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.

Caveats

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.

References

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