theory behind mixing solutions

[gregm]

When you add 10 mL organic solvent and 10 mL water you do not get 20 mL final solution. Can someone tell be the reason why this happens? I am unable to find a conclusive answer.

[tom jupille]

Methanol molecules (for example) stick more tightly to water molecules than they do to each other.

[Dan]

There was an interesting discussion on this topic a while back. Check it out at:

http://www.sepsci.com/chromforum/viewtopic.php?t=6500

Regards,
Dan