Paragraph 4 REAGENTS

4.1

Sulfuric acid, concentrated (ρ = 1.84 g/ml).

4.2

Sodium hydroxide solution, 30 g per 100 ml, ammonia free.

4.3

Sulfuric acid, 0.05 M solution. } for variant (a) (see page 21)

4.4

Sodium or potassium hydroxide, 0.1 M solution, carbonate free. } for variant (a) (see page 21)

4.5

Sulfuric acid, 0.1 M solution. } for variant (b) (see page 21)

4.6

Sodium or potassium hydroxide, 0.2 M solution, carbonate free.} for variant (b) (see page 21)

4.7

Sulfuric acid, 0.25 M solution. } for variant (c) (see page 21)

4.8

Sodium or potassium hydroxide, 0.5 M solution, carbonate free. } for variant (c) (see page 21)

4.9

Indicator solutions:

Mixed indicator:

4.9.1

Solution A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and make up to 1 litre with water.

Solution B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1 volume of A with 2 volumes of B.
This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution. Use 0.5 ml (10 drops).

Methyl red indicator:

4.9.2.

Dissolve 0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water. Filter if necessary. This indicator (4 to 5 drops) may be used instead of the preceding one.

4.10

Anti-bump granules of pumice stone, washed in hydrochloric acid and ignited.

4.11

Urea.