Originally Posted by ohhlalaa

ok i see that, but how does that help me with the question? in the question it doesn't tell you whether or not the cations are soluble or insoluble with the anions... so even if i figure out all the possibilities of each one that doesnt help because im still left with a whole bunch of possibilities..

like how am i susposed to figure out what anion it is...

i found that Ca, Al and Sr are all soluble with CH3COO (acetate), nitrate (No3) Br and I... but im stumped on how im susposed to know if Ca is susposed to be soluble/insoluble in the solution, is Al soluble/insoluble in the solution and if Sr is soluble/insoluble in the solution.

zzz

EDIT: its a grade 11 AP chem. problem btw, for all those wondering.

ok test 1: Ca2+, test 2: Al3+, test 3: Sr2+

-all 3 are soluble with nitrate, acetate, chloride, bromide, iodide so obviously if they are telling you that through those 3 tests alone, you could deduce what the unknown cation is then none of these are the correct answers.

-move on to sulphate, well calcium sulphate is insoluble, aluminum sulphate is soluble, strontium sulphate is insoluble --- this result here should set off warning bells because the unknown was soluble in aluminum

-sulfide would give you the same results as above, so this is a possibility as well.

-hydroxide is also a possibility for the correct answer. this is because one of the test results is different from the rest. while calcium and aluminum are insoluble, strontium is soluble. (in fact this is probably more correct for the answer)

-phosphate, carbonate, sulphite are not possible because all 3 are insoluble, so this would tell you nothing about the identity of the unknown.

-you are looking for something out of the ordinary so you want a case in which 2 are soluble but the other is insoluble or vice versa.

Originally Posted by ohhlalaa

ok i see that, but how does that help me with the question? in the question it doesn't tell you whether or not the cations are soluble or insoluble with the anions... so even if i figure out all the possibilities of each one that doesnt help because im still left with a whole bunch of possibilities..

like how am i susposed to figure out what anion it is...

i found that Ca, Al and Sr are all soluble with CH3COO (acetate), nitrate (No3) Br and I... but im stumped on how im susposed to know if Ca is susposed to be soluble/insoluble in the solution, is Al soluble/insoluble in the solution and if Sr is soluble/insoluble in the solution.

zzz

EDIT: its a grade 11 AP chem. problem btw, for all those wondering.

When Ca is soluble with X anion, it means its soluble in that solution.
The question is asking to you to find the anion in the unknown solution. You need to think about WHY the professor dude used those 3 tests and in that order. & you don't want to look at the anions that give the SAME solubility, you want conflicting ones because that will help you ultimately determine the anion in the solution. The reason why we chose sulphate was because its the only anion with DIFFERENT solubilities amongst Ca Al & Sr. It's the easiest anion to use process elimination using those cations as tests. You don't need to know the actual results of what happens when you add Ca Al & Sr. This is more so a question of logic.

thanks guys for all your help!!!!!!!

-topic closed-

noob

/12chars