International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 13 Issue: 01 | Jan 2026
p-ISSN: 2395-0072
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Comparative study of natural and synthetic indicators in acid-base titration supported by UV-Visible spectral analysis R. Kanmani1, C. Dhilip2, P. Dineshkumar3, S. Dinesh4 1, Assistant Professor, Sri Vijay Vidyalaya College of Pharmacy, Tamil Nadu, India.
2, 3, 4, B. Pharm students, Sri Vijay Vidyalaya College of
Pharmacy, Tamil Nadu, India. -------------------------------------------------------------------------***------------------------------------------------------------------------
Abstract- Objective: To assess the effectiveness of natural indicators derived from Celosia cristata flowers and red dragon fruit peel in acid–base titrations and to compare their performance with commonly used synthetic indicators in terms of accuracy, sensitivity, and color transition.
Methodology: Petals of Celosia cristata and peels of red dragon fruit were collected and ground using a mortar and pestle. The crushed materials were subjected to maceration for 24 hours using ethanol and acetone as solvents. The extracts were then filtered using Whatman filter paper. The obtained filtrates were utilized as natural indicators for acid–base titrations and stored in amber-colored bottles to prevent degradation. Conclusion: The natural indicators exhibited titration end points comparable to those of synthetic indicators. UV–visible spectroscopic analysis confirmed their pH-responsive behavior. Hence, these natural extracts can serve as effective, ecofriendly alternatives to conventional synthetic indicators in acid–base titrations. Keywords: Celosia cristata, red dragon fruit peel, pH measurement, acid–base titration, UV–visible spectroscopy.
Introduction Acid–base chemistry is a core area of chemistry that provides the basis for understanding related topics such as acid–base titrations, buffer solutions, and salt hydrolysis. The concept of acids and bases requires students to grasp different levels of representation, including observable (macroscopic), particle-level (microscopic), and symbolic interpretations. Acid–base titration is a quantitative analytical method used to measure the concentration of an acidic or basic solution by reacting it with a standard solution of known strength. It can also be described as a laboratory technique designed to obtain information about solutions containing acidic or basic substances. A wide range of compounds, including both organic and inorganic substances, can be analysed through titration based on their acidic or basic nature. During the titration process, an acid reacts with a base or vice versa, and the completion of the reaction is detected using a suitable indicator. Acid–base titrations may involve combinations of strong and weak acids and bases and are commonly applied to determine the concentration of unknown solutions and to assess the relative strength of acids or bases. Different types of indicators are used in acid–base titrations, with commonly employed laboratory indicators including methyl red, methyl orange, phenolphthalein, phenol red, methyl yellow, pentamethoxy red, bromophenol blue, and thymol blue. Among these, phenolphthalein and methyl orange are most widely used. Indicators are substances that undergo a visible color change within a specific pH range. Most indicators are organic compounds, and phenolphthalein is often preferred due to its sharp and easily noticeable color transition, especially in strong acid–strong base titrations. Methyl orange is generally selected for strong acid–weak base titrations because it changes color rapidly near the equivalence point. In weak acid–weak base titrations, neither phenolphthalein nor methyl orange is appropriate, as the pH change near the equivalence point is not sufficiently steep; therefore, indicators are usually not used. For titrations involving a weak acid and a strong base, phenolphthalein is commonly chosen because it provides a distinct color change at the equivalence point. Because acid–base titrations are based on neutralization reactions between acids and bases, they are also known as neutralization titrations. Indicators are colored pigments or dyes that can be obtained from various natural sources such as plants, fungi, and algae. Nearly all red, blue, or purple-colored fruits and flowers contain a group of natural pigments called anthocyanins, which exhibit pH-dependent colour changes.
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