gravimetric determination of sulfate in fertiliser

[123456k]

how could the results obtained be affected if:
a) the mixture in step 5 of the procedure were not tested with more barium chloride solution?
not all sulfate have been reacted and therefore the precipitate is understated. 
b) the filtrate were not tested with silver nitrate solution when the precipitate was washed in step 8.
to rid of impurities from the solution so that the precipitate from the filter paper are rid of impurities.
Step 5:
boil the mixture for a further minute then remove it from the heat and allow the precipitate to settle. ensure no sulfate ions remain in the solution by adding several more drops of barium chloride solution.if more percipitate forms add 3ml of barium chloride solution and testfor unreatedsulfate ions.

step 8:
collect the last drops of filtrate in a 100 ml beaker and test for the presence of chloride ions by adding a few drops of silver nitrate solution to the filtrate. if solution becomes cloudy, wash the precipitate with a further 10ml of warm water and repeat the test

dont think my answer is not right and too brief. please help

[Greatness]

5)a) The barium chloride needs to be in excess so that all the sulfate will react with the barium to form the barium sulfate precipitate. However if there is insufficient barium chloride added, the results obtained may have lower sulfate and sulfur percentages and masses.
b) The reason for doing the silver nitrate test is to investigate whether or not there are still Cl ions still on the filter paper/precipitate content. By washing the precipitate with deionised water a few times, it is possible to dissolve the Cl ions into the filtrate. However, when the solution continues to go cloudy when silver nitrate is added, it indicates that there are still Cl ions present in the precipitate. This would increase the weight of the precipitate slightly for this experiment, producing a higher recording of mass for the precipitate and consequently a higher value for the percentage of sulfur.

[Water]

Just curious,


doesn't the question just ask, "how could the results obtained  be affected"

so



a) Decrease in Mass than expected value

b) Increase in Mass than expected value.




Or do we have to explain it as well? Cause not sure if the question is asking for an explanation.  Just making sure, don't want to waste unnecessary time in exam.

[123456k]

i dunno its apart of a prac question. i'm asumming there should be a explamation. Thanks for the help guys

[Greatness]

yeah we did that prac as well and our teacher wanted explanations as well. But in the exam it would depend on how many marks the quesiton is worth. If one mark then it would be safe to just state if it would increase or decrease i assume.

[123456k]

true. i havent done the prac yet. just getting prepared