Message-Id: <v01540b01b05f839789b2@[208.155.130.241]>
Date: Mon, 6 Oct 1997 23:10:50 -0800
To: pinhole@exploratorium.edu
From: roaminlohman@telis.org (R and D Lohman)
Subject: Re: basic chemistry questions from new teacher
Dear Jory:
Here are a few answers regarding your list based on my own experience with
student labs at the 9th grade level.
Bromothymol Blue: It's a very useful pH sensitive dye/indicator whose
color changes from a deep blue to a green then to a yellow as pH passes
from slightly basic to slightly acidic. I've used it for detecting and
measuring relative amounts of carbon dioxide in human breath and car
exhaust. A simple test with it is to bubble your breath through a weak
solution of BThB (as I often write it) using a drinking straw. The
solution rather quickly changes color through the sequence I mentioned
earlier. You can heat the solution gently, which drives the carbon dioxide
out, if you want to see the colors reverse.
After carbon dioxide has been added to a solution and it is yellow in color
you can make the indicator work in a more-or-less quantitative fashion by
adding weak ammonia, drop by drop, to the solution in order to move it back
to where it started in color. The number of drops of ammonia added are
proportional to the concentration of the carbon dioxide added.
Limewater: This is actually calcium hydroxide, a rather weak base. It's a
good indicator of carbon dioxide, too, since it turns milky white when the
gas is bubbled through it. It forms calcium carbonate as a precipitate.
HCl: Yes it's hydrochloric acid. 3N diluted 3 to 1 will give you 1N. 1N
means that one mole of HCl (36.5 grams) is added to 1 liter of water to
form the solution.
Yes, 1% means 1 gram/100 ml's of water.
I believe there are elements that sublimate at room temperature, such as
iodine crystals. I hope someone else can confirm this. I also imagine it
would depend on the combination of temperature and pressure.
Good luck in your teaching,
Rich Lohman (roaminlohman@telis.org)
>1) What are these substances and what exactly are they used for. I've
>seen them asked for in Labs or merely found them on my chemical shelf and
>am curious:
> - Bromothymol Blue
> - Methylene Blue - (I know it's a stain for looking at cells
> under a microscope, but how does it work)
> - Limewater Solution
> - liquid blueing
> -phenol red
> - Bristol's Media
>
>2) I'm assuming HCL is hydrochloric acid, (right?). If I have a 3 Normal
>solution and want to get to 1 Normal solution to I dilute it 1 part to 3
>parts water? What exactly does 1 Normal mean?
>
>3) I have a 1% solution of Bromothymol Blue on my shelf. Does that mean
>1 gram of powder for 100 mls of water?
>
>4) On a more general note, do all elements have to transition through a
>liquid phase on their way to becoming a gas from a solid, (a student's
>question)
>
>Thanks in advance,
>
> Jory Gessow
> Middle School Science Teacher
> Tehiyah Day School, El Cerrito
> gessow@well.com