C4 GCSE OCR Gateway (9-1): Testing for anions

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  • Created by: Aleena
  • Created on: 19-03-18 19:12
What are Anions?
negative ions
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What is the overall charge of a Halide ion?
-1
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How do you test for Halide Ions?
First add dilute nitric acid then few drops of silver nitrate solution.Then you use the colour of the precipitate formed to find out what halide ion it is.
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Why do you add the dilute nitric acid first?
This is because you need to get rid of any carbonate ions that are present, as they also produce a pale precipitate with silver nitrate-which would confuse the results.
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Why can't you use hydrochloric acid instead of the nitric acid?
This is because you would be adding chloride ions, confusing the results even more!
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what colour is the precipitate when chloride ions are present?
white
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what colour is the precipitate when Bromide ions are present?
cream
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what colour is the precipitate when Iodide ions are present?
yellow
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How do you test for Carbonates?
First add barium chloride- if there's any carbonate ions present it will produce a white precipitate of barium carbonate. Then, you add dilute hydrochloric acid to this. If carbonate ions are present the mixture will fizz
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Why is there fizzing?
This is because carbon dioxide is produced as the acid reacts with the carbonate.
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How can you test whether carbon dioxide is being produced?
bubble it thru some limewater-if it turns cloudy, carbon dioxide is present
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what is the word equation for the test for carbonate ions?
barium carbonate + acid ---> barium ions + carbon dioxide + water
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What colour of solution will you end up with after all the barium carbonate has reacted?
colourless solution cotaining Ba2+ ions
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How do you test for Sulfate Ions?
First add some barium chloride solution, if any sulfate ions are present a white precipitate of barium sulfate will form.
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How can you test whether barium sulfate is present?
Add some HCl acid - if there's no reaction & if the white precipitate doesn't dissolve-sulfate ions are present rather than carbonate ions
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Other cards in this set

Card 2

Front

What is the overall charge of a Halide ion?

Back

-1

Card 3

Front

How do you test for Halide Ions?

Back

Preview of the front of card 3

Card 4

Front

Why do you add the dilute nitric acid first?

Back

Preview of the front of card 4

Card 5

Front

Why can't you use hydrochloric acid instead of the nitric acid?

Back

Preview of the front of card 5
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