ion testing Flashcards
(21 cards)
Describe how to carry out a flame test to test for ions
Clean a nichrome wire using hydrochloric acid
Turn the bunsen burner onto the blue flame
Dip the wire into the substance being tested
Place the wire in the flame and record the colour
Colour of the flame test on lithium
Crimson
Colour of the flame on sodium
Yellow
Colour of the flame on potassium
Lilac
Colour of the flame on Calcium
Orange-red
Colour of the flame on copper
Blue-green
Why must the nichrome wire be cleaned first before carrying out a flame test?
To remove any unwanted ions that might obscure the colour of the flame
What is a precipitate
An insoluble solid suspended in a liquid
What colour precipitate forms when sodium hydroxide reacts with calcium
White
What colour precipitate forms when sodium hydroxide reacts with copper (II)
Blue
What colour precipitate forms when sodium hydroxide reacts with iron (II)
Green
What colour precipitate forms when sodium hydroxide reacts with iron(III)
Brown
What colour precipitate forms when sodium hydroxide reacts with aluminium
White, but 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
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
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
What colour precipitate forms when silver nitrate is added to a chloride solution?
A white precipitate
What colour precipitate forms when silver nitrate is added to a bromide solution?
Cream
What colour precipitate forms when silver nitrate is added to an iodide solution?
Yellow precipitate
