Description of experiment
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Needed compounds:
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stannous chloride : SnCl2
arsenic trioxide : As4O6
hydrochloric acid : HCl
Class:
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elem=As,Sn
redox
Summary:
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Arsenic in oxidation state +3 is quickly reduced to elemental arsenic by
tin(II) chloride in hydrochloric acid.
Description:
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Dissolve some arsenic trioxide in moderately concentrated hydrochloric acid
(20% HCl by weight or so): A colorless liquid is obtained. The As2O3 does not
dissolve quickly, some heating is needed to get all of it dissolved.
In a separate test tube prepare a solution of tin(II) chloride in moderately
concentrated hydrochloric acid. If high grade SnCl2 is used, then a completely
clear solution is obtained without hydrolysis products of tin(IV).
Add the solution of tin(II) chloride to the solution of As2O3: Over a period of
appr. 30 seconds a black precipitate is formed and a dark grey mirror is formed
on the glass. Immediately after mixing the liquid first turns brown and turbid,
but this color quickly intensifies and shifts to grey/black. After a few hours
all of the precipitate has settled at the bottom.