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Specialty Chemistry Forums => Other Sciences Question Forum => Topic started by: 7055 on November 23, 2009, 01:09:49 AM

Title: Methanol/water mix, freezing point is not linear, why?
Post by: 7055 on November 23, 2009, 01:09:49 AM

I have come across a few tables giving the freezing point of methanol/water mixtures on the internet and the freezing point of various mixtures of water and methanol are not linearly lower with greater percentages of methanol. Why is that? For example why would 100% methanol freeze at -145 f and 90% methanol 10% water freeze at -230 farenheit?

http://www.ashland.com/pdfs/technical/AD%20Chemicals%20-%20Freeze-Flash%20Point.pdf

Title: Re: Methanol/water mix, freezing point is not linear, why?
Post by: Borek on November 23, 2009, 03:27:55 AM

Why do you expect linearity? It works only for ideal solutions (or solutions that can be approximated as ideal).

Title: Re: Methanol/water mix, freezing point is not linear, why?
Post by: 7055 on November 23, 2009, 03:39:32 AM

Can you explain more? What are ideal solutions?

Title: Re: Methanol/water mix, freezing point is not linear, why?
Post by: Borek on November 23, 2009, 04:07:03 AM

http://en.wikipedia.org/wiki/Ideal_solution

Title: Re: Methanol/water mix, freezing point is not linear, why?
Post by: 7055 on November 30, 2009, 05:23:06 PM

I have read that definition before but it doesn't make sense to me

Title: Re: Methanol/water mix, freezing point is not linear, why?
Post by: marquis on November 30, 2009, 06:44:58 PM

See if the definition for eutectic mixtures makes more sense.  It seemed to be a better definition of what you commonly see (older solders, antifreeze, etc.)

Title: Re: Methanol/water mix, freezing point is not linear, why?
Post by: 7055 on November 30, 2009, 07:18:33 PM

No it doesn't really. All I've really gotten out of it is that non ideal mixtures melting points aren't linear but I don't know why.