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$\ce{Mg}$ powder is stirred into $\ce{CuSO4}$, what is the balanced molecular equation for this reaction ? I have $\ce{Mg + CuSO4 -> Mg2SO4 + Cu}$. Also, is the ionic equation the same as the net ionic equation? I believe it is not, because Copper would act as a spectator ion, however, I am not too sure.

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2 Answers 2

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Your equation is very close, but you it is not $\ce{Mg2SO4}$. $\ce{Mg^{2+}}$ has a charge of $2+$, and $\ce{SO4^{2-}}$ has a charge of $2-$. They combine in a ratio of 1:1, so the result is

$$\ce{Mg + CuSO4 -> MgSO4 + Cu} ~ .$$

The ionic equation does not include the $\ce{SO4^{2-}}$, and in the case of this equation the net ionic equation is the same as the ionic equation. Ionic equations look at what happens to electrons. In this case, electrons are being transferred from the magnesium to the copper (since the copper is bonded to $\ce{SO4^{2-}}$ it is in the form $\ce{Cu^2+}$).

$$\ce{Mg + Cu^{2+} -> Mg^{2+} + Cu} ~ .$$

Since the charge on the $\ce{SO4^{2-}}$ doesn't change, it's just a spectator ion.

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    $\begingroup$ I also have to note that in some circumstances the reaction can be ... lively. $\endgroup$
    – permeakra
    Sep 13, 2014 at 13:11
  • $\begingroup$ Ebullient, one might even say. $\endgroup$ Mar 27, 2018 at 23:33
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The answer given is what all the textbooks say, and what the examiner wants. However, magnesium will displace hydrogen from water if copper ions are present which act as a catalyst. So what really happens is bubbles of hydrogen are liberated and white magnesium hydroxide solid is produced.

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  • $\begingroup$ Did you actually try this? With aluminum metal added to copper sulfate solution, copper is produced: chemistry.stackexchange.com/a/128099/79678. A piece of burning magnesium can burn in water, making magnesium fires hard to extinguish. But magnesium powder is not a piece of burning magnesium and it only slowly reacts with very hot water. This is worth a quick experiment. $\endgroup$
    – Ed V
    May 22, 2021 at 20:23

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