Paragraph 4 REAGENTS

4.1

Hydrochloric acid solution, 50% (V/V): dilute an appropriate volume of hydrochloric acid (ρ = 1.18 g/ml) with an equal volume of water.

4.2

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

4.3

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

4.4

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

4.5

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

4.6

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

4.7

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

4.8

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

4.9

Indicator solutions:

4.9.1

Mixed indicator:

Solution A: dissolve 1 g methyl red in 37 ml sodium hydroxide 0.1 M 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 solution A and 2 volumes of solution B.
This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution. Use 0.5 ml (10 drops) of this indicator solution.

4.9.2

Methyl red indicator solution:

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

4.10

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

4.11

Ammonium sulfate.