Formaldehyde, it is ant aldehyde, methanal is a colourless poisonous gas with a pungent suffocating smell. Let's well dissolve in water. And the water 40% - ny solution of formaldehyde are called formalin. It is transparent colourless liquid with a peculiar pungent smell. For establishment of authenticity of solution of formaldehyde it is recommended to use the general reaction of restoration of silver on aldehydes from connections (reaction of a silver mirror). It is possible to identify formaldehyde from other aldehydes by means of reactions of formation of the painted accession products with phenols in the presence of the concentrated sulfuric acid (Hitchcock's reaction).
It is required to you
- Flask with a capacity of 50-100 ml or test tube
- pipette, 2 test tubes
- 10% solution of nitrate of silver
- 2H solution of caustic sodium
- 25% solution of ammonia
- glass with the hot (boiling) water
- formalin
- salicylic acid
- sulfuric acid
Instruction
1. Carry out reaction of a silver mirror for definition of aldehyde among other organic matter. Clean a flask or a test tube from mechanical pollution, wash out the brush with soap water and rinse with the distilled water.
2. In a flask pour 15 ml 10% solution of nitrate of silver and 15 ml 2H of solution of caustic sodium. Add gradually 25% solution of ammonia until the deposit which is formed in the beginning is not dissolved.
3. Add carefully on a wall 0.5-1 ml of formalin and place a flask in a glass with the hot (boiling) water. Soon in a flask the beautiful silver mirror is formed.
4. For definition of formaldehyde among other aldehydes use condensation reaction (Hitchcock's reaction). Pour 3 ml of the concentrated sulfuric acid in a test tube. Carefully add 3 drops of formalin. The received solution is called Kobert's reactant.
5. Place in other test tube a little salicylic acid, add 2 drops of sulfuric acid and in a few minutes mix with one drop of the prepared reactant. Soon there will be a pink coloring (sometimes weak heating for this purpose is necessary).