Organic Analysis Flashcards
Test for primary and secondary alcohols and why is there a colour change
Use acidified potassium dichromate
This oxidises the alcohol and causes an orange to green colour change
This is due to the Cr2O72- ion being orange and reduced to the Cr3+ green ion
As both primary and secondary give a colour change, fractionally distillate to collect the products produced after oxidation
This product can then be tested to see if an aldehyde or ketone was formed
Test for aldehydes or ketones (Fehlings/Benedicts solution), colour change, conditions, why it occurs
Blue solution (Cr2O72-) to brick-red precipitate (Cr3+) for aldehydes
Warm solution (hot water bath) added to test solution
Fehlings solution is an oxidising agent which only oxidises aldehydes not ketones
Test for aldehydes or ketones (Tollens reagent), colour change, conditions, why it occurs
Tollens has oxidising agent [Ag(NH3)2]+
Warm solution (hot water bath) added to test solution
Silver mirror formed on inside of test tube in aldehydes as they are oxidised
How to make Tollens reagent
Put some silver nitrate solution in a test tube
Add a few drops of NaOH and a pale brown precipitate forms
Add a few drops of dilute ammonia until precipitate dissolves
Test for carboxylic acids and limitation
React with sodium carbonate
Bubble gas through limewater as CO2 and water is produced
Only works if only carboxylic acid is present as this works for all other acids too
What is mass spectrometry for?
Finding the relative molecular mass of a compound
How does infrared spectroscopy use the bonds?
Bonds in a molecule absorb infrared radiation at characteristic wavenumbers
What 2 things do the frequency of infrared radiation absorbed by a covalent bond depend on?
The atoms on either side of the bond
The position of the bond in the molecule
What can you do with the fingerprint region?
Compare it against a library of known spectra to identify the molecule
What if there are extra peaks in the fingerprint region?
There are impurities in the sample
How does global warming happen in relation to covalent bonds
CO2, methane and water vapours covalent bonds absorb infrared radiation from the sun to re-emit some back to the Earth
