Question

I need to make a `"6 M"` solution of `"KI"` in `"50.00 mL"`. I tried to dump `"49.8 g"` of `"KI"` into `"50.00 mL"` of water in a volumetric flask, but I can't dissolve it. What can I do? Also, is it okay that the volume reading is above the mark??

Answer 1

What you could have done was put a little bit in at a time into a flask that already contains some amount of water, dissolving it a bit at a time. It's easier to swish around when there isn't a lot of solid in the flask.

Then when all `"49.8 g"` dissolves, as it should (its solubility is `"70 g/50 mL"` in water at `20^@ "C"`), add more water until you reach exactly `"50.00 mL"`.

Granted, that amount of solid will displace the water quite a bit, so ask your instructor what he/she is looking for.

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Alternatively, if you have a sonicator, that should help dissolve it by sending vibrations through the flask.

Or, heat it up in a capped flask on a hot plate to, say, `60^@ "C"` (`140^@ "F"`) while using a magnetic stir bar, and then let it cool down. It'll speed up the solvation, but capping it will prevent a lot of vapors escaping and dehydrating the solution.