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Acid base titration - end point indicators preparation

Acid-base titration

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Instant Notes in Analytical Chemistry Amazon

Instant Notes in Analytical Chemistry

by D. Kealey, P.J. Haines

Acid-base titration » Indicators preparation

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Different indicators require different methods of preparation. In the following table we have collected some basic information about indicators and their solutions. See more complete list of pH indicators at www.ph-meter.info (note that this list doesn't contain information about solution preparation).

pH indicators used for end point detection
indicator namepH
color
pH
color
prepared as
Methyl violet0.1
yellow
2.7
violet
0.05% water
Cresol red0.2
red
1.8
yellow
0.1% water
Thymol blue1.2
red
2.8
yellow
0.05% water
2,4-Dinitro phenol2.8
colourless
4.7
yellow
0.1% ethanol
Congo red3.0
blue
5.2
yellow/orange
0.1% water
Methyl orange3.1
red
4.4
yellow/orange
0.1% water
Bromocresol green3.8
yellow
5.4
blue
0.1% water
Methyl red4.4
red
6.2
yellow/orange
0.1% ethanol
Chlorophenol red4.8
yellow
6.4
purple
0.1g in 24 mL of 0.01 M NaOH, dilute to 250 mL
Litmus5.0
red
8.0
blue
0.5% water
Bromocresol purple5.2
yellow
6.8
purple
0.05% water
Bromothymol blue6.0
yellow
7.6
blue
0.05% water
Phenol red6.4
yellow
8.2
red/violet
0.05% water
Neutral red6.8
red
8.0
orange
0.01% in 50% v/v ethanol
Creosol red7.0
orange
8.8
purple
0.1% water
Thymol blue8.0
yellow
9.6
blue
0.05% water
Phenolphthalein8.2
colourless
9.8
red/violet
0.5% ethanol
Thymolphthalein9.3
colourless
10.5
blue
0.2% ethanol
Alizarin yellow GG10.0
bright yellow
12.1
brown/yellow
0.1% ethanol

Please note, that different sources list different methods for indicator preparation. For example for 2,4-dinitro phenol some sources propose to prepare 0.1% ethanol solution, while other suggest using just a saturated water solution.

Colors of some of the indicators listed in the table above:

colors of methyl violet indicator in different pH solutions colors of thymol blue indicator in different pH solutions colors of congo red indicator in different pH solutions colors of methyl orange indicator in different pH solutions colors of chlorophenol red indicator in different pH solutions colors of litmus indicator in different pH solutions colors of bromocresol purple indicator in different pH solutions colors of bromothymol blue indicator in different pH solutions colors of phenol red indicator in different pH solutions colors of neutral red indicator in different pH solutions colors of thymol blue indicator in different pH solutions colors of phenolphthalein indicator in different pH solutions

Colors on the pictures can slightly differ from reality, as hues displayed depend on the monitor calibration. pH values listed on the pictures refer to the actual pH of the solution as prepared, not the pH at which indicator changes color. In lab reality colors will be less saturated, as to be sure colors are well visible we used an excess of indicators.

See also detailed discussion on the pH indicators equilibria and color changes.


Page was last modified on May 31 2009, 00:40:18.

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