Question 256469

The minerals of a 1.05 X 103 kg ore sample from a South African mine in Mpumalanga were extracted by acid leaching to make up a solution whose volume was 45.8 dm3 . When this solution was analysed, it was found to contain 0.00112 mol.dm−3 of Fe2+(aq) ions and 0.0142 mol.dm−3 of Mn2+(aq) ions. The solution was slowly made alkaline to selectively precipitate the first metal ion (as a metal hydroxide) from the second. The first precipitate was then filtered off from the remaining solution, dried and reduced to its pure metal form. The pH of the remaining solution was carefully adjusted for the second time until the entire concentration of the second metal ion, together with a trace concentration of the first metal ion, were co-precipitated as metal hydroxides. This co-precipitate was also filtered off, dried, and reduced to the metal form.

2.1.1 The pH at which maximum separation of the two metal ions was achieved. (6)

2.1.2 The percentage mass impurity of the metal that was obtained from the last precipitate.

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