Abstract
Commonly used indicators for acid-base titrations are synthetic, and this work was focused to identify the eco-friendly natural indicators and to determine their pKa values. The analytical potential of the flower extracts is very promising as seen in its application in acid-base titrimetry. These selected flower extracts were found to perform well in titrating strong acid-strong base than in weak acid-strong base. We have obtained a sharp and clear colour change from red to brownish yellow for the Bougainvillea glabra extract, from red to yellow for the Bauhinia purpurea extract, and from red to brownish yellow for the Impatiens balsamina extract. All the three flower extracts gave clear colour change with acids and bases, and the colour change was maintained with different acids and bases. The sharp contrast between their colours in acid and base made the pigment suitable for use as acid-base indicators. As these flower extracts have very simple,cost-effective, environment friendly extraction procedure and excellent performance with sharp colour change in end points of the titrations, it would be possible to replace the standard indicators being used in conventional laboratories with natural flower indicators.
Highlights
Titration is the most common laboratory method of quantitative chemical analysis that is used to determine the concentration of analyte. e most of the modern laboratories are equipped with digital automatic titrators that are facilitated with sensors, some of them do not require indicators, the accuracy is high, and human errors reduced than conventional titration methods
E end points detected for acid-base titrations using the flower extracts as indicators were found to be very similar to those of standard indicators used in laboratories (Table 3)
Methyl red, Bauhinia purpurea, and Impatiens balsamina indicators show a value very close to the standard indicator, phenolphthalein. e pH range of Bougainvillea glabra and Bauhinia purpurea is very close to the pH range of phenolphthalein (8.2–10.0)
Summary
Titration is the most common laboratory method of quantitative chemical analysis that is used to determine the concentration of analyte. e most of the modern laboratories are equipped with digital automatic titrators that are facilitated with sensors (pH sensor/voltage electrode), some of them do not require indicators, the accuracy is high, and human errors reduced than conventional titration methods. E chemical substances possess an apparent change in colour of the analyte and titrant reacting mixture very close to the point in the ongoing titration known as indicator, which helps to examine and determine the equivalence point in acid-base titrations [3, 4]. E blue and red pigments of flowers were isolated and extensively studied by Willstatter in 1913. Natural indicators such as litmus to indicate specific pH levels have been developed. E substances in the plant products such as tea, red cabbage, or grapes react with acids or bases resulting in changes at the molecular level which causes their colour to be different at different pH. The purple orchid tree, is an exotic tropical tree that blooms over a long period of time. e beautiful and orchid-like flowers of Bauhinia purpurea are native to India. e petals of Bauhinia contain chalcone and butein as colouring pigments [10]
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