Testing dissolved silver with chloride ions
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One of the classical reactions in chemistry is when silver ions reacts with chloride and forms silver chloride. From two colorless solutions mixed together a thick white precipitate is formed.
Youtube video of AgNO3 mixed with NaCl
This reaction can be used as a sensitive test of silver in solutions.
Silver chloride is soluble more or less in certain solutions.(extensive list of solubility)
- Cyanide, sodium thiosulfate and ammonia can dissolve large amounts of silver chloride.
- Strong chloride solutions can dissolve small amounts of silver chloride, for example concentrated Aqua Regia.
- Concentrated hydrochloric or sulfuric acid can dissolve some silver chloride.
Strong acids can be diluted to precipitate any dissolved silver chloride. Ammonia needs to be neutralized, for example by HCl, before the silver will precipitate.
( Please look up and enter GRF search thiosulfate+silver+chloride )
Hoke pg 91-92
This test also is already familiar. On several occasions in the past you have added hydrochloric acid (or table salt) to solutions that contain silver, and you have seen silver chloride form and settle as a white precipitate. You observed that a small amount of silver produced a surprisingly large amount of chloride. Your purpose when examining spent solutions, to see whether they are worthless or not, is to recognize small quantities of precious metals-dissolved in a relatively large quantity of liquid. Accordingly you must give your eye some practice in recognizing small precipitates and thin clouds. Thus, take one drop of silver nitrate solution (left over from the acquaintance experiments of Chapter V, for instance) and dilute it with an ounce or so of plain water; then add a few drops of hydrochloric acid. You will see the same white cloud of silver chloride, but much less dense than before. It is interesting to repeat this, diluting one drop of silver nitrate with a pint of water, stirring well. This will convince you that the test, properly conducted, is indeed delicate. Do not let this fact lose its economic significance-that is, if you find that a certain solution contains so little silver that the test gives only a thin cloud, you must realize that it is not worth refining. This test for silver can be used on either nitric acid or sulphuric acid solutions; also on pickling solutions (which contain both nitric and sulphuric acid). Cyanide or ammonia solutions require slightly different handling; use a test tube or small beaker and take only a few drops of the unknown solution, and cautiously add five or six drops of hydrochloric acid; the ammonia mixture will become hot; with cyanide solutions there will be bubbles of the deadly hydrocyanic acid gas, which should be driven off by gentle heating. As soon as all the alkalinity is neutralized, the familiar silver chloride cloud will be visible. A few other metals beside silver will give a white doud with hydrochloric acid. You will recall from Chapter VII, that lead has a white insoluble chloride; so has mercury. In other words if your unknown gives a white precipitate on the addition of hydrochloric acid, it may contain silver, or lead, or mercury. Here is a way to settle all doubts: separate out a pinch of the white stuff, either in a filter or by letting it settle; wash it with considerable hot water, and if it dissolves it is lead chloride. Suppose it does not dissolve-that means it is either silver chloride or mercury chloride; add a few drops of strong ammonia . . . mercury chloride turns black, and silver chloride dissolves. These tests are easy and to most people fascinating.
- Hoke - Refining Precious Metal Wastes,"TESTING FOR SILVER IN SOLUTION" page 91-92
- Saltlakemetals, extensive list of solubility