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Acid-base Titration

Acid base titration is based on reaction of acid and base to form salt and water. In this titration, neutralization reaction is involved so it is also called as neutralization titration.

Acid –base reactions are very fast and divided into three types according to their nature.

Acidimetric titration
Alkaline substance is titrated with standard acid is called as acidimetric titration

Alkalimetric titration
Acidic substance is titrated with standard base is called as alkalimetric titration.

Non-aqueous titration
Susbance which can not be titrated satisfactorily either by acidimetry or alkalimetry in aqueous solution are titrated by non-aqueous solvents and called as non-aqueous titration.

Acid-base indicator:
The indicator used in acid-base titration is called as acid-base indicator. The important feature of acid-base indicator is that it has one color in acidic medium and develops another color in alkaline medium. This color change is not sudden but occurs within a small range of pH, this range is called as pH range of indicator.

Example of Acid-base indicator and its pH range is shown in table.

Indicator Color in acid Develop color in alkali pH range of indicator
Phenolphthalein Colorless Red 8.3 – 10.0
Methyl red Red Yellow 4.5 - 6.5
Methyl Orange Pink Yellow 3.0 – 4.5
Ethyl orange Red Orange 3.0 – 4.5
Quinaldine red Colorless Red 1.4 – 3.2
Azolitmin (Litmus) Red Blue 5.0 – 8.0

Application of acid-base titration:
For determination of irons in pharmaceutical preparation
To analyze mixture of acids
To analyze mixture of bases

Indicator used in non-aqueous titration:
Non-aqueous titration is simple and accurate and has been analogous to acid-base titration.

Many organic compounds are poorly water soluble or very weakly reactive in water are titrated by non-aqueous titration. The indicator used in non-aqueous titration is shown below in table.

Indicator Color change
Basic Neutral Acidic
Crystal violet
0.5 % in glacial acetic acid
Violet Blue-green Greenish yellow
Methyl red
0.2 % in dioxin
Yellow - Red
1-naphthol benzein
0.2 % in acetic acid
Blue or greenish blue Orange or yellow Green
Oracet blue B
0.5 % in glacial acetic acid
Blue Purple Pink
Thymol blue
0.2 % in methanol
Yellow - Blue
Quinaldine red
0.1 % in ethanol
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