Anthocyanins as Acid/Base Indicators: Applications and Activities for High School Students Brett Hale Heath Dawley Southeast Missouri State University.

Anthocyanins as Acid/Base Indicators: Applications and Activities for High School Students

Brett HaleHeath Dawley

Southeast Missouri State UniversityBioQUEST 2008

Fruits_and_vegetables2. (Picture). URL: http://www.firodiyaheartfoundation.org/images/fruits_and_vegetables2.jpg

USING PLANTS IN HIGH SCHOOL CHEMISTRY

*Wanted to use anthocyanins as acid/base indicators

*Were familiar with the famous red cabbage acid/base indicator.

*Decided to try out other anthocyanins as acid/base indicators, having students explore the uses of chemicals derived from plants.

*Designed 4 activities to help students explore this area

PRE-ACTIVITY: CHEMISTRY AND MATH

pH=-log [H3O+]

*For later activities reference solutions at the unit pHs from 1-14 are needed.

*Though the teacher can pre-make these, it is also a good activity to have students do.

*They will take 1.00 M HCl and 1.00M NaOH, and add it to distilled water, while exploring the math relationships of dilution.

*Goal here is to see that pH is a logarithmic pattern. Taking 5 mL of each acid or base and diluting it to 50 mL and repeating the pattern gives you what you need.

*Students are required to show all their work, or figure out the pattern and explain it.

ACTIVITY ONE- PLANT PIGMENT CHROMATOGRAPHY

Chorophyll a and b, Xanthophylls, Carotenes, Anthocyanins

*Students will be given leaves from plants with a high anthocyanin concentration.

*Students will perform paper chromatography to separate out the plant pigments in the leaves.

*Students will roll a coin over the leaf to place the pigments on the filter paper.

*Suggested solvent is a petroleum ether/acetone mixture.

*Students will calculate Rf values for the pigments and compare to some standard Rf values.

*Using this information the students will identify the plant pigments.

ACTIVITY ONE CONT.- WHICH ACT AS ACID/BASE INDICATORS?

Which of the pigments will change color?

•Using the chromatographs produced in part one, students will test which pigments can be used as acid/base indicators

•The pH range samples generated in the pre-activity are used

•The students dip the paper from each pigment type into the standard solutions

•They will discover that anthocyanins change color in very acidic and basic environments

ACTIVITY TWO: CONSTRUCTION OF A PH SCALE

A single group of plant pigments provides a lot of different colors.

*Many high school students have used pH paper, but now they will construct their own scale based on anthocyanins from plants.

*Each student group will be given an anthocyanin rich plant. Examples include red cabbage, grapes, blueberries, tomatoes, strawberries, plums, or raspberries. The plants should be different for each group.

*Each will then place some of their plant material in a beaker and boil it to extract the anthocyanins. Decanting the liquid will give them their own acid/base indicators (Withers, 2001).

*The students will then take a little of each of the pH reference solutions and put them into 14 test tubes, adding a small amount of their natural indicator.

ACTIVITY TWO CONT. FINDING THE PH OF AN UNKNOWN

Plants + Acid or Base -> Color Change

*Students need a reason to use their new color scale, so we will use it to find a pH range of an unknown acid or base.

*Placing a small amount of their natural indicator into a sample of the unknown, students will compare their color to their color scale to get an estimated pH range.

*Students will then collaborate all of their estimates to get the most precise estimate possible.

*Students must record all their observations and reasoning.

ACTIVITY THREE: QUANTITATIVE ANALYSIS

Time to use some math!

*Now students will test the accuracy of their pH measurement using a handheld pH meter.

*Students will also graph real data as they titrate their unknown. The main data they will be collecting will be pH and volume of titrant added.

*Using Excel, students will construct a graph of pH vs. mL of titrant, and analyze the graph to determine the unknown’s concentration. If their anthocyanin indcator changes color they will indicate that, too.

ACTIVITY THREE CONTINUED

At halfway to the equivalence point pKa=pH

*Students will then be required to come up with a hypothesis for the existence of yellow tomatoes based on the data they have learned.

EXTENSIONS

There’s lots more to learn!

*Students could look at spectroscopy of the anthocyanins to measure absorbance at different wavelengths of light, and use a database to help identify specific anthocyanins (See Kalb and Howard).

*While fresh fruit was used in our trials, it would be a great variation to try frozen and canned, to see if these processes had any effect on the anthocyanins.

QUESTIONS??

???

REFERENCES

Learning requires you to get help from others.

 Blueberry_Cluster. (Picture). URL:http://www.oregonberry.com/Blueberries.htm Accessed: June 19, 2008. Fruits_and_vegetables2. (Picture). URL: http://www.firodiyaheartfoundation.org/images/fruits_and_vegetables2.jpg Kalb, Dee A., and G. W. Howard. "Analysis of Plant Pigments Using Paper Chromatography and Visible and/or UV Spectroscopy." Purdue University Instrument Van Project. Purdue University. <http://www.chem.purdue.edu/teacher/table_of_contents/UVVUS/UVVIS.Plant%20Pig ments_CH.pdf>. Accessed: June 19, 2008.

LYC11. (Yellow tomato picture). URL: http://www.magicgardenseeds.com/images/product/LYC11/LYC11.jpg. Accessed June 19, 2008.

REFERENCES

So does teaching!

 Marsden, Steve. "Separation of Plant Pigments by Paper Chromatography." Chemtopics.Com. 19 Aug. 2007. <http://www.chemtopics.com/unit06/pchrom.pdf>. Accessed: June 19, 2008.

Massengale. Chromatography of plant pigments. URL: http://www.biologyjunction.com/chromatography_plant_pigments.htm

NASA. Chromatography of leaf pigments: Lesson 2 of 2. URL: http://media.nasaexplores.com/lessons/01-037/9-12_2. Accessed: June 18, 2008.

Plant Pigment Chromotography. Milanareaschools.Org. <http://milanareaschools.org/~wbenya/Biology/documents/chromatography%20lab.pdf >. Accessed June 19, 2008.   Red Acre Cabbage. (Picture). URL: www.seedfest.co.uk/seeds/cabbage/cabbage.html Accessed: June 19, 2008.

REFERENCES

In fact, teaching is learning!

 Red Cabbage Acid Base Indicator. 27 Feb. 2002. University of Minnesota. <http://www.chem.umn.edu/services/lecturedemo/info/Cabbage_Indicator .html>. Accessed: June 19, 2008.

Red Cabbage pH paper. URL: http://www.ipse.psu.edu/activities/paper/red_cabbage.pdf Accessed: June 19, 2008.

Reiss, Carol. Experiments in Plant Physiology. Englewood Cliffs, NJ: Prentice Hall, 1994.

Senese, Fred. Water to Wine. General Chemistry Online. 31 July 2007. Frostburg. <http://antoine.frostburg.edu/chem/senese /101/features/water2wine .shtml>. Accessed: June 19, 2008.

REFERENCES

Thank you!

 Strawberry. (Picture). URL: http://www.arabidopsisthaliana.com/strawberry/strawberry.jpg Accessed: June 19, 2008.

Tomato_pd. (Picture). URL: http://collectingtokens.files.wordpress.com/2007/08/tomato_pd.jpg. Accessed: June 19, 2008

Withers, G. (2001). Natural indicators: How do they work? GIPSE. URL: http://www.cmu.edu/gipse/materials/pdf-2001/natural_ph_indicators.pdf. Accessed: June 19, 2008.