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Precipitation Reactions

Test for carbon dioxide - if the gas given off is bubbled through limewater if it turns cloudy (white precipitate is formed) the gas is identified as carbon dioxide.CO2(g) + Ca(OH)2(aq) → CaCO3(s) + H2O(l)
Test for sulfates - the solution is acidified with dilute hydrochloric acid (to remove carbonate ions, which would also give a white precipitate), then barium chloride or barium nitrate is added. If a sulfate is present a white precipitate is formed.BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq)Ba2+(aq) + SO42-(aq) → BaSO4(s)
Test for halides - silver nitrate solution is added. This gives a white precipitate with chlorides, a cream precipitate with bromides and a yellow precipitate with iodides.AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)Ag+(aq) + Cl-(aq) → AgCl(s)

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Specification: Edexcel Chemistry (8CH0), AS-level, Topic 4B: The elements of Group 7 (halogens). Topic: Types of Reaction.

Key terms in this lesson

precipitate
An insoluble solid that forms and separates out of a solution during a reaction.

More in Types of Reaction

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