C12.4 Testing for positive ions
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How can you carry out a flame test carefully?
Use a nichrome wire loop and dip it in concentrated HCL acid and then heat it to clean it first
What happens after you clean the wire loop?
Dip it in acid again and dip it into that metal compound that is being tested Hold the loop in the roaring blue flame of a bunsen burned Identify the metal ion in the ompound
What happens if the compound contains a mixture of metal ions?
Some flame colours can be masked E.g the intense yellow colour of sodium ions can dominate other colours
What is the colour when Lithium is added to a Bunsen burner?
Crimson
What is the colour when Sodium is added to a Bunsen burner?
Yellow
What is the colour when Pottasium is added to a Bunsen burner?
Lilac
What is the colour when Calcium is added to a Bunsen burner?
Orange-red green
What is the colour when copper is added to a Bunsen burner?
Green
How can you test for metal cations?
Test with sodium hydroxide Can be used to identify metal ions that form insoluble hydroxides in precipitation reactions
What colour does Al, Ca and Mg make when reacting with sodium hydroxide?
Forms white precipitates
How can you distinguish between Aluminium, Calcium and Magnesium?
Add more sodium hydroxide and then the precipitate formed with aluminum ions dissolves However Mg and Ca will not dissolve
How can you distinguish between Mg and Ca?
Do a flame test Calcium gives of an orange-red flame Magnesium produces no colour at all
What is the colour when Copper(II) is added to sodium hydroxide?
Blue precipitate appears
What is the colour when Iron (II) is added to sodium hydroxide?
Green precipitate
What is the colour when Iron (III) is added to sodium hydroxide?
Brown precipitate