C12: Chemical analysis
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What is chemical analysis?
The process of establishing what chemicals are present in a substance
In everyday language, what is a “pure” substance
A substance that has had nothing added to it and is in its “natural state”
In chemistry, what is a “pure” substance?
A substance made of a single element or compound
How can pure substances be distinguished from impure ones?
By their boiling and melting points
Describe the melting and boiling points of pure substances
One very specific temperature
Describe the melting and boiling point of impure substances
They change state at a range of temperatures
What is a formulation?
A complex mixture designed as a useful product
Give three examples of formulations
Fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods
What is chromatography?
A process to separate the constituents of a mixture
In paper chromatography, what is the stationary phase and what is the mobile phase?
Paper is stationary, solvent (usually water or ethanol) is the mobile
How can chromatography show the difference between pure and impure substances?
Pure ones will not separate into a number of spots
How is the Rf value calculated?
Distance moved by spot/distance moved by solvent
What does a substance’s Rf value depend on?
How soluble it is in the solvent
In chromatography, why must the substance be placed on a pencil line?
Pencil will not dissolve in the solvent (insoluble)
In chromatography, why must the solvent height be lower than the pencil line?
So that the substances do not dissolve into the solvent off the paper
How can hydrogen be tested for?
Makes a squeaky pop when a plit is placed in it
How can oxygen be tested for?
Relights a glowing splint
How can carbon dioxide be tested for?
Bubble through limewater; turns it cloudy/milky
How can chlorine be tested for?
Bleaches damp litmus paper white
What is a flame test?
A test to identify metal ions (cations)
What is the colour of the flame produced from compounds containing; lithium, sodium, potassium, calcium, copper
Crimson, yellow, lilac, orange-red, green
Which solutions produce white precipitate on addition of sodium hydroxide?
Solutions containing aluminium, magnesium, and calcium ions
How can a solution of aluminium ions be distinguished from calcium and magnesium ones?
It’s precipitate will dissolve in excess sodium hydroxide
What is the colour of the precipitate formed from the addition of sodium hydroxide to a solution containing copper (II) ions?
Blue