2016/10/17 (Mon) ~ 21 (Fri)
by Gigi Wu and Tun-Cheng Chien
The 2016 Chemistry Week at National Taiwan Normal University (NTNU) was organized by the Student Association of Department of Chemistry, NTNU and sponsored by Departments of Chemistry, NTNU and the ACS Taiwan Chapter. The objective of the Chemistry Week was to build awareness of chemistry and promote the value of chemistry in everyday life. The event was supervised by Professor Yi-Hsin Liu (Dept of Chemistry, NTNU) and was projected to demonstrate interesting chemical reactions and provide fundamental chemistry knowledge to gather the science en thusiasts, especially non-science majored students, on campus.
The main theme of the 2016 Chemistry Week was Chemistry Secrete Investigation and was held in the week of 2016/10/17 (Mon)~21 (Fri) at the atrium of Cheng Zheng building at the main campus of NTNU. 25 chemistry-majored students (fresh- man and sophomore years) participated as volunteered staffs to help organize the event and prepare the demonstration and approximately 200 students have stopped by and visited our booth during the week.
Five simple experiments were demonstrated in the event. The experiments are summarized below:
I.DIY Fingerprint developer
Ninhydrin is often used as a stain for developing TLC in the organic laboratory to identify primary and secondary amines. Since it was first used for developing latent fingerprints in 1954, ninhydrin has also become the most common method used to reveal prints on porous surfaces. Nearly all forensics labs use ninhydrin for this purpose. Ninhydrin is cheap, sensitive, and commercially available in disposable spray cans. The developed print is high-contrast purple that is readily visible on most paper backgrounds. This experiment usually takes about 30 minutes for color development. The procedures include:
- Fill sprayer with 10% Ninhydrin alcohol solution.
- Leave fingerprint on a piece of paper.
- Spray Ninhydrin alcohol solution on the fingerprint.
- Stick the tape onto the position of fingerprint.
- Wait for minutes, and the fingerprint appears.
The chemistry behind the experiment can be summarized as the following reactions:
The visitors pressed their fingerprints on paper, and then used ninhydrin to get their own fingerprint development. This reaction really surprised a lot of visitors. Hence, we have the opportunities to introduce this interesting experiment and the principle to more people.
Ninhydrin solution can react with primary and secondary amines. After touching the solution, the fingertips turned purple.
II. Redox Indicator
Redox indicators change their colors at specific potential differences. Indicator compounds must have a reduced and oxidized form with different colors, and the redox process must be reversible.
In experiment A, a ‘blue bottle’ experiment was demonstrated. An alkaline solution of glucose acts as a reducing agent and reduces added methylene blue from a blue to a colorless form. Shaking the solution raises the concentration of oxygen in the mixture and this oxidizes the methylene blue back to its blue form. When the dissolved oxygen has been consumed, the methylene blue is slowly reduced back to its colorless form by the remaining glucose, and the cycle can be repeated many times by further shaking. The cycle can be repeated many times.
In experiment B, indigo carmine was used to replace methylene blue in experiment A. Indigo carmine is very cheap, safe, easily obtained and produces a range of stunning colors. The basic principle is the same as experiment A. However, indigo carmine changes colour from yellow to red, and then to green. These demonstrations can be used to support teaching of redox chemistry, and illustrating aspects of color chemistry.
These experiments take approximately 10-15 minutes. We took the opportunity to explain the roles of oxygen and glucose in the experiments, in which glucose serves as a reducing agent, and oxygen serves as an oxidizing agent.
Blue bottle reaction:
Figure 2. From left to right: Blue bottles: oxidized form and reduced form of methylene blue solution; Traffic Lights: reduced form, the first oxidized form and the second oxidized form of indigo carmine solution
III. Acid-base indicator
Red cabbage contains pigments called anthocyanins which display the purplish color of the red cabbage and become a perfect nature indicator for acid and base. In this experiment, we applied the red cabbage extract as the acid-base indicator in various solutions in different pH, and then observed the changes of color.
IV. DIY Slime
A solution of polyvinyl alcohol (PVA) can be made into slime by adding borax solution, which creates crosslinks between polymer chains. In this activity, some interesting properties of the slime are investigated. Visitors were delighted to make the slime in different ratio of borax and polyvinyl alcohol by themselves and glad to understand what happened about this malleable and elastic plaything.
Summary and future perspectives
With the assistance from department faculty and senior students, the staffs were able to conduct the activities successfully. Students in the NTNU main campus are non-Science majored students, mostly from the area of Literature, Social Sciences, Education and Business Management. It is a great opportunity for us to promote the awareness and the knowledge of Chemistry in this special circumstance. Both visitors and the staffs learned lessons from this activity. Especially, the visitors can get hang-on experiences and saw demonstration and explanation of the background knowledge. For us, the staffs, we learned about not only how to cooperate with each other but how to represent clear demonstration. People willing to become teachers in the future can improve their teaching and experimental skills at the same time. We look forward to the same activity next year. All the experience gained in this year would be great beneficial to improve the activity next time.