Synthesis Techniques Flashcards
When do you heat under reflux?
In reactions involving volatile liquids to ensure reactants/products do not escape.
What is the method for heating under reflux?
- Add anti-bumping granules to a round bottom flask.
- Do not stopper the flask.
- Attach a condenser vertically to the flask and allow cold water to flow through it.
- Heat reaction mixture so that it boils gently, using a heating mantle.
What is the method of purifying an organic liquid mixed with another immiscible liquid?
- Add liquid to a separating funnel.
- Allow the layers to settle then run off and dispose of the aqueous layer.
- IF acidic impurities are present, add sodium hydrogen carbonate and shake well.
- IF the crude product is alkali, and needs neutralising, add dilute acid until the mixture is neutral.
- Dry the crude product by adding anhydrous sodium sulfate and swirling the mixture.
- The pure product can then be separated by distillation.
What is the method for making water-soluble inorganic salts from acid and SOLUBLE base?
- Carry out an acid-base titration (with an indicator) to find out how much acid solution is needed to neutralise 25cm³ of the alkaline solution
- Transfer 25cm³ of an alkaline solution to a clean conical flask.
- Using a biuret add the correct amount of acid to neutralise the alkali (don’t add indicator).
- Transfer the neutralised solution to a clean evaporating basin and heat over a bunsen flame to remove the water until crystals begin to form.
- Leave the mixture to cool in the evaporating basin
- Filter and wash solid with cold distilled water.
- Heat the solid to dry (below the boiling point), cooling and weighing periodically until there is no change in mass.
What is the method for making water-soluble inorganic salts from acid and INSOLUBLE base?
- Warm excess insoluble base in dilute acid until the solution is neutralised. Leave to cool
- Filter off excess base and transfer filtrate to a clean, dry evaporating basin to heat until crystals start to appear.
- Allow it to cool before filtering the mixture and washing the solid residue in cold distilled water.
- Heat the solid to dry (below the boiling point), cooling and weighing periodically until there is no change in mass.
What is the method for making water-insoluble inorganic salts from soluble salts in solution?
- Add equal volumes of the desired salt solutions in a beaker to form a precipitate of the insoluble salt and filter.
- Wash precipitate several times with cold DI water.
- Heat the solid to dry (below the boiling point), cooling and weighing periodically until there is no change in mass.
Describe the method of separating mixtures of miscible liquids with unique boiling points.
Simple distillation.
- Put anti-bumping granules in a pear-shaped flask and set up distillation apparatus (with a thermometer).
- Heat the mixture with a bunsen flame (or heating mantel) until it boils gently.
- When the vapour is about two degrees lower than the boiling point place a conical flask at the end of the condenser.
- Collect until the temperature rises above the boiling point
- Repeat if there are more compounds in a clean conical flask.
What is recrystallisation used for?
To purify solid crude organic products with small amounts of impurities.
Describe the method to purify solid crude organic products with small amounts of impurities.
Recrystallisation:
- Select a solvent that your products is soluble in when hot and insoluble when cold.
- Dissolve the mixture in the minimum quantity of hot solvent and hot vacuum filter to remove any insoluble impurities.
- Leave the filtrate to cool until crystals form and collect via vacuum filtration.
- Allow the solid to dry under an inverted filter funnel.
Describe the method for vacuum filtration.
- Connect a conical flask to a vacuum pump via the sidearm and dampen a piece of filter paper in the Buchner funnel.
- Switch on the vacuum pump and then carefully pour in the mixture to be filtered.
- Disconnect the pump from the flask before turning off the pump to avoid ‘suck back’.
