[T.I.M.]

Hello everyone, I was wondering if there was anyone on this forum that would be able to give me some help into finding these 6 inorganic salts by their mutual interactions.... I'm going to have to find out what each salt is by elimination, and can only react them with each other and/or water. Nothing else is allowed.

barium nitrate
lead nitrate
magnesium sulphate
potassium iodide
sodium carbonate
zinc nitrate

I have no idea if there is an easy starting point. Will I have to mix them all together and see what happens, or is there a much easier way of distinguishing between them?

Any help would be HUGELY appreciated. Thanks.

[Borek]

I have no idea if there is an easy starting point. Will I have to mix them all together and see what happens, or is there a much easier way of distinguishing between them?

Mix solutions, observe changes - and think!

Check solubility tables of all possible salts resulting from mixing of the above. Check also colors of the insoluble salts.

[T.I.M.]

How do you work out the possible salts?

[Albert]

You can check a solubility table: for each cation find out a salt whose anion is in one of compounds you have in the beginning (i.e. BaCO₃ has a low Ksp, as well as BaSO₄).

[T.I.M.]

I'm still now quite getting it. How do you work out what displaces what?

For example, I have found out that Magnesium sulphate and barium nitrate froms a white ppt as barium sulphate is formed... is there a way of knowing what displaces what?

[Albert]

Mixing the two, you will yield a white precipitate, which is barium sulphate. Once you have separated the solution (containing magnesium and nitrate ions) from barium sulphate, adding another compound, you yield another precipitate (what about MgCO₃?).

[T.I.M.]

What I mean is, can you use the electrode potentials or something to determine what is more reactive?

For example... will magnesium sulphate also form a white ppt with zinc nitrate? Yielding zinc sulphate?

Will there be a reaction between magnesium sulphate and potassoium iodide?

etc etc.

[Yggdrasil]

I'm still now quite getting it. How do you work out what displaces what?

For example, I have found out that Magnesium sulphate and barium nitrate froms a white ppt as barium sulphate is formed... is there a way of knowing what displaces what?

When you disolve magnesium sulfate in water, it dissociates to form Mg²⁺ and SO₄^2- ions.  When barium nitrate dissolves, it forms Ba²⁺ and NO₃^2- ions.  Therefore, in a solution containing magnesium sulfate and barium nitrate, you will have two classes of cations (Mg²⁺ and Ba²⁺) and two classes of anions (SO₄^2- and NO₃^2-).  Since salts are combinations of one anion and one cation, you will have salts which can be formed:

Magnesium sulfate
Magnesium nitrate
Barium sulfate
Barium nitrate

It is your task to find out which of these four salts is insoluble (if any).  This is the case in any double displacement reaction.  So, whenever you have barium ions and sulfate ions in the same container, you will form a barium sulfate precipitate.  The other salts (magnesium sulfate, magnesium nitrate, and barium nitrate) do form in solution, but because they are soluble you will not see their formation because they won't form a precipitate.

[T.I.M.]

Right, OK. But how do you know that the barium forms with the sulphate... do you just know or is there a method of working it out.

Like potassium iodide added to sodium carbonate...there is K+ I- Na2+ and CO3-, right?

What goes to what and is there a ppt?

Sorry for sounding so pathetic.

[Borek]

Google preicpitation tables or solubility rules.