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

Table 2

Absorption of 10 solutions at pH 7.29, 7.32, 7.36, 7.39, 7.53, 7.59, 7.95, 7.99, 8.14, and 8.52 for all the three follower extracts and methyl red indicator.

Indicator	Parameter	Absorption of 10 solutions at pH from 7.29 to 8.52
		7.29	7.32	7.36	7.39	7.53	7.59	7.95	7.99	8.14	8.52
Impatiens balsamina	λ 1	0.028	0.026	0.021	0.020	0.018	0.018	0.017	0.017	0.015	0.015
	λ 2	0.361	0.362	0.366	0.370	0.373	0.375	0.376	0.379	0.382	0.416
	Acid max	0.325	0.325	0.325	0.325	0.325	0.325	0.325	0.325	0.325	0.325
	Base max	0.577	0.577	0.577	0.577	0.577	0.577	0.577	0.577	0.577	0.577
Bauhinia purpurea	λ 1	0.069	0.056	0.052	0.044	0.033	0.026	0.020	0.022	0.017	0.013
	λ 2	0.581	0.604	0.614	0.646	0.642	0.641	0.659	0.663	0.674	0.712
	Acid max	0.132	0.132	0.132	0.132	0.132	0.132	0.132	0.132	0.132	0.132
	Base max	0.752	0.752	0.752	0.752	0.752	0.752	0.752	0.752	0.752	0.752
Bougainvillea glabra	λ 1	0.07	0.06	0.05	0.05	0.05	0.05	0.04	0.05	0.05	0.04
	λ 2	0.04	0.04	0.04	0.04	0.06	0.06	0.07	0.08	0.09	0.13
	Acid max	0.11	0.11	0.11	0.11	0.11	0.11	0.11	0.11	0.11	0.11
	Base max	0.04	0.04	0.04	0.04	0.04	0.04	0.04	0.04	0.04	0.04
Methyl red	λ 1	0.372	0.339	0.286	0.262	0.264	0.261	0.258	0.262	0.258	0.227
	λ 2	2.326	2.363	2.392	2.314	2.357	2.368	2.379	2.398	2.452	2.760
	Acid max	2.796	2.796	2.796	2.796	2.796	2.796	2.796	2.796	2.796	2.796
	Base max	2.42	2.42	2.42	2.42	2.42	2.42	2.42	2.42	2.42	2.42