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Acid and base pH indicators

Colors and pH range for color change of acid base indicators is given together with pKa and structures of the indicators

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The ranges for the color changes are given in the table below the figure, together with the corresponding pK_a value of the indicators.

The molecule structure of each indicator is shown below the table.

See also pKa values of inorganic acids and bases, organic nitrogen compound and alcohols and carboxylic acids.

acid base pH indicators

Trade name	pH start	pH end	pKa	low pH color	high pH color
Cresol red - step 1	0.2	1.8	1.0	red	yellow
Malachite green -step 1	0.2	1.8	1.3	yellow	green
Thymol blue - step 1	1.2	2.8	1.7	red	yellow
Methyl yellow	2.9	4.0	3.3	red	yellow
Methyl orange	3.1	4.4	3.5	red	yellow
Bromophenol blue	3.0	4.6	4.1	yellow	blue
Congo red	3.0	5.0		blue-violet	red
Methyl orange in xylene cyanol (screened)	3.2	4.2		grey-violet	green
Bromocresol green	3.8	5.4	4.7	yellow	blue
Methyl red	4.4	6.2	5.1	red	yellow
Methyl purple	4.8	5.4		purple	green
Bromocresol purple	5.2	6.8	6.4	yellow	purple
Azolitmin (litmus)	4.5	8.3		red	blue
Bromothymol blue	6.0	7.6	7.3	yellow	blue
Phenol red	6.4	8.0	8.0	yellow	red
Neutral red	6.8	8.0		red	yellow
Cresol red -step 2	7.2	8.8	8.5	yellow	reddish-purple
Naphtholphthalein	7.3	8.7		pale red	greenish-blue
Thymol blue - step 2	8.0	9.6	9.2	yellow	blue
Cresolphthalein	8.2	9.8		colorless	purple
Phenolphthalein	8.3	10.0	9.5	colorless	red-pink
Thymolphthalein	9.0	10.5	9.2	colorless	blue
Alizarin yellow R	10.1	12.0	11.2	yellow	red
Indigo carmine	11.4	13.0		blue	yellow
Malachite green -step 2	11.5	13.2		green	colorless

Structure of ph acid base indicator

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