Hi all, regarding this experiment, does anyone know why must the solution be kept below 80 degree celsius during the precipitation stage, why is it necessary to wash the precipitate until it is free from chlorine and the possible sources of error?
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In the meanwhile (while you set up your user account on ChemicalForums, make your post and await helpful replies there), I'll offer brief comments on your queries.
Keeping the solution below 80% will avoid sample splatter of the solution (containing the Ni2+ cations that you're carrying out quantitative analysis on), which is one possible source of error.
Chlorine has (relatively) high molar mass. If your precipitate remains contaminated by Cl- ions (from the hydrochloric acid used in the procedure), your calculations will be in error. Remember you're basing your stiochiometric calculations (for this quantitative analysis) on the assumption the dried precipitate obtained is pure bis(dimethylglyoximato)nickel(II).
There are *many* (I can spot over a dozen) possible sources of error, present in every stage of this experiment. I won't list them out here, but you should be able to infer, deduce and elaborate on at least a half-dozen of them, based on just the following readings (read all of them, in the order given below).
http://www.kimia.um.edu.my/images/kimia/lab%20manual/level1/lab%20manual%20yr%201%20inorganic.pdf
http://www.cpachem.com/en/Clas/Ni-grav.asp
http://academic.cengage.com/resource_uploads/downloads/0030355230_17071.pdf
http://chemlab.truman.edu/CHEM222manual/pdf/nickelgrav.pdf
Lastly, a reminder & recommendation that all chemistry discussions beyond 'A' levels, are best done on ChemicalForums.