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??

1 Answer
Truong-Son N.
Feb 14, 2016

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.

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.

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