3.6 Organic Analysis
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How do you test for alkenes? What is the result ?
Shake in mixture with bromine water Positive test is orange -> colourless
How do you test for haloalkanes ? What is the result ?
*Add NaOH (aq) and warm (forms alcohol and X- ion) *Add HNO3 and AgNO3 *Result : precipitate of AgX *Chlorine is white, Bromine is cream, Ionine is yellow.
How do you test for alcohols ? What is the result ?
• Add acidified K2Cr2O7 and heat • Positive result is colour change from orange to green • No change for tertiary alcohols
What two methods are used to test for aldehydes ?
• Warm with Fehlings solution, positive is blue to red brick ppt • Add equal volume of Tollens Reagent, positive result is a silver mirror forming.
How do you test for carboxylic acids?
Add Na2CO3, positive result is CO2 being released (effervescence).
What is mass spectrometry ? How does it work ?
• Used to find relative molecular masses of organic compounds • Compound is dissolved in solution, ionised by high voltage to form +1 ions • It is then accelerated by a negatively charged plate • When they reach the plate/detector they cause a current • Time of flight is used to work out m/z value.
What does the x axis show on a mass spectrometry graph
The m/z ratio, since most ions are +1 it is effectively Mr.
Why are multiple m/z peaks produced when a molecule is put into a mass spectrometer ?
• The molecular ion is shown as a peak, but it fragments into smaller molecules which are also shown as peaks • Also, due to the isotopes of atoms, different peaks are seen.
How does gas chromatography work ?
• A stream of gas carries a mixture of vapours through a column packed with solids, different compounds move through at different speeds, so are separated • The amount of each compound can then be measured