[Ben04]

Hello,
I have been trying to understand the reason why potassium chloride is less soluble in water than sodium chloride. My chemistry textbooks state that the solubility of a salt in water decreases as its lattice energy increases. What confuses me is that the lattice energy in NaCl is bigger than in KCl, so what is NaCl more soluble if the ionic bond in KCl is easier to break?

I understand that Potassium is heavier than Sodium, which should make it easier to dissolve sodium salts, but then why is it that KBr is more soluble than KCl? The bromide ion is heavier than the chlorine ion... I understand though that the bond becomes weaker larger ions...

Thank you,
Ben

[Borek]

My chemistry textbooks state that the solubility of a salt in water decreases as its lattice energy increases.

All other things unchanged - yes.

But as the radii of cations and anions change, solvation changes, and the comparison becomes more difficult.

[Enthalpy]

All the simple reasoning I've seen about solubility fail on one salt or an other. Leave them in the textbooks and use experimental data.

[mjc123]

You might find this thread interesting: https://www.chemicalforums.com/index.php?topic=81896.msg297925#msg297925

[AWK]

Hello,
I have been trying to understand the reason why potassium chloride is less soluble in water than sodium chloride.

This statement is true below ~30°C only.