organic analysis

Question 1

How would you distinguish a tertiary alcohol from a primary/secondary alcohol?

Answer 1

1. Add 10 cm^3 od acidified potassium dichromate soluition in a test tume
2. Warm the mixture gently in a hot water bath
3. if a colour change from orange to green occurs, it is either a 1º or 2º alcohol whereas if no colour change occurs then a 3º alcohol is the sample

Question 2

How would you distinguish an aldehyde from a ketone using Benedict’s/Fehling’s solution?

Answer 2

1. Add 2cm^3 of either to a test tube
2. Add 5 drops of the sample to test tube
3. Put the test tube in a hot water bath for a few minutes
4. If an aldehyde, colour change from blue to red. If a ketone, no colour change

Question 3

How would you produce Tollen’s reagent?

Answer 3

1. Put 2cm^3 of 0.10 moldm^-3 silver nitrate in a test tube
2. Add a few drops of dilute NaOH solution so that a light brown ppt forms
3. Add drops of dilute ammonia solution until the brown ppt dissolves completely

Question 4

What could you use Tollen’s reagent to test for?

Answer 4

Aldehyde- silver mirror forms

Question 5

How do you test for carboxylic acids?

Answer 5

Add 2cm^3 of sample to test tube
Add 1 small spatula of solid sodium carbonate
If solution begins to fizz, bubble gas through some lime water.
If limewater turns milky, the gas is CO2 so the original sample was a carboxylic acid

Question 6

How do you test for alkenes?

Answer 6

Add 2cm^3 of sample into test tube
Add 2cm^3 of bromine water to test tube
Shake
If alkene present solution goes from orange to colourless