fertiliser - sulfate prac question (1 Viewer)

[sig]

From what I know this prac involves forming of precipitates to determine the amount of sulfate present in fertiliser commonly using barium chloride etc.

Anyway my question is...is filter paper a viable and practical method or not? After researching i've been hearing a lot of things. 1. it's very inaccurately practically 2. results won't be very accurate with this method 3. insoluble precipitate formed would be too fine for the filter paper

Is there any other method besides a filter paper method? Say that using a sintered glass filter is not an option and this prac needs to be done in a reasonable amount of time (1 hour). Is there any suggestions to seperating the insoluble from the soluble solution ACCURATELY and reliably?

 

[jm1234567890]

sintered glass filter + vacuum pump

it is in my summary

I don't think there are many other ways to separate solid form liquid.

lol, does your school have sintered glass filters?

filter paper is good enough for high school prac, just use fine filter paper with a vacuum pump.

 

[Xayma]

Originally posted by sig
From what I know this prac involves forming of precipitates to determine the amount of sulfate present in fertiliser commonly using barium chloride etc.

Anyway my question is...is filter paper a viable and practical method or not? After researching i've been hearing a lot of things. 1. it's very inaccurately practically 2. results won't be very accurate with this method 3. insoluble precipitate formed would be too fine for the filter paper

Is there any other method besides a filter paper method? Say that using a sintered glass filter is not an option and this prac needs to be done in a reasonable amount of time (1 hour). Is there any suggestions to seperating the insoluble from the soluble solution ACCURATELY and reliably?

Our filter paper didnt work, because the precipitate had time to redissolve and basically become fine again. If you slowly heat it for 15 minutes or so it will form bigger crystals which should be stopped. But my school is full of errors, so Im not surprised (we didnt have enough time to filter the mixture after the HCl because there was still undissolved solids in )

 

[jm1234567890]

hmm... I didn't know about the slowly heat thingy, I just used HCl

 

[Xayma]

Originally posted by jm1234567890
hmm... I didn't know about the slowly heat thingy, I just used HCl

Slowly heating them 'digests' it, which makes the crystals bigger, so in theory shouldnt go through the pores in the filter paper.

 

[sig]

nah our school doesn't have sintered glass filters...we have to find alternatives

anyone know the possibility of decanting...wash...decanting...wash then evaporating? or does that cause many errors as well?

 

[Li0n]

what sing failed to mention was that this is an assesment task, and if the accuracy of our results are within 5% then thats 4 marks, if they are withtin 10% then thats 2 marks.

 

[Xayma]

Well your unlikely to get them like that within a time limit.

Because:

a) You need to filter the remaining fertiliser after dissolving it.
b) You need to ensure that only the sulfate comes out of solution.
c) You need to use a sintered glass filter or as an alternative, heat for about 15 minutes (do not let it boil) and slowly cool it then carefully filter it (with 2 bits of filter paper, and probably 2 or 3 filters going at once)

 

[04er]

is it just a coincidence that this is the assessment task for my school as well?

 

[04er]

Originally posted by Xayma
Well your unlikely to get them like that within a time limit.

Because:

a) You need to filter the remaining fertiliser after dissolving it.
b) You need to ensure that only the sulfate comes out of solution.
c) You need to use a sintered glass filter or as an alternative, heat for about 15 minutes (do not let it boil) and slowly cool it then carefully filter it (with 2 bits of filter paper, and probably 2 or 3 filters going at once)

Our chem lessons are 80 minutes long. Would that be sufficient (to do the prac itself and then write up results, analysis and conclusion)?

 

[Xayma]

I doubt it, you wont have the time to 'digest' the precipitate (ie the heating of it), you will definately have to have multiple filters and remember to wash the filtrate with ethanol, it dehydrates it and makes it dry alot quicker.

 

[tina_goes_doo]

We just started talking about this in class today. The teacher said you could filter it through either using sintered glass or paper using a Buchner funnel. (suction filtration)

And he said something about using ashless filter paper for more accurate results. (after you 'digest' the ppt)

I dunno, we're going deeper into it tomorrow and it's late now

 

[Adz_h]

sig n lion, maguid sed we have sintered glass filter

sig n lion, maguid sed we have sintered glass filter

 

[MaryTylerMoore]

Hey ,

Sintered glass funnels are the best. Try a Porosity 4 as that is the best compromise between pore size and speed of filtration.

If you use the filter paper and filter funnel, it's not going to be as accurate, but at least you can say in your discussion (the next syllabus point after the prac) that it was an obvious flaw and you should use a Buchner/Scintered Glass funnel next time.

It's best to heat up both solutions, but not to boiling temperature. Use a magnetic stirrer and slowly pour in the barium nitrate into the ammonium sulphate or fertiliser. The high heat increases particle collisions and crystal size.

Also, constant stirring prevents sudden saturation and subsequent immediate precipitation.

After that, add a fairly large amount of acetone. Acetone is an organic solvent which is hydrophillic and causes the ions to repel forming larger aggregates/crystals of BaSO4.

The use of water to create a vacuum is wasteful so it might be better to use vacuum pumps if you have them.

 

[Li0n]

oh well, time to forge results !

 

[kalinda]

we just crushed the fertiliser the weighed it
then dissolved it in warm water
then filtered it - the sulfate dissolved in the water
the added excess BaCl to form a white ppt
the filters that with fine filter ashless paper
then weighed the crucible and teared it. put the paper + BaSO4 in and burnt off the paper
the weighted it again to get the amount of BaSO4
then found the amount of SO4 in the sample
then calculated the percentage