Is this the best way to seperate the two salts? heating to 100C letting it cool to ~50C then filtering?

Edited January 1, 200917 yr by Aaron_S

Assuming you mean the fractional distillation of the two salts in solution, boiling will not drive off KCl or NaCl. The distillate will be pure water, and even if it were a solution containing one of the salts, both salts are very soluble in water so filtering would leave you with nothing.

Ahh, sorry I meant fractional crystallization. doh!

Look up solubility curves of NaCl and KCl. You'll find that NaCl has very little swing in solubility from 100C to 0C while KCl is quite a bit more soluble at 100C than 0C. So yes, dissolving in boiling water, filtering (if there is other gunk in the mix), and cooling will give a crop of crystals rich in KCl. It is possible that there will be no NaCl, but that depends largely on how much of each is in the original sample.

So fractional crystallization would give a pretty much pure KCl yield?

The mix is 66% KCl and 33% NaCl.

 

By adding enough water (at 100c) to dissolve 100g of the mix, cooling to 0, and filtering. My maths say that the precipitate will be 12.5% NaCl and 87.5% KCl and the remaining solute, 57.7% KCl and 43.3%. Is there a way to get a purer sample (~95-99%), without redoing it 5 times?