I did a project for lab chemistry where my aim was to see which substance, from a selection of 4 chlorides, recrystallises from a solution to form the most crystals. The 4 chlorides were KCl, NaCl, MgCl2 and CaCl2.

Question

KCl and NaCl didn't form any crystals, they formed a saturated solution whereas MgCl2 and CaCl2 formed crystals. It seems as if the charges on the positve ion of the chloride are important here; but why? How do I explain my results? Conclusion??

Answer 1

If you had removed all the moisture, potassium and sodium chloride would have formed crystals. The solubility of those is much higher than magnesium and calcium chloride, so as moisture is removed, the magnesium and calcium start to form crystals first. Now as to why the solubility is different for alkali and alkaline earth chlorides, books have been written on that. It was the forte of inorganic chem texts in the 20's and 30's, as well as some in depth study of the rare earth series.

I remember my first chem text as a youngster that I read had hundreds of pages on characteristics of the elements, and relating that to periodicity. I wish you would have had aluminum chloride in your experiment.

Here is my suggestion: look at a table or chart of solubilities, look at trends on the chlorides by period of the metal ion.