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Needed compounds:----------------- sodium hydroxide : NaOH sulphuric acid : H2SO4 sodium silicate : Na2SiO3 silver nitrate : AgNO3Class:------ elem=Ag,Si precipitationSummary:-------- Silver salts give a yellow precipitate with silicates. This precipitate becomes white on addition of sulphuric acid. When a large quantity of sodium hydroxide is added, then a dark, almost black, solid is created.Description:------------Add a few drops of syrupy water glass (sodium silicate solution, appr. 35%)to a solution of silver nitrate: A bright yellow precipitate is formed. Thepieces of the precipitate are fairly hard and brittle.Add some sulphuric acid (appr. 1 mol/l): The precipitate does not dissolve,but it becomes white. The structure also changes, it becomes more yelly like.Probably the sulphuric acid causes the yellow compound (silver silicate) todecompose, forming white sparingly soluble silver sulfate, combined withsparingly soluble silicic acid.Decant the liquid and keep part of the precipitate and add some solid sodiumhydroxide: A vigorous reaction occurs and a lot of heat is produced (reactionbetween excess sulphuric acid and water with the NaOH). Besides this, a blacksolid is produced in small quantities, this probably is metallic silver.

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