1. Chemical tests to identify anions
Connector –
What is an anion?
What happens when potassium nitrate is heated?
What gas will turn moist red litmus paper blue?
What is the chemical test for water vapour?
An anion is an atom or group of atoms with a negative charge.

2. Experiment – Testing for anions.1
Carry out the following tests and record the test and your observations:
1. Testing for hydroxides
Use a glass rod to put a spot of sodium hydroxide on red litmus paper and on universal indicator paper. Repeat using ammonia soln.
2. Testing for carbonates and sulphites
Put a sample of sodium carbonate in a boiling tube, then carefully add an equal dilute HCl. Pour the invisible gas from the boiling tube into another boiling tube that contains 2cm3 of limewater and gently shake.
Repeat the experiment using sodium sulphite, but this time test the gas using
a piece of filter paper soaked in acidified Na2Cr2O7;
moist blue litmus paper, over the mouth of the boiling tube.
Write word and balanced symbol equations for the two decomposition reactions.

3. Hydroxides OH-

4. Write the balanced symbol equation Write the balanced symbol equation
Carbonates, sulphites
Write the balanced symbol equation
Write the balanced symbol equation

5. Carbonates

6. Sulphite ion; SO32-

7. Questions

8. Experiment – Testing for anions.2
Carry out the following tests and record the test and your observations:
3. Testing for sulphates
Put 2cm3 of sodium sulphate in a test tube add the same volume of dilute HCl, and barium chloride soln.
4. Testing for halide ions
In separate test tubes put 2cm3 of potassium chloride, potassium bromide and potassium iodide soln.,
to each one add 2cm3 of dilute nitric acid followed by 2cm3 of silver nitrate soln. – record your observations
Now add 2cm3 of dil. ammonia soln.
Then add 2cm3 of conc. ammonia soln.
Write word and balanced symbol equations for the reactions that occurred in the precipitation reactions.
(Note: Ignore the acids in tests 3 & 4.)

9. Write the balanced symbol equation
Sulphate
Write the balanced symbol equation

11. Write the balanced symbol equation
Halide ions
Write the balanced symbol equation
Silver nitrate + potassium bromide silver bromide + sodium nitrate
CREAM
Silver nitrate potassium iodide silver iodide sodium nitrate
YELLOW

12. Halide ions

13. Summary Litmus paper turns __________ if hydroxide ions are present.
If you add __________ acid to sulphite ions the __________ gas produced turns litmus paper __________ .
If you add hydrochloric acid to carbonate ions the __________ gas produced turns __________ milky.
Barium chloride solution produces a white __________ with sulphite and sulphate ions but only the __________ ion precipitate will dissolve in hydrochloric acid.
Adding acidified __________ nitrate solution to halides forms a precipitate that is white with chloride ions, __________ with bromide ions and yellow with __________ ions.
blue carbon dioxide cream hydrochloric
iodide limewater precipitate red silver
sulphite sulphur dioxide

14. Testing for anions 1
Dil. HCl
Sodium hydroxide soln..
Solid Sodium carbonate
Solid Sodium sulphite
limewater
Red litmus paper
Blue litmus paper
Solution of acidified potassium (or sodium) dichromate
Strips of filter paper (to be dipped into acidified K2Cr2O7)
UI paper
Test tubes
Boiling tubes
Test tube racks
Testing for anions 2
Dil. HCl
Dil. HNO3
Sodium sulphate soln
NaCl soln.
NaBr soln
NaI soln
Barium chloride soln.
Silver nitrate soln
Dilute Ammonia soln.
Concentrated ammonia soln
Test tubes
Boiling tubes
Test tube racks