Chemical Analysis – summary
notes
pure substances are made 100% of one type of element OR
compound
impure substances are mixtures, containing more than one type of
element / compound
pure substances have fixed melting, boiling and freezing points
impure substances melt / boil / freeze over a range of temperatures
a formulation is a mixture that has been designed to do something
useful. formed by mixing several substances together in careful
quantities to produce a product with required properties.
Cation tests are used to test for the positive (usually metal) ions in a
substance.
Flame Tests
1. Dip a nichrome wire loop OR a damp splint (must be damp else
it’ll just burn with a yellow flame, may want to use as the flame will
last longer) into HCl to remove any cations that may be present and
could affect results
2. Dip wire/splint into SOLUTION you wish to test
3. hold wire/splint over a roaring blue bunsen burner flame
4. record the colour that appears:
Li+ → crimson
Na+ → yellow
K+ → lilac
Ca 2+ → orange/red
Cu 2+ → green
If a sample contains a mixture of metal ions, their flame colours may
mask each other. In this case, another method should be used.
Group 1 ions only use flame tests because they form soluble
hydroxides.
Sodium Hydroxide Test
add NaOH to an unknown solution:
Coloured precipitate: Cu 2+ → blue, Fe 2+ → green and may oxidise
to brown, Fe 3+ → brown
notes
pure substances are made 100% of one type of element OR
compound
impure substances are mixtures, containing more than one type of
element / compound
pure substances have fixed melting, boiling and freezing points
impure substances melt / boil / freeze over a range of temperatures
a formulation is a mixture that has been designed to do something
useful. formed by mixing several substances together in careful
quantities to produce a product with required properties.
Cation tests are used to test for the positive (usually metal) ions in a
substance.
Flame Tests
1. Dip a nichrome wire loop OR a damp splint (must be damp else
it’ll just burn with a yellow flame, may want to use as the flame will
last longer) into HCl to remove any cations that may be present and
could affect results
2. Dip wire/splint into SOLUTION you wish to test
3. hold wire/splint over a roaring blue bunsen burner flame
4. record the colour that appears:
Li+ → crimson
Na+ → yellow
K+ → lilac
Ca 2+ → orange/red
Cu 2+ → green
If a sample contains a mixture of metal ions, their flame colours may
mask each other. In this case, another method should be used.
Group 1 ions only use flame tests because they form soluble
hydroxides.
Sodium Hydroxide Test
add NaOH to an unknown solution:
Coloured precipitate: Cu 2+ → blue, Fe 2+ → green and may oxidise
to brown, Fe 3+ → brown
