Paragraph 4 REAGENTS

4.1

Sulfuric acid solution 50% (V/V): dilute an appropriate volume of sulfuric acid (ρ = 1.84 g/ml) with an equal volume of water.

4.2

Potassium sulfate.

4.3

Copper oxide (CuO), 0.3-0.4 g for each determination or an equivalent quantity of copper sulfate pentahydrate (0.95 to 1.25 g) for each determination.

4.4

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

4.5

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

4.6

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

4.7

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

4.8

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

4.9

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

4.10

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

4.11

Indicator solutions:

4.11.1

Mixed indicator:

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).

4.11.2.

Methyl red indicator solution:

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

4.12

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

4.13

Potassium thiocyanate.