[abdi]

Hello my name is abdi and i'm new here. This seems to be a very good forum about chemistry and I have a question which i cannot get my head around.
Here it is

You are provided with solutions of three different salts in water. One is chloride, another is sulphate and a third is nitrate. As a result of what you have discovered about the solubilities of compounds in water, describe how you would decide which was which.

I want to know the reason for an answer because I really want to understand this question. Thank you.  

[xiankai]

u need to have learnt the solubility rules, so u know how to distinguish the three as that is what the question asks for.

[abdi]

Thanks for the answer xiankai but what are the solubility rules

[mike]

Did you previously learn about the solubilities of anions? For example if you add silver nitrate (or Ag+) to a solution of Cl- ions you will get a precipitate of AgCl silver chloride. This is a test for Cl- ions in solution.

You would have probably investigated or studied how to precipitate other ionsas well.

[abdi]

so for example can i add iron(II) to the sulphate to get iron sulphate because iron (II) has valency charge 2+ and sulphate 2-

[Donaldson Tan]

do you know a list of common salts that are water-soluble or not?

based on their solubilities, you add reagents to make a particular salt that confirm the presence of particular anion/cation.

eg. presence of chloride is confirmed by formation of a white precipitate (AgCl) when aqueous silver nitrate is added to the test solution. AgCl is water-insoluble.

[abdi]

was it right what I said for the sulphate or is it wrong

[Karakth]

Iron (II) Sulphate (VI) is soluble. All Iron (II) salts are soluble except hydroxide, sulphate (IV), phosphate and carbonate.

Now, the question didn't specify the oxidation number of S in the sulphate, so you should assume it's sulphate VI, which is soluble as an Iron (II) salt.

The above was taken from my practical chemistry handbook. I'm not sure about the exam rules in other countries, but we are allowed to have this book with us in our practical exam.

[abdi]

how would I decide then which is which

[mike]

Barium chloride (BaCl2): test for sulfate (SO42-)
Ammonium molybdate: test for phosphate (PO43-)
Brown ring test (Fe2+/H2SO4): test for nitrate (NO3-)

these are some of the standard anion tests, you can search on the net for more too.

[xiankai]

its safer to use barium nitrate to test for sulfate because if Ag+ is present, a false positive may be generated.

another possible test for nitrate is to add NaOH and a bit of Al, followed by heating, which would produce NH3, which then can be tested for.