result is bromine water is decolourised (orange to colourless)
Testing for Haloalkanes:
Add NaOH (aq) and warm, acidify with HNO3 , add AgNO3 (aq)
Result: precipitate of AgX (for Cl=white, for Br=cream, for I=yellow)
Testing for alcohols:
Add acidified K2Cr2O7 (potassium dichromate(VI)) and heat
Result: colour change from orange to green for 1 0 and 20 alcohols (note: no change for 30 alcohols)
Testing for aldehydes (2 ways):
Warm with Fehling’s solution, result: brick red ppt forms (from blue solution)
Warm with Tollens’ reagent, result: “silvermirror” (Ag(s) ppt) forms
How do you test for carboxylic acids?
Add Na2CO3 (aq)
result: CO2 (g) given off - effervescence
Mass spectrometry: Used to find the relative molecular masses of organic compounds.
Mass spectrometry process:
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.
How does gas chromatography work and what does it tell you?
A 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
Why do atoms and chemical bonds absorb infrared radiation?
They are constantly vibrating - they can absorb infrared radiation that is the same frequency as their frequency of vibration
What effect do heavier atoms have on the frequency of vibration? Vibrate slower
What do the troughs on an infrared spectrum show? The 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 wavenumber of 1500cm-1
Many peaks, caused by complex vibrations of the whole molecule.
Unique to every compound, so can be used to identify compounds
What does GCMS stand for? Gas chromatography linked to mass spectrometry
What effect does a stronger bond have on the frequency of vibration? Vibrate faster
How does infrared spectroscopy work?
Every bond has a unique vibration frequency in the infrared region of the EM spectrum
Bonds absorb radiation that has the 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
How do you test for aldehydes? What is the result?
Warm with Fehling’s solution, result: brick red ppt forms (from blue solution)
Warm with Tollens’ reagent, result: “silver mirror” (Ag(s) ppt) forms