Plant Extract As Acid Base Indicator: An Overview (2025)

NATURAL INDICATORS AS ALTERNATIVE TO SYNTHETIC ACID BASE INDICATORS

In acid-base titrations, indicators are used to show sharp color change at intervals of pH. Natural pigments in plants are highly colored substances and may show color change with variation of pH. An attempt has been made to investigate the indicator activity of flower pigments and to replace synthetic indicators as they have certain disadvantage like chemical pollution, availability problems and high cost. Alcoholic extract of Hibiscus rosasinensis, Calotropis gingantia, Brassica oleracea-capitata, Rosa chinensis, Brassica oleracea-italica, Ixora chinensis, Cantharanthus roseus gives sharp intense color change as compared to phenolphthalein and methyl orange. Herbal indicators are evaluated by using different titrations of acids versus bases. The flowers were cleaned by distilled water and cut into small pieces and macerated for two hours in 25 ml of 90% ethanol. The equimolar titrations were performed using 10ml of titrant with three drops of indicator. The mean and standard deviation for each type of acid base titrations were calculated from results the obtained. In all these titrations, promising results were obtained when it was tested against standard synthetic indicators. Titration show sharp color change at the equivalence point and the extract was found to be very useful and accurate for indicating the neutralization point. Natural indicators employed in the acid base titrations was found economic, safe and an efficient alternative for traditional indicators. Keywords: Herbal indicator, economic, accurate indicator, efficient alternative, sharp end point

Acids, Bases and Indicators

ACID-BASE INDICATORS

The first part of this table lists some common acid-base indicators in alphabetical order along with the approximate pH range(s) at which a color change occurs. Following this is a table of the same indicators ordered by pH range, which includes the nature of the color change, instructions on preparation of the indicator solution, and the acid dissociation constant pK, when available.

The behaviour and properties of some acid-base indicators: a review

Journal of Science and Humanities Studies , 2020

This review focuses on Seven Acid-Base Indicators from the azo class and from the second type: Methyl Orange; Methyl Red; Methyl Yellow; Alizarin Yellow R; Alizarin Yellow GG; Tropaeolin O and Magneson I. These indicators show different colors involving the chemical reaction in aqueous solutions as results as change the acidity of solution causing the formation two different structure forms one in acid form and another in basic forms with possibility formation of resonance structures. Different variables such as temperature; ionic strength; solvents; concentrations; pressure; substituent's; position of function group and surfactant that influence on the behavior of Acid-Base indicators were explained. The electronic absorption spectral, equilibrium, terminological aspects and characteristics as well as the possible schemes of formation two compounds at isosbestic point are discussed. The contributions of different methods using to estimate the dissociation constant for it is discussed.

20. Thin-layer chromatography of acid-base indicators

Acid-base indicators. Acid-base indicators dyes or pH indicators dyes are substances, which are used in chemistry laboratories to visualize end-points of a acid-base titration experiment through color change(s) in different pH environments [ 1 , 2 ]. They constitute a group of organic compounds, like weak acids or weak bases, which react with water and create acid-base conjugate pairs, where both forms are differently colored. In acidic solution protonated structural forms of the dyes exist, whereas in basic solutions deprotonated forms exist. The key structural feature that varies between the acidic and basic forms for acid-base indicator dyes is change in the electronic conjugation (i.e. alternative resonance structures) throughout these molecules. The change in electronic conjugation in various pH environments provide the color changes to 'indicate' a titration end-point. Highly conjugated systems generally absorb and reflect specific wavelengths of light in visible region of the electromagnetic spectrum. pH indicator dyes can be one-colored (e.g. phenolphthalein), when only one form is colored, second or other forms are colorless, two-colored (e.g. methyl orange) or multicolored (e.g. alizarin red S), when each form of the indicator dye is differently colored. Sometimes mixtures of indicator dyes are used, which gradually change the colors in the broad range of pH -these kinds of indicators are known as universal indicators. Fluorescent indicators also exist, which change the color of fluorescence or start to fluoresce at specific pH of solution.

Investigation of a Simple and Cheap Source of a Natural Indicator for Acid-Base Titration: Effects of System Conditions on Natural Indicators

Green and Sustainable Chemistry, 2012

This study investigated a natural indicator for acid-base titration which is extracted from guinea corn leaves popularly called "waakye leaves" in Ghana. Four types of acid-base titration were studied: strong acid versus (v/s) strong base, strong acid versus weak base, weak acid versus strong base, and weak acid versus weak base. The indicator color change, pH range and the average titre values were determined for each type of acid-base titration. These values were comparable to those obtained from three standard indicators: methyl orange, methyl red and phenolphthalein. Total flavonoids (TF) and condensed tannin (CT) from the crude leaves extract were determined which might be the major reasons for the activity of the extract as an indicator for simple acid-base titration. The authors suggest that the natural indicator is cheap, available, simple to extract, user and environmentally friendly and could be an excellent replacement for standard indicators.

Investigation of a simple and cheap source of a natural indicator for acid-base titration: effects of system conditions

2012

This study investigated a natural indicator for acid-base titration which is extracted from guinea corn leaves popularly called “waakye leaves ” in Ghana. Four types of acid-base titration were studied: strong acid versus (v/s) strong base, strong acid versus weak base, weak acid versus strong base, and weak acid versus weak base. The indicator color change, pH range and the average titre values were determined for each type of acid-base titration. These values were comparable to those obtained from three standard indicators: methyl orange, methyl red and phenolphthalein. Total fla-vonoids (TF) and condensed tannin (CT) from the crude leaves extract were determined which might be the major rea-sons for the activity of the extract as an indicator for simple acid-base titration. The authors suggest that the natural in-dicator is cheap, available, simple to extract, user and environmentally friendly and could be an excellent replacement for standard indicators.

Natural Dyes Characterization of Local Plants as Acid-Base Indicator

EduChemia (Jurnal Kimia dan Pendidikan)

Hanjuang, mangosteen, putat, and tabelian plants are used by people of Lanjak deras Village as natural dyes for woven cloth and food so that they can be used as an alternative substitute synthesis indicators that are limited in a remote area. The purpose of the study is to determine the best type of solvent in extracting the samples, pH range, UV spectrum profiles, precision, and accuracy of the plant's extract as indicator. The sample was the plants that are used by the people of West Borneo as natural dyes, namely putat flower, tebelian stem, mangosteen leave, and hanjuang leave. Each sample was macerated with four types of solvents, namely aquadest, ethanol, methanol, and (1:1) ethanol:methanol, then the extract was testing by pH range. The extracts providing color changes were determined for its UV-Vis spectrum profile, stability, accuracy, and precision. The results showed that ethanol and methanol were suitable for extracting mangosteen leaves, methanol for putat flowers, ethanol for hanjuang leaves, and (1: 1) ethanol:methanol for tebelian stems. Mangosteen leaf extract, putat flower, and tebelian stem gave a pH range of 12-14, while hanjuang leaf extract did not change color. The phytochemical test results and UV spectrum profile of mangosteen leaf extract, putat flower, and tebelian stem indicated the presence of phenolic compounds. The powder and extract solution had high stability. Mangosteen leaf extract, putat flower, and tebelian stem had precision and accuracy with the medium category. These data indicated that mangosteen leaf extract, putat flower, and tebelian stem have potential as indicators of acid-base.

Natural indicator as a eco-friendly in acid base titration

Journal of chemical and pharmaceutical research, 2014

Today synthetic indicators are the choice of acid-base titrations. But due to environmental pollution, availability and cost, the search for natural compounds as an acid-base indicator was started. The present vocation highlights the exploit of Euphorbia mili, Erythrina varigata and Nelumbo nucifera methanolic and aqueous extract of the flowers of plants as an acid-base indicator in titrations. This natural indicator is easy to extract as well as easily available. Promising results were obtained when it was compared against standard synthetic indicators. Titration shows sharp color change at the equivalence point. The equivalence points obtained by the flowers extract coincide with the equivalence points obtained by standard indicators. These natural indicators are found to be a very useful, economical, simple, accurate and eco-friendly

NATURAL INDICATOR: AN UNIQUE REPLACEMENT FOR STANDARD INDICATORS

Present study investigated a natural indicator for acid-base solution which is collected from Ripe fruit of puisak, light yellow Dahlia flower, Orange Mari Gold flower and Red Salvia flower. Colour change of the indicator and pH range were determined for each type of acid-base solution. These values were comparable to those obtained from the standard indicators. Colour pigments were extracted from the flowers via cold extraction using soxhlet extractor. The pH value of the extracts with wavelengths of absorption was determined using UV/Visible spectrophotometer. From the result obtained, all the extracts exhibited sharp contrast between their colours in acid and base. The maximum wavelengths of absorption obtained from all extract fall within the visible region of electromagnetic spectrum. These values are almost similar to that obtained from synthetic indicators. It is on these bases that we concluded that natural indicators could be an excellent replacement for synthetic indicators since they are cheap, readily available, simple to extract, non toxic and also environment friendly.