What is the solubility of KHCO3 in water?

Answer 1

The required answer is in the Wikipedia article "Potassium Bicarbonate".

To wit, 33.7 g/100 mL at 20 degrees celsius; 60 g/100 mL at 60 degrees C.

At higher temperatures, decomposition with the release of carbon dioxide may be an issue as such a reaction is said (ibid) to occur between 100 and 120 degrees C.

It is typical for acid carbonates (containing HCO3 (-) ion) to decompose by losing CO2 and H2O thus forming the carbonate, CO3 (2-) anion. This is a simple case of disproportionation.

Alkali metal carbonates will lose the remaining CO2 at some temperature below, at or above their melting point. Less electro-positive metals' bicarbonates and carbonates decompose correspondingly more easily, i.e. at lower temperatures.

Classroom tests with exhaled breath and "lime water" (cloudy/clear) and demonstration of "lime light", if followed by test (NB after cooling the residue!! (dilute HCl aq) shows that a small lump of marble loses its fizziness. It also loses its solidity, becoming powdery. It is now "quicklime", CaO, and will absorb moisture and CO2 from the atmosphere. The marble does not melt.