3.3.6 organic analysis

Question 1

how do you test for primary and secondary alcohols?

Answer 1

reagent: sample solution + potassium dichromate solution acidified with dilute sulphuric acid
positive: orange to green colour change
explanation : alcohol is oxidised so potassium dichromate is reduced to chromium ions

Question 2

how do you test for alkenes?

Answer 2

reagent : shake sample solution with a few drops of bromine water
positive : orange to colourless
explanation : double bond breaks and a dibromoalkane is formed

Question 3

how do you test for carboxylic acids?

Answer 3

reagent : add sodium carbonate
positive: fizzing bubbling or effervescence
explanation: acid base reaction occurs producing co2

Question 4

how do you test for aldehydes using Tollens?

Answer 4

reagent : add tollens and warm
positive : silver mirror if aldehyde is present
explanation: tollens acts as an oxidising agent, oxidation of aldehyde
into a carboxylic acid, tollens reduced to solid silver

Question 5

how do you test for aldehydes using fehlings?

Answer 5

reagent : add fehlings
positive: brick red precipitate
explanation: fehlings reagent is oxidising agent, oxidation of aldehyde into carboxylic acid

Question 6

how do you test for halogenoalkanes ?

Answer 6

reagent: add NaOH then warm then add silver nitrate
positive: precipitate formed
explanation: nucleophilic substitution of halogenoalkane to form an alcohol

Question 7

what colour precipitates do chloride, bromide and iodide form?

Answer 7

chloride : white
bromide : cream
iodide : yellow

Question 8

what does mass spectroscopy do?

Answer 8

determine the m/z of a peak to several decimal places
can help distinguish between compounds that have very similar relative mrs

Question 9

in infrared spectroscopy what is the fingerprint region?

Answer 9

part of infrared spectra that can be compared to a database to identify the molecule