Volumetric Acid-Base Titration by using of Natural Indicators and Effects of Solvent and Temperature

Bahadori A* and Maroufi NG

University of Applied Science and Technology, Iran

*Corresponding author:Ali Bahadori, University of Applied Science and Technology, Iran

Received: December 28, 2015; Accepted: April 07, 2016; Published: April 15, 2016

Abstract

In this work, many natural sources as acid-base indicators which are extracted from different parts of fruits, flowers and plants were investigated for volumetric acid-base titration at room temperature, 60°C, 92°C and 98°C. Pigments from some fruits and plants were extracted, separated, and purified in carbon tetrachloride, chloroform, ethanol, methanol and toluene as solvents. These indicators in acid-base titrations shown sharp color changes with variation of pH at the equivalence point and we could determine the pH range. For some indicators the color of indicator in different solvents was similar that suggested there was no obvious modification of chemical structure of indicators in different solvents. In addition, the effect of temperature on indicators and their stability were studied. The result proved to be acceptable in introducing natural pigments as suitable acid - base indicators. These natural indicators are found to be a very useful, economical, simple, accurate and nature-friendly.

Keywords: Acid- base indicator; Natural pigment; Solvents; Titration; pH

Introduction

Several types of synthetic chemical indicators are available for different types of titrimetric analyses. Acid-base indicators are known as pH indicators. Acid–base indicators are substances (dyes) which change color with pH. They are usually weak acids or bases, which when dissolved in water dissociate slightly and form ions. Volumetric analysis is one of the major quantitative techniques. In titrimetry, the equivalent point is usually determined by the end point in the titration. The end of point in traditional titrimetry is usually indicated by some substances added into the analyte solution, which change color immediately after the equivalent point has been attained. These substances are generally referred to as indicators. Several types of indicators are available for different types of titrimetric analyses. Most pH indicators are either weak organic acids or bases dyes which accept or donate electrons [1]. Although there are automated titration apparatus that determine the equivalent point between reacting species, indicators are still needed for teaching and research laboratories for simple titration [2]. Commercial indicators are expensive and some of them have toxic effects on users and can also cause environmental pollution [3]. For these reasons there has been an increasing interest in searching for alternative sources of indicators from natural origins. Historically, plants have been used for the extraction of a majority of natural dyes. As interest in natural dyes grew, information from the old literature was collected and traditional dyeing practices in different regions were documented and compiled by various researchers. The use of natural dyes as acidbase indicator was first reported by Sir Robert Boyle in collection of assays “Experimental History of Colors” in 1664 [4,5]. A large number of dyes are obtainable as natural products. In Nigeria, several workers have extracted a number of dyes from a variety of local plants. According to Akpuaka et al. [6] and Osabohien et al. [7], the local plants - Camwood, Redwood, Henna, Annato, Rothmania, Terminalia, Indiqovine, Kola, Banana, Tumeric, Roselle and Ginger all contain different types of dyes which are used for various purposes. Natural dyes are derived from natural resources and based upon their source of origin; these are broadly classified as plant, animal, mineral, and microbial dyes although plants are the major sources of natural dyes. Recent environmental awareness has again revived interest in natural dyes mainly among environmentally conscious people. Natural dyes are considered eco-friendly as these are renewable and biodegradable. Ekandem et al. [8] and Eze et al. [9] have reported their findings on the use of some natural dye extracts as indicators in acid-basetitrimetry. In recent years, there are numerous natural acidbase indicators that can be obtained from common flowers, fruits and vegetables [3,10].

Among of natural dyes as acid-base indicator, Flavones, Flavonols, Anthocyanidins, Anthocyanins are some types of indicator, which have been studied in order to substitute these compound instead of synthetic indicators [11,12]. For example, the chemical structure forms and colors of an anthocyanin at different pHsare presented in Figure 1.

Figure 1: The chemical structure forms and colors of an anthocyanin at different pHs.

    
    
    Figure 1:  The chemical structure forms and colors of an anthocyanin at
different pHs.

In this work, we report the findings of our investigations on the acid-base indicator properties of dyes obtained from parsley, coriander, borage, allium ampeloprasum, red cabbage, tulip petals, rose petals, rosa damascene, red onion skin, curcuma, cinnamon, ginger, saffron, black pepper, red pepper, yellow pepper, coffee, quince leaf, strawberry, sour berry, cornelian cherry, carrot, green walnut in different solvents at different temperature.

Materials and Methods

Flowers, plants and fruits materials

Parsley, coriander, borage, allium ampeloprasum, red cabbage, tulip petals, rose petals, rosa damascene, red onion skin, curcuma, cinnamon, ginger, saffron, black pepper, red pepper, yellow pepper, coffee, quince leaf, strawberry, sour berry, cornelian cherry, carrot and green walnut were purchased from Agricultural Research Center Tabriz. Samples include flowers, plants leaves and petals and fruits skins. The samples were washed thoroughly under tap water, cleaned by distilled water, air-dried and powdered using mechanical blender.

Chemicals required

Carbon tetrachloride, chloroform, ethanol, methanol, toluene, NaOH and HCl were purchased from Sigma- Aldrich chemical. All other chemicals were of analytical reagent grade and were purchased from Merck. All solutions were prepared using double distilled water.

Apparatus

Reagent bottle, weighing balance, spatulas, hot plate, shaker, oven, electric grinder, test tubes, test tube stand, droppers, 50mL burettes, wash bottle, beaker, spatula, pipettes, pipette filler, funnel, clamp stand, tissue paper, magnetic stirrer, watch glass, volumetric flasks of 25mL & 50mL, conical flask, pH paper, A digital pH meter (Switzerland OHAUS2100) with glass and calomel electrodes, measuring cylinders.

Preparation of flowers, plants and fruits extract in different solvents

2 grams of samples powder were mixed with 50mL of carbon tetrachloride, chloroform, ethanol, methanol and toluene as solvents for 48h with stirring. The solution was shaken and swirled well, until the entire compound dissolved. The extract is filtered with suction using a Buchner funnel, filter paper and the filter flask [13,14]. The resulted aqueous extract was evaporated to one-fifth of its original volume and then used as natural indicator for acidimetric and alkalimetry. The extract was preserved in light closed container and stored away from direct sunlight.

Change of color samples in equivalent points at different solvents

Results and Discussion

Change of color samples in equivalent point at different solvents

Prepared natural indicator samples were used for titration. The experimental work was carried out using the same set of glass wares in the order of strong acid versus strong base with five drops of natural indicator at room temperature. 5.0 mL of 0.1 M NaOH was separately titrated with 0.1 M HCl using the natural indicators extracted from samples in order to determine equivalent points. The results of titration with colors observed in acidic and alkali media are summarized in Table 1. And volume of acid consumed is reported in Table 2. For example, it was observed that the natural indicator (Curcuminoidsextracted from curcuma dissolved in Ethanol) when added to the acid produced a sharp yellow color as indicated in Table 1. After titration by strong base was observed distinctive and sharp color change that shown equivalent point in this sample. The presence of Curcuminoids in curcuma and anthocyanins were responsible of sharp color changes in red cabbage, red onion skin, tulip petals, borage occurred at the end point of the titrations [11,15]. Therefore, we can say that it is always beneficial to use these natural indicators in acid base titrations because of its economy, simplicity and availability.

Table 1: Natural indicator samples in different solvents and color observed in acidic and alkaline condition.




  
    Solvent 
    Media 
    Samples 
  
  
    Cur-cuma 
    Cinna-mon 
    Ginger 
    Saffron 
    Black    pepper 
    Yellow    pepper 
    Red    pepper 
    Coffee 
    Quince    leaf 
    straw-berry 
    Corne-lian    cherry 
    Green    walnut 
    Carrot 
    Egg-plant    skin 
    Red    onion skin 
    Rosa    dama-scene 
    Tulip    petals 
    Borage 
    Coria-nder 
    Parsley 
  
  
    Toluene 
    Acidic 
    Yellow 
    Brown 
    Yellow 
    Yellow 
    Green 
    Yellow 
    Red 
    Brown 
    Green 
    Orange 
    Green 
    Dark    Brown 
    Orange 
    Purple 
    Purple 
    Pink 
    Red 
    Pink 
    Green 
    Green 
  
  
    Alkaline 
    Red 
    Brown 
    Yellow 
    Yellow 
    Green 
    Yellow 
    Orange 
    Brown 
    Brown 
    Orange-pink 
    Brown 
    Dark    Brown 
    Orange 
    Green 
    Green 
    Brown 
    Red 
    Green 
    Green 
    Green 
  
  
    Tetra-chloride 
    Acidic 
    Yellow 
    Light    Brown 
    Yellow 
    Yellow 
    Green 
    Yellow 
    Red 
    Brown 
    Green 
    Orange 
    Red 
    Yellow-    Green 
    Orange 
    Purple 
    Purple 
    Pink 
    Red 
    Pink 
    Green 
    Green 
  
  
    Alkaline 
    Red 
    Dark    Brown 
    Yellow 
    Yellow 
    Green 
    Yellow 
    Red-    Orange 
    Brown 
    Green-    Brown 
    Orange-    Pink 
    Brown 
    Yellow 
    Orange 
    Green 
    Green 
    Brown 
    Red 
    Green 
    Green 
    Green 
  
  
    Chloro-form 
    Acidic 
    Yellow 
    Brown 
    Yellow 
    Yellow 
    Green 
    Yellow 
    Red 
    Brown 
    Green 
    Orange 
    Red 
    Green 
    Orange 
    - 
    Red 
    Red 
    - 
    Red 
    Green 
    Green 
  
  
    Alkaline 
    Red 
    Brown 
    Yellow 
    Yellow 
    Green 
    Yellow 
    Red 
    Brown 
    Green 
    Orange-    Pink 
    Brown 
    Green 
    Orange 
    - 
    Red 
    Red 
    - 
    Red 
    Green 
    Green 
  
  
    Ethanol 
    Acidic 
    Yellow 
    Light    Brown 
    Yellow 
    Yellow 
    Green 
    Yellow 
    Red 
    Very    Light Brown 
    Green 
    Orange 
    Red 
    Yellow-    Green 
    Orange 
    Purple 
    Purple 
    Purple 
    - 
    - 
    Green 
    Green 
  
  
    Alkaline 
    Red 
    Dark    Brown 
    Yellow 
    Yellow 
    Green 
    Yellow 
    Red 
    Very    Dark Brown 
    Green-    Brown 
    Orange-    Pink 
    Red 
    Yellow-    Green 
    Orange 
    Green 
    Green 
    Yellow-    Green 
    - 
    - 
    Green 
    Green 
  
  
    Metha-nol 
    Acidic 
    Yellow 
    Brown 
    Yellow 
    Yellow 
    Green 
    Yellow 
    Red 
    Brown 
    Pale    Green 
    Orange 
    Orange 
    Yellow-    Green 
    Orange 
    Purple 
    - 
    Pink 
    Red 
    Purple 
    Green 
    Green 
  
  
    Alkaline 
    Red 
    Brown 
    Yellow 
    Yellow 
    Green 
    Yellow 
    Red 
    Brown 
    Medium    Spring Green 
    Orange-    Pink 
    Very    Light Brown (Wheat) 
    Dark    Brown 
    Orange 
    Green 
    - 
    Brown 
    Purple 
    Green 
    Green 
    Green



Table 1:  Natural indicator samples in different solvents and color observed in acidic and alkaline condition.

Table 2: Volume (mL) of acid used to reach the equivalent point of acid-base titrations and color change in titration.




  
    Material 
    Alkaline 
    NaOH as    Titrate (mL) 
    Acidic 
    HCl as    Titrant (mL) 
  
  
    1 
    Curcuma 
    Red 
    5 
    Yellow 
    5 
  
  
    2 
    Red    cabbage 
    Purple 
    5 
    Red 
    5 
  
  
    3 
    Red    onion skin 
    Green 
    5 
    Purple 
    3.9 
  
  
    4 
    Tulip    petals 
    Purple 
    5 
    Red 
    4.6 
  
  
    5 
    Borage 
    Light    Green 
    5 
    Colourless 
    5



Table 2:  Volume (mL) of acid used to reach the equivalent point of acid-base
titrations and color change in titration.

The pH range of indicators

We were performed this investigation for three samples curcuma, borage and tulip petals. Initially, pH meter shown pH=12/8 for strong base. When acid added little by little, the pH range was between 8/52 (alkaline) to 5/87 (acidic) after titration in case of curcuma. In case of borage, the pH range was between 6/88 (alkaline) to 4/68 (acidic) and tulip petals shown the pH range 8/70 (alkaline) to 4/43 (acidic). The results pH range of indicators is shown in Table 3. The possible factors that might have contributed to the pattern of the pH variation as well as titer value could be temperature, ionic strength, colloidal particles and organic solvents [2]. Another reason could be the chemical composition of the natural indicators. Curcuminoids have the capacity to produce sharp color changes at certain pH ranges as compared to non-curcuminoids derivatives because of the functional groups (e.g. o-methoxy phenolic groups and keto and enol forms in solid phase and solution) in flavonoids and tannins. The chemical structure of curcumin is shown in Figure 2. It can exist at least in two tautomeric forms, keto and enol. The keto form is preferred in solid phase and the enol form in solution. Curcumin is a pH indicator. In acidic solutions (pH <7.4) it turns yellow whereas in basic (pH >8.6) solutions it turns bright red [15,16]. The colors of curcumin at different pHsare presented in Figure 3. In borage and tulip petals Flavonoids have the capacity to produce sharp color changes at certain pH ranges as compared to non-flavonoid derivatives because of the functional groups (e.g. OH) inflavonoids. The plants and fruits such as borage and tulip petals have a mixture of anthocyanins and other pigments that indicate a wide range of pH [11] Figure 1.

Figure 2: The chemical structure forms of curcumin in enol (a) and keto (b).

    
    
    Figure 2:  The chemical structure forms of curcumin in enol (a) and keto (b).

Figure 3: The colors of curcumin at different pHs.

    
    
    Figure 3:  The colors of curcumin at different pHs.

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Citation: Bahadori A and Maroufi NG. Volumetric Acid-Base Titration by using of Natural Indicators and Effects of Solvent and Temperature. Austin Chromatogr. 2016; 3(1): 1041. ISSN 2379-7975

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