Description of experiment
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Needed compounds:
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sulphuric acid : H2SO4
potassium tetrathionate : K2S4O6
sodium nitrite : NaNO2
Class:
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elem=N,S
precipitation
redox
Summary:
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A solution of tetrathionate reacts with nitrite in acidic solution. A green
compound is formed, which however is unstable and after a few minutes, the
solution decomposes. It becomes turbid and light yellow. Most likely the yellow
material is finely divided sulphur.
Description:
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Dissolve some potassium tetrathionate in water and add a solution of sodium
nitrite to this: No visible reaction occurs. The liquid remains clear and
colorless.
Add a single drop of 2M sulphuric acid: Where the concentration of acid becomes
higher, the liquid becomes lime green. After shaking, the liquid is very pale
yellow.
Add more 2M sulphuric acid and swirl: The liquid becomes lime green and there
is a slow production of a colorless gas. This gas reacts with air, giving a
brown gas, so the colorless gas must be nitrogen monoxide.
Shake the lime green liquid: When the liquid is shaken, then the production of
gas becomes much faster. When shaking is stopped, then the production of gas
slows down. The color of the liquid also becomes lighter. At a certain moment,
the liquid quickly becomes opaque and yellow. This yellow compound most likely
is sulphur.
Remark: What is the nature of the lime green compound, which is formed
initially? Is this some oxo anion with both sulphur and nitrogen in it?