C8: Chemical Analysis Flashcards
How can we test to see if a substance is pure or not?
Testing to see what the melting/boiling point is
If it is pure it will be very specific
What are formulations?
Mixtures of certain substances to fulfil a specific purpose e.g.
-Paints
-Fuels
-Alloys
-Fertilisers
What is chromatography?
The separating of a mixture to identify it’s constituent substances e.g. pigments in ink, drugs in urine sample
What is the stationary phase?
What the substances move up e.g. chromatography/filter paper
What is the mobile phase?
The solvent e.g. water
How does the solvent move up the paper?
Due to capillary action
This pulls the substances in the mixture upwards, with lighter particles being moved further up the stationary phase
Where is the starting line drawn?
Just above the water line, in pencil (so it won’t move)
All measurements are made from this
What is the equation to calculate Rf (retention factor) values?
Rf value = distance substance moved/distance mobile phase moved
what can Rf values be compared against?
Known substances to identify them
What is the test for hydrogen?
Lit splint produces a squeaky pop
What is the test for oxygen?
Will relight glowing splint
What is the test for carbon dioxide?
Causes limewater to turn cloudy when bubbled through it
What is the test for chlorine?
Bleaches blue litmus paper
What do flame tests test for?
Metal ions
What colour will the flame turn if lithium is present?
Crimson
What colour will the flame turn if sodium is present?
Yellow
What colour will the flame turn if potassium is present?
Lilac
What colour will the flame turn if calcium is present?
Orange-red
What colour will the flame turn if copper is present?
Green/blue
How do we test for metal ions in a solution?
Add sodium hydroxide to make metal hydroxide (coloured precipitate)
What colour precipitate will aluminium, calcium and magnesium produce?
White
What happens when excess sodium hydroxide is added to aluminium?
The white precipitate will dissolve
What colour precipitate will copper (II) (Cu2+) produce?
Blue
What colour precipitate will iron (II) (Fe2+) produce?
Green
What colour precipitate will iron (III) (Fe3+) produce?
Brown
What is an example of an ionic equation for metal ions in a solution?
Cu2+ + 2OH- -> Cu(OH)2
How do we test for carbonates?
- React with hydrochloric acid to produce carbon dioxide
- Set up delivery tube so any gas involved will be collected
- Limewater will go cloudy
How do we test for halide ions?
Will produce a precipitate when mixed with silver nitrate & nitric acid
-Chlorine ions = white
-Bromide ions = cream
-Iodide ions = yellow
What will be produced when sulphate ions are mixed with barium chloride & hydrochloric acid?
A white precipitate
What is flame emission spectroscopy?
Involves analysing the wavelengths of light emitted from a flame, which can be used to identify ions accurately
What are benefits of flame emission spectroscopy?
It is accurate, sensitive, unbiased & rapid
What is a pure substance?
Made up of 1 element or compound
What is a mixture?
Lots of different things in it, not chemically bonded together
What is the test for pure substances?
- Get crystals of pure solution into a very, very thin tube
- Melt in melting point apparatus
- See if it melts at one temp, or slowly over a range of temperatures
Why is a lid put on the chromatography beaker?
To stop the solvent evaporating
What colour will the flame turn if barium is present?
Green
