Why does magnesium carbonate have no flame color?

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Discussion Overview

The discussion centers around the flame color observed when performing a flame test on magnesium carbonate, specifically why there is no color change compared to the bright white flame associated with burning magnesium. The scope includes theoretical explanations and experimental observations related to flame tests and the behavior of different magnesium species.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Experimental/applied

Main Points Raised

  • One participant notes that magnesium traditionally produces a bright white flame, but magnesium carbonate does not show a color change during a flame test.
  • Another participant questions the expectation of a color change, prompting further exploration of the underlying reasons.
  • A third participant clarifies that the flame of burning magnesium is distinct from a flame test, indicating a potential misunderstanding of the two processes.
  • It is mentioned that magnesium in magnesium carbonate exists as Mg2+ ions, which have different electronic configurations compared to metallic magnesium, affecting the flame test results.
  • One participant explains that metallic magnesium produces bright white light when it burns due to its reaction with oxygen, but this does not apply to the ash formed after combustion.
  • Another participant raises an interesting point about the presence of absorption lines for magnesium in the solar spectrum, questioning why these are not observed in flame spectra and suggesting that the white light from burning magnesium may be due to thermal emission from magnesium oxide.

Areas of Agreement / Disagreement

Participants express differing views on the reasons behind the lack of color change in the flame test for magnesium carbonate, with no consensus reached on the underlying mechanisms or expectations.

Contextual Notes

Participants discuss the differences between metallic magnesium and magnesium ions, highlighting the dependence on electronic configurations and the nature of the substances involved in the flame test.

Who May Find This Useful

Individuals interested in chemistry, particularly those studying flame tests, electronic configurations, and the behavior of metals in combustion reactions.

Emily2277
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I've read that magnesium traditionally has a bright white flame. When I performed a flame test on magnesium carbonate in lab, there was no color change to the flame. Why is this?
 
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I don't know why that is, but I do have to ask, why do you think there should be?
 
You are mistaking flame of a burning magnesium with flame test, these are two separate things.
 
In addition to what Borek mentioned, Mg ≠ Mg2+ (which is the form of magnesium in magnesium carbonate)

The color in a flame test depends on the electronic structure of the substance in question. Mg metal and Mg2+ ions have different electron configurations, so they will behave very differently in a flame test.
 
Metallic Magnesium is used fireworks to produce a bright white light,
That's what happens when Magnesium combines with Oxygen.
It's not possible though to burn the resulting ash in more Oxygen and get more light.
 
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Interesting question. In the spectrum of the sun, there are prominent absorption lines in the green due to Magnesium. I don't know why we don't observe them in flame spectra.
I would guess the white light emitted by burning magnesium is due to the thermal emission from the solid magnesium oxide formed.
Compare this to the intense emitted by calcium oxide (limelight!).
 

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