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For some reason it has been very difficult to find the right answer for this question as there's so much conflicting information to be found online. Some mention a reaction where carbonic acid is made, others mention carbonates and hydroxide end product but nothing seems to be precise.

But can the reaction be as simple as this (a double displacement reaction) where magnesium bicarbonate and sodium chloride are the end products: $$ \ce{2NaHCO3 + MgCl2 -> 2NaCl + Mg(HCO3)2} $$

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  • $\begingroup$ Is the reaction to occur in water (aqueous)? $\endgroup$ – BH2017 Jan 30 '13 at 17:13
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The chemicals must be in water, since magnesium bicarbonate decomposes when dried. So I will assume that the mixing is done in water. To start with, both salts are strong electrolytes and so they immediately dissociate to give $\ce{Na+}$ ions, $\ce{HCO3-}$ ions, $\ce{Mg^{2+}}$ ions, and $\ce{Cl-}$ ions. As Brenton Home has pointed out, none of the possible compounds formed from these are insoluble and there is no gas formation due to the decomposition of the bicarbonate because the resulting solution is not acidic.

So the answer is that there is no reaction.

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I thought I would start out in saying that I think this is a random, but great question. This is because as you said there's so little information out there regarding this sort of reaction so it was an interesting little puzzle for me to figure out for you.

My guess would be that the reaction you detailed would not occur. This double replacement reaction would occur in aqueous solution as otherwise the product of magnesium bicarbonate probably wouldn't have a chance of forming since at least one other alkali earth metal bicarbonate salt, calcium bicarbonate, does not exist outside of aqueous solution. I tell you this piece of information instead of whether magnesium bicarbonate exists outside of aqueous solution because I just don't know for certain whether it does. Evidence for this theory that it doesn't exist out of aqueous solution includes (in addition to the point raised above about calcium bicarbonate):

  • Magnesium bicarbonate's predicted partition coefficient is -0.809 according to chemspider which is identical to the predicted partition coefficient for calcium bicarbonate which makes it very likely that it is highly water soluble.

Since it occurs in aqueous the only driving force to the reaction would be the production of an insoluble salt, in your reaction, however, there is no insoluble products that results.

Therefore I suspect an alternate reaction would occur. Namely:

$$\ce{2NaHCO_3 + MgCl_2 -> 2NaCl + MgO + H_2 O + 2 CO_2}$$

As this reaction would lead to three insoluble products and thus would invoke a greater drive for the reaction.

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  • $\begingroup$ I think that there is an oxygen missing to equilibrate your reaction (and that it is likely to be as MgO, since magnesium is unlikely to be reduced in the process). And I agree that it would be necessary that the initial poster provide some background on the conditions. $\endgroup$ – PLD Jan 30 '13 at 17:51
  • $\begingroup$ Not magnesium oxide, which is too sttongly basic to form along with carbon dioxide. If you get a reaction at all it's magnesium carbonate. $\endgroup$ – Oscar Lanzi Oct 8 '16 at 11:02
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There can be a reaction, maybe. A simple double displacement gives nothing, but perhaps magnesium bicarbonate can "disproportionate" in an acid base sense:

$\ce{Mg^2+ + 2HCO3- -> MgCO3(s) + CO2 + H2O}$

where the reaction would be driven by the magnesium carbonate precipitating. I would need to look up the relevant equilibrium constants (acid-base for carbonate amd bicarbonate ions, precipitation of the magnesium carbonate) and be given solution concentrations to see whether we really get this reaction.

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  • $\begingroup$ Can't get \ce to work the way I want, so I need it before each formula? $\endgroup$ – Oscar Lanzi Oct 8 '16 at 11:16

protected by Community Oct 8 '16 at 14:09

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