Tetra, if I understand your description correctly you simply added sodium carbonate to a solution of manganese II salt and got a precipitate of
manganese II carbonate. What's the issue? What did you expect to happen? If your solutions are too concentrated then you tend to get a slimy,
difficult to filter, precipitate. In this case try diluting the resulting suspension and warm it for a few hours, this will often cause the initial
slimy ppt to crystallize, become granular and more easily filtered. This is a general comment for most precipitation reactions e.g. more dilute
solutions give more easily filtered precipitates. It is a common mistake for people to try using excessively concentrated solutions for precipitation
reaction and then wondering why they got an unfilterable gloop!
In the case of Mn2+ it is better to use warm (40 C) sodium bicarbonate solution because it is less alkaline than sodium carbonate and therefore
generates less basic Mn carbonate. The Mn2+ basic carbonates tend to oxidize and turn brown rapidly when dried. You should read an old inorganic
chemistry book or two, these are the sorts of things described under the preparation of individual compound such as manganese carbonate etc.
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