Just some help on a question (1 Viewer)

[ahohen_77]

Can someone help me on this question....describe a test which a student could use in the school laboratory to identify the 'white soluble solid' as potassium sulphate OR sugar

 

[spice girl]

dissolve in water, then add barium nitrate.

ppt: sulfate
no ppt: sugar

just make sure there's no sulfate impurities in the sugar

 

[mitochondria]

You could do this as well:

Add concentrated sulphuric acid to both unknown samples, the one which turns brown/black is sugar

This happens because sulphuric acid dehydrates sugar to form water and eventually the sugar will decompose to form carbon, which appears as a black substance.

Note: this is an exothermic reaction which gives of a large amount of heat during reaction. Also steam and sulphur dioxide are formed during this reaction. This experiment should be conducted inside a fume cupboard.

 

[freaking_out]

yep, i think they would expect u to use a simple method like spice girls (which is deduced from solubility tables) rather than the "innovative" mitochondria's method.

 

[xiao1985]

Originally posted by freaking_out
yep, i think they would expect u to use a simple method like spice girls (which is deduced from solubility tables) rather than the "innovative" mitochondria's method.

lolz, but his method is do-able... now i got a xiao's method, which is not do-able:

------- do not do this to the real sample ------

taste it... if it is sweet, den tis sugar... other wise, tis potassium sulfate....

------- again, neva try it in a real circumstance -------

 

[freaking_out]

Originally posted by xiao1985
lolz, but his method is do-able... now i got a xiao's method, which is not do-able:

------- do not do this to the real sample ------

taste it... if it is sweet, den tis sugar... other wise, tis potassium sulfate....

------- again, neva try it in a real circumstance -------

maybe he can get u to do the tasting.

 

[mitochondria]

lol.. you know.. I actually had a question like this in one of my chem prac test.. one of my friend went totally blank about this question but he put down something like xiao's method.. but there's actually an improved method suggested by his father and I think we'll all agree to that:

get your friend to taste it


got picked on by freakie...

but still, the mitochondria's method is very do-able, consider that it's only one step over spice girl's two stepS

 

[freaking_out]

i heard that back in those days- chemists used to taste things to identify them and stuff.

 

[mitochondria]

well.. i think that's right actually, have you heard about a joke (well.. black-humour ) about what happened in Rome? Lead is actually sweet in taste and they have been using it to... *ahem* I think i don't have to go into details.. and maybe you should reconsider about the downfall of Rome?

 

[spice girl]

lead acetate was the sweetener in roman days

 

[freaking_out]

Originally posted by spice girl
lead acetate was the sweetener in roman days

but they still had great thinkers and stuff didn't they- so yeah, maybe lead acetate made them get hyped up.

 

[mitochondria]

Ooooooh.. thanks for the correction spice girl otherwise I'd be still in the dark.. anyways.. well, you see frekie, the great thinkers are only a tiny portion of the population, so in a scientific point of view, maybe they are those who didn't like sweet stuff? In a stereotpyical viewpoint those people don't like sweet things.. that works for me (Do you have CHOCSOC @ USYD?)

 

[xiao1985]

Originally posted by spice girl
lead acetate was the sweetener in roman days

lolz, dat's an idea....

*xiao thinks of next time his annoy cousin cums ova, n brins out a home made cake...*

 

[freaking_out]

Originally posted by mitochondria
... (Do you have CHOCSOC @ USYD?)

do u mean a chocolate society- well i heard there's one at usyd.

 

[Xayma]

Or you could test to see if they combust (Im not sure about Potassium Sulphate and if it combusts normally) but sugar will only combust if there is a catalyst and cigarette ash happens to work (well you may as well make use of all the smokers)

 

[freaking_out]

Originally posted by Xayma
Or you could test to see if they combust (Im not sure about Potassium Sulphate and if it combusts normally) but sugar will only combust if there is a catalyst and cigarette ash happens to work (well you may as well make use of all the smokers)

what the hell- how can u combust a solution?

 

[Xayma]

It said "soluble white solid" never said it was just the solution

 

[spice girl]

i guess u can do a flame test on it. if it's lilac color it's prolly the K2SO4. i'll leave it to u guys to guess wot color the sugar would give.

 

[mitochondria]

ummm.. just a thought.. why not analyse their emission spectra the one with a semi-band (chopped into bits) like structure must be sugar..

 

[freaking_out]

Originally posted by mitochondria
ummm.. just a thought.. why not analyse their emission spectra the one with a semi-band (chopped into bits) like structure must be sugar..

sif high schools have the machinery to do that!