Prepartaion For Organic Practical Flashcards
When something is combusted what are the possible observations and what could they mean?
It burns with a clear non-smokey flame. Low carbon to hydrogen ratio, could be an alcohol.
It burns with a smokey flame. High carbon to hydrogen ratio. Could be a cyclic alkane or cyclic alkene.
What are the only types of compounds they could ask about?
Hydrocarbons, alcohols and halogen alkanes.
If a substance is added to water, what are the two possible observations and what do they mean?
Two layers can form- it does not hydrogen bond with the water.This means a halogen alkane as they don’t have strong dipoles.
It can dissolve fully- it hydrogen bonds with the water meaning a short chain alcohol.
How can the C=C bond be tested for?
Add bromine water, stopper test tube and shake. If the C=C is present it will go colourless and two layers will form.
Add dilute sulphuric acid then potassium manganate (VII). Shake or put in a beaker of warm water. If C=C present the purple solution will go colourless and two layers will form.
How can the OH group be tested for?
Add a small piece of sodium or add solid phosphorus chloride and test the gas formed with damp blue litmus paper or a glass rob dipped in concentrated ammonia.
If sodium is added to a solution and it contains the OH group, what will happen?
Bubbles form and sodium dissolves. A white solid forms in its place.
What is the test for alcohol?
Add phosphorus pentachloride. It should produce Steamy fumes that turn blue Litmus paper red.
You could also add a dichromate. It should go from Orange to green. This will only happen with primary and secondary secondary alcohol.
How do you tell the difference between a tertiary alcohol and other alcohols?
Add dilute sulphuric acid and aqueous potassium dichromate (VI) then warm in a beaker of hot water.
When testing to find differentiate between tertiary and other alcohols what are the possible observations and what do they mean?
The orange solution can turn green meaning it is a primary or secondary alcohol.
It if stays orange it is a tertiary alcohol.
How do halogenalkanes react with water?
They are insoluble and will form 2 layers.
How do you test for the C-Cl, C-Br and C-I group in halogenalkanes?
Add ethanol and aqueous silver nitrate and dilute nitric acid. Stand in hot water.
White precipitate= C-Cl group.
Cream precipitate= C-Br group.
Yellow precipitate = C-I group.
How can the identity of the halogen in the precipitate formed by adding silver nitrate be found?
Add ammonia solution.
Dissolves in dilute ammonia= AgCl a chloroalkane
Soluble in concentrated ammonia= AgBr a bromoalkane
Insoluble in concentrated ammonia= AgI an iodoalkane.
How do you oxidise a primary or secondary alcohol?
Distill it with sulphuric acid and potassium dichromate (VI) and it will form an aldehyde.
If you heat it under reflux it will form a carboxylic acid.
Water will also form in both instances.
What happens when a secondary alcohol is refluxed with an oxidising agent?
It will form a ketone and water.
What is Brady’s reagent used for?
Add it to an aldehyde or ketone and it will give a yellow or orange precipitate.
