Chapter 3.1- Testing for Ions

Question 1

What is the procedure to test for carbonate ions (CO3^2-)?

Answer 1

• add a dilute strong acid to the suspected carbonate

- collect any gas formed and pass it through limewater

Question 2

What is the positive test observations for carbonate ions?

Answer 2

• fizzing/colourless gas is produced

- the gas turns limewater cloudy

Question 3

What is the procedure to test for sulfate ions (S04^2-)?

Answer 3

-add dilute HCl and barium chloride to the suspected sulfate

Question 4

What is the positive test observations for sulfate ions?

Answer 4

a white precipitate of barium sulfate is produced

Question 5

What is the procedure to test for halide ions?

Answer 5

• dissolve suspected halide in water
• add an aqueous solution of silver nitrate
• note the colour of any precipitate formed
• if the colour is hard to distinguish then add aqueous ammonia (first dilute, then concentrated)
• note the solubility of the precipitate in aqueous ammonia

Question 6

What is the positive test observations for chloride ions and what it the equation of the reaction?

Answer 6

• silver chloride is formed
• white precipitate which is soluble in dilute NH3 (aq)
• Ag^+(aq) + Cl^-(aq)===AgCl(s)

Question 7

What is the positive test observations for bromide ions and what is the equation for this reaction?

Answer 7

• silver bromide is formed
• cream precipitate which is soluble in conc NH3 (aq) only
• Ag^+(aq) + Br^-(aq)==AgBr(s)

Question 8

What is the positive test observations for iodide ions and what is the equation for this reaction?

Answer 8

• Silver iodide is formed
• yellow precipitate which is insoluble in dilute and conc NH3(aq)
• Ag+(aq) + I^- ==AgI(s)

Question 9

What is the procedure to test for ammonium ions, NH4^+?

Answer 9

• add sodium hydroxide solution to the suspected ammonium compounds and warm very gently
• test any gas evolved with red litmus paper

Question 10

What are the positive test observations for ammonium ions and what is the equation?

Answer 10

• ammonia gas will turn red litmus paper blue
• ammonia gas has a distinctive smell (Ammonia gas is hazardous-this should be tested with care.)
• NH4^+(aq) + OH^-(aq)==NH3(aq) + H20(aq)

Question 11

What order should you carry out the anion tests in?

Answer 11

1. carbonate test
2. sulfate test
3. halide test

Question 12

Why do you need to carry out test for anions in a particular order?

Answer 12

• carbonates give a positive result for the sulfate test (BaCO3)
• sulfates can give a positive result for the halide test (Ag2SO4)