Development of Acid–Base Indicators from Natural Pigments in Agar Gel

Abstract

Teaching chemistry necessitates hands-on activities to help students deeply understand chemistry concepts and relate scientific principles to daily life. However, constraints in accessing laboratory equipment and materials pose significant challenges for educators in conducting experiments. This paper proposes the development of a pH indicator gel derived from natural plants and juices to enhance the teaching of acid−base topics. The aim is to foster interest and inquiry in students through the predict− observe−explain (POE) strategy. The pH indicator gel was formulated by combining agar gel with various natural indicators and immersing it in different buffer solutions with pH values ranging from 2 to 12. The resultant color changes in the pH indicator gels were compared to the colors of reference solutions spanning the same pH range. Experimental results demonstrated that the gel modified its color in a manner akin to the color change exhibited by the corresponding extract indicator in the buffer solutions across the entire pH range. Moreover, the agar gel was able to be reused multiple times while continuing to display alternating color changes in response to the pH of the solution. The pH indicator gel was utilized in teaching acid−base topics to a group of 24 student teachers in Cambodia. This hands-on activity stimulated interest and curiosity in the student teachers, leading to more engaged observations during the experiment. Feedback from these student teachers highlighted that the pH indicator gel was an effective teaching aid for conveying acid−base concepts and helped boost their engagement in laboratory experiments.

Dyeing Cloth Green Using Red Onion Skin: A pH-Responsive Dye and Aluminum-Ion Complex

“…The green color is created by mixing yellow and blue. Red onions contain quercetin, − a yellow pigment, and anthocyanin − that changes color in response to various factors such as pH and complexation. − The aluminum ions act as centers for the chelation of the anthocyanin dyes, which dramatically affect their optical properties. The complex between anthocyanin and aluminum ions forms a blue dye. − The mixing of the blue complex and yellow quercetin forms a green dye.…”

Evaluating torenia fournieri Flower Extract as a Natural Acid-Base Titration Indicator

“…Synthesis indicators that are often used in practical work usually use phenolphthalein, litmus paper, methyl red, and bromine thymol red. However, the use of synthetic indicators often becomes a problem in practice [2], this is because the price is relatively expensive and in some areas outside Java it is difficult to obtain them. To overcome this problem, an alternative replacement for the synthetic indicator is needed.…”