Unit 8 - Chemical analysis Flashcards
How can we test if a substance is pure?
Pure substances have very specific melting/boiling points which can be used to test for them.
What is a formulation?
A mixture of certain quantities of substances designed to fulfil a purpose
What is chromatography?
The separating of a mixture to identify its constituent substances
What are the phases?
Stationary phase - filter paper
Mobile phase - solvent (eg water) moves up the stationary phase due to capillary action
Line is drawn in pencil so it won’t move with the solvent
How do we calculate the Rf value?
Distance substance moved ÷ distance mobile phase moved
How do we test for carbon dioxide?
Bubble through limewater to turn cloudy
How do we test for hydrogen?
Lit splint will cause a squeaky pop
How do we test for oxygen?
Glowing splint will relight
How do we test for chlorine?
Bleach blue litmus paper
What are the flame test results for metal ions?
Lithium - Crimson
Sodium - Yellow
Potassium - Lilac
Calcium - Orange/Red
Copper - Green
How do we test for metal ions in a solution?
Adding sodium hydroxide to make coloured precipitate (metal hydroxide)
How can you test for a carbonate?
Carbonates react with acid to produce carbon dioxide, then bubble solution through limewater to see if a cloudy/milky colour appears
How can you test for halide ions?
Mix with silver nitrate and nitric acid to form a precipitate. Different coloured silver halide precipitates form, depending on the halide ions present
What colour precipitate do chloride ions form?
White precipitate of silver chloride
What colour precipitate do bromide ions form?
Cream precipitate of silver bromide
What colour precipitate do iodide ions form?
Pale yellow precipitate of silver iodide
How do you test for sulphate ions?
Add hydrochloric acid and barium chloride
What colour precipitate is formed if a sulphate ion is present?
White precipitate
What colour solid precipitate is formed from solutions of metal ions?
Iron (II) - Green
Copper (II) - Blue
Iron (III) - Brown
What metal ions form a white precipitate?
-Aluminium
-Calcium
-Magnesium
How can you differentiate between the metal ions that produce white precipitates?
Add excess sodium hydroxide (NaOH)
What happens to Aluminium ions when excess NaOH is added?
Dissolves
What happens to Calcium ions when excess NaOH is added?
Unchanged
What happens to Magnesium ions when excess NaOH is added?
Unchanged
What is an instrumental method?
Flame emission spectroscopy
How does flame emission spectroscopy work?
Analyses the wavelengths of light emitted from a flame to identify ions accurately
What are the advantages of flame emission spectroscopy?
It is accurate, sensitive and rapid
