U4- Extraction and purification Flashcards
Distillation
Used to purify a compound by separating it from a non-volatile or less-volatile material.
Has two applications:
>Identification of a compound (thro boiling point)
>Purification of a compound (as they have different boiling points)
Distillation Setup
Steam distillation
Special type of distillation for temperature sensitive materials like natural aromatic compounds.
Steam distillation (http://bit.ly/1neY5aK)
Fractional distillation
separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which one or more fractions of the compound will vaporise. Used in the oil industry in the separation of crude oil into fractions that are used mostly as fuels.
Fractional distillation (http://rsc.li/2bVREXX)
Possible experiments for distillation include:
Preparation of benzoic acid by hydrolysis of ethyl benzoate; Preparation of ethyl ethanoate (http://bit.ly/1PbLXO5) ;
Preparation of cyclohexene from cyclohexanol.
Refluxing/Heating under reflux
technique used to apply heat energy to a chemical reaction mixture over an extended period of time. The liquid reaction mixture is placed in a round-bottomed flask along with anti- bumping granules with a condenser connected at the top. The flask is heated vigorously over the course of the chemical reaction; any vapours given off are immediately returned to the reaction vessel as liquids when they reach the condenser.
Possible experiments to use Refluxing include:
Preparation of benzoic acid by hydrolysis of ethyl benzoate; Preparation of ethyl ethanoate.
(https://bit.ly/2n4gpW5)
Vacuum filtration
Vacuum filtration can be carried out using a Buchner funnel. These methods are carried out under reduced pressure and provide a faster means of separating the precipitate from the filtrate.
Possible experiments for FD include:
Preparation of benzoic acid by hydrolysis of ethyl benzoate; Preparation of ethyl ethanoate.
Preparation of potassium trioxolatoferrate(III);
Preparation of aspirin;
Preparation of benzoic acid by hydrolysis of ethyl benzoate; Identification by derivative formation.
Hot filtration
For a funnel with a perforated plate, filtration material in the form of filter paper is placed on the plate, and the filter paper is moistened with a solvent to prevent initial leakage. The liquid to be filtered is poured into the cylinder and drawn through the perforated plate/fritted glass disc by vacuum suction.
Hot filtration method is mainly used to separate impure solids from a hot solution. This is done in order to prevent crystal formation in the filter funnel and other apparatuses that comes in contact with the solution. As a result, the apparatus and the solution used are heated in order to prevent the rapid decrease in temperature which in turn, would lead to the crystallization of the solids in the funnel and hinder the filtration process.
Videos
How to use a Buchner funnel - http://bit.ly/1TV62wb Vacuum filtration - http://bit.ly/22ZuoLm
Recrystillation
laboratory technique used to purify solids, based upon solubility. The solvent for recrystallisation must be carefully selected such that the impure compound is insoluble at lower temperatures, yet completely soluble at higher temperatures. The impure compound is dissolved gently in the minimum volume of hot solvent then filtered to remove insoluble impurities. The filtrate is allowed to cool slowly to force crystallisation. The more soluble impurities are left behind in the solvent.
Recrystallisation can also be achieved where the pure compound is soluble in the hot solvent but not the cold solvent and the impurities are soluble in the hot and cold solvent. The impure compound is dissolved in the hot solvent. As it cools down the impurities stay in the solvent and can be filtered off.
Selection of a suitable solvent for recrystallisation
Neither the compound nor the impurities should react with the solvent. Other factors to consider will be the solubility of the compound and the impurities in the solvent, and the boiling point of the solvent (if the boiling point is too low, it will not be possible to heat the solvent to dissolve the impurities as it will evaporate off too easily).
Possible experiments include:
Preparation of benzoic acid by hydrolysis of ethyl benzoate; Preparation of potassium trioxalatoferrate(III);
Preparation of acetylsalicylic acid.
Solvent extraction
Solvent extraction can be an application of the partition of a solute between two liquids. It is based on the relative solubility of a compound in two different immiscible liquids, usually water and an organic solvent. The partition coefficient is expressed as the concentration of a solute in the organic layer over that in the aqueous layer. The two solvents form two separate layers in the separating funnel and the lower layer is run off into one container and the upper layer is poured out into another container. The quantity of solute extracted depends on the partition coefficient and on the number of times that the process is repeated.
Possible experiments include:
Preparation of ethyl ethanoate; Extraction of caffeine from tea.
The largest risk when using a separating funnel
Pressure accumulates during mixing if gas evolving reactions occur. This problem can be easily handled by simply opening the stopper at the top of the funnel routinely while mixing. This should be done with the top of the funnel pointed away from the body. When shaking, hold the stopper in place or it can become dislodged causing the liquids will spill. To account for this, simply hold the stopper in place with one hand.
Liquid-liquid extraction using a separating funnel - http://bit.ly/1OPnUZo Industrial extraction of caffeine - http://bit.ly/22ZuvXg
