Required Practical 4 Flashcards
How do you test for group 2 ions?
Dilute sulphuric acid or NaOH or ammonium solution.
What changes occur when dilute sulphuric acid is mixed with group 2 ions?
Magnesium - Colourless solution.
Calcium - Slight white precipitate.
Strontium - White precipitate.
Barium - White precipitate.
What changes occur when NaOH is added to group 2 cations?
Magnesium - White precipitate.
Calcium - Slight white precipitate.
Strontium - Slight white precipitate.
Barium - Colourless solution.
What changes occur when ammonium solution is added to group 2 ions?
Magnesium - White precipitate of Mg(OH)₂
Calcium - No change.
Strontium - No change.
Barium - No change.
What is a safety precaution when testing for group 2 ions?
Some barium salts are toxic so wear gloves.
How do you test for ammonium ions?
1) Add NaOH.
2) Heat in water bath.
3) Hold damp red litmus paper over mouth of test tube.
4) If it turns blue, ammonium ions are present.
How do you test for hydroxide ions?
It will turn damp red litmus paper blue.
How do you test for carbonate ions?
1) Add a small volume of HCl to the carbonate in a test tube.
2) Use a delivery tube to transfer the gas produced into a second test tube containing limewater.
3) Shake the lime water test tube.
4) The limewater will go cloudy if carbonate ions are present.
What is the equation(s) for testing for carbonate ions?
Na₂CO₃ + 2HCl —-> 2NaCl + H₂O + CO₂
Ca(OH)₂ + CO₂ —-> CaCO₃ + H₂O
How do you test for sulphate ions?
1) Add HCl and barium chloride solution.
2) A white precipitate forms if sulphate ions are present.
Why is HCl added when testing for sulphate ions?
To remove any other compounds which may react.
What is the equation for testing for sulphate ions (MgSO₄) ?
MgSO₄ + BaCl₂ —-> BaSO₄ (s) + MgCl₂
What are the safety precautions when testing for sulphate ions?
Barium chloride is harmful so gloves and a lab coat must be worn.
What is the test for halide ions?
1) Add nitric acid.
2) Add silver nitrate.
Chloride ions form a white precipitate.
Bromide ions form a cream precipitate.
Iodide ions form a yellow precipitate.
How can halide ions be further tested?
By adding dilute and concentrated ammonia solution.
Dilute ammonia solution will dissolve a chloride ion precipitate but not the others.
Concentrated ammonia solution will dissolve a bromide ion precipitate but not an iodide ion precipitate.
