C8 Chemical analysis Flashcards
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 melting/boiling points
Describe the melting and boiling points of pure substances
One very specific temperature
Describe the melting and boiling points of impure substances
They change state over a temperature range
How does adding an impurity affect the melting an boiling point of a substance?
It lowers the melting point and increases the boiling point
What is a formulation?
A 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 mobile
What does the number of spots on a chromatogram tell you about the chemical tested?
The number of spots is the number of compounds in the mixture
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 substances be placed on a pencil line?
Pencil will not dissolve in the solvent
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 splint 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 milky (cloudy)
Why does carbon dioxide turn limewater cloudy?
Solid calcium oxide forms
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 a lithium containing compound?
Crimson
What is the colour of the flame produced from a copper containing compound?
Green
What is the colour of the flame produced from a sodium containing compound?
Yellow
What is the colour of the flame produced from a potassium containing compound?
Lilac
What is the colour of the flame produced from a calcium containing compound?
Orange-red
Other than flame tests, how can metal ions be identified?
Use of sodium hydroxide
Which solutions produce white precipitates on addition of sodium hydroxide?
Solutions containing aluminium, magnesium, calcium ions
How can a solution of aluminium ions be distinguished from calcium and magnesium ones?
Its precipitate will dissolve in excess sodium hydroxide
How can compounds of calcium and magnesium be distinguished from each other?
Using flame tests calcium compounds produce an orange - red flame
What is the colour of the precipitate formed from the addition of sodium hydroxide to a solution containing copper (II) ions?
Blue
What is the colour of the precipitate formed from the addition of sodium hydroxide to a solution containing iron(II) ions?
Green
What is the colour of the precipitate formed from the addition of sodium hydroxide to a solution containing iron(III) ions?
Brown
What is the reaction that occurs when iron (III) reacts with sodium hydroxide?
Fe3+ + 3OH- –> Fe(OH)3
What is the test for carbonates?
Add an acid to generate carbon dioxide gas
What is the test for halides?
Add silver nitrate and nitric acid to generate a solid silver halide precipitate
What are the colours of the silver halides?
Silver chloride white, silver bromide cream, silver iodide yellow
What is the test for sulphate ions?
Add barium chloride and hydrochloric acid, forms white precipitate
What is an instrumental method?
Use of scientific technology to perform chemical analysis
What are the disadvantages of instrumental methods?
They are accurate (gives correct results), sensitive (only needs a small sample to work), rapid (a lot faster than other tests)
What are the three advantages of instrumental methods?
A trained person is needed to operate the technology, the technology can be very expensive
What is flame emission spectroscopy?
An instrumental analysis tool for identifying metal ions
How is flame emissions spectroscopy carried out?
Sample placed in a flame, light emitted is passed through a spectroscope to give a spectrum which can be compared to a reference
