Saturday, March 13, 2010

Trolled by the cryoscopic effect

Refers to the depression of the freezing point of a solution due to the presence of some solute, or impurity. This does not depend on the nature of the impurity, just on its relative amount w.r.t the solvent. So, this means that the equivalent amount of potassium chloride and sodium chloride will lead to the same depression of the freezing point of water. Which is, of course why the put some salt in the water pipes in North East India, where it is cold. Also why they put ethanol/glycerol as antifreeze in car radiators.

Here is the Wikipedia page. Observe that the cryoscopic constant of water is K=1.86 C/M. Assuming a van't Hoff factor of i=1 for glycerol, for a 20% mass/vol solution, that comes to a comcentration of 2M. So, the maximum freezing point depression should be about 4 C. Which means that the cell stock should have thawed at -4C. And when I grabbed the cells from the -80 C freezer, I should have scraped some off and stuck them back in pronto. Not left them on the benchtop (on ice) for five minutes where they thawed out. I tried blaming the croscopic effect, but the calculation shows that without the depression of freezing point, the stock would have thawed out at 0 C, as such, it did at -4 C. And they should have not thawed out more than, say -70 C.

95% personal stupidity
5% being trolled by the cryoscopic effect.