I just want to clarify my understanding of whether metathesis can be used to form other products by combining an acid and a base (do special rules apply whether its strong/weak acid/base)?

Say I want to form some $\ce{Na2CrO4}$. There's many ways to do this but the most obvious one I can think of is:

$$\ce{2NaOH(aq) + H2CrO4(aq) ->Na2CrO4(aq) + 2H2O}$$

Can you then just filter out the $\ce{H2O}$ to get your desired product? How would you do so? I'm used to looking at these in terms of net ionic equations where two aqueous reactants for a solid precipitate but since everything here would cancel out (except water) is this even a viable possibility?

  • $\begingroup$ That's going to be difficult since $\ce{CrO4^{2-}}$ does not have a charge of -1. Other than that, you're basically talking about evaporating the solvent, which is definitely a thing you can do. Ideally, it's not water, because evaporating water is a pain. Though lyophilization might work. $\endgroup$ – Zhe Oct 25 '17 at 15:50
  • $\begingroup$ As Zhe pointed out, you'd need to evaporate not filter the water out. But I'd agree that this is a metathesis reaction since you could isolate the two different compounds by physical means. // Evaporation with heat is a messy process since as the liquid surface disappears the solid starts to splatter. $\endgroup$ – MaxW Oct 25 '17 at 20:47
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    $\begingroup$ This is not what I thought when I read ‘metathesis’ … $\endgroup$ – Jan Oct 26 '17 at 4:51

You obviously cannot ‘filter water out’ as water is a liquid at STP and the solvent in which your reaction occurs in. However, you can evaporate your solution whereby the solvent gets removed and the lower vapour pressure contents (mainly solids or oils) will remain. While water can be more difficult to evaporate at a standard rotavap, it is by no means impossible.


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