Paragraph 4 REAGENTS

Methyl red indicator solution

4.1

Dissolve 0.1 g of methyl red (C₁₅H₁₅N₃O₂) in 50 ml of ethanol (95% in a 100 ml) volumetric flask. Make up the volume to 100 ml with water. Mix thoroughly.

Diluted hydrochloric acid solution, about 0.5 M

4.2

Mix 1 volume of hydrochloric acid HCl (ρ = 1.18 g/ml) with 20 volumes of water.

Sodium hydroxide solution, about 0.5 M

4.3

Must be free of carbon dioxide. Dissolve 20 g of sodium hydroxide (NaOH) in pellet form in a 1 litre volumetric flask containing about 800 ml of boiled water. When the solution has cooled, make up to 1000 ml with boiled water and mix thoroughly.

Standard sodium hydroxide solution, about 0.025 M

4.4

Must be free of carbon dioxide. Dilute the 0.5 M sodium hydroxide solution (4.3) 20 times with boiled water and mix thoroughly. The value of the solution expressed as boron (B) is to be determined (see paragraph 9).

Boron calibration solution (100 mg/ml B)

4.5

Dissolve 0.5719 g of boric acid (H₃BO₃), weighed to the nearest 0.1 mg, in water in a 1 litre volumetric flask. Make up to volume with water and mix thoroughly. Transfer to a plastic bottle for storage in a refrigerator.

4.6

D-mannitol (C₆H₁₄O₆) powder.

4.7

Sodium chloride (NaCl).