RP 6: Testing for Organic Functional Groups Flashcards
To determine between primary/secondary/tertiary alcohols, we add what substance and do what?
Add acidified potassium dichromate.
Warm.
When acidified potassium dichromate is added, what colour change will happen for primary and secondary alcohols?
They will change from orange to green.
What happens to dichromate ions in terms of reduction and colour change when alcohols are added?
Addition of primary and secondary alcohols causes orange dichromate ions to be reduced into green dichromate ions
What will happen to the colour change when tertiary alcohols when acidified potassium dichromate is added?
Remains orange
What are the problems with testing for primary/secondary/tertiary alcohols?
We will not be able to tell whether the alcohol is primary or secondary.
Describe 2 further tests we could do to see if an alcohol is primary.
What 2 organic molecules can be produced from primary alcohols?
Oxidise the alcohol under reflux. If it tests positive for carboxylic acid then it’s a primary alcohol.
Oxidise the alcohol under distillation. If it tests positive for an aldehyde then it’s a primary alcohol.
Describe a further test we could do to see if an alcohol is secondary.
What organic molecules can be produced from secondary alcohols?
Oxidise an alcohol under reflux. If it tests positive for a ketone, it is a secondary alcohol.
Describe how we can test for aldehydes using Tollen’s reagent.
Add Tollens
If a silver mirror forms then then the substance is an aldehyde.
What is Tollen’s made from?
[Ag(NH3)2]+ complex
Give the half equation for the reduction of silver ions in Tollens reagent.
Ag + e- -> Ag+
Describe how to test for aldehydes using Fehlings?
Add Fehlings to a test tube.
Add 5 drops of the substance you are testing.
Heat to 80C using a waterbath
If aldehydes are present, colour change from blue to brick red will occur.
Why should you use a water bath when heating aldehydes and ketones?
Aldehydes and ketones are very flammable, so could catch alight if heated with a bunsen burner.
What substance do we add to our sample when testing for carboxylic acids?
Sodium carbonate
What happens when we add the sodium carbonate to the substance if it is positive for carboxylic acid?
It will fizz and produce CO2 gas.
What are the issues with the test for carboxylic acids?
Bubbles of gas will be produced for any acid, therefore we cannot tell for sure if the acid is carboxylic.
