Module 1 – Development of practical skills in chemistry Flashcards
Explain the method of PAG5- Preparation of a pure organic liquid:
Purifying an organic liquid
General method:
• Put the distillate of impure product into a separating funnel
• wash product by adding either: sodium hydrogencarbonate solution , shaking and
releasing the pressure from CO2 produced or sodium chloride solution
•Allow the layers to separate in the funnel, and then run and discard the aqueous layer.
•Run the organic layer into a clean, dry conical flask and add three spatula loads of drying agent (e.g. anhydrous sodium sulphate,calcium chloride) to dry the organic liquid. When dry the organic liquid should appear clear.
• Carefully decant the liquid into the distillation flask
•Distill to collect pure product
Key points:
• Sodium hydrogencarbonate will neutralise any remaining reactant acid.
• Sodium chloride will help separate the organic layer from the aqueous layer
• The layer with lower density will be the upper layer. This is usually the organic layer
• The drying agent should be insoluble in the organic liquid and not react with the organic liquid
• Decant means carefully pour off organic liquid leaving the drying agent in the conical flask
Explain the method of distillation
In general used as separation technique to separate an organic product from its reacting mixture. Need to collect the distillate of the approximate boiling point range of the desired liquid.
Note the bulb of the thermometer should be at the T junction connecting to the condenser to measure the correct boiling point
Note the water goes in the bottom of the condenser to go against gravity. This allows more efficient cooling and prevents back flow of water.
Electric heaters are often used to heat organic chemicals. This is because organic chemicals are normally highly flammable and could set on fire with a naked flame.
Explain the method for reflux
Reflux is used when heating organic reaction mixtures for long periods. The condenser prevents organic vapours from escaping by condensing them back to liquids. The reactant vapours of volatile compound are condensed and turned to the reaction mixture.
Never seal the end of the condenser as the build up of gas pressure could cause the apparatus to explode. This is true of any apparatus where volatile liquids are heated including the distillation set up
Anti-bumping granules are added to the flask in both distillation and reflux to prevent vigorous, uneven boiling by making small bubble form instead of large bubbles
