Natural Plant Extracts as Acid-Base Indicator and Determination of Their pKa Value

Table 4

Calculated pKa and pH range of indicators.

Indicator	pKa	pH range
Bougainvillea glabra	6.9966 ≈ 7.0	6.0–8.0
Impatiens balsamina	4.3766 ≈ 4.4	3.4–5.4
Bauhinia purpurea	7.0328 ≈ 7.0	6.0–8.0
Methyl orange	3.4003 ≈ 3.4	2.4–4.4