Talc powder is made of talc purified, crushed and dried. It should be identified from the following aspects:

1. Properties: Talc powder is white or off-white, fine, non-sand-like powder. It feels slippery to the touch. It is odorless and tasteless. Talc powder is insoluble in water, dilute hydrochloric acid or dilute sodium hydroxide solution.

Identification method: Take 0.2g of talc powder, put it in a platinum crucible, add the same amount of calcium fluoride or sodium fluoride powder, stir, add 5ml of sulfuric acid, slightly heat, immediately cover the platinum crucible with 1 drop of water, wait for a while After a while, remove the crucible cover, and the water droplets appear white and cloudy. Take 0.5g of this product powder, put it in a beaker, add 10ml of hydrochloric acid solution, cover it with a watch glass, heat it to a slight boil, shake the beaker from time to time, and keep it at a slight boil for 40 minutes, take Then, filter with fast filter paper, and wash the residue with water for 4~5 times. Take about 0.1 g of the residue, put it in a platinum crucible, add 10 drops of sulfuric acid and 5 ml of hydrofluoric acid, and heat it until white smoke of sulfur trioxide is emitted, remove it and cool it. Then, add 10ml of water to dissolve, take 2 drops of the solution. Add 1 drop of magnesium reagent, and dropwise add sodium hydroxide solution to make it alkaline, resulting in a sky blue precipitate.

Check: Take 10g of talcum powder for pH, add 50ml of water, boil for 30 minutes, replenish the evaporated water from time to time, filter, and the filtrate shows a neutral reaction when it encounters litmus paper.

2. Soluble in water: take 5g of talc, add 30ml of water, boil for 30 minutes, replenish the lost water from time to time, let it cool, filter, add 5ml of water to the filter residue to wash, combine the washing liquid with the filtrate, evaporate to dryness, and dry at 105 ° C for 1 Hours, the residue should not exceed 5mg.

Soluble matter in acid: take 1g of talc, add 20ml of dilute hydrochloric acid, soak at 50°C for 15 minutes, filter. Take 10ml of the filtrate, add 1ml of dilute sulfuric acid, evaporate to dryness, ignite to constant weight, and the residue should not exceed 7.5mg.

3. Iron salt: take 10g of talc, add 30ml of water, heat and boil for 30 minutes, replenish the evaporated water at any time, let it cool, filter, add 1ml of dilute hydrochloric acid and 1ml of potassium ferrocyanide test solution to the filtrate, and do not show blue immediately color.

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