RP5 - Distillation of a product from a reaction / Oxidation of Alcohols Flashcards
Reagents and conditions need for making aldehyde from a primary alcohol
Reagent - Acidified potassium dichromate (VI) solution
Conditions - Excess alcohol, warm gently, distil aldehyde out as it forms
Why does water go in the bottom of the condensor
To go against gravity. This ensure the condenser remains full of water and allows more efficient cooling so more of the aldehyde condenses.
Why are bunsen burners not used to heat the primary alcohols and what should be used instead
Organic chemical are highly flammable and could set on fire if we used a naked flame so electric heaters should be used instead.
Why is the collection flask/vessel filled with ice
So more of the aldehyde condenses and therefore improves the yield
What apparatus is needed for distillation when making aldehyde
Thermometer with bulb at the T junction connecting to the condensor
Clamped round bottom flask
Electric heater
Liebig condensor
Collection flask
Anti-bumping granules
Bung
Reagents and conditions for making a carboxylic acid from primary alcohol
Reagent - Acidified potassium dichromate solution
Conditions - Excess potassium dichromate, heat under reflux
Why must a bung NOT be used when heating under reflux
Causes build up of gas pressure which could cause an explosion.
Why are anti-bumping granules used in both reflux and distillation
Prevent formation of large bubbles.
Equipment for reflux
Vertical condensor
Water out at top and water in at bottom
Clamps on condenser and flask
Round bottom flask
Why is a thermometer needed when making aldehyde from distillation
So temperature does no go above boiling point of the aldehyde
What is fractional distillation used for
Separating liquids with similar boiling points
How to maximise yield of aldehyde
Cool the distillate/ collection vessel
Keep the temperature of the solution below the boiling point
Describe the process for fractional distillation
Heat the flask (strongly), with a Bunsen burner or electric mantle
This causes vapours of all the components in the mixture to be produced.
Vapours pass up the fractionating column.
The vapour of the substance with the lower boiling point reaches the top of the fractionating column first.
The thermometer should be at or below the boiling point of the most volatile substance.
The vapours with higher boiling points condense back into the flask.
Only the most volatile vapour passes into the condenser.
The condenser cools the vapours and condenses to a liquid and is collected.
Ethanol can be oxidised by acidified potassium dichromate(VI) to ethanoic acid in a two-step process.
In order to ensure that the oxidation to ethanoic acid is complete, the reaction is carried out under reflux.
Describe what happens when a reaction mixture is refluxed and why it is necessary, in this case, for complete oxidation to ethanoic acid.
A mixture of liquids is heated to boiling point for a prolonged time
Vapour is formed which escapes from the liquid mixture, is changed back into liquid and returned to the liquid mixture
Any ethanal and ethanol that initially evaporates can then be oxidised
