Consider a solution that is 2.5×10 2 M in Fe2+ and 1.4×10 2 Min Mg2+. If potassi

Question

Consider a solution that is 2.5×102 M in Fe2+ and 1.4×102 Min Mg2+.

If potassium carbonate is used to selectively precipitate one of the cations while leaving the other cation in solution, which cation will precipitate first?

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Part B

What minimum concentration of K2CO3 is required to cause the precipitation of the cation that precipitates first?

Express your answer using two significant figures.

1.2×109

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Part C

What is the remaining concentration of the cation that precipitates first, when the other cation just begins to precipitate?

Express your answer using two significant figures.

Fe2+] =   M  

Explanation / Answer

Part A: Fe2+ions precipate first when potassium carbonate (K2CO3) is added to the solution.

Reason: The concentration of ferrous ions (Fe2+) in the solution, that is, the number of parts of ferrous ions in 100 parts of the solution is greater than the concentration of Magnesium (Mg2+) ions in the same solution. Hence it can be concluded that carbonate ions (CO32-) ions of potassium carbonate will prefer to react with ferrous ions that are more in abundance.

Part B: I see that you have already arrived at the correct answer.

Part C: Since Fe2+ and Mg2+ are similarly charged cations (2+), and they are present in the same solution, the concentration of Fe2+ ions would be (2.5 - 1.4)* 10-2 = 1.1 * 10-2 M

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