Chemistry Unit 3 Chemical Tests

When you heat some metals, they burn with a distinctive colour flame.

LITHIUM - burns crimson-red

SODIUM - burns yellow-orange

POTASSIUM - burns lilac

CALCIUM -burns brick-red

BARIUM - burns green

If you add a few drops of sodium hydroxide to a solution of any of the following metals, a coloured precipitate will form.

CALCIUM - WHITE

COPPER (II) - BLUE

IRON (II) - SLUDGY GREEN

IRON (III) - REDDISH BROWN

ALUMINIUM - WHITE AND THEN TURNS COLOURLESS

MAGNESIUM - WHITE

There are 3 ways to detect ammonia:

1) It smells similar to cat wee. It is very distinctive.

2) Ammonia turns damp red litmus paper blue.

3) If you add sodium hydroxide to a solution that contains ammonia ions, ammonia is given off.

• To test for Carbon dioxide. you bubble it through limewater and if carbon dioxide is present, the limewater will turn cloudy.
• You can add dilute acid to a carbonate and test to see if carbon dioxide is released.
• If you heat some carbonates, they change colour:
• Copper carbonate turns from green to black and it stays black when cool.
• Zinc carbonate will turn from white to yellow, but will return to white when it cools.

• To test for a sulphate ion, you add dilute HCl and barium chloride solution.
• A white precipitate of barium sulphate forming tells you that the original solutions was a sulphate!

To test for chloride, bromide or iodide ions, add dilute nitric acid and silver nitrate solution.

• A chloride gives a white precipitate.
• A bromide gives a cream precipitate.
• a iodide gives a yellow precipitate.

To identify NITRATES....

• Mix solution with aluminium powder.
• Add sodium hydroxide and heat.
• Nitrate will be reduced to ammonia.
• Test for ammonia with damp red litmus paper, which will turn blue.

Other things to note are...

• Organic compounds burn when heated.
• Compounds with C=C bonds decolourise Bromine water.
• You'll need to find the empirical formula of an organic compound.