Re: pinhole Student Questions

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From: Steven Eiger (eiger@montana.edu)
Date: Wed Nov 29 2000 - 11:39:22 PST 

Message-Id: <l03102803b64b0a110b83@[153.90.150.107]>
Date: Wed, 29 Nov 2000 12:39:22 -0700
From: Steven Eiger <eiger@montana.edu>
Subject: Re: pinhole Student Questions

>>Here are only some of the questions my students asked this month that I
>>cannot answer. If you have thoughts on any of these, I would appreciate your
>>response. Thank you! Jhumki Basu
>
>>10. If I dissolve green food coloring in water uniformly and freeze the
>>water, the ice cubes are not uniformly green. How come?
>
 There are a few ways to look at this. One is that solute has a
colligative effect - which means that it will lower the freezing point. As
impure water begins to freeze, the nascent ice crystals, the ice lattice,
often excludes solute, the remaining liquid freezes at a lower tmeperature;
water molecules are added to the lattice, and solute gets more and more
concentrated in the remaining liquid. The reverse takes place upon
thawing. You can suck on a popsickle and notice that the first juice
coming off is sweeter than the icier parts left. Eventually you have almost
pure ice left, in color and taste. I suspect this is what is happening to
your food coloring. Happy trails and be good to your horse, STeve

Steven Eiger, Ph.D.

Department of Cell Biology and Neuroscience and the WWAMI Medical Education
Program
PO Box 173148
Montana State University - Bozeman
Bozeman, MT 59717-3148

Voice: (406) 994-5672
E-mail: eiger@montana.edu
FAX: (406) 994-7077

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