Constructing a Colour Chart for Hibiscus as an Acid Base Indicator, Essay Example

Abstract

The primary quality of the natural pH indicators demonstrates a colour change ranging from a mainly alkaline quality or violet colour changing to red which takes place in increments of increasing hydronium ion concentration.  In my research, I documented this phenomenon being   designated as the colour moderation increment of the anthocyanin indicator.  The magnitude of the colour change and the instrumentation is not abrupt.  As the experiment progressed, I observed the colour change occurring in subtle differences.  The intensity of the colour change increments on the scale of the pH assessment has a diverse variety with distinct indicators. In the research, I accessed the literary works of ABC (2015), Abou- Arab et al. (2012), Abugri et al. (2012), Bhagat et al. (2009), Gupta et al. (2012), Flinn Scientific, Inc. (2000), Grudpan et al. (2010), Maciel et al. (2012), Mungole & Chaturvedi (2011), Nuryandi et al. (2013) and Yakasai et al. (2005).

Introduction

Hibiscus subdariffa is an herb that I saw having a perennial quality reaching a height of 2.5 m.  The hibiscus plant flower is composed of anthocyanin which may be applied in neutralization titrations as an acid base titrant.  The anthocyanin is a dye that is attributed to the colour varying from purple to pink in plants that flower.  In the experiment, I observed that the pigment derived from the flower of the plant becomes modified in accordance with the hydronium ion saturation of a solution.  The research question that was explored is the construction of a colour chart within a predetermined range of colours for the hibiscus anthocyanin derivative as an acid base indicator (Gupta et al., 2012; Yakasai et al., 2005).

Objective

The goal of the experiment is to determine the parameters of the anthocyanin indicator when substances that have extremely basic or acidic pH. This infers ascertaining at which point the pH responses will not have the capacity of being reversed. This is the point of inflection of the colour modification process (Nuryanti et al. 2013; Yakasai et al., 2005).

Background

Hibiscus rosa sinensis is a type of flowering plant which is part of the mallow family. The hibiscus rosa sinenis plants become expansive in its size. The hibiscus is a plant which is composed of several hundred different species that are inherent to the temperate, warm, subtropical and tropical areas of the world. The flowers of the hibiscus plant are the hermaphrodite quality and receive pollination by means of insect transmission. The leaves of the hibiscus plant are lanceolate, ovate and alternate. The leaves of the hibiscus are frequently encountered with a lobed or toothed margin. The hibiscus flowers are outstanding. I have found the hibiscus flowers to be large, trumpet shaped with numerous petals (Abugri et al., 2012: Bhagat et al., 2009).

The petals of the hibiscus flower are beautiful. They range from, white to pink to yellow and are between four to eighteen centimeters wide. There are many people who boil the hibiscus petals and drink the tea which is derived. The hibiscus tea has been found to be a natural diuretic which is composed of vitamin C and applied as a mild medicine. People who have kidney dysfunctions and dieters frequently consume the hibiscus teat without aggregating sugar. The hibiscus tea is well known for the famous characteristics of being a natural diuretic. In the laboratory experiment, I have discovered that the flowers of the hibiscus rosa are efficient in the treatment of hypertension (Grudpan et al., 2010: Mungole and Chaturvedi, 2011).

In addition, the flowers can be applied in order to create birth control medicine. The Ayurveda medicine which originates from India applies the white hibiscus and the red coloured hibiscus in medicine. The hibiscus roots are placed through the process of ebullition in order to create a variety of concoctions which are applied to treat illnesses including hair loss and cough. The flowers of the hibiscus plant are boiled with other types of flowers in order to create hair oils. The flowers and the leaves of the hibiscus plant are ground in order to create a thin paste by adding a slight amount of water. In addition, the lathery paste is applied a hair shampoo. I have learned that the hibiscus plant has numerous healing qualities (Flinn Scientific, Inc. 2000; Maciel et al., 2012).

The colour modification in the anthocyanin is attributed to the ionization of the pH indicator. The ionized form of the anthocyanin takes a distinct color than the non- ionized category. The ionization of the anthocyanin derived from the hibiscus is mostly influenced by acids and bases. This is attributed to the anthocyanin reacting with weak bases or acids. In the circumstance of interacting with weak bases, the anthocyanin takes on the quality of a weak base. The factor of ionization is extreme in acids and minimal in alkalis. The ionization factor is attributed due to the mutual hydroxyl ions (OH ^–) (Gupta et al., 2012).

In reviewing that the significant indicator phenolphthalein is a weak acid, I learned that the Oswald Theory can be delineated by the following formula. Phenolphthalein is represented as Hph. The phenolphthalein acquires the qualities of ionizing in a solution to a limited extent

Hph ? H⁺ + ph^–

In the left side of the formula, the Hph is clear and colourless. The right side of the equation produces a Ph^– ion which is clear. The molecules of the phenolphthalein prior to dissociation are clear and colourless which the Ph^– ions have the quality of being rose coloured. In the proximity of an acid, the ionization factor of the Hph is minimal. The equilibrium is transferred to the left side of the equation as a result of the hydronium ions. Consequently, the solution remained in a clear and colourless condition. As the alkali was aggregated, the hydronium ions were extracted by the addition of the hydroxyl ions which were found in the water molecules. As a result, the equilibrium migrated to the right side of the equation. The saturation of the phenolphthalein molecules was increased and the colour of the solution was transformed to pink. The basic Oswald theory of colour modification demonstrated that the colours transformation of the indicators had been the subject of revision (Gupta et al., 2012).

The plant dyes are usually designated flavonoids. The flavonoid category incorporates anthocyanin, isoflavanol, anthocyanidin, flavanol, isoflavanol and flavone. The anthocyanins are in the glycoside category and the proprietary aglycones, which is the liberated pigment that is applied as the result of the extraction is designated as anthocyandins. The colours of flowers are manifest as an outcome of the anthocyanins. The varied pigments in the hibiscus rosa sinensis are attributed to a number of pigments that are found mixed with distinct substances in the plants leaves and petals. These materials are composed of the identical amounts of due to the delineation of the carbon framework (Gupta et al., 2012).

Furthermore, the parts of the hibiscus flower are only distinct in accordance with the quality of the substituent categories. The anthocyanin is usually soluble in water and the origin of the pigmentation in the flower takes place in the cell sap. The cell sap is attributed for the diverse variety of pigmentation in the hibiscus flower. The residues subsequent to the titration of the flowers’ extract has the quality of being conventionally red. In addition, the metallic residues usually have a blue colour. In the neutral solution, the residues from the anthocyanin have a purple characteristic (Bhagat et al., 2009).

The anthocyanin indicator is a faint acid and the equilibrium demonstrated in a solution which is aqueous is delineated as the following relationships:

Indicator + H₃O⁺ ?H₂O + H_indicator

Indicator + H₂O ? OH^– + H⁺_indicator

The independent variable is the pH of the anthocyanin derivative (Gupta et al., 2012; Yakasai et al., 2005).  The dependent variable which is being manipulated is the colour manifested by the hydronium ions of the anthocyanin weak acid.  The dependent variables are:

1. The changes of colour.
2. The increments of hydronium ion concentration of the solution being added.
3. The hydroxyl ion concentration of the base being added.
4. The hydronium ion saturation of the weak acid applied as the titration neutralizing acid – base indicator.

^?H₃O⁺ =KH _Indicator * ^?H_Indicator (^?H_Indicator)^-1

This is considering the [H_Indicator] and [Indicator] are the saturations of the basic and acidic formats of the indicator. In the formula VH_Indicator and V_Indicator of the coefficients of activity. The relationship is man8ifested in the equation

-Log [H_Indicator] [Indicator]^-1 – Log [VH_Indicator][V_Indicator]^-1 + pKH_Indicator = pH

The majority of the indicators which are applied for the testing of acids and bases are compounds which are derived from organic substances. These compounds demonstrate the qualities of weak bases and acids. The responses of the transference of protons for the substances are manifested by the structural modifications with the framework and apparition, within the colour collections.

The equilibrium of the anthocyanin solution serving as indicator is primarily affected by the ionic robustness and thermal qualities of the solution. A modification in the characteristics of ionic robustness has the capacity of causing a shift in the equilibrium and consequently modify the hue or the color of both forms. This is designated as the salt effect. Consequently, in the creation of color comparison charts for determining the pH of an aqueous solution infers that the saturation of the indicator must be similar and that the quality of ionic robustness is required to be equivalent (Gupta et al., 2012; Yakasai et al., 2005). The modification of color equilibrium in any specific ionic robustness has the capacity of being delineated as the following formula:

Log [H_Indicator] [H_Indicator^–]^-1 + pK_Indicator + pH

The anthocyanin in the hibiscus petals are organic acids which have a weak quality. These weak acids donate protons in order to become transformed to conjugate bases. The distinct models of molecules have the characteristic of distinct light reflection which causes the manifestation of a change of hue or colour. The compounds which formulate molecules which do not have different qualities of reflecting light have the potential of being applied as acid bases indicators (ABC, 2015; Flinn Scientific, Inc., 2000).

The molecule which is representative of the anthocyanin that has two protons which are donated to a B- L acid. As a result, the molecule has the capacity of reflecting red luminescence (see Appendix 1). The molecules which have the capacity of donating only one proton have the quality of reflecting blue luminescence (Appendix 2). Consequently, the molecule having the quality of donating only one proton has the ability of responding as a conjugate base and receiving a proton. This quality enables the molecule to revert is colour quality back to the reddish scale. The molecule which donates only one proton has the capacity of responding as a B – L acid and making a donation of its proton (ABC, 2015; Flinn Scientific, Inc., 2000).

In the circumstance of the molecule which is representative of the conjugate bas that does not have any addition protons to donate beside the one, the molecule acquires the characteristics of reflecting luminescence which is green to yellow. As a B- L conjugate base the molecule has the capacity of accepting protons. The acceptance of one proton initiates the reaction of the color reverting back to the bluish scale. The acceptance of two protons causes the modification to revert to the reddish colour scale. The more elevated the saturation of hydronium ions that is manifested by the solution, the higher the saturation of anthocyanin that is inserted (ABC, 2015; Flinn Scientific, Inc., 2000).

Consequently, the fewer are the number of molecules of the anthocyanin base acid indicator that donates protons. The lower the level of the hydronium ion concentration, the lower the level of anthocyanin acid base indicator which is required and the greater the number of molecules which donate protons. Notwithstanding, if the hydronium ion concentration attains an extremely elevated level or an extremely low level, the solution will attain a level of equilibrium with the combination of the molecules which donate one proton, two proteins or accept one or two protons. The apparent colour of the solution manifested by the anthocyanin acid base indicator would be similar to the following schema:

Experimental Procedure

Materials

Procedure

The hibiscus petals should be separated from the other parts of the flower. After this process has been conducted, 0.5 kg should provide more than sufficient pH indicator for the entire experiment. The hibiscus petals should be finely cut with the knife on the chopping board. After being finely cut on the chopping board, the hibiscus petals should be placed into the mortar and finely ground with the pestle. After the pestle and mortar are applied, the hibiscus petals which have been cut and ground should be placed into the six containers. Subsequent to being placed in the six containers. 350 ml of the ethanol should be distributed between the six containers. The cut and ground hibiscus petals had been placed into the containers and left to soak for fifteen minutes (ABC, 2015; Flinn Scientific, Inc., 2000).

The six Hirsh filters were placed into the six Erlenmeyer flasks. The residue had been allowed to seep into the Erlenmeyer flask for fifteen minutes. The residue containing the hibiscus petals and the ethanol remaining in the Hirsh filters was placed into a water container for subsequent disposal. Approximately 40 ml of the hibiscus petal / ethanol extract remained for the application of the chemical tests. The eye droppers had been applied in order to place the anthocyanin extract into six testing tubes. The solution had been agitated by means of applying the shish- kebab sticks to the testing tubes and solution. The eyedropper had been able to take 10 ml capacity with each trial (ABC, 2015; Flinn Scientific, Inc., 2000).

The same amount of substrate was allowed from reach of the groups of household chemical. Lemon juice had been initially added to the first testing tube. The testing tube acquired a bright red colour. The next chemical which was applied had been the tartaric acid. The testing tube acquired a bright red colour. Vinegar had been subsequently applied to the testing tubes and the vinegar acquired a reddish to purplish red colour. The tap water was next applied into the testing tubes with the eye dropper. The tap water demonstrated no change in the colour. The subsequent chemical which was evaluated had been lemonade. The lemonade turned to a purple colour when inserted with the anthocyanin extract. Afterward, baking soda had been applied. The baking soda converted into a blue to blue green colour. The final chemical which had been evaluated was the laundry detergent. The laundry detergent converted to a yellowish – green colour (ABC, 2015; Flinn Scientific, Inc., 2000).

Results

Discussion

The range in pH varies from 1 to 14. Substances that manifest a pH of 7 are deemed to be neutral. Neutral infers that the chemical has neither the qualities of acids or bases. The designation of pH implies the hydrogen potential. This quality infers the capacity of the chemical as a donor or acceptor of hydronium ions to other substances. Substances which are acidic have the tendency of donating protons while chemicals which are caustic have the capacity of accepting protons (Abugri et al., 2012).

Chemicals which have a pH that inferior to 7 are acknowledged as acids. The term acid is derived from the Latin word acidus. Acidus is translated as sour. This is due to the gustatory sensation provided by acids. There are particular acids which include nitric and sulfuric acid which have the capacity of acutely burning human skin. There are other acids which are not as robust. The majority of the foods which are consumed by human beings are acidic in their origins (Grudpan et al., 2010).

A chemical which has a pH that is superior to 7 is designated as a base. The bases cause a bitter gustatory sensation in addition to having a slimy perception to the touch. This is a perception that is commonly felt in laundry detergents. Bases have the characteristic of reacting in a vituperating manner with acids. In the case of weak abases and acids which include vinegar (acetic acid) and baking soda (sodium bicarbonate), the acids make a fizzing sound when combined with caustic chemicals. This is a result of the expulsion of carbon dioxide. Notwithstanding the chemical reaction, baking soda, vinegar and carbon dioxide are not hazardous (ABC, 2015; Flinn Scientific, Inc., 2000).

The bases and the acids causes reactions which have the outcome of water and salt. There are a variety of salts which are present bedside sodium chloride. The pH indicators are substances which become modified in colour when affected by bases or acids. The modification in colour is reversible. The aggregation of a base or an acid to water reduces or enhances the pH of the solution and the colour of the indicator will become modified as a result (ABC, 2015; Flinn Scientific, Inc., 2000).

Indicators are pigments or dyes which are extracted from diverse sources. These sources include the leaves of the hibiscus subdariffa. The pigment that had been extracted during the experiment was anthocyanin. Anthocyanin has the quality of changing colour when exposed to a base or acid. The application of natural pigments as indicators of caustic or acidic qualities had finally been discovered by Sir Robert Boyle.  In 1664. The experiments had been published in the essay collection titled: The Experimental History of Colours. Sir Robert Boyle contributed to the body of scientific knowledge in his treatise regarding acids and bases by the application of indicators in order to classify the substances. The concepts which had been expressed by Sir Robert Boyle may have originated earlier with the medieval and gothic era artists. The medieval and gothic era artists applied pigments that were naturally derived from limewater and vinegar in order to formulate the distinct paints that were applied as watercolours (ABC, 2015; Flinn Scientific, Inc., 2000).

The indicators which have the acid – base detecting qualities are expansive organic molecules which manifest as weak acids.  These wreak acids have the capacity of donating hydronium ions to the molecules of water in order to create conjugate bases. The outstanding quality of the indicators is that the acid component demonstrated by H_{indicator aqueous and} the conjugated base demonstrated by ln^– manifest different colours.

ln^–_aqueous + H₃O ⁺_aqueous ? H₂O + Hln^–_aqueous

In the equation, the components of ln^–_aqueous represents color B_. The component of Hln^–_aqueous is representative of colour A. The non-charged indicating molecule is represented in the equation by Hln^–_aqueous. The indicating ion in water is demonstrated by ln^–_aqueous subsequent to its sacrifice of the hydrogen ion. The natural hibiscus anthocyanin extract behaves as a Brønsted acid. Brønsted acids have the quality of donating hydronium ions. The distinct colours that had been reviewed in the experiment are attributed to LeChâtelier’s principle (ABC, 2015; Flinn Scientific, Inc., 2000). The colour modifications are examples of reactions that are reversible. The colour reactions which are reversible can be easily compelled to react in either direction.

The hues manifested by the indicator solution are reflective of the equilibrium position for the equation demonstrated in the previous paragraph. The colour of the solution is reliant on the saturation of H₃O⁺ ions. The pH of the solution is reliant on the saturation of the H₃O⁺ ions (ABC, 2015; Flinn Scientific, Inc., 2000).

There are three potential scenarios. The first is that the majority of the molecules are present in the form of Hln^–. Consequently, the colour demonstrated by the solution is the colour manifested by the Hln^– component. The second scenario is that the majority of the indicator molecules are present in the form of ln^– and the colour manifested by the solution is the identical colour manifested by the ln^– component. The third scenario is that the solution is composed of identical amounts of the Hln^– and ln^– components (ABC, 2015; Flinn Scientific, Inc., 2000). The precise saturation of the H₃O⁺ ions will be reliant on the quality of the anthocyanin and the equilibrium constant applied in the equation:

ln^–_aqueous + H₃O ⁺_aqueous ? H₂O + Hln^–_aqueous

The anthocyanin was derived from the hibiscus subdariffa leaves by a method designated as extraction. Extraction is the process that is applied in order to create tea from teabags and the ebullition of water. The hue manifested by the anthocyanin indicator is reliant on the saturation of H₃O⁺ ions. The saturation of the H₃O⁺ ions is manifested by the colour acquired by the indicator and the pH scale. The correlation between the pH and the saturation of the H₃O⁺ ions is demonstrated by the following formula:

-log [H₃O⁺] = pH

The saturation of the H₃O⁺ ions in the solution varies from the concentration of 1M in HCl (hydrochloric acid) to 10^-14 M in NaOH 1 M. In water which has a neutral hydronium ion concentration, the saturation of the H₃O⁺ ions is equivalent to 10^’7 M. The log of the concentration is the exponent in base 10 in terms of the sa6turation. Consequently, the negative logs of the conventional H₃O⁺ saturations are positive integers which vary from 0- 14, considering the pH of water at 7. The acidic substances manifest pH lower than 7 and the bases have pH which are higher than 7 (ABC, 2015; Flinn Scientific, Inc., 2000).

In the range of the acidic solutions, the pH of as robust acid solution will manifest a lower pH level than a less saturated weak acidic solution. Consequently, the pH values equivalent to 0.1 and 0.01 M hydrochloric acid solutions are between one and two. The pH value of vinegar (acetic acid) 0.1 M would be approximately 3. Considering the basic perspective of the pH scale, a base solution that is more concentrated will manifest a more elevated pH than a weak base or less concentrated solution (ABC, 2015; Flinn Scientific, Inc., 2000).

As a result, the values of the pH which are 0.1 and 0.01 Sodium hydroxide solutions are found between the values of twelve and thirteen, whereas the pH of ammonia which is 0.1 M is estimated at eleven. Consider that the pH scales are assessed in logarithmic values. This infers that a solution which has a pH between three and four demonstrates that the solution with the pH of three has ten times the amount of acidity as the solution which has the pH of four. The acidity of a solution which has a pH of three is one hundred fold more acidic than a solution which has a pH of five (ABC, 2015; Flinn Scientific, Inc., 2000).

The reviewed extract of the hibiscus flower had been applied in order to ascertain the final point of the HCl- NaOH titrations in saturations of 0.01, 0.1 and one mole for each liter. The anthocyanin extract started to change color with a pH of approximately 4.3. This is adequate for the titration process when comnduict8ing the titration with a robust acid and a robust base. This is required due the wide range of the equivalence point. Consequently, the hibiscus extract changed its colour in the presence of a pH of 4.3 generated by the titration of HCl with NaOH (ABC, 2015; Flinn Scientific, Inc., 2000).

The demonstration in the experiment manifested that the outcomes had been in accordance with a percentage uncertainty which varied between 0 to 1.4% in the circumstance of the 0.1 M and one molar titrating agents. Notwithstanding, the titrating agent of 0.01 Molar NaOH- HCl demonstrated an apparent discrepancy in attaining more than one fifth of the comprehensive pH for the hibiscus extract indicator. The uncertainty had been the outcome of the effect of the indicator’s acid quality regarding the titrant at a molar concentration of 0.01M. The observation had been manifest in addition to the reduction of the inflection point in the pH of the aqueous systems from the saturated system. The inflection point had been demonstrated in the aqueous diluted system to be between n 5.3 to 8.7 and 3.0 to 10.5 for the saturated mixture (Gupta et al., 2012).

Conclusion

The hibiscus flower extract demonstrated efficacy in being an inexpensive indicator in the acid- base titrating processes. The hibiscus flower extract demonstrated an elevated level of precision in the detection of the concluding point in the process of the acid- based chemical titrations.  The precision was manifested by the hibiscus flower extract during the processes when the saturation of the titrants had been applied in the range of 0.1 M to one molar concentrations. The sensitivity of the hibiscus flower extract was manifest in titrant saturations which were as low as ? 0.01M. The range of the sensitivity of the hibiscus flower extract has demonstrated its effectiveness as an acid base indicator.

References

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