We did an experiment to find out how much sulphate was in a sample of homemade fertiliser. This is the method:
Å Finely grind a small quantity of fertiliser using a mortar and pestle. Weigh out accurately about 1.0 g
of fertiliser into a 100 mL beaker. Record the mass of fertiliser to three decimal places.
Ç Add about 50 mL of deionised water and stir to dissolve as much of the fertiliser as possible. Filter
the mixture into an approx. 500 mL beaker, washing the residue (the solid trapped in the filter paper)
several times with a small amount of deionised water.
É Add about 3 mL of 2 M hydrochloric acid to the filtrate (the solution passes through the filter paper)
and then add more deionised water so that the total volume of solution is now about 200 mL [Don't
have the total volume of solution larger than about 200 mL as both boiling and filtering will take too
long.]
Ñ Boil the solution for 3 minutes.
Ö Slowly add 15 mL of 0.5 M barium chloride solution to the hot solution, stirring all the time. Record
your observations.
Ü Boil for another minute, then remove the beaker from the heat and allow the beaker and contents to
cool.
á This step is only feasible if your barium sulfate clumps sufficiently for it to settle. Ensure that no
more sulfate ions remain in solution by adding a couple of drops of barium chloride solution to the
supernatant solution. (If more BaSO4
forms, add 3 mL more barium chloride solution to precipitate the
remaining sulfate ions.)
à Name a filter paper around the edge using a pencil or insoluble ink and weigh the named filter paper.
Once again, record its mass to three decimal places.
â Filter the barium sulfate using a buchner funnel and vacuum filtration - filtration is more rapid if most
of the solution is filtered before the bulk of the solid is poured on to the filter paper. Ensure that the solid
remains on the paper.
ä Carefully remove the damp filter paper and residue from the Buckner funnel, put it where directed and
allow the filter paper and barium sulfate to dry overnight. Then, reweigh the filter paper and barium
sulfate.
The weight of my precipitate was 1.5575g
I understand that we are fidning the concentration of sulphate in the feriliser, I just don't understand what the precipitate consists of. Is it pure sulphate (because you use BaCl2 to neutralise the BaSO4) or is it actually BaSO4 and I am required to calculate the amount of sulphate?
And also, what do I write in my results analysis section? I thought we would be told what the correct measurement was so we could compare and contrast, but we haven't so now I'm confused about how I analyse my results.
