Research Article
Natural Plant Extracts as Acid-Base Indicator and Determination of Their pKa Value
Table 3
Titration results of flower extracts and commercially available indicators.
| | Indicator | Titrand/titrant | Colour change | Required volume of titrant |
| | Phenolphthalein | NaOH/HCl | Pink to colourless | 8.87 ± 0.0577 | | NH4OH/HCl | Pink to colourless | 14.57 ± 0.0577 | | CH3COOH/NaOH | Colourless to pink | 12.07 ± 0.0577 |
| | sMethyl orange | NaOH/HCl | Yellow to red | 9.17 ± 0.0577 | | NH4OH/HCl | Yellow to red | 15.67 ± 0.1155 | | CH3COOH/NaOH | Red to yellow | 5.27 ± 0.0577 |
| | Methyl red | NaOH/HCl | Yellow to red | 8.97 ± 0.0577 | | NH4OH/HCl | Yellow to red | 16.13 ± 0.0577 | | CH3COOH/NaOH | Red to yellow | 12.13 ± 0.0577 |
| | Bougainvillea glabra | NaOH/HCl | Brownish yellow to red | 8.97 ± 0.0577 | | NH4OH/HCl | Brownish yellow to red | 15.17 ± 0.0577 | | CH3COOH/NaOH | Red to brownish yellow | 12.23 ± 0.0577 |
| | Impatiens balsamina | NaOH/HCl | Brownish yellow to red | 9.07 ± 0.0577 | | NH4OH/HCl | Brownish yellow to red | 15.3 ± 0.1 | | CH3COOH/NaOH | Red to brownish yellow | 12.13 ± 0.0577 |
| | Bauhinia purpurea | NaOH/HCl | Yellow to red | 8.93 ± 0.0577 | | NH4OH/HCl | Yellow to red | 15.27 ± 0.0577 | | CH3COOH/NaOH | Red to yellow | 12.3 ± 0.1 |
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