C12 Chemical Anaylsis Flashcards
what is a pure substance?
a substance which is made up of just one substance (an element or compound)
what are the fixed points of a substance?
the melting and boiling points of an element or compound
what do impurities do to the melting and boiling points of a substance?
lower the melting point
increase the boiling point
what is a formulation?
a mixture that has been designed as a useful product with set proportions of substances in the mixture
what is the Rf value of a substance?
a measurement from chromatography: the distance a spot of substance has been carried above the base line divided by the distance of the solvent front
what is a positive test for hydrogen?
a lighted splint ‘pops’
what is the positive test for oxygen?
a glowing splint relights
what is a positive test for carbon dioxide gas?
limewater turns milky (cloudy white)
what is a positive test for chlorine gas?
damp blue litmus paper turns white (as it gets bleached)
what is the flame colour for lithium ions?
crimson
what is the flame colour for sodium ions?
yellow
what is the flame colour for potassium ions?
lilac
what is the flame colour for calcium ions?
orange-red
what is the flame colour for copper ions?
green
how do you carry out a flame test?
- dip a nichrome wire loop in HCl and heat it. dip it again in HCl
- dip wire in metal compound being tested
- hold wire in roaring blue flame of a bunsen burner
- use the colour of the flame to identify the metal ion
what is a precipitate?
an insoluble solid formed by a reaction taking place in a solution
what positive metal ions produce a white precipitate when reacted with sodium hydroxide?
aluminium
calcium
magnesium
how can you tell that aluminium ions are in a compound when sodium hydroxide is added?
it forms a white precipitate
if more sodium hydroxide is added, the precipitate dissolves
what colour precipitate is formed when copper (II) ions are present?
blue
what colour precipitate is formed when iron (II) ions are present?
green
what colour precipitate is formed when copper (III) ions are present?
brown
how do you test for carbonates?
add a dilute acid and test the gas given off using limewater to see if it is carbon dioxide
what is the test to see if halide ions are present?
add dilute nitric acid to remove carbonate ions
add silver nitrate and see if a precipitate forms
what colour precipitate is formed when iodide ions (I-) are present?
yellow
what colour precipitate is formed when bromide ions (Br-) are present?
cream
what colour precipitate is formed when chloride ions (Cl-) are present?
white
how do you test for sulfate ions?
- add dilute HCl to remove any carbonate ions
- add barium chloride solution
- a white precipitate tells you that sulfate ions are present
what are the advantages of modern instrumental methods of chemical analysis?
- highly accurate and sensitive
- quicker
- small samples can be analysed
what are the disadvantaged of modern chemical analysis?
- very expensive
- requires specialist training to use
- often gives results that can only be interpreted by comparison with data from known substances
what is flame emission spectroscopy?
an example of an instrumental method of chemical analysis
how does flame emission spectroscopy work?
- the sample is heated in a flame which excites electrons and makes them jump to higher energy levels
- when they jump back down the energy is released as light
- the wavelengths of light produced are analysed by passing it through a spectroscope
how does flame emission spectrosopy identify metal ions?
each metal ion absorbs and gives out its own characteristic radiation pattern called a line spectrum
this can then be compared with a database
how can flame emission spectroscopy be used to find out the concentration of a metal ion?
the spectrometer can measure the intensity of light with a specific wavelength for a metal ion
this can then be compared with intensities of light from known concentrations of metal ions
