[MSTA ] Red Cabbage pH Indicator in Respiration Labs

Deborah Duncan deb50duncan at gmail.com
Thu Mar 22 22:36:07 CDT 2012


Red Cabbage pH Indicator in Respiration Labs
<http://feedproxy.google.com/~r/ScienceStuff/~3/8blm6TDGaVc/red-cabbage-ph-indicator-in-respiration.html>
from Science Stuff<http://www.google.com/reader/view/feed/http%3A%2F%2Ffeeds.feedburner.com%2FScienceStuff>
 by Amy (aka Science Stuff)

<http://3.bp.blogspot.com/-F0kWj62QIqI/T2hztOv3tZI/AAAAAAAABb0/v25wi4JW53g/s1600/CabbageStart.jpg>

A new twist on using cabbage juice?

Most every science teacher is aware that the juice extracted from red
cabbage makes an excellent acid/base indicator.  But at our school, we
recently used it for a different (but related) purpose.  Our biology
classes do a cellular respiration
lab<http://www.teacherspayteachers.com/Product/Lab-Using-Cabbage-Juice-to-Observe-CO2-Production-in-Cell-Respiration>
in
which the students observe the production of carbon dioxide during
respiration.  Normally we use phenol
red<http://www.teacherspayteachers.com/Product/Lab-Gas-Exchange-in-Cellular-Respiration>
as
an indicator.  Our supply of phenol red was running low and we looked for
an alternative.  The answer was cabbage juice indicator!!

How was red cabbage used as an indicator of carbon dioxide?  I'll come back
to that in a minute.  First, here is a little background about red
cabbage......

Background:   Red cabbage contains a natural pH indicator in the form of
the pigment, anthocyanin.  It is a water soluble pigment that is commonly
found in nature in red cabbage, of course, as well as purple plums, grapes,
and apples.  Red cabbage juice will turn a wide variety of colors in the
presence of acids and bases.  In a neutral solution, the cabbage is a
fairly dark purple color.  In the presence of acids, the cabbage juice will
turn red/pink, and in the presence of bases, the cabbage juice turns a
greenish-yellow color.

How to Make Cabbage Juice Indicator:  This process is so simple that I
usually allow my students to make their own indicator.  Simply chop up a
head of red cabbage.  Place a small handful of cabbage leaves into a
beaker.  Cover the leaves with water and boil for about 15 minutes.  As the
cabbage boils, the pigment will be extracted from the leaves and the water
will turn a dark purple color.  Use a slotted spoon to remove the cabbage,
or pore the solution through filter paper.  Your indicator is now ready to
use!

Our Cellular Respiration Lab:  In order to complete the chemical reactions
of cellularrespiration, oxygen is required.  Carbondioxide is released
during the reactions and is given off as a wasteproduct.    Although it is
very difficultfor us to observe the conversion of glucose to ATP, it is
possible toobserve the gas exchange that must take place in order for
respiration to becarried out.   The lab that we do at our school has three
objectives:
1.   To observe therelease of carbon dioxide during cellular respiration in
animals.
2.   To determine ifplants carry out the same gas exchange as animals.
3.   To observe,record, and analyze the results of an acid-base indicator.

<http://2.bp.blogspot.com/-xhsLtZQ5NnY/T2h4X_rRTaI/AAAAAAAABb8/KRzU_T4nLpM/s1600/Part+1+Tubes+1+-+4+copy.jpg>

In the first part of our lab, the student will learn how to use the cabbage
juice to indicate the presence of carbon dioxide.  (See above photo.)
 Carbon dioxide and water will react to form carbonic acid.  Since our
breath and carbonated beverages contain carbon dioxide, the color change
from dark purple to pinkish/red indicates the formation of carbonic acid.

<http://2.bp.blogspot.com/--yzhqBuiyO0/T2h6AJGdj6I/AAAAAAAABcE/Ya-27uH8Hhk/s1600/Part+2+Tubes+1+-+3+copy.jpg>

In the second part of the lab, we want the student to determine if plants
also give off carbon dioxide during cellular respiration.  As you can see
in the above photo, the first tube serves as a control, the second tube
contains germinating seeds, which have a high rate of respiration, and the
third tube contains dry seeds, which are alive, but dormant.  The photo
clearly shows that the germinating peas are releasing carbon dioxide.
 (Since the peas are not photosynthetic, they are not consuming carbon
dioxide.)  In the tube containing the dry peas, there is a very slight
color change that does not show clearly in this photo.  The dry seeds do
carry out cellular respiration, but at a very slow rate.  The results seen
in the above photo were obtained after allowing the tubes to sit for just
24 hours.

This lab is easy to set up, easy to clean up, and best of all, our students
really enjoy doing it.

-- 
Deborah
I live in my own little world, but that's ok they know me here.
Deborah Duncan, Neshoba Central High School
http://nchsdduncan.wikispaces.com
http://msta.wikispaces.com
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