I'm having trouble interpreting the results I got for my experiment.

As you should be well aware of, lithium and strontium both burn with crimson red when they are placed in a flame. Now, I can't decide which one it is.

Then I was told to do an experiment with the same salt where I had to add dilute hydrochloric acid and barium chloride. I had no visible change.

Does this last test help me with identifying between strontium and lithium? What element is it?

  • 1
    $\begingroup$ What are the salts you used? Generally in differentiating lithium and strontium you can have another reagent such as hydrochloric acid or barium chloride and create a solid precipitate. $\endgroup$
    – user3735
    May 6 '14 at 22:53
  • $\begingroup$ @Jun-GooKwak Hi sir, We were given an unknown salt and have to work out the what cation and anion are available. We were only allowed to do two test which I have describe above in the question. Yes, I added hydrochloride acid and barium chloride and I had no change. What does that mean? Is it Lithium that is present or Strontium? $\endgroup$
    – The DON
    May 6 '14 at 22:58
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    $\begingroup$ I really do not see, that $\ce{LiCl2}$ or $\ce{SrCl2}$ are insoluble. They should be separable with $\ce{(NH4)2CO3}$. $\endgroup$ May 7 '14 at 1:48
  • $\begingroup$ I'd concur with Martin's last comment: differentiating them by addition of carbonate seems logical, as the strontium salt should precipitate out. $\endgroup$
    – Greg E.
    May 7 '14 at 4:59

If your solution contains only $\ce{Li+}$ or $\ce{Sr^2+}$, you can differentiate them by adding a sulfate solution (for example, $\ce{Na2SO4}$ or diluted sulfuric acid). If strontium is present, a white, fine-crystalline precipitate of $\ce{SrSO4}$ will form. In the case of lithium, the solution will remain clear. This is because $\ce{SrSO4}$ is much less soluble in water than $\ce{Li2SO4}$ ($\pu{0.0132 g}$ versus $\pu{34.8 g}$ in $\pu{100 g}$ of $\ce{H2O}$ at $\pu{20 ^\circ C}$ (reference)).

Adding diluted $\ce{HCl_{aq}}$ and $\ce{BaCl2}$ to a solution is commonly used as a test for $\ce{SO4^2-}$ (if it is present, $\ce{BaSO4}$ precipitates). Maybe this could help you to distinguish between $\ce{Li+}$ and $\ce{Sr^2+}$ given the different solubilities of their sulfates. If your unknown salt readily dissolves in water and $\ce{SO4^2-}$ is found to be present in the solution, then it is likely that you have lithium sulfate. Strontium sulfate as unknown salt would not readily dissolve and therefore not give a positive test.

However, if your solution can contain more ions besides $\ce{Li+}$ or $\ce{Sr^2+}$, I would suggest to try the separation with ammonium carbonate which is already mentioned in the comments to your question.



Lithium chromate is listed as being exceptionally soluble in water. Strontium chromate is listed as being insoluble.

  • $\begingroup$ The OP clearly states that there is no chromate involved. $\endgroup$ May 7 '14 at 1:49
  • $\begingroup$ Add a drop of potassium chromate solution on a white drop plate. Precipitate means strontium; no precipitate means lithium. If two horses differ in height by only a quarter hand, how do you tell the black horse from the white horse? $\endgroup$
    – Uncle Al
    May 8 '14 at 14:52

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