chemical tests

test for hydrogen

hold a lit splint near the top of the test tube

hear a squeaky pop

test for oxygen

use a glowing splint

it will reignite

test for carbon dioxide

bubble the gas through limewater

limewater turns cloudy

test for ammonia

use damp red litmus paper

turns blue

test for chlorine

use damp litmus paper

turns white (bleaches)

flame test

used to show the presence of certain metal ions (cations) in a compound.

• A platinum or nichrome wire is dipped into concentrated hydrochloric acid to remove any impurities.

• The wire is dipped into the salt being tested so some salt sticks to the end.

• The wire and salt are held in a non-luminous (roaring) bunsen burner flame.

• The colour is observed.

Properties of the platinum or nichrome wire is:

• Inert

• High melting point

colours in flame tests

lithium-red

sodium-yellow

potassium-lilac

calcium- orange-red

copper- blue-green

colours of ions formed after adding sodium hydroxide

ammonium- will turn damp red litmus paper blue

copper (II)- blue precipitate

iron (II)- green precipitate

iron (III)- brown precipitate

test for carbonates

add hydrochloric acid- if present fizzing will occur

test b checking for the presence of carbon dioxide using limewater

test for halides

other impurity is sulfides

test for sulfates

other impurity is sulfides

chemical test for presence of water

Add anhydrous copper (II) sulfate (CuSO₄) to a sample.

If water is present the anhydrous copper (II) sulfate will change from white to blue.

physical test for presence of water

If the sample is pure water it will boil at 100^oC