The+Use+of+Natural+Dyes+as+pH+Indicators

= The Use of Natural Dyes as pH Indicators =

Planned by:

Kristen Park __ [|(klp158@psu.edu] __ )

Brittany Buterbaugh (blb302@psu.edu)

Grade level: 5th and 6th graders

Topic: Natural dyes as pH indicators

National Standards: NSES Standard D Grades 5-8 (Physical Sciences & History of Science) State Standards: > > **Instructional Objectives: ** >  1) Students will be able to define pH (namely, pH<7 is an acid and pH>7 is a base). > 2) Students will be able to explain how a color change relates to pH in natural dyes > 3) Students will be able to explain the difference between synthetic and natural dyes > > **Content Explanation ** Before synthetic dyes were created, ancient civilizations used natural dyes for their dying purposes. When acids or bases are added to the natural pigments from plants, fruits and vegetables, it changes the pH of the solution. The color of some natural dyes will change with a change in pH. Both berries we will be using contain anthocyanins, which are red at a low pH (<7) and blue at a high pH (>7). These changes occur due to changes of the structure of the molecule from the addition of acid or base. Since pH is related to the concentration of hydrogen ions in the solutions, the addition of the acid will cause the pH to drop. We will also explain that distilled water has a pH of 7, which is neutral. The hydrogen ions then change the structure of the anthocyanin causing the color change of the solution. Bases have the opposite effect. The pH rises when a base is added and the concentration of hydrogen ions decreases. The removal of hydrogen ions causes a structural change of the anthocyanin, again causing a color change.
 *  "Substances react chemically in characteristic ways with other substances to form new substances (compounds) with different characteristic properties. In chemical reactions, the total mass is conserved. Substances are often placed in categories or groups if they react in similar ways; metal is an example of such a group."
 * "In historical perspective, science has been practices by different individuals in different cultures. In looking at the history of many peoples, one finds that scientists and engineers of high achievement are considered to be among the most valued contributors to their culture."
 * 3.4.7.A "describe and conduct experiments that identify a chemical and physical property"
 * <span style="color: black; font-family: Arial,sans-serif;">3.7.7.A "Describe safe procedures for using tools and materials."


 * <span style="color: black; font-family: Arial,sans-serif;">Materials, Equipment, & Set Up **
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">2 pints of blueberries
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">1 pint of cherries
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">½ cup water (per set up)
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">Fine mesh strainer
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">Vinegar
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">Baking soda
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">Containers for dyes/fruits
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">400 mL beaker
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">Hot plate/ electric kettle
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">Stirring utensils
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">pH probes


 * <span style="color: black; font-family: Arial,sans-serif;">Activity **


 * <span style="color: black; font-family: Arial,sans-serif;">STUDENT SAFETY: **<span style="color: black; font-family: Arial,sans-serif;"> Risk of burn due to boiling water. Use care when pouring the hot water from the vessel. Also, must wear goggles due to the use of liquids.

<span style="color: black; font-family: Arial,sans-serif;"> Students will add ½ cup of hot water from hot plate or electric kettle to 1 pint of blueberries or cherries. Stir the mixture of water and berries to extract the color from the fruit. Once the color is extracted, strain the berries out of the solution.

<span style="color: black; font-family: Arial,sans-serif;"> A prepared, cooled solution will be provided for the students. Students will have three containers. The cooled dye solution will separated into three containers. Into one of the containers with the dye, the student will add vinegar. Into another container, the student will add baking soda solution. The third container will remain as is. Students will be given pH probes to test the pH of each solution. The students will record the substance added, the color of the solution, and the resulting pH from the probe.


 * <span style="color: black; font-family: Arial,sans-serif;">Body of the Lesson: **

<span style="color: black; font-family: Arial,sans-serif;">(a) Engagement (4 minutes): <span style="color: black; font-family: Arial,sans-serif;">(b) Exploration (8 minutes):
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">What ancient civilizations have you been studying in class?
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">How do you think these civilizations dyed their clothes?
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">We will explain that they used natural dyes from plants, fruits, and vegetables.
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">What do you know about acids, bases, and pH?
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">We will explain how acids and bases affect pH.
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">Guiding question: How will adding a base/acid affect the pH and color of the natural dye from blueberries/cherries?
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">We will demonstrate the effects of adding acids and bases to one of the solutions (either blueberries or cherries). We will show them how vinegar and baking soda affect the pH and the color of the solutions. Then, we will have them predict what the vinegar and baking soda will do to the other solution, as well as what they think the pH will do. Afterwards, we will have them test their predictions with the solution provided. A table will be provided for them to record their data.

<span style="color: black; font-family: Arial,sans-serif;">(c ) Explanation (3 minutes):
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">After the students have performed their task, we will have them explain their results to us and whether their predictions were correct. We will then clear up any confusion the students may have about the natural dyes that we have picked up on from their explanations.

<span style="color: black; font-family: Arial,sans-serif;">(d) Evaluation (5 minutes):
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">Students must explain the visual effect of acids and bases on natural dyes.
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">Student must explain the effect of adding an acid or base to the natural dye (pH change-higher or lower) and how this relates to the color changes observed.

<span style="color: black; font-family: Arial,sans-serif;">(e) Elaboration: **__<span style="color: black; font-family: Arial,sans-serif;">Resources: __** <span style="font-family: Arial,sans-serif;">Calder, B. (n.d.). Natural Dye Lesson Plan. University of Maine. <span style="font-family: Arial,sans-serif;">Senese, F. (2010). //What household substances can be used as acid/base indicators?// Retrieved March 3, 2011, from General Chemistry Online!: http://antoine.frostburg.edu/chem/senese/101/acidbase/faq/household-indicators.shtml
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">If there is time, we will provide real life examples of acids and bases that they or someone they know may use in daily life and explain how the pH relates to these.
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">Heartburn/antacid tablets (acid/base reaction, causes neutralization, pH =7)
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">Fruits are acidic
 * <span style="color: black; font-family: Arial,sans-serif; vertical-align: baseline;">Etc.