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Mechanochemistry with Anthocyanin Indicators Using Solid Acids and Bases

Mechanochemistry with Anthocyanin Indicators Using Solid Acids and Bases
Contributors
Dean Campbell
Professor | Bradley University
Mortars containing butterfly pea flowers ground together with various colorless solids
Summary
In this activity, dried anthocyanin-containing flowers are combined with acidic, basic, and neutral powders using mortars and pestles in a demonstration of mechanochemistry. Students first research which solids they would like to use for this activity on the basis of maximum efficacy and minimum hazard. The data that they collect are used to inform the instructor as to which chemicals are to be made available for the students to use in their own laboratory trials.
Keyword Tags
Acid-Base Chemistry
Mechanochemistry
File (PDF, PPT, image, etc)
gctlc-learning-object-mechanochemistry-acid-base-anthocyanin-2-instructor-guide.docx
gctlc-learning-object-mechanochemistry-acid-base-anthocyanin-2-student-instructions.docx
Digital Object Identifier (DOI)
https://doi.org/10.59877/MJTE8865
Learning Goals/Student Objectives
In performing this experiment, a student will be able to:
- use mortars and pestles to do mechanochemical syntheses
- use anthocyanins as pH indicators
- assess the acid and base strength of selected solids
- assess the toxicity of selected acids and bases
- compare the utility of solvent-free mechanochemical synthesis vs. synthesis involving species dissolved in solvents
- compare the “greenness” of the pH indicators in this lab experiment with other pH indicator systems
Object Type
Laboratory experiment
Activities/Technology (e.g., in-class activities, online games, hands-on activities/manipulatives, outreach, virtual tools, etc.)
Audience
High School (Secondary School)
Introductory Undergraduate
Upper/Advanced Undergraduate
Common pedagogies covered
Context-based learning
Hands-on learning
Problem-based learning
Green Chemistry Principles
Less Hazardous Chemical Syntheses
Safer Solvents and Auxiliaries
Use of Renewable Feedstocks
Design for Degradation
U.N. Sustainable Development Goals (SDGs)
Responsible Consumption and Production
Safety Precautions, Hazards, and Risk Assessment
There are many possible alternatives for chemicals to be used in this activity, including:
sucrose (neutral) CAS # 57-50-1
table salt (neutral) CAS # 7647-14-5
citric acid CAS # 77-92-9
ascorbic acid CAS # 50-81-7
sodium acetate (base) CAS # 127-09-3
sodium hydrogen carbonate (base) CAS # 144-55-8
magnesium hydroxide (base) CAS # 1309-42-8
PubChem lists all of the above as EPA Green circle - The chemical has been verified to be of low concern

salicylic acid CAS # 69-72-7
This compound is not listed as EPA Green circle and PubChem says “The toxic effects of salicylic acid and salicylates are complex.” PubChem also notes there is no indication of carcinogenicity to humans. We will likely not use in future.

phenolphthalein (indicator not used in this activity) CAS# 77-09-8
PubChem describes phenolphthalein as being carcinogenic to some animals, and possibly carcinogenic to animals.

In all cases, precautions, including proper personal protective equipment such as goggles and gloves, should be used when working with these substances. Avoid spilling the compounds on clothing. Avoid inhaling any dust produced by grinding materials in mortars and pestles. Always wash your hands after completing the experiments and demonstrations.
Teacher Recommendations or Piloting Data (if available)
When we performed these experiments we observed the following colors:

Neutral compounds and butterfly pea flowers:
Table salt (sodium chloride):
Powder: blue, purply blue ,blue
Streak: blue
Water added: violet

Table sugar (sucrose):
Powder: dark blue slightly tinted purple, blue,very pale blue, blueish purple, dark bluish purple, light blue, blue, blue,darker blue
Streak: no data
Water added: very blue and dark,blue

Acidic compounds and butterfly pea flowers:
Ascorbic acid:
Powder: lavender,very light purple,blue,dark purple
Streak: slightly more true purple
Water added: dark true purple,darker purple,purple,purple

Citric acid:
Powder: noticeably darker blue, magenta pinkish,magenta,pink,light purple
Streak: purple and a little pink
Water added: purple

Salicylic acid (perhaps more toxic than the other compounds and we will likely not use in future):
Powder: lighter purple but not pink at all
Streak: no data
Water added: no data

Basic compounds and butterfly pea flowers:
Magnesium hydroxide:
Powder: very soft baby blue,light blue,very slight green,green shift,lightish blue,whiter blue
Streak: green, green,green showed up more
Water added: green,deep blue green, very green with slight hint of blue,turquoise/green,cyan green

Sodium acetate:
Powder: navy blue
Streak: sky blue
Water added: dark blue

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Submitted by

Dean Campbell
Reviewed by
Karen Parrish
Published on
Moderation state
Published
Time required (if applicable)
Three sessions approximately 30 minutes each
Related Learning Objects
Acids, Bases, and pH
Other notes/information
see related learning object for more info
Creative Commons License
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.