Testing for Ions | A Level Chemistry | OCR, AQA, Edexcel

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This week we are revising Testing for Ions

A-Level Chemistry can be tough but fortunately we’ve made this tutorial to help you score the A* you need for questions on everything to do with Testing for Ions.

In a chemical lab you will often be presented with an unknown compound and asked to identify it. Luckily, the nature of the ions presents can be easily figured out by systematically carrying out a series of qualitative tests.

Carbonate anions can be tested for by mixing the unknown compound with a dilute acid. If carbonate anions are present, they will react wit H+ in the acid to form CO2.

Carbon dioxide turns limewater cloudy. Any carbon dioxide produced by the reaction between the acid and the carbonate anions, is collected via a collecting tube and bubbled through lime water. Carbon dioxide will react with lime water to give a white Calcium carbonate precipitate that turns the solution milky white.

Sulfate anions can be tested for by the displacement of barium ions. If a small amount of barium chloride solution is added to an acidified solution of sulfate ions, a displacement reaction takes place in which the barium ions displace the cation in the sulfate compound to form a white precipitate of barium sulfate.

Halide ions can be tested for by mixing the unknown compound with acidified silver nitrate solution. Upon the addition of silver nitrate, a silver halide precipitate will form as a result of a displacement reaction. The colour of the precipitate will be different for each halide.

To be sure of the identity of the halide, concentrated ammonia solution can then be added. Different silver halides will have different solubilities. Some silver halide precipitates will re-dissolve upon addition of ammonia solutions but others will not. Positive test results for different halide ions are collected in the table below.

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[Strawberrypie]

For ocr a Biology alevel practical 12 is a research practical what would you be doing, in terms of what is the research about and would they provide me with a topic to research and only then and there in the lab I’d be researching that specified topic? What is that practical about?