Lowering of the freezing point on adding a solute is a colligative property of solutions, it doesn't matter what the nature of the solute is (of course we have to assume ideal solutions). So when it is required to use an antifreeze - why are glycerol, glycol, methanol, etc. commonly used? For a given decrease in freezing point, a given value of molality is required - in other words a particular number of moles for the liquid's given mass. For the same number of moles, it should be simply more economical to use any substance with lower molar mass. Solubility in the solvent will obviously play a role - but there are many more solutes which are more soluble than alcohols. Why isn't $\ce{NaCl}$ used, for instance? Its molecular mass is not very high, and it is soluble to an appreciable degree. It's also more economical (moreover it will dissociate in water and generate twice the number of moles, so twice the decrease in boiling point).

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    $\begingroup$ You're mixing two things - alcohols lower melting point because they have low melting point themselves - not via collgative properties. $\endgroup$
    – Mithoron
    Jul 24 '15 at 15:07
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    $\begingroup$ The Wikipedia article on the matter is concise and nicely informative, seems to me. $\endgroup$
    – hBy2Py
    Jul 24 '15 at 15:45

The main reason ionic substances like salts are not used is because they tend to be corrosive to metals.

Polar organic liquids tend to be the best because many are very soluble in water, and they are fairly inert under the conditions antifreeze is used.


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