INTRODUCTION:

Indicators are substances that change the color when they are added to solution and there is a change in pH of that solution. pH measures acidity or basicity of solution which is based on the concentration of hydrogen and hydroxide ions present in solution. Indicators work by change in their structure in response to changes in pH, which alters their absorption of visible light, resulting inchange in color of solution. In chemistry indicators used to determine the pH of solution or rection, such as in titrations.^1,8

Synthetic indicators used in acid base titration have are not easily available, and expensive to produce. So this negative impacts can be overcomeby use of eco-friendly, easily available and cost-effective natural indicators, pH paper made from plant-based or other natural materials serves as a color-changing indicator to approximate the pH of a solution. When immersed in a liquid, it shifts in color depending on the acidity or basicity present. In acid-base titrations, natural alternatives to synthetic indicators are available and can be effectively utilized. By using these alternatives, we can reduce the negative impact on the environment and also make the process more cost effective.^2,7,9

Indicators are dyes/pigments that can be isolated from a variety of sources including plants, fungi and algae. Anthocyanins are water-soluble pigment show red colour, blue and purple colors of many fruits, flowers and leaves. Anthocyanins are part of the broader flavonoid family—plant-based pigments produced for multiple purposes, such as attracting pollinators and shielding against ultraviolet radiation. A notable feature of anthocyanins is their ability to shift color based on the pH level of their surroundings. They typically appear red in acidic environments and turn blue or purple in alkaline conditions. This makes them valuable as natural pH indicators in scientific experiments and in every day applications, such as in testing the pH of soil, water or food.^3,9

In present study, we usechina rose (Hibiscus rosa sinensis), Onion (Allium cepa), and Beetroot (Beta vulgaris) and turmeric (Curcuma longa) as anaturaland effective indicator for acid-base titration. These selected natural plants contains specific pigments which having similar properties as synthetic indicators. Hibiscus rosa sinensis belongs to malvaceae family. This plant is native to East Asia which is also known as China rose, Hawaiian hibiscus. This plant widely cultivated for its showy flowers, which are used for ornamental purposes and in traditional medicine.^{4,5,8,11,12,20.}

Allium cepa, commonly known as onion, which is used as natural indicator in era of various scientific and educational settings. The outermost thin and transparent layer of the onion contain pigment called anthocyanin, which is sensitive to change in pH.¹⁴ Beet contain a pigment called betalain, that causes change in color of solution as change in pH.^15,16 Curcuma longa, commonly known as turmeric, commonly used spice. turmeric contain pigment called curcumin, which has been found to have several properties that make it usefull natural indicator.¹⁷

MATERIALS AND METHODS:

1. Sample collection:

Fresh samples were collected from botanical garden in PRES Institute of Pharmacy College Loni.

2. Sample preparation:

For Hibiscus rosa sinensis: To isolate the bioactive constituents from Hibiscus rosa-sinensis, fresh petals were carefully collected and air-dried at ambient temperature. Their weight was monitored consistently to confirm complete drying. After full dehydration, the petals were finely ground using a mortar and pestle to produce a uniform powder. A 20-gram portion of the powdered material was measured for extraction purposes.

Distilled water and methanol served as the extraction solvents. The powdered petals were soaked in these solvents for a defined duration to facilitate the release of active compounds. After the soaking period, the mixtures were filtered to separate the liquid extract. The resulting extracts were then stored in individual containers for subsequent testing and evaluation.^6,13

For Allium cepa:

Samples of Allium cepa were gathered, thoroughly cleaned, and left to dry. From the dried material, a 10-gram portion was accurately measured and then subjected to maceration using methanol and acetone in separate procedures. After allowing the mixtures to stand for 24 hours, they were filtered through Whatman filter paper. The resulting liquid extracts were then utilized in titration experiments to evaluate their effectiveness as pH indicators.¹⁸

For Beta vulgaris:

To isolate the colorant from beetroot, 100 grams of finely chopped beetroot were immersed in two solvent mixtures: Ethanol–Hydrochloric acid (99:1, v/v) and Ethanol–Water (1:1, v/v). The mixture was allowed to stand for 45 minutes. Afterward, it was cooled for 15 minutes, and the softened beetroot pieces were mashed to release the pigment. The liquid portion was filtered, and the remaining solid was further squeezed to maximize extraction. The collected liquid was then evaporated to concentrate the pigment extract. The final concentrated solution was stored in a sealed, light-protected container to avoid degradation of the active constituents.^15,16

For Curcuma longa:

Turmeric rhizomes were sliced and air-dried for 48 hours before being ground into a fine powder. A 100-gram sample of this powder was subjected to extraction using 132mL of 70% ethanol in a Soxhlet apparatus. The extract was then concentrated under vacuum at 50°C and subsequently dried in a desiccator to eliminate any remaining moisture. The process yielded approximately 15 grams of crude extract, equating to an extraction efficiency of 18.67%.¹⁹

Preparation of natural pH paper and litmus paper: Fresh petals of Hibiscus rosa-sinensis were washed thoroughly and blended into a paste. Distilled water was added to this paste to prepare an aqueous extract. The mixture was filtered to eliminate solids, and standard filter paper was cut into small rectangular strips. These strips were soaked in the hibiscus extract for several minutes, then removed and air-dried on a Petri dish. To ensure complete drying, the strips were further placed in an oven at 60°C for 30 minutes. Once ready, the natural pH paper was tested by dipping it into both acidic and basic solutions to produce red and blue (litmus-like) indicator strips, respectively.

3. Experimental methodology:

In the experimental procedure, the extract from each sample was utilized separately. Additionally, another experiment was conducted using a standard synthetic indicator i.e. phenolphthalein. To begin, 10ml of the acid was measured into a conical flask and 1.0ml of the phenolphthalein indicator was added using a 1.0ml dropper. A 50ml burette was then filled with the base and titrated against the acid until a clear color change was observed, indicating the end of the titration reaction. The first titration was performed using the standard synthetic phenolphthalein indicator. Each titration was performed using either the natural plant extract or a conventional indicator. The procedure was repeated three times for accuracy, with the endpoint readings noted during each trial. An average of the three readings was then computed to obtain a final value.

Indicators Used:

Phenolphthalein

Methyl red

Prepared natural indicators

Acid Base Titration Procedures:

1. Strong Acid Vs base (Sulphuric acid and sodium hydroxide):

To perform an accurate titration, 10mL of 0.1N sulphuric acid was measured and transferred into a clean conical flask. To detect the endpoint of the neutralization, three drops of phenolphthalein indicator were introduced. Sodium hydroxide solution (0.1N) was gradually dispensed from a burette into the acid until a faint but persistent pink color appeared, signaling the completion of the reaction. This titration process was repeated several times to achieve concordant readings, ensuring the reliability and precision of the results. The same procedure was followed using natural indicators in place of phenolphthalein, and the endpoints were carefully recorded.

2. Strong Acid VS Weak Base (Sulphuric acid and Sodium Carbonate):

For this titration, 10mL of 0.1N sulphuric acid was poured into a conical flask. Phenolphthalein indicator (3 drops) was added to identify the neutralization point. Sodium carbonate solution of the same normality (0.1N) was slowly titrated from a burette into the acid until a stable light pink hue was observed, indicating the endpoint. To ensure accuracy, the titration was repeated until consistent (concordant) values were obtained. The experiment was also conducted using plant-based indicators as substitutes for phenolphthalein, and the resulting endpoints were documented.

3. Weak Acid Vs Strong Base (Acetic acid and sodium hydroxide):

A volume of 10mL of 0.1N acetic acid was carefully transferred to a conical flask. To indicate the completion of the reaction, three drops of phenolphthalein were added. Titration was performed by gradually adding 0.1N sodium hydroxide solution from a burette until a faint pink color persisted, indicating the endpoint. The procedure was repeated multiple times to achieve concordant results, ensuring the data's accuracy. Natural indicators were also employed following the same method, and the endpoints were noted for comparison.

Observation:

Table 1: Titration of H₂SO₄against NaOH

Sr. No.	Indicator	Constant burette reading (ml)	Color Change
1.	Phenolphthalein	10.3	Colorless to faint pink
2.	Hibiscus rosa sinensis	11	Faint pink to green
3.	Allium cepa	10.4	Faint pink to pale yellow
4.	Beta vulgaris	10.5	Faint pink to Colorless

Table 2: Titration H₂SO₄against Na₂CO₃

Sr. No.	Indicator	Constant burette reading(ml)	Color Change
1.	Methyl Orange	11.3	Colorless to faint pink
2.	Hibiscus rosa sinensis	10.6	Faint pink to green
3.	Allium cepa	10.9	Faint pink to pale yellow

Table 3: Titration of CH₃COOH against NaOH

Sr. No.	Indicator	Constant burette reading(ml)	Color Change
1.	Phenolphthalein	11.3	Colorless to faint pink
2.	Hibiscus rosa sinensis	11.7	Faint pink to green
3.	Allium cepa	11	Faint pink to pale yellow
4.	Beta vulgaris	11.2	Faint pink to Colorless

RESULT AND DISCUSSION:

Environmental concerns have led to a growing interest in finding natural alternatives for synthetic indicators in acid-base titrations. The high cost and limited availability of synthetic dyes have made it necessary to search for eco-friendly and sustainable options. This study focuses on the use of plant extracts as natural indicators for acid-base titrations. The extracts from different plants i.e. Beta vulgaris, Hibiscus rosa sinensis, Allium cepa were tested for their effectiveness in indicating the endpoint of Acid Base titration.

CONCLUSION:

The results demonstrated that the plant extracts provide sharp and intense color changes, which shows same results as synthetic indicators. Additionally, the use of plant extracts as indicators is simple, accurate, and economical. Hence, plant extracts could be a identical and typical alternative to synthetic Indicator and their utilization could be an environmentally friendly and cost-effective solution.

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Received on 24.12.2024 Revised on 15.04.2025

Accepted on 19.06.2025 Published on 24.07.2025

Available online from July 28, 2025

Res. J. Pharmacognosy and Phytochem. 2025; 17(3):205-208.

DOI: 10.52711/0975-4385.2025.00033

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