acid base indicators


   acid base indicators

Weak Acids and Bases can be used as Acid-Base indicator. An acid-base indicator is a weak acid or a weak base. An Indicator acid base indicator does not change color from pure acid to pure alkali solution at particular hydrogen ion concentration, but to a certain extent, color change takes place over a range of hydrogen ion concentrations. This range is termed the color change interval and is articulated as a pH range.

The use of acid base indicators

Weak acids are titrated in the presence of indicators that alter a little in alkaline situations. Weak bases ought to be titrated in the presence of indicators that alter their colours under a little acidic condition.

Popular acid-base indicators:

Examples of acid-base indicators are:

• Thymol blue

• tropeolin OO

• methyl yellow

• methyl orange

• bromphenol blue

• bromcresol green

• methyl red

• bromthymol blue

• phenol red

• neutral red

• phenolphthalein

• thymolphthalein

• alizarin yellow

• tropeolin O

• nitramin

• trinitrobenzoic acid.

Common Acid-Base Indicators

Indicator * pH * Range * Qty per 10 ml * Acid * Base

Thymol Blue 1.2-2.8 1-2 drops 0.1% solution in aqueous red yellow

Pentamethoxy red 11.2-2.3 1 drop 0.1% soln. in 70% alcohol red-violet colorless

Tropeolin OO 1.3-3.2 1 drop 1% of aqueous solution red Yellow
Tropeolin OO 1.3-3.2 1 drop 1% of aqueous solution red Yellow

2,4-Dinitrophenol 2.4-4.0 1-2 drops 0.1% solution in 50% alcohol colourless Yellow

Methyl yellow 2.9-4.0 1 drop 0.1% solution in 90% alcohol red Yellow

Methyl orange 3.1-4.4 1 drop 0.1% aqueous solution red Orange

Bromphenol blue 3.0-4.6 1 drop 0.1% aqueous solution yellow blue-violet

Tetrabromphenol blue 3.0-4.6 1 drop 0.1% aqueous solution yellow blue

Alizarin sodium sulfonate 3.7-5.2 1 drop 0.1% aqueous soln yellow Violet

α-Naphthyl red 3.7-5.0 1 drop 0.1% solution in 70% alcohol red Yellow

p-Ethoxychrysoidine 3.5-5.5 1 drop 0.1% aqueous solution red Yellow

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