Paragraph 4 REAGENTS
Hydrochloric acid solution, 50% (V/V): dilute an appropriate volume of hydrochloric acid (ρ = 1.18 g/ml) with an equal volume of water.
Sulfuric acid, 0.05 M solution. } for variant (a) (see page 21)
Sodium or potassium hydroxide, 0.1 M solution, carbonate free. } for variant (a) (see page 21)
Sulfuric acid, 0.1 M solution. } for variant (b) (see page 21)
Sodium or potassium hydroxide, 0.2 M solution, carbonate free. } for variant (b) (see page 21)
Sulfuric acid, 0.25 M solution. } for variant (c) (see page 21)
Sodium or potassium hydroxide, 0.5 M solution, carbonate free. } for variant (c) (see page 21)
Devarda’s alloy — powdered so that 90 to 100% will pass through a sieve with apertures less than 0.25 mm square, 50 to 75% will pass through a sieve with apertures of less than 0.075 mm square. (Pre-packed bottles containing a maximum of 100 g are recommended.)
Sodium hydroxide solution, 30 g per 100 ml, ammonia free.
Indicator solutions:
Mixed indicator:
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Solution A: dissolve 1 g methyl red in 37 ml 0.1M sodium hydroxide solution and make up to 1 litre with water.
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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.
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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 solution:
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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.
Ethanol, 95%.
Sodium nitrate.