Cation Identification: Precipitation Reactions (1 Viewer)

[BrownyTheBrown]

Hi peoples,

i was wondering if you could tell me some information on which cations are present in a solution when:


* F- gives a white ppt but not with Cl- or OH-
*No ppt with chloride or sulfate but ppt with OH- ; decolorises acidified MnO4-
*No ppt with Cl- or SO4 2- but ppt with OH- ; forms red colour with SCN-


any help would be appreciated as i have scoured the net so many times with no answers at all.

thanks

 

[TheKing]

check your solubitlity rules.....
earlier this year or maybe prelim
will definately be in your text book
remember keywords: SOLUBILITY RULES

 

[scotty schaefer]

ok- the first one I believe is Calcium, the second is a little hard , I think the substance you called Mn04- should actually be Potassium Permanganate, if so then the cation in the second solution is Iron 2+, the third is definitely Iron 3+. I may be wrong so please feel free to correct me if I am wrong. If you have any other queries I am sure anyone would be willing to answer them for you.

 

[BrownyTheBrown]

thanks heaps for that scotty. i have one more that is troubling me aswell:

i need a cation that gives a white ppt with sulfate but not with chloride or hydroxide???

i thinks it may be calcium but i'm not sure; thanks

 

[xiao1985]

may also be ba 2+ i believe...
to distinguish between ba2+ and ca2+, add F- i think...

ba2+ no ppt
ca2+ white ppt

 

[BrownyTheBrown]

oooooo!!! thanks that cleared it up for me, but is the cation in the solution still calcium when:


F- gives a white ppt but not with Cl- or OH- or SO4(2-) ???

 

[xiao1985]

i believe ca 2+ form a ppt with so4 2-...

not with cl -
(not sure but i believe) a ppt with oh -

 

[kalinda]

for the difference between Ba and Ca the best thing is to do a flame test

 

[xiao1985]

i still believe the F- test is more accurate
have the soln , ppt out all the ca 2+ by adding excessive F -
then add H2SO4 to see if any ppt form... since all Ca 2+ has being removed by the means of ppt, any ppt now would mean the presence of Ba 2+, given that it has being given that the only possible cations in soln is Ca 2+ and Ba 2+...

btw, forgot to add: flame test is a perfectly valid method too =)