Test for anions

Question 1

test for hydroxide ions method and equipment

Answer 1

Test 4: Test for hydroxide ions in aqueous solution

a) Test about 1 cm3 of 0.4 mol dm–3 sodium hydroxide solution in a test tube with red litmus paper or universal indicator paper.
b) Record your observations. Dispose of the test tube contents.

This approach can also be used to test for the alkaline gas, ammonia, which forms hydroxide ions when it comes into contact with water.

c) Take 5 drops of 1 mol dm–3 ammonia solution and place on a filter paper and place inside a petri dish with lid. Dampen a piece of red litmus paper with deionised water and place on the other side of the petri dish. Replace the lid and observe over a few minutes.
d) Record your observations.

 0.4 mol dm–3 sodium hydroxide solution  red litmus paper (or universal indicator paper)  1.0 mol dm–3 ammonia solution (freshly prepared)  petri dish with lid.

Question 2

test for carbonate ions

Answer 2

Test 5: Test for carbonate ions in aqueous solution

a) Have about 2 cm3 of calcium hydroxide (limewater) ready in a test tube.
b) To about 3 cm3 of 0.5 mol dm–3 sodium carbonate solution in a test tube, add an equal volume of 1.0 mol dm-3 dilute hydrochloric acid.
c) Immediately put in delivery tube with open end into the limewater test tube. Make sure that the end of the tube is below the level of the liquid.
d) Record your observations. Dispose of the test tube contents

 0.5 mol dm–3 sodium carbonate solution  0.5 mol dm–3 hydrochloric acid  0.02 mol dm–3 calcium hydroxide solution (limewater)

Question 3

test for sulfate ions

Answer 3

Test 6: Test for sulfate ions in aqueous solution

a) To about 1 cm3 of 0.1 mol dm–3 magnesium sulfate solution in a test tube, add an equal volume of dilute hydrochloric acid followed by an equal volume of 0.1 mol dm–3 barium chloride solution.
b) Record your observations. Dispose of the test tube contents.

Test 6  0.1 mol dm–3 barium chloride solution  0.1 mol dm–3 magnesium sulfate solution

Question 4

test for halide ions

Answer 4

Test 7: Test for halide ions in aqueous solution

Test for chloride, bromide and iodide ions in aqueous solution

a) Place about 10 drops of 0.1 mol dm–3 potassium chloride in a clean test tube. 
Add about 5 drops of dilute nitric acid. Shake well.
b) To the solution add another 10 drops of 0.05 mol dm–3 silver nitrate solution.
c) Then add an excess of 2 mol dm–3 ammonia solution and shake to mix thoroughly. Dispose of the tube contents
d) Repeat steps a) and b), but this time add an excess of concentrated ammonia solution, working in a fume cupboard. Dispose of the tube contents
e) Repeat steps a) to d) but using potassium bromide and then potassium iodide instead of potassium chloride.

 0.1 mol dm–3 potassium chloride solution  0.1 mol dm–3 potassium bromide solution  0.1 mol dm–3 potassium iodide solution  0.1 mol dm–3 nitric acid  0.05 mol dm–3 silver nitrate solution  concentrated ammonia solution (in a fume cupboard)  2.0 mol dm–3 ammonia solution (in a fume cupboard, freshly prepared and labelled ‘ammonia solution’).

Question 5

Test 8: Test for halide ions in solid salts using concentrated sulfuric acid

Test for chloride, bromide and iodide ions in solid potassium halides and conditions

Answer 5

Note: Gloves must be worn for this procedure

These experiments must be done in a fume hood

a) Place a small spatula of solid potassium chloride in a clean dry test tube.
b) Slowly add a few (2 to 5) drops of concentrated sulfuric acid.
c) Record what happens.
d) Test the gas evolved with moist blue litmus paper, taking care that the paper does not touch the sides of the test tube.
e) Repeat this experiment with solid potassium bromide, but this time test the gas produced using a narrow strip of filter paper that has been dipped in acidified potassium dichromate solution.
f) Repeat this experiment with potassium iodide, but this time test the gas produced using a narrow strip of filter paper that has been dipped in lead nitrate solution.

 potassium chloride solid  potassium bromide solid  potassium iodide solid  0.1 mol dm–3 lead nitrate solution (or lead ethanoate solution)  blue litmus paper  filter paper  small spatula.  concentrated sulfuric acid in dropping bottles (in a fume cupboard)  0.5 mol dm–3 acidified potassium dichromate(VI) solution (in a fume cupboard, see below)

Question 6

equipment

Answer 6

 test tubes and stoppers  test-tube racks  plastic graduated dropping pipettes  deionised or distilled water  forceps