We used to use 4M stuff a lot for cleaning chromatography resins in my PhD.
it's quite entertaining because it's massively exothermic going into solution. So, oooh, for instance, if you make up 10 litres of 4M NaOH the lazy way (put 10L glass duran with 9 L of water in it onto magnetic stirrer, throw in *calculates* 400g NaOH) it tends to sit round the bottom of the duran no matter how fast you are stirring. And get REALLY hot. And then, sometimes, fracture the glass slightly. So when the unsuspecting PhD student comes back half an hour later and picks up his 4M solution by the neck of the duran, the flat bottom of the duran stays where it is and 9 litres of brutally strong base hit you in the stomach and crotch. Mmmm, soapy balls.
( the mighty badger Aphrodite, on a bar stool, by your side, Tue 1 Feb 2011, 18:13, 1 reply)

Wouldn't that be "just over 1M"?
400g NaOH = 10 moles.

10 Moles in 9 and a bit litres = approx 1.1 Molar?

But my school days are now a far-off land, so may be talking nonsense.
( Ghoti Fingers, Tue 1 Feb 2011, 18:41, closed)

You are correct
I do believe the mighty badger may have meant 1600g.
(Petite chien is going to do science to it, Tue 1 Feb 2011, 19:09, closed)