test tube uncapped on the laboratory bench for several hours, the chemist notes that only the surface layer of the green precipitate has turned a dark brown colour.
Explain these observations.
Practise Edexcel GCSE Chemistry Qualitative analysis: tests for ions with exam-style questions for Foundation and Higher tier. 127 questions, matched to the Edexcel GCSE Chemistry (1CH0) specification and written in Paper 1 and Paper 2 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.
