CP7 - 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 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 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 → CO2 + 2NaCl + H2O
How can you test for sulfate ions?
- Add HCl to remove any CO3 2- ions as these will obscure the results - Add a couple of drops of barium chloride - If sulfate ions are present a white precipitate of barium sulfate 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 of drops of nitric acid to react
with any carbonate ions which might
obscure the experiment - Add a couple of drops of silver nitrate
- Observe the colour of the precipitate
What colour precipitate is formed when silver nitrate is added to a 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 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 two 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.
