Required practical 7 - Identifying ions Flashcards
How do you carry out a flame test to identify metal ions?
- Clean a platinum wire loop by dipping it in HCl and then holding it in the blue flame of bunsen burner until it burns without any colour.
- Dip the loop into the sample you want to test and put it into the blue flame of the bunsen burner.
- Record the colour of the flame.
List precautions to take when using a bunsen burner
- Don’t leave unattended.
- Turn off gas or leave on orange safety flame when not in use.
- Tie back long hair.
- Keep flammable chemicals away from the flame.
What is the result of the flame test on lithium ions?
Lithium ions, Li⁺: crimson flame
What is the result of the flame test on sodium ions?
Sodium ions, Na⁺: yellow flame
What is the result of the flame test on potassium ions?
Potassium ions, K⁺: lilac flame
What is the result of the flame test on calcium ions?
Calcium ions, Ca²⁺: orange-red flame
What is the result of the flame test on copper ions?
Copper ions, Cu²⁺: green flame
Why must the wire be cleaned before carrying out a flame test?
To remove any unwanted ions that might obscure the colour of the flame.
Why can a flame test not be used when a compound contains a mixture of metal ions?
The flame colours of some ions may be hidden by the colours of other metal ions.
How can you test for carbonate ions?
- Add a few drops of HCl to the sample containing carbonate ions in a test tube.
- Connect this test tube to a test tube of limewater.
- If carbonate ions are present, carbon dioxide will be produced. Limewater will turn cloudy when CO₂ is bubbled through.
Write the chemical equation for the reaction between HCl and Na₂CO₃
Na₂CO₃ + 2HCl → 2NaCl + CO₂ + H₂O
How can you test for sulphate ions?
- Add HCl to remove any CO₃²⁻ as these will obscure the results.
- Add a couple of drops of barium chloride.
- If sulphate ions are present a white precipitate of barium sulphate will form.
Write the chemical equation for the reaction between BaCl₂ and MgSO₄
BaCl₂ + MgSO₄ → BaSO₄ + MgCl₂
BaSO₄ is a white precipitate.
How do you carry out a test for halide ions?
- Add a couple drops of nitric acid to react with any carbonate ions which might obscure the experiment.
- Add a couple drop of silver nitrate.
- Observe the colour of the precipitate.
What colour precipitate is formed when silver nitrate is added to chloride solution?
White precipitate of silver chloride.
What colour precipitate is formed when silver nitrate is added to a bromide solution?
Cream precipitate of silver bromide.
What colour precipitate is formed when silver nitrate is added to an iodide solution?
Yellow precipitate of silver iodide.
What colour precipitate forms when sodium hydroxide reacts with calcium ions?
White precipitate.
What colour precipitate forms when sodium hydroxide reacts with copper(II) ions?
Blue precipitate.
What colour precipitate forms when sodium hydroxide reacts with iron(II) ions?
Green precipitate.
What colour precipitate forms when sodium hydroxide reacts with iron(III) ions?
Brown precipitate.
What colour precipitate forms when sodium hydroxide reacts with aluminium ions?
White precipitate forms at first.
Redissolves with excess NaOH to form a colourless solution.
What colour precipitate forms when sodium hydroxide reacts with magnesium ions?
White precipitate.
Given 2 solutions, how can you identify which contains aluminium ions and which contains magnesium ions?
Add excess sodium hydroxide.
Both will form white precipitates but the one containing aluminium ions will redissolve to form a colourless solution.
