organic analysis Flashcards
how do you test for alkenes
shake with bromine water
result = bromine water decolourised from orange to colourless
how do you test for haloalkanes
add NaOH (aq) and warm, acidify with HNO3, add AgNO3
result: precipitate of AgX
Cl=white
Br=cream
I=yellow
how do you test for alcohols
add acidified K2Cr2O7 and heat
colour change from orange to green for primary and secondary alcohols
how do you test for aldehydes
- warm with Fehlings
- warm with Tollens
how do you test for carboxylic acids
add Na2CO3
result CO2 given off = effervescence
what is mass spectrometry
used to find the relative molecular masses of organic compounds
compound is dissolved in solution, ionised by a high voltage supply (to mostly 1
+ ions), accelerated by a negatively charged plate, becomes a beam of ionised molecules, reach detector and cause a current to flow. time of flight used to work out m/z value and plot graph
what does the x axis show on a mass spectrum
show m/z value (mass / ionic charge)
since most ions are +1 this effectively shows Mr
why are there multiple peaks when molecules are put into a mass spectrometer
molecular ion is shown as a peak, but will also fragment into smaller molecules, so these peaks are shown as well
also, due to isotopes of atoms, different peaks may be seen
how does gas chromatography work and what does it tell you
stream of gas carries a mixture of vapours through a column packed with solids, different compounds move through at different speeds, so they are separated
the amount of each compound can then be measured
what does GCMS stand for
gas chromatography linked to mass spectrometry
what might GCMS be used for
powerful chemical analysis - forensic work, measuring water pollution, drug testing on athletes, racehorses
what is high resolution mass spectrometry
gives Mr to 3 dp or 4 dp
what does high resolution mass spectrometry allow
distinguish between compounds that have same Mr to nearest whole number, but are made up of different atoms and therefore have different values of Mr to 3dp
why do atoms and chemical bonds adsorb infrared radiation
constantly vibrating - they can absorb infrared radiation that is the same frequency as their frequency of vibration
what effect does a stronger bond have on the frequency of vibration
vibrate faster (with higher frequency)
what effect do heavier atoms have on the frequency of vibrations
vibrate slower (lower frequency)
how does infrared spectroscopy work
every bond has a unique vibration frequency in the infrared region of the EM spectrum
bonds adsorb radiation that has same frequency as their frequency of vibration
infrared radiation emerged from a sample is missing the frequencies that have been absorbed - this information can be used to identify the compound’s functional group
what happens inside an infrared spectrometer
beam of infrared radiation with a range of frequencies is passed through the sample
radiation that emerges is missing frequencies that have been absorbed by the bonds in the sample
graph is plotted of intensity against frequency of radiation
what do the troughs on an infrared spectrum show
frequencies where radiation has been absorbed - match to table to find out which bonds they represent
what is the fingerprint region
area of the infrared spectrum below wavelength of 1500 cm-1
many peaks, caused by complex vibrations of the whole molecule. unique to every compound, so can be used to identify compounds
