Observations
  • Home
  • Observations
  • Trendcasting
  • Odds 'n Ends
  • Science/Technology/Experiments
  • Mental Health

Anthocyanin pH Indicator from Red Cabbage...

4/19/2012

4 Comments

 
Picture
Video below:
This is a follow-up post to the previous entry on acids and bases. The demonstration video illustrates the pH response of anthocyanin, the dye extracted from red cabbage leaves. Anthocyanin, sometimes referred to as "anthocyan"  can be extracted from many vegetables, fruits, and flowers using any one of several methods.
Despite the fact that this experiment has been around for several years, it still has the potential to have value in the study of natural acid and base indicators. The chemistry of natural indicators, particularly anthocyanin, is very complex and still contains mysteries about its structure and role in nature. I had originally intended to include the Indian spice turmeric in this post, also as an indicator of pH, but while working with it I found that it has the possibility of being used as an imaging material. So, I will continue working on that area and post as soon as I have concluded the research. After the video, the writeup will provide a step-by-step procedure to red cabbage leaf extraction, and useful links to fill out the discussion. Enjoy!


Picture
I have included the photo of the pH chart because it  had some glare in the video. These indicator test strips work just fine for a general test of average pH in solution. I use them frequently in gardening to test the pH of soil before planting flowers or vegetables. The best way to test the soil is to take several samples from multiple locations being considered for planting. Then, place a small amount of soil from each location into a test tube or other container, add distilled water and agitate. Let the soil particles settle and then test for the pH. A chart of the best pH for vegetables or flowers can be located online, and the soil can be amended as needed. But now, lets get some red cabbage extract!
Materials for the experiment:
Red cabbage, available all year around in most markets.
Distilled water.
Blender (stirring can be used instead but will take longer).
Hydrochloric acid (available at hardware stores as muriatic acid, 28% HCl).
Sodium Hydroxide (available at hardware stores as lye, or drain cleaner NaOH 100%.
Coffee filters or filter paper to separate the cabbage mush from the liquid.
Acetone (optional for additional experiments). Hardware store.
Ethyl Alcohol 70% (optional, rubbing alcohol from the drugstore for additional experiments).
Procedure:
First, prepare the cabbage extract by either tearing or cutting three or four cabbage leaves into small pieces and place into the blender. Add a small amount of hot distilled water and blend until the color is as dark as possible. This takes less than 2 minutes. Filter twice to allow collection of the cabbage mush and the clean extract of anthocyanin. Discard the mush and set the extract aside and prepare the acid and base.
CAUTION! The next step is to prepare the HCl and NaOH solutions. Muriatic acid tends to fume and is a strong acid. Lye is a strong base and can cause burns. Wear gloves, protective eye wear, and prepare with adequate ventilation.
0.1 Molar solution sodium hydroxide. Dissolve 4.0 grams of NaOH (lye) in enough distilled water to make 1 liter. This has a pH of 13.
0.1 Molar hydrochloric acid solution. Add 17 ml of muriatic acid (28% HCl) to make 1 liter of solution. This has a pH of 1.
Then follow this serial dilution procedure:
  1.     Label 13 test tubes or other containers from 1 to 13.
2.     Place 9.0 ml of distilled or deionized water in all test tubes except #1 and #13.
3.     Prepare solutions in the acid range in the following manner:
a.     Place 10.0 ml of 0.1 M HCl in test tube #1. (pH = 1)
b.     Transfer 1.0 ml of 0.1 M acid from test tube #1 to test tube #2 and mix thoroughly. (pH = 2)
c.      Transfer 1.0 ml of acid solution from test tube $2 to test tube #3 and mix thoroughly. (pH = 3)
d.     Continue making the serial dilutions by transferring 1.0 ml of the most recently diluted acid solution to the next test tube until six acid solutions of pH 1 to 6 have been prepared. Be sure to mix each thoroughly before the transfer.
4.     Add 10.0 ml distilled or deionized water to test tube #7. (pH = 7)
5.     Prepare solutions of base in the following way:
a.     Place 10.0 ml of 0.1 M NaOH in test tube #13. (pH = 13)
b.     Transfer 1.0 ml of 0.1 M NaOH from test tube #13 to test tube #12 and mix thoroughly. (pH = 12)
c.      Continue making serial dilutions of the base going from pH 12 down to pH 8 by transferring 1.0 ml of the most recently diluted basic solution to the next test tube and mixing thoroughly each time. Then, add enough of the anthocyanin extract to see the color change as in the video. To extract with acetone or ethyl alcohol, simply place a small amount of cabbage leaves in a glass container and add the solvent to just cover the leaves. Allow 24 hours with occasional stirring to get the extraction. Filter and proceed with any other experiments.
Here are some links to check out:
Chemistry of anthocyanin in detail with experiments here.
Wikipedia entry for anthocyanin. Check out the test tube photo with the blue sample. I am not sure how that happens. This entry also includes a list of some of the other sources of anthocyanin here.
American Science and Surplus source of pH paper. Look under lab supplies for pH paper but, there are other suppliers as well here.
Recipe for the Yamada universal indicator here.
I think that this is an interesting area of investigation and as always, I  welcome comments. Color me gone...










4 Comments

Acids, bases, and pH...

4/2/2012

1 Comment

 
Picture
This is the first part of a two-part post on pH and some experiments with natural indicators. This first installment will describe what it means when a substance is neutral, acidic, or basic. The second post will be an improved extraction of anthocyanin from red cabbage leaves, and the use of the spice turmeric as an indicator of acidity. Both have interesting chemical characteristics and the experiments will be helpful in illustrating acids and bases, but will also include metal complexes made from plant extracts.
Understanding the basis of pH can be complicated and sometimes difficult to explain. But I have tried to make it as readable as possible and have not gone deeply into the math and real complexities of understanding the art and science of acids and bases. So, this will be a primer and if you are new to the subject, I hope that it will be helpful and informative.
So, let’s get started with three important definitions:
Ion- An atom or molecule in which the total number of electrons is not equal to the number of protons giving it a net positive or negative electrical charge.
Anion- An ion that has more electrons than protons giving it a net negative charge. (Remember that electrons are negatively charged and protons are positively charged).
Cation- An ion that has fewer electrons than protons giving it a net positive charge.
Almost every liquid that we see has either an acidic or basic characteristic with the exception of pure or very well distilled water. In this case the ions are balanced and have no measurable charge. But most other water from the tap or well, will have an ionic charge. This can be relatively small or quite noticeable.  So, to measure how acidic or basic a liquid may be, we use a scale that goes from 0 to 14. Since distilled water is electrically neutral, it has a pH of 7. The way we think of the relative charge of a liquid is to look at how the ions have influenced the liquid. The pH scale is focused on the concentration of hydrogen ions (H+), and hydroxide ions (OH-). The pH scale for acids is from 0 to 7, (relative number of H+ ions) with 0 being a strong acid and 7 being neutral. And, in this example, a pH of 6.9 would be a very weak acid. The pH scale for bases is from 7 to 14, (relative number of OH- ions), with 14 being a strong base and 7 neutral. In this instance a pH of 7.1 would be a very weak base.
And here is a quick side thought: Since we are talking about ions which are extremely small, the pH scale is logarithmic, meaning that each number on the scale from 0 to 14 is a ten-fold difference between numbers. Why? A strong acid can have one hundred million, million, (100,000,000, 000,000), times more hydrogen ions than a strongly basic solution so the numbers are just too large to use effectively, so 0 to 14 works more easily. So, let’s see if we can put this information into the proverbial nutshell:
Acid- A solution that has an excess of (H+) ions.
Base- A solution that has an excess of (OH-) ions.
Strong acid- An acid that has a very low pH (0-4).
Strong base- A base that has a very high pH (10-14).
Weak acid- An acid that only partially ionizes in water and has a pH closer to neutral (5-7).
Weak base- A base that only partially ionizes in water and has a pH closer to neutral (7-9).
And what happens when an acid is mixed with a base, for example, Hydrochloric acid (HCl) and Sodium Hydroxide (NaOH)? The ions react to neutralization with water and a salt as the products:
HCl + NaOH ---> NaCl + H2O
There is a great deal of information on acids, bases, and pH on the web to check out if you are interested in going deeper into the subject. If you are looking for a list of everyday items and their pH, check here.
Stay tuned for the next post…


1 Comment

    Author

    The author has an eclectic background in chemistry, electronics, writing, mental health, and community action...Ken

    Archives

    June 2021
    March 2020
    September 2019
    August 2018
    August 2017
    March 2017
    December 2016
    November 2016
    October 2016
    August 2016
    April 2016
    December 2015
    September 2015
    May 2015
    March 2015
    February 2015
    December 2014
    November 2014
    October 2014
    September 2014
    August 2014
    July 2014
    June 2014
    May 2014
    April 2014
    March 2014
    February 2014
    December 2013
    November 2013
    October 2013
    August 2013
    July 2013
    June 2013
    May 2013
    April 2013
    March 2013
    February 2013
    January 2013
    December 2012
    November 2012
    October 2012
    September 2012
    August 2012
    July 2012
    June 2012
    May 2012
    April 2012
    March 2012
    February 2012
    January 2012
    December 2011
    November 2011
    October 2011
    September 2011
    August 2011
    July 2011
    June 2011
    May 2011

    RSS Feed

    Categories

    All
    Acid And Bases
    Amateur Scientist
    Anodizing Aluminum
    Anthocyanin Indicator
    Ant Orientation
    Artificial Intelligence
    Bar And Cr Code
    Cable Tie
    Carbon Dioxide Fun
    Catalase And H2o2
    Chemical Art
    Cold Cathode
    Color Hot Glue Sticks
    Common Chemicals
    Copper Plating
    Cyanotype/Blueprint
    Dot Com
    Electroluminescence
    Epoxy Art
    Experiments
    Hydrogels
    Infrared Photography Basics
    Magnetic Money
    Old Textbooks
    Photograms
    Science
    Static Electricity Detector
    Technology
    Yogurt