How to Lead
Lead - 82-th element of the periodic table - represents a very dense, but soft, malleable and easily fusible metal dull gray. Both the lead and its alloys, as well as many of its compounds are very widely used in various fields of industry. This material was once widely used as an additive in motor fuel, but was withdrawn from production due to extremely high toxicity. Since all without exception lead toxic derivatives, the question of its definition is very relevant.
You will need:
- clean tube; - Potassium iodide solution; - acetic acid; - Spirit lamp or gas burner; - Ice or cold water container; - sulfuric acid.
Instruction how to identify lead
Suppose you have a water sample. It is necessary to determine whether there are lead compounds soluble therein. How can I do that? There is a very distinctive and highly sensitive response, which can rightly be called one of the most beautiful in chemistry. It is based on the ability to lead react with iodine to form a poorly soluble compound PbI2.
Pour some water from this sample to a clean tube of refractory glass, add to it a solution of potassium iodide bit - KI, Acidify with a few drops of acetic acid (for better reaction).
Shake the contents of the tube. If the contained water soluble lead compounds fall yellow precipitate of lead iodide. He was unremarkable in appearance. But if well-heated tube on the alcohol lamp flame or gas burner (pellet thus should disappear), and then rapidly cooled, for example by placing in ice or cold water container, the precipitate RbI2 fall again, but now in the form of a beautiful golden crystals. It's very spectacular, impressive sight, so the reaction is often used as a demonstration experiment.
As can be determined even lead ions in solution? For example, using sulfuric acid or any of its soluble salts. When interacting with lead ion Pb ^ 2 + type reaction occurs: K2SO4 + Pb (NO3) 2 = PbSO4 + 2KNO3. The resulting lead sulfate precipitates as a dense white precipitate.
But, for example, loss of the same kind with the sludge - a characteristic response and barium ion. How can I be sure that this is not barium sulfate? For this it is necessary to conduct the reaction control, add to the sludge strong alkali solution, then heated tube. If this is the lead sulfate, the precipitate gradually disappears due to the formation of a soluble complex salt. The reaction takes place on such a scheme: PbSO4 + 4NaOH = Na2 [Pb (OH) 4] + Na2SO4. Barium sulfate with the same control test will remain as a precipitate.