Hi ultimaonline, what do u mean by ''contaminating salt
crystals?'' Do u mean the crystals will be acidified? And why is c)
methyl orange is added to indicate the end of the rxn not
acceptable? Because i thought by ensuring endpoint, we can be sure
that neutralisation takes place and thus, pure crystals are
formed?
It means the crystals will be a mixture of sulfuric acid
crystals and nickel sulfate crystals.
Methyl orange will contaminate the crystals, just as excess
sulfuric acid would (see preceeding statement).
You have to redo the titration without indicator, once
you've determined the correct volume of acid to be added in
the preliminary titration (ie. with indicator).
hopefully, my last 2 qns on this thread :)
1) Is it a requirement for substances to be separated by paper
chromatography to be liquids? If not, any eg. of solid substances
that can be tested?
2) In an expt, 4.0cm3 of 1.0mol/dm3 aq iron(iii) chloride was
mixed with 4.0cm3 of 1.0mol/dm3 aq NaOH.
Fecl3(aq) + 3NaOH(aq) => Fe(OH)3(s) + 3Nacl(aq)
What would be observed when the rxn was complete?
a) Brown ppt in a green soln
b) Green ppt
c) Brown ppt in yellow soln
d) Green ppt in pale yellow soln
The substance to be tested via paper chromatography need to be
soluble in the solvent used (eg. water, ethanol, etc). Solids will
not travel up the chromatograph paper.
NaOH is limiting, and Fe3+(aq) is in excess. Hence, the product
is a brown ppt of Fe(OH)3 in excess Fe3+(aq) which is a pale yellow
solution.