# How to test for magnesium and calcium oxide?

Is there a way to test for $\ce{MgO}$ and $\ce{CaO}$?

I want to prove that $\ce{MgO}$ and $\ce{CaO}$ are created from their respective calcinations.

$$\ce{MgCO3 (s)->[heat] MgO(s) + CO2(g)}$$

$$\ce{CaCO3 (s)->[heat] CaO(s) + CO2(g)}$$

• For iron clad proof!?! Use $200,000 x-ray diffractometer. – MaxW Feb 7, 2017 at 3:14 • I assume these are 2 separate solutions, one with MgCO3 and one with the CaCO3, and not a single mixture of the two? Or do I have that wrong? Feb 7, 2017 at 5:22 • @airhuff - ?!? the (s) in the chemical equations means solids not solutions. – MaxW Feb 7, 2017 at 5:30 • @MaxW, brain-skip on my part, slipped right by me, thx. My first thought for a quick and dirty test is to heat the salts under an inert gas stream, measure the CO2 coming off by whatever means, then weigh the remaining solid and see if it all adds up. If you really want to be sure, digest the solid, dilute like crazy, and measure by Mg or Ca ICP-AES or AA! Feb 7, 2017 at 5:44 • @MaxW, yes, proof is by degrees. And I said to measure the Mg and Ca by ICP or AA. The liberated$\ce{CO2}$(g means gas here ;) would simply be measured by any number of classical techniques (titration in cheap$\ce{CO2}$coulometer, IR detector, adsorb and weigh, etc.). You could also measure the oxygen in the (undigested) solid by classical pyrolytic Mertz oxygen analysis (~35$ analysis), though the latter could have a 10% + relative uncertainty in this matrix. Feb 7, 2017 at 6:34

Test for formation of metal oxides

The formation of metal oxides can be tested by their reaction with water. Magnesium oxide is almost insoluble in water(0.0086 g/100 mL (30 °C)) and magnesium hydroxide is formed in only negligible amount. However calcium oxide is soluble in water and forms calcium hydroxide to a large extent.

Differentiating magnesium oxide and calcium oxide

You can differentiate magnesium oxide and calcium oxide through salt analysis. Magnesium oxide is primarily $\ce{Mg^2+}$ and calcium oxide $\ce{Ca^2+}$. For $\ce{Mg^2+}$, use ammonium phosphate test (forms mainly white crystalline mineral or struvite)

$$\ce{Mg^2+ + NH4+ + PO4^{3−} <=> MgNH4PO4↓->[H2O] MgNH4PO4⋅6H2O}$$

$\ce{Ca^2+}$ is detected through ammonium oxalate test (a white precipitate is formed)

$$\ce{Ca^2+ + C2O4^{2−} + 2H2O ⟶ CaC2O4 ⋅2H2O}$$

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