20A.5 Flashcards
what are more separating methods
- solvent extraction
- Washing
- Drying
- Filtration
- recrystallisation
- determination of Melting temp
- determination of boiling temp
what is solvent extraction
using a solvent to remove a desired organic product from the other substances in the reaction mixture
the solvent used in solvent extraction should have which features
- the solvent should be immiscible (not form a mixture) with the solvent containing the desired organic product
- The desired organic product should be much more soluble in the added solvent than in the reaction mixture
what is the method of solvent extraction
place the reaction mixture in the separating funnel, then add the chosen solvent - it should then form a separate layer
- place a stopper at the neck of the funnel and gently agitate the contents of the funnel for a short while (put ur finger on the stopped, invert it, open the tap, agitate in a circular motion, close the tap, and return the funnel to its original position)
- allow the contents to settle to two layers
- remove the stopper and open the tap, allow the lower layer to drain into a flask, and then do the same to allow the upper layer to drain into a separate flask.
to gain more of the desired organic product in solvent extraction what should we do
add the solvent in portion for the same total volume since it removes more if the desired product.
after using solvent extraction to remove the desired organic product what should we next
the desired organic product would be mixed with the solvent used to extract it so to get it on its own we take it through simple or fractional distillation obtaining its purest version.
what is washing using for
to remove the impurities from a liquid
why might we use NaHCO3 in washing
to remove any excuses acid present (this applies to everything)
what are the features of the solvent used in washing method
it should be able to dissolve the solid impurities but as little as possible of the liquid being purified
what is the method for washing
the impure solid will be stirred in some solvent and then the mixture if filtered, if the solid is already in a filter funnel before starting we add the solvent on top of the solid, then we take the mixture but it in a separating funnel then its shaken, then we allow the two liquid layers to separate, then allow the lower layer to drain into a flask, and then do the same to allow the upper layer to drain into a separate flask.
how do we dry a organic solid
no specail technique is needed it just needs to be left in a warm place, or in a desiccator with a suitable drying agent
why do we need a drying agent
because many of the organic liquids we use may partially or fully dissolve in water, therefore water might be an impurity that needs to be removed using a drying agent
what is the features required from a drying agent
to absorb water and not react with the organic liquid
what drying agents do we use and why
we usually use anhydrous salts, such as calcium chloride, magnesium sulfate, and sodium sulfate, and we use them since the from hydrated salts, so when they come into contact with the water of the organic liquid they absorb the water as water of crystallisation
what is the method of drying
the drying agent is adding to the liquid organic product and then left or a while (before use the drying agent is powdery but after it absorbs the water it becomes more crystalline) after that we add the drying agent again if it remains and if it remains powdery this is an indication that the liquid is dry, then we remove the drying agent via decantation, or filtration
what is decantation
pouring the organic liquid of the solid drying agent
what is the principal behind recrystallisation
it is that a solid compound to dissolved in a suitable solvent that can dissolve all of or most of the impurities without dissolving the compound being purified
what is the method of recrystallisation
- add impure solid to a conical flask
- add some of the chosen solvent and warm until the mixture nears the boiling temp
- if there is undissolved solid, add further solvent and warm until the mixture boils again
- continue adding further solvent and heating until all of the soluble solid has dissolved
- if insoluble impurities are present, then hot filtration could be done using fluted filter paper in a heated funnel
- allow the liquid to cool until crystals of the organic solid have formed
- more crystals can be obtained by cooling the solution below room temp in an ice bath
- the mixture is then filtered to remove soluble impurities using a Buchner funnel or Hirsch funnel
- the crystals are washed with small amounts of ice-cold solvent and then dried in a desiccator or warm oven
why does the impure solid in recrystallisation need to be dissolved in minimum volume
to make sure that the pure solid will crystallise when the solution is cooled
why is hot filtration used in recrystallisation
to make sure that the pure solid does not recrystallise and this stage
why are crystals of pure solid formed once the solution is cooled
because the solid if less soluble in cold solvent than in hot solvent
why do we wash the crystals made in recrystallisation with ice-cold solvent
remove any soluble impurities, and to make sure that very little of the pure solid dissolves
how do you draw the Buchner and Hirsch funnels
page 276
what is filtration under reduced preasure
it is one that uses a vacuum pump such as Buchner and Hirsch funnel
