Name ________________________________________ Date _________________ Period ____________ A NTHOCYANINS BACKGROUND INFORMATION The world around us is filled with interesting things: people, plants, fungi, buildings, teachers, pretzels, bubble gum, sphincters, balloons, radios, cars, calculators, pirates, rubber stamps, pennies and anthocyanins. The last item in this litany is what is of particular interest to us right now. Anthocyanins are a class of chemical that respond to variations in pH. They do so by either gaining or loosing an H or an OH group. This slight change in the structure of the molecule causes it to either absorb or reflect a different wavelength of light. This, to humans (excepting the poor, colourblind Mr. Syracuse, boo hoo), is perceived as a change in colour. Thus, these types of molecules are particularly useful if you are in need of a pH indicator, but are at some sort of happinin’ party, with only beets or red cabbage lying around. Today we are going to investigate a number of different, naturally-occurring anthocyanins. SAFETY NOTE Please recall the safety procedures sheet that you signed at the beginning of this year. This lab will involve some fairly strong acids and bases, and care must be taken at all times to avoid injury. Observe the following rules: Always wear safety goggles Never mix chemicals unless directed to do so by your teacher ALWAYS ADD ACID TO WATER, NEVER WATER TO ACID If you spill an acid or a base, call your teacher to help you clean it up When rinsing out test used test tubes, take caution. You do not know what is or was in them Use a separate dropper for each solution. Mixing droppers will contaminate solutions Be aware of what you and those around you are doing at all times PROCEDURE You will be using various acids, bases, and indicators to determine the pH or colour change of certain substances. Follow the procedures very carefully to avoid a timely mix-up. 1. Decide on which three anthocyanins you will use in the first part of this lab. 2. Prepare the extracts as directed by your teacher. 3. Obtain nine test tubes per group; three for each anthocyanin. You will need a test tube rack. 4. Label three tubes with whatever acid you have selected, label three as distilled water, and label three with whatever base you have selected 5. Fill the tubes with your anthocyanin first, as depicted in figure Note the colours of the various tubes in table Add either acid, distilled water, or your base to the tubes. 8. Note the colour change, if any, in table Carefully pour the contents of your tubes, one at a time, in the sink. Take care not to splash.

Anthocyanin IAnthocyanin IIAnthocyanin III Acid Water Base Figure 1. Preparation of tubes for first test. 10. You will now use your three anthocyanins, and perhaps those of your lab buddies, to determine the approximate pH of an unknown solution. Caution: because you do not know if the solution is an acid or a base, you should treat it with extreme care. 11. Test the unknown solution using the procedure you used in the first part of the lab. Record your results and hypotheses in the data table. Anthocyanin and original colour Acid __________Distilled WaterBase __________ Table 1. Determination of colour changes for anthocyanins at various pH levels.

Table 2. Tests of unknown solution AnthocyaninOriginal colourColour with addition of unknownpH hypothesis ANALYSIS You will now need to analyze your findings. Compare notes with your lab buddies, and see if you can figure out what the approximate pH of the unknown was. Even if you can only narrow it down to either acid, base, or neutral, that is at least a start. 1. What do you think the pH of the unknown was? 2. What was the actual pH, as given by your teacher? 3. How far off were you? Can you explain why or why not? 4. Why might plants produce these substances known as anthocyanins? 5. What about their chemical properties do you think might help the plant? 6. Do you think anthocyanins have anything to do with plant reproduction? If so, how? 7. Onions don’t smell when added to a base, but they will in an acid. Why do you think this is?