- What determines whether a salt would dissolve in NaOH? I'll definitely do some lab tests in the future, but I want to know the chemistry behind it. For example, I get that calcium salts would all precipitate due to Ca(OH)2, but I don't understand why NaCl dissolves and Na2CO3 doesn't (unless the chart is messed up again).
Which chart are you using? Anyways, determining solubility is mainly based on understanding of chemical reactions (specifically double replacement/precipitation), ions, and periodic trends (often, using periodic trends is how to predict ion behavior in reactions, especially cations).
So, when you put a salt in a solution, think about the cation and the anion of the salt. In this case, for sodium carbonate, the cation is Na+ and the anion is (CO3)2-. Since Na+ is a highly reactive alkali metal (same with the others in its group), it will dissolve pretty much always dissolve, and NaOH itself is no exception. Then, you would have to look at which ions are present: Na+, OH-, and (CO3)2-. None of those can combine to make a solid, insoluble precipitate, so Na2CO3 really should be able to dissolve in NaOH (check in lab). Usually when I use NaOH to do a precipitate test I dissolve the powder in water first and then add NaOH so you can see it better, plus you can check its solubility in water first (that can tell a lot!).