Re: Pinhole Digest #789 - 12/07/01

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From: blohman@coastside.net
Date: Fri Dec 07 2001 - 19:47:48 PST 

Message-Id: <3.0.6.32.20011207194748.0085c100@coastside.net>
Date: Fri, 07 Dec 2001 19:47:48 -0800
From: blohman@coastside.net
Subject: Re: Pinhole Digest #789 - 12/07/01

We do the surface area volume lab with phenylthaleine in the agar. We add
a little vinegar to shift the agar to clear. Then we put the cubes in a
weak ammonia solution. They turn a lovely pink. After doing the surface
area/ volume comparison it is fun to put a straw through the agar to model
a circulatory system. This is a great lab.

At 12:20 AM 12/7/01 -0700, you wrote:
>Pinhole Digest #789 - Friday, December 7, 2001
>
> paper towels as acid/base indicators?
> by "Geoff Ruth" <gruth@leadershiphigh.org>
> bio lab
> by "Geoff Ruth" <gruth@leadershiphigh.org>
> Re: pinhole paper towels as acid/base indicators?
> by <NFetter@aol.com>
> Re: pinhole paper towels as acid/base indicators?
> by "Geoff Ruth" <gruth@leadershiphigh.org>
>
>
>----------------------------------------------------------------------
>
>Subject: paper towels as acid/base indicators?
>From: "Geoff Ruth" <gruth@leadershiphigh.org>
>Date: Wed, 5 Dec 2001 21:10:15 -0800
>
>Today in lab I noticed that paper towels I used to clean up some
>spilled weak base (dilute sodium hydroxide) turned pink, while those
>that I used to clean up some spilled weak acid (vinegar) turned
>green. How cool is that? Does anyone have any idea of what the
>chemistry is going on in here?
>
>- Geoff
>
>----------------------------------------------------------------------
>
>Subject: bio lab
>From: "Geoff Ruth" <gruth@leadershiphigh.org>
>Date: Wed, 5 Dec 2001 21:11:01 -0800
>
>A bio teacher at my school tried to do a lab showing how diffusion is
>affected by the volume of a cell. She cut up blocks of agar of
>various sizes, and then put them in a NaOH solution -- the agar is
>supposed to turn a different color as the sodium hydroxide penetrates
>the agar cubes to different depths.
>
>The problem is that the lab didn't work -- there was no color change
>with the NaOH. We tried using 0.1M and roughly 0.4M NaOH.
>
>Has anyone done this lab successfully? And does anyone know what the
>chemical reaction going on here is?
>
>Ta ta,
>Geoff
>
>----------------------------------------------------------------------
>
>Subject: Re: pinhole paper towels as acid/base indicators?
>From: <NFetter@aol.com>
>Date: Thu, 6 Dec 2001 14:51:22 EST
>
>Hi Geoff,
>Were those white paper towels or brown ones? The brown ones contain a
complex
>mixture of chemicals some of which may respond to pH changes. I do know what
>they are, because there are so many. If you used white towels, they are
>mostly cellulose, resin binder, and a little bleach residue, none of which
>should be pH sensitive or change color as pH changes.
>Neil Fetter
>
>----------------------------------------------------------------------
>
>Subject: Re: pinhole paper towels as acid/base indicators?
>From: "Geoff Ruth" <gruth@leadershiphigh.org>
>Date: Thu, 6 Dec 2001 11:58:01 -0800
>
>Yeah, they were brown paper towels. So it's some sort of biological,
>naturally-occurring acid/base indicators -- like litmus?
>
>Cool.
>
>>Hi Geoff,
>>Were those white paper towels or brown ones? The brown ones contain a
complex
>>mixture of chemicals some of which may respond to pH changes. I do know what
>>they are, because there are so many. If you used white towels, they are
>>mostly cellulose, resin binder, and a little bleach residue, none of which
>>should be pH sensitive or change color as pH changes.
>>Neil Fetter
>>
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>----------------------------------------------------------------------
>End of Pinhole Digest
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