Natural Resources As Indicator In Acidimetric Titration

Published Date: 02 Nov 2017

Manoj A. Suva*, Bhakti J. Ladva

Assistant Professor, Aksharpreet Institute of Pharmacy, Jamnagar, Gujarat, India.

Corresponding author: [email protected]

Abstract: In routine experiments synthetic indicators are the choice of acid base titrations. But due to their limitations like environmental pollution, availability and higher cost leads to look for natural compounds as an acid base indicator was started. The present work highlights the exploit of the acidified methanolic and aqueous extract of the fruit of Opuntia ficus indica plants as an acid base indicator in acid base titrations. Natural indicator is easy to prepare, easily available and have no toxic effects and promising results were obtained when it was tested against standard synthetic indicators. Titration shows sharp colour change at the equivalence point. The equivalence points obtained by the fruit extract correlate with the equivalence points obtained by standard indicators. In case of strong acid and strong base titration, the results obtained in the fruit’s extract matched with the results obtained by standard indicator. Hence, natural indicator is found to be a very useful, economical, simple to prepare and accurate for the acid-base titrations.

Keywords: Natural indicator, Acid base indicator, Titration, Opuntia ficus indica

Introduction

In 1664, the use of natural dyes as acid-base indicator was first reported by Sir Robert Boyle in collection of essays "Experimental History of Colours." Almost any flower such as blue, purple or red in colour contains class of organic pigment called anthocyanins that change colour with pH. The term titrimetric analysis refer to the quantitative chemical analysis carried out by determining the volume of solution of accurately known concentration which is required to react quantitatively with a measured volume of a solution of the substance to be determined. The addition is done until reaction is complete. This is called the end point or equivalence point of the reaction. The end point is detected by using a chemical compound known as an indicator. Indicator may be used internally or externally. Many acid base titration themselves indicate the end point of the reaction.1 The anthocyanins are group of flavonoid compounds. The extract was preserved in tightly closed container and stored away from direct sunlight.2 The intention behind this study is simply to bring in market the use of plant pigments and to increase the wealth of traditional medicinal system of India which is mostly plant based and to help farmers regarding cultivation, collection of plants as well as to industry regarding preparation of natural indicators.3 Anthocyanidins (anthocyanins) are plant pigment, which are responsible for red violet-blue colour seen in plant flowers4. The appearance of red color is due to presence of flavonoids, phenols and anthocyanins. Anthocyanins may serve as pH indicators in the presence of acids or alkalies.5 A pH indicator is a halo chromic chemical compound that is added in small quantity to a solution so that the pH (acidity or basicity) of the solution can be determined visually. Hence, a pH indicator is a chemical detector for hydronium ions (H3O+) or hydrogen ions (H+) in the Arrhenius model. Generally, the indicator causes the colour of the solution to change depending on the pH.

Plant mucilage contains D-glucose, D-galactose, Larabinose, D-xylose, L-rhamnose and D-galacturonic and glucuronic acids and sugars like hexoses, pentoses6.

The flavonoid components of the plant are isorhamnetin and its glucoside, penduletin, luteolin, kaempferol, quercetin, quercetin, rutin, flavonol 3-O-glycosides (quercetin, kaempferol, and isorhamnetin), dihydroflavonols, flavonones, and flavanonols. Opuntia ficus indica fruit contains betalain pigments which has a good potential for the use as a natural food colorant.7-8 Betalains are a class of red and yellow indole derived pigments found in plants of the Caryophyllales, where they replace anthocyanin pigments. Betalains are aromatic indole derivatives synthesized from tyrosine. They are not related chemically to the anthocyanins and are not even flavonoids.9 Betalain is a glycoside and consists of a sugar and a colored portion. Their synthesis is promoted by light.10 The major betalain is betanin is extracted from red beet roots. Betanin is a glucoside, and hydrolyzes into the sugar glucose and betanidin. It is used as a food coloring agent, and the color is sensitive to pH. 11

Material and Methods

Identification and collection: Opuntia ficus indica was identified from the department of the Pharmacognosy at college Akshar-Preet institute of pharmacy. Fruits were collected during summer season. Opuntia ficus indica fruits were collected for the purpose of study of natural indicator and it is available throughout the year. Several plant pigments like Anthocyanins, flavonoids present in which acts like natural indicator. Fruits were washed and cleaned by distilled water, grinded by a mechanical blender and soaked in 50 ml methanol for 48 hours and then triturated in mortal and pestle and the resulting solution were filtered through muslin cloth. The resulted methanolic extract was used as natural indicator for acidimetry and alkalimetry. The extract was preserved in light closed container and stored away from direct sunlight. Following the similar process aqueous extract of fruit was prepared, filtered and used as aqueous natural indicator. Analytical grade HCl, NaOH, CH3COOH, NH4OH, phenolphthalein, methyl orange, and phenol red were made available by the Department of Chemistry at college Aksharpreet institute of pharmacy. Reagents and volumetric solutions were prepared as per standard. The experimental work was carried out by using the same set of glass wares for all types of titration. Same aliquots were used for both titrations the standard indicator and fruit extract. The equinormal titrations were performed using 10 ml of titrant with four drops of natural indicator. A set of four experiments each for all the types of acid base titrations were carried out. The t-value and standard deviation for each type of acid base titrations were calculated from results obtained.

Results and Discussion

The fruit extract were screened for its use as an indicator in acid base titration and the results were compared with the results obtained by standard indicators phenolphthalein, methyl orange and phenol red. The results of the screening for strong acid-strong base (HCl & NaOH), strong acid-weak base (HCl & NH4OH), and weak acid-strong base (CH3COOH & NaOH), weak acid-weak base (CH3COOH & NH4OH) are shown in table 1 and 2.

TABLE 1- Colour change in titration

Titrant

Titrand

Indicator colour changes and PH range

Standard

Methanolic fruit

extract of OFI

Aqueous fruit extract of OFI

HCl

NaOH

Colourless to pink (PH)

Pink to Yellow

Pink to Yellow

HCl

NH4OH

Pink to yellow (MO)

Pink to light yellow

Pink to light yellow

CH3COOH

NaOH

Colourless to pink (PH)

Pink to light yellow

Pink to light yellow

CH3COOH

NH4OH

Yellow to red (PR)

Pink to light yellow

Pink to light yellow

Keyword: - PH= Phenolphthalein, MO= Methyl orange, PR= Phenol red, OFI= Opuntia ficus indica

The strength of acid and bases (HCl, CH3COOH, NaOH, NH4OH) taken were 0.1 N, 0.5 N and 1 N. Four different types of titration performed were strong acid/strong base, strong acid/weak base, weak acid/strong base, and weak acid/weak base. The titrant v/s titrand were NaOH v/s HCl, NH4OH v/s HCl, NaOH v/s CH3COOH, NH4OH v/s CH3COOH. The colour changed from pink to green in the case of methanolic fruit extract of Opuntia ficus indica as natural indicator and the colour changed from pink to greenish yellow in the case of aqueous fruit extract of Opuntia ficus indica as natural indicator. The standard deviation ranged from ±0.05 to ±2.9 in methanolic fruit extract and aqueous fruit extract of Opuntia ficus indica. The results obtained showed that the routinely used indicator can be replaced successfully by fruit extract.

TABLE-2 Statistical Data of Methanolic and Aqueous Fruit Extract Of OFI as Natural Indicator for Acid Base Titration

Titration

Titrant V/s Titrand

Strength in

Normality

Methanolic fruit

extract of OFI as

natural indicator

t value ± S.D*

Aqueous fruit

extract of OFI as

natural indicator

t value ± S.D*

NaOH v/s HCl

1.0

PH v/s MFE

0.2299 ± 0.53

PH v/s AFE

0.1564 ± 0.26

0.1

PH v/s MFE

0.4482 ± 0.09

PH v/s AFE

1.3468 ± 0.09

0.5

PH v/s MFE

0.4650 ± 0.35

PH v/s AFE

0.8577 ± 0.11

NH4OH v/s HCl

1.0

MO v/s MFE

0.0470 ± 0.05

MO v/s AFE

2.1290 ± 0.05

0.1

MO v/s MFE

1.2647 ± 0.25

MO v/s AFE

0.4475 ± 0.09

0.5

MO v/s MFE

0.4475 ± 0.09

MO v/s AFE

1.7964 ± 0.09

NaOH v/s CH3COOH

1.0

PH v/s MFE

1.0917 ± 0.33

PH v/s AFE

0.3638 ± 0.67

0.1

PH v/s MFE

0.2772 ± 0.14

PH v/s AFE

0.0447 ± 0.09

0.5

PH v/s MFE

0.8956 ± 0.09

PH v/s AFE

2.1226 ± 0.05

NH4OH

v/sCH3COOH

1.0

PR v/s MFE

0.4045 ± 0.20

PR v/s AFE

0.7256 ± 0.22

0.1

PR v/s MFE

0.0446 ± 0.09

PR v/s AFE

2.1231 ± 0.05

0.5

PR v/s MFE

0.2426± 0.16

PR v/s AFE

2.1231 ± 0.05

The table represents t value and standard deviation for four type of titration.

*All values are t value ± S.D. for n = 4

Keyword:- HCl :Hydrochloric acid, CH3COOH :Acetic acid, NaOH :sodium hydroxide, NH4OH :Ammonium hydroxide, PH :Phenolphthalein, MO :Methyl orange, PR :Phenol red, MFE :Methanolic fruit extract, AFE :Aqueous fruit extract, OFI : Opuntia Ficus Indica.

Conclusion

The results obtained in all the types of acid base titrations showed that due to the presence of flavonoids it produces sharp colour changes at end point of titrations. The standard deviation calculated for synthetic indicator and methanolic and aqueous fruit extract of natural indicator showed very less variation in the results. Thus statistically also it proves the use of natural indicator in acid base titrations. As the methanolic and aqueous fruit extract provide similar results, methanolic and aqueous fruit extract can be used with equal reliability and accuracy for acid base titration. Thus the use of natural indicator in acid base titration is more beneficial because of its economy, easy to prepare, simplicity, easy availability, pollution free inert and accurate results.

Acknowledgement

The completion of any project depends upon the cooperation, coordination and combined efforts of several sources of knowledge, skill, labour and time and the precious guidance and encouragement provided by guide on several occasions and so my heart feels sincere gratitude to them. We are thankful to H.O.D. Mr. Suresh Sakhiya of Aksharpreet institute of pharmacy, Jamnagar for this scholarly encouragement of my academic activities.