Unit Three, Chapter Thirty Three - Practical Skills and Techniques Flashcards
What is the most accurate method of measuring mass?
Weighing by difference
How to weigh by difference?
(1) Dry, clean weighing boat is weighed empty
(2) sample is added, and mass is recorded
(3) Sample is transferred to the container to be used in the experiment
(4) weighing boat and residual material are reweighed, mass is recorded
(5) accurate mass of the sample is produced from the difference between the two recorded masses
What is a desiccator?
A closed vessel that contains a drying agent (desiccant)
How to carry out vacuum filtration
(1) Mixture of a solid and a liquid is poured through a filter paper into a Büchner funnel
(2) The solid is trapped by the filter
(3) The liquid is drawn through the funnel into the flask below by a vaccum
How to carry out refluxing
(1) The liquid reaction mixture is placed in a pear-shaped flask, along with anti-bumping granules, with a condenser at the top
(2)The flask is heated vigorously over the course of the chemical reaction
(3) Any vapours given off are immediately returned to the reaction vessel as liquids when they reach the condenser
What is the purpose of anti bumping granules?
To minimise the tendency for violent boiling, which is a safety hazard
Why is distillation used?
To purify a compound from a mixture of liquids by a process of hearing and cooling the liquids to separate them rom each other
Why is vacuum filtration used?
To separate a solid from a liquid
Why is refluxing used?
To apply heat energy to a chemical reaction mixture over an extended period of time
What is solvent extraction used for?
To purify a compound by using its different solubility between two solvents
How to carry out solvent extraction
(1) The aqueous layer is added to the separating funnel
(2) The organic solvent is then added to the funnel
(3) The stopper is put on firmly and then the funnel is inverted
(4) The tap is opened to release any pressure build-up caused by the solvent vaporising
(5) The tap is closed and the mixture is inverted several more times over the course of a few minutes
(6) The layers are then allowed to separate, the lower aqueous layer can be removed by turning the tap, the top organic layer is collected in a separate flask
(7) Not all the product will have been extracted, so the aqueous layer is mixed with fresh organic solvent to extract more of the remaining product (repeat x2/3)
(8) Organic solvent and product are then treated with an anhydrous salt to remove any remaining water
(9) Salt is removed by filtration
What is recrystallisation used for?
To purify solids by removing unwanted by-products
How to carry out recrystallisation
(1) Dissolve the impure crystals in the minimum volume of hot solvent
(2) Filter the hot solution to remove any insoluble impurities
(3) Allow the solution to cool and crystallise
(4) Filter off the crystals using vacuum filtration and wash with cold solvent
(5) Allow the crystals to dry in the oven and then cool in a desiccator
