# Identification of lithium and strontium salts

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?

• 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. – Jun-Goo Kwak May 6 '14 at 22:53
• @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? – The DON May 6 '14 at 22:58
• I really do not see, that $\ce{LiCl2}$ or $\ce{SrCl2}$ are insoluble. They should be separable with $\ce{(NH4)2CO3}$. – Martin - マーチン May 7 '14 at 1:48
• I'd concur with Martin's last comment: differentiating them by addition of carbonate seems logical, as the strontium salt should precipitate out. – 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.