Magnesium Carbonates Reaction Under Various Test?

[John Ker]

Homework Statement

If you had a solution of Magnesium carbonate, what results would you expect from the following four tests: Precipitation Test, Flame Test, Benedicts Reagents Test, Dilute Acid Test.

Could someone take a look at my reasoning to how the Magnesium Carbonate would react under these conditions, thanks!

The Attempt at a Solution

[/B]
Precipitation Test:

MgCO3(aq)+CaCl2(aq) → MgCl2(aq) + CaCO3(s)

When Magnesium Carbonate reacts with Calcium Chloride, it will produce Magnesium Chloride and Calcium Carbonate, Calcium Carbonate is a precipitate in this case, hence the test will be positive. Flame Test:

When testing for metal ions within the solution, Mg, the metal, does not produce visible light within the spectrum, hence the test will produce no color when placed under the flame. Benedicts Reagent:

Magnesium Chloride is not a simple sugar, hence it will produce blue under both the room temperature and heated solutions. Dilute Acid Test:

MgCO3 à Mg+ + CO3-

2H+ + CO3 à H2O + CO2(g)

CO2 will rapidly form, giving a positive to the Dilute Acid Test.

 

[Borek]

what results would you expect from the following four tests: Precipitation Test

Is it really how the question was worded? "Precipitation test" doesn't say anything about anion/cation added, so it can be either positive or negative, depending on what you use.

Other than that your logic looks OK (although I am not convinced about practicality of the calcium carbonate precipitation, magnesium carbonate is rather weakly soluble so the concentration of CO₃^2- will be low, making the precipitation difficult to observe).