Tests for Anions
Do now:
What sorts of elements form negative ions?
Why? Draw ions of Cl and F.
What types of elements react together to
form an ionic bond. Explain how this
happens.
Negative ions revision
Non-metals form negative ions. This is because
they are on the right of the periodic table, so
they need to gain negative electrons to get a full
outer shell.
Ionic bond revision
REMEMBER the bond is the electrostatic forces of
attraction between the negative ion and the positive ion.
Test for carbonate ions
Watch the video.
Write down the method to test for
carbonate ions and what happens with a
positive test.
Test for carbonate ions
Add dilute acid to the unknown solid. It should fizz
and produce a gas.
Bubble the gas through limewater and if it goes
cloudy it is producing carbon dioxide.
This is a positive test for carbonate ions.
Carbon dioxide
Ionic equation
CO32-(s) + 2H+(aq) → CO2(g) + H2O(l)
Write equations for copper (II) carbonate,
calcium carbonate and (challenge) sodium
Chemical equations
Carbon dioxide
Carbon dioxide
Carbon dioxide
Carbon dioxide
Test for halide ions
What group are the halogens in?
Watch the video.
Write down the method to test for halide ions
and what happens with a positive test for each
halide.
Halide ion
IBr-
Cl-
Colour of precipitate
formed
Test for halide ions
Add nitric acid to dissolve the compound and remove
any carbonate ions (as they may form a precipitate with
the silver ions).
Then add silver nitrate and record the colour of the
precipitate.
Halide ion
Colour of precipitate formed
Cl-
White
Br-
Cream
I-
Yellow
Test for sulfate ions
Watch the video.
Write down the method to test for sulfate
ions and what happens with a positive test.
Test for sulfate ions
Add dilute nitric acid (to remove any unwanted
carbonate ions), followed by barium chloride
solution.
White precipitate tells you sulfate ions were present.
Ionic equation
Ba2+(aq) + SO42-(aq) → BaSO4(s)
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