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Old 01-19-15, 09:57 AM
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cyccommute 
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Originally Posted by corrado33
Any solute will work. Sugar, salt, alcohol. I'd simply use really watered down gatorade. It won't lower the freezing point that much, but it may give you the extra few degrees you need.
No, not any solute would work...at least not in reasonable concentrations. To get a freezing point depression of -30°C, you would need a 16 molal solution of ethanol in water. At 46g/mole, that's 740g of ethanol per kilogram of solution or 74% ethanol. Drinking alcohol is typically 35% ethanol so the concentration is double that of straight vodka. 45 ml (3 shots) of a 35% ethanol solution is enough to put a 180 lb (82 kg) man over the legal limit. 15 ml (1 shot) of 74% ethanol should be enough to put the same man near or over the limit. That's not a lot of volume.

10 shots (150 ml) of 35% would be enough to put the same man into unconsciousness. The same volume of 74% would raise the blood alcohol level to 0.4% to 0.5% which is enough to kill him.

Sugar is similar to alcohol in its freezing depression and would require 16 moles/kg of solution. It would be like drinking candy.

For salt, you'd need an 8 molal solution which is 8 moles of sodium chloride/kg of solution for a -30°C depression. That's 467g of salt per kg of solution. Sodium chloride is saturated at 350g/L so it's basically impossible to get enough in the water to depress the freezing point enough. There are other salts you could use but I don't many of them would be palatable nor all that safe to drink nor even as soluble as sodium chloride is.

Edit: You'd still need 16 moles of particles. There isn't a combination of salts, sugars and ethanol that would give you that level of particles and still be drinkable. Insulation is much more effective without making you drunk or sick or both.
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