HCl Test - Greenish Yellow Chlorine
Concentrated hydrochloric acid does not fume out chlorine on its own — it takes an oxidiser to pull it free. Manganese dioxide is exactly that: heated with the concentrated acid, it oxidises the chloride to chlorine gas while itself being reduced. The evolved gas is unmistakable, a greenish-yellow with its own sharp smell, and its appearance is the confirmatory evidence every Class 10 syllabus asks for that hydrochloric acid contains chlorine at all.
5 steps · Hydrogen Chloride · Study of Compounds
What you will use
Apparatus
- Flask
Chemicals
- Manganese Dioxide
- Concentrated Hydrochloric Acid
The steps
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Add manganese dioxide to the flask.
A dark, unreactive powder. Nothing happens until the acid meets it.
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Pour concentrated hydrochloric acid onto it.
Little happens cold. This reaction needs heat to go.
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Attach a burner under the flask.
The flame is lit; the burner slider now controls how hot the flask gets.
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Heat the mixture.
The dark powder reacts as it warms.
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Watch the gas coming off.
A greenish-yellow gas fills the flask — chlorine, with its own sharp, choking smell.
What it shows
Manganese dioxide oxidises the chloride in concentrated hydrochloric acid to chlorine gas, itself being reduced to manganese(II) chloride, with water formed alongside. The greenish-yellow gas is chlorine and nothing else on this bench looks like it — its appearance is the proof that the acid heated to get it there was carrying chlorine all along.