16.3.1 Preparation of Indicator Solutions

Preparation of some indicator solutions are described below:

0.1% Methyl orange solution: Dissolve 1 g of the substance in 1000 ml of hot water and filter if necessary. Alternatively, 0.1 g may be dissolved in 100 ml of hot water. ( pH range: red 2.9 4.6 orange yellow)

0.1% Postassium ferricyanide ( external indicator): Dissolve 1 g in water and dilute to 1 liter.

1% Diphenylamine: Dissolve 1 g of the solid in 100 ml of concentrated H ₂SO ₄. The solution of its sulphonate is better than this solution for the titration of Fe ²⁺ and K ₂Cr ₂O ₇.

1% Methyl red solution: Dissolve 1 g of solid in 500 ml of alcohol and dilute with water to 1 liter. ( pH range: red 4.2 6.3 yellow).

1% Starch solution: Make a paste of 1 g of soluble starch with cold water in a beaker with the help of a glass rod. Slowly add 100 ml of boiling water and boil for 3 4 minutes. If it is to be kept for many days, add 0.5 g of salicylic acid (or 1 g of HgCl ₂ or a few drops of chloroform or formalin). Keep it in a stoppered bottle so that it is not spoiled by bacteria.

2% Litmus solution (blue): Dissolve 2 g of powdered litmus in 100 ml of water and boil...