A hydrogen carbonate which exists in solid state

A good example is the existence — or non-existence — of lithium hydrogen carbonate. Some say it only exists in solution; some quote it as a solid. The commonly accepted reason for the existence of solid hydrogen carbonates, hydrogen sulfites and so on is that large, low-charge cations are needed to stabilize large, low-charge anions in the crystal lattice.

So if the explanation is valid, it would seem unlikely that solid lithium analogs such as lithium hydrogen carbonate exist. I perused two authoritative sources for their opinion. First, the classic compendium, General and Inorganic Chemistry by J. It exists only in solution when carbonate dissolves in water saturated with CO 2 under pressure. The non-existence of solid lithium hydrogen carbonate makes sense from the lithium cation not being large enough to stabilize a large low-charge anion.

It also makes sense from the lithium isodiagonality with the alkaline earth elements. That is, similar to calcium carbonate, there is an equilibrium between the aqueous lithium and hydrogen carbonate ions with the sparingly-soluble lithium carbonate, carbon dioxide and water:.

So to test this hypothesis, I mixed saturated aqueous solutions of lithium chloride and sodium hydrogen carbonate. The solution, initially clear, became cloudy, both with a fine precipitate and with a gentle effervescence.

The reaction continued for many minutes until there was a thick precipitate. Thus the above reaction does seem to occur.

As an aside, there are plenty of compounds which require "waters of hydration" in their crystal structure.

It just seems to me that if I placed Li 2 CO 3 in a pressure cell with water and CO2 at a billion gigapascals of pressure, I could make the bicarbonate salt, but perhaps some other structure is more likely This is because, lithium ion has a very high charge density therefore it distorts the structure of hydrogen carbonate ion and readily converts it to carbonate ion, which is smaller in size as compared to hydrogen carbonate ion.

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Improve this question. Why is magnesium peroxide only metastable but by the time you get to barium the peroxide is fully stable? Polarization by small, densely packed cations tends to pull polyatomic anions like peroxide or bicarbonate apart, leaving smaller nations in the compound like oxide or carbonate. It appears that LiHCO3 becomes more elusive as time passes.

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