Topic 9: Seperate Chem P2 Flashcards
What is an ion?
A charged atom, molecule or particle
Why must a test for a specific ion be unique?
Tests are used to identify ions and must be unique so that the test gives an easily observed result which is specific to the ion that is present.
Describe how you would carry out a flame test for ions
-Clean a nichrome wire using hydrochloric acid.
- Turn the Bunsen burner onto the blue flame.
- Dip the wire in a solution of the substance being tested.
- Place the wire in the flame and record the colour.
What is the result of the flame test on lithium ions?
Crimson Flame
What is the result of the flame test on sodium ions?
Yellow flame
What is the result of the flame test on potassium ions?
Lilac flame
What is the result of the flame test on calcium ions?
Orange-red flame
What is the result of the flame test o copper ions?
Blue-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 the ions will blend together so the individual flame colours won’t be seen meaning the ions can’t be identified.
What is a precipitate?
An insoluble solid suspended in a liquid.
Without using the flame test, how can you test for aqueous metal ions?
Add sodium hydroxide solution to the metal ions. Observe the colour of the precipitate.
What colour precipitate forms when sodium hydroxide reacts with calcium ions?
White
What colour precipitate forms when sodium hydroxide reacts with copper(Il) ions?
Blue
What colour precipitate forms when sodium hydroxide reacts with iron (Il) ions?
Green
What colour precipitate forms when sodium hydroxide reacts with iron (III) ions?
Brown
What colour precipitate forms when sodium hydroxide reacts with aluminium ions?
White (initially)
With excess NaOH, the precipitate re-dissolves to form a colourless solution
What is observed when sodium hydroxide reacts with ammonium ions?
A pungent smelling gas is produced
(NH3) which will turn damp red litmus paper blue.
How could you distinguish between two solutions containing aluminium ions and calcium ions?
Add excess sodium hydroxide.
Both will form white precipitates initially. The precipitate formed from aluminium ions will re-dissolve to form a colourless solution.
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, they will react with the acid to produce carbon dioxide which will turn the limewater cloudy when it is bubbled through limewater.
Write the chemical equation for the reaction between HCl and Na2CO
Na, CO3 + 2HCI → CO, + 2NaCl + H2O
How can you test for sulfate ions?
- Add HCI to remove any CO,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 BaCl, and MgSO4
BaCI2 + MgSO4 → BaSO4+ MgCl2
BaSO4 is a white precipitate
How do you carry out a test for halide ions?
- Add a few drops of nitric acid to react with any carbonate ions which might obscure the result.
- Add a couple of drops of silver nitrate.
- Observe the colour of the precipitate.
