Cabbage Lab
Step One: Preparation of anthocyanin solution.
(aka
cabbage leaf juice)
Obtain a slice of cabbage.
Start a hot water bath in a large (600 mL-ish) beaker, add cabbage and
let it boil for a good 5 minutes.
Step Two: Pre Lab Math
Calculate the molarity of the following solutions:
pH
= 2 ____ M
HCl (aq)________ pH = 8 M NaOH
pH
= 4 ____ M
HCl (aq)________ pH = 10 M NaOH
pH
= 6 ____ M
HCl (aq)________ pH = 12 M NaOH
Step Three: Division of Labor
Within your group get the following done rather quickly
1. Filter out the cabbage chunks so all you
have left is cabbage juice. Put the
solid cabbage in the garbage. Be
careful, as the cabbage juice and cabbage are hot.
2. Clean 13 test tubes and label them in pencil
with the following information; plain juice, then pH values from 1 to 12. (Example pH 1, pH 2)
Step Four: Understanding the Concept of Dilutions and
Performing Them.
When something is diluted the amount of solute (Oh no vocab)
remains the same while the solvent volume increases. One example of this is someone brews you a
cup of coffee and it is way too strong for you so you add some water to
it. You have just performed a
dilution. The amount of coffee is the
same in the cup but there is more water (solvent) added to it, thus diluting
the coffee.
You are going to make serial dilutions of 0.1 M HCl (pH 1) and
0.01 M NaOH (pH 12) in order to get a complete pH range of chemicals.
1. Obtain 10 mL of 0.1 M HCl and place into
the pH one test tube.
2. Measure out 9 mL of distilled water and
place it into pH 2 test tube.
3. Using a measuring
pipet remove 1 mL of solution from pH 1 and transfer it into pH 2. Mix the contents of pH 2 by sucking up the
mixture and squirting it out again.
4. Again using the same pipet, remove 1 mL of
solution from pH 2 tube and add contents to pH 3 tube. Add 9 mL of water and mix the solution.
5 Continue with this process until you have
tube pH 6 filled.
6. Into tube 7 add 9 mL of distilled water.
7. Using a clean new test tube, obtain 10 mL
of 0.01 M NaOH and place it into pH 12 tube.
Do the dilutions in the same manner as you did above until you have
filled the pH 8 tube.
Remember NaOH is a strong base so it has high numbers on the pH
scale. By performing a dilution on pH of
12 down to pH 8, you are causing a dilution with respect to
Mixing of Cabbage
Juice and A/B Solutions
1. Using a clean
new pipet, add roughly 5 mL of cabbage juice to each
test tube. When you do this DO NOT let
the pipet touch the sides of the test tubes and cause contamination.
2. Add a wooden splint to each test tube and
mix the solutions.
3. You have just make
your own pH indicator scale using natural plant pigments (anthocyanins). These are the same pigments imbedded on the
strips of the pH paper you used earlier.
4. Compare your pH scale with other lab
groups.
Testing other
Solutions
To
test the pH of solutions you brought from home, do the following;
1. Place about 9 mL of your solution in a
test tube. Add 5 mL of cabbage
juice. Mix with a wood splint. Compare resulting color to the color of your
scale.
2.
On a data sheet create a table of the
solutions you tested and their resulting pH.
Questions and
Concepts
pH 1 Color
Answer the following
questions on your data sheet.
1. Draw 13 test tubes lined up next to each
other. Label each as you did the actual
test tubes in the lab.
2. For each solution, identify its color
either by labeling it or coloring it in on the test tube.
3. Starting with pH 1 (0.1 M HCl) label each
test tube according to its molarity based upon the dilutions you
performed. An example is provided for
you.
0.1 M HCl