$\ce{Mg}$ 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.


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.

  • 1
    $\begingroup$ I also have to note that in some circumstances the reaction can be ... lively. $\endgroup$ – permeakra Sep 13 '14 at 13:11
  • $\begingroup$ Ebullient, one might even say. $\endgroup$ – Oscar Lanzi Mar 27 '18 at 23:33

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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