Reliability of sulfate prac. (1 Viewer)

[Affinity]

it's not reliable because fertillisers are usually heterogenous(unless it's a just a single compound, without insoluble solids), and the sulphate content varies from each sample taken.

 

[Victorist]

I said:

1) Need to use sintered glass crucible with vaccum for filtering as BaSO4 is very fine.
2) 1.0g of fertiliser is too little, to more fertilier you weigh out the less % of human error, and weighing errors.
3) Repeat the experiment.
4) Make sure excess BaCl2 was used.
4) Use high accuracy electronic balance.

I forgot to say:

Dissolve in HCL, not water.
Filter off suspended solids.

Hopefully it will get me some marks.

 

[LadyMoon]

couldnt fertiliser also contain Phosphate? or is it just me?
tis was like my fouth point: i said that the precipitate couldnt might not have all been BaSO4, as the fretiliser might have contained traces of Phosphate or other ionic complexes.

 

[Frigid]

hmmm... good point... as far as i know, we chuck acid in to get rid of the carbonates... but yeah, phosphates?

let us suppose they do not exist.

SHIT I FORGOT TO MENTION YOU CAN CHECK RELIABILITY BY CHECKING THE BACK INFORMATION PANEL OF YOUR FERTILISER!!!! >.<

 

[ND]

Originally posted by Affinity
it's not reliable because fertillisers are usually heterogenous(unless it's a just a single compound, without insoluble solids), and the sulphate content varies from each sample taken.

Now why didn't i think of that...

hmmm... good point... as far as i know, we chuck acid in to get rid of the carbonates... but yeah, phosphates?

let us suppose they do not exist.

SHIT I FORGOT TO MENTION YOU CAN CHECK RELIABILITY BY CHECKING THE BACK INFORMATION PANEL OF YOUR FERTILISER!!!! >.<

The HCl would stop the phosphates precipitating out (check conquering chem if you wanna know why - the ion tests section). Comparing your value with the given one wouldn't be reliability, it would be validity; you could get the same value every time (not that you would, as Affinity explained), but it'd be way out.

 

[Yam]

I just said all the stuff about it not being accurate then like "if the student was able to reproduce these results consistently, it would be reliable, albeit at producing inaccuate results"

 

[keepin_sanity]

Originally posted by Frigid

that's all well and good, but as i said before, in the scope of the sulfate prac, there isn't much to be said of reliability:
yes, it's very reliable; reliable for repeated INACCURATE results!!!
everyone repeat with me: gravimetric analysis suxxorz.

I know! I agree...I was just posting what my teacher told me about reliability and validity...it was a pretty dodge question. I concentrated on validity anyway so hopefully I'll get some sympathy marks or something!

 

[PJG]

A similar question was asked in this years CSSA Trial Exam paper (worth 4 marks), of which the marking guidelines suggested the following response.

• Minimise loss of precipitate by studying temperature vs solubility curves of all components of the fertiliser and compare with the solubility of the precipitate to determine the optimum practical temperature of the solvent during filtering.
• Use the minimum amount of solvent for rinsing the precipitate.
• Use small and frequent rinsing out of containers to make rinsing more efficient.
• Test filtrate for the presence of sulfate ions using Barium Chloride and if still present add more Barium Chloride and refilter.
• Dry precipitate slowly and weigh to constant mass.

Responses such as The experiment should be repeated a number of times in order to increase the reliability are clearly insufficient.

 

[Affinity]

hey... that's a different question.
this one asks you the assess the reliability, not asking you to improve it

 

[william]

the reliability also depend on the temperature , the higher the temperature, the higher the solubility, thus more BaSO4 ppt lost

 

[william]

repeat the experiment, but keep the variables constant