distillation

Question 1

distillation

Answer 1

-is the process in which a liquid is vaporized, re-condensed (turned back into liquid) and collected in a container
-distillation may be defined as the separation of the constiteunts of a mixture including a liquid by partial vaporization of the mixture and separate ollection of the vapors

Question 2

seperation may include

Answer 2

-separation of a liquid from non-volatile impurites
-the separation of a liquid from one or more other liquid, with which it may be miscible, partially misicble or immicible

Question 3

apparatus

Answer 3

the process of vaporizing a liquid mixture in one vessel and condensing the vapors into another vesse is called distillation
-the liquid being distilled is heated in a flask, which is sometimes called a ditillation flask or distillation pot or still
-the vapors are condensed on a cool surface usually water-cooled condenser
-the boiling point of mixtures depends upon mole fractions of the component present:
-in pure substances the temperature remains constant during distillation process so long as both vapor and liquid are present
-in miscible liquid mixtures the temperture increases throughout process become composition of vapor changes continuosly

Question 4

type of disillation

Answer 4

-simple distillation
-fractional distillation
-steam distilltion
-vacuum distillation
-destructive distillation

Question 5

simple distillation

Answer 5

-is a process if converting a liquid into its vapors, transferring the vapors to another place, and recovering the liquid by condensing the vapour, usually by leading contact with a cold surface. The apparatus used consist of three parts:
-still in which volatile material is vaporized
-condenser in which vapours are condensed
-reciever in which distillate is collected
-can produce patial separation of components with different boiling points in a liquid micture
-the process is generally used for separation of liquids from non-volatile solids e.g prepartion of distilled water and recovery of alcohol in the preparation of dry extracts
-is practiced for a mixture in which the boiling points of the components differ by at least 70C
-it is also followed for the mixture contaminated with nonvolatile particles (solid or oil) and those that are nearly pure with less that 10% contamination

Question 6

double distillation

Answer 6

is the process of repeating distillation on the collected liquid in ordro to enhance the purity of the separated compounds

Question 7

process for simple distillation

Answer 7

-on laboratory scale, a distillation flask with side arm slopping downwards is used
-the temp at which the vapors distil is observed on a thermometer
-thermometer is inserted through a corsk and having its bulb just below the level of the side arm
-the size of the flask should be good enough to hold the volume double than required volume
-bumping due to heating is avoided by adding a small chip of porous pot before the start of distillation in the flask
-if the process is interrupted, a fresh chip should be added. they will prevent superheating of the liquid being distilled and they willl cause a more controlled boil, elimination he possiblity that the liquid in the distillation flask will bump into the condenser
-chips should not be added to the superheated liquid, otherwise an instantaneous evolution of a large volume of vapours will occur

Question 8

condenser

Answer 8

a condenser is a heat exchanger its surface is kept colid by a stream of cold water. it should have the following properties:
-constuction of condenser should be such that it can be easily cleaned
-the broken parts may be easily replaced so that the cost of new one is saved
-provide maximum cooling surface because the rate of condensation is directyl proportional to the cooling area
-condensing surface should be good conductor of heat, therefor where practicable metal condensers are preferred over glass
-water used for cooling must leave the condenser quickly so as to provide space for water to get in and provide cold surface
-water must flow in opposite direction to vapors so that the condensed liquid should leave the condenser in as cool a condition as possible

Question 9

limitation of simple distallation

Answer 9

-it produces a distillae that is always impure at any temp range between the ranges of boiling points of the components. therefore, it is impossible to completely separate the components in a mixture with simple distillation
-relatively pure substances can be obtained froma mixture with simple distillation of the boiling points of the componenets differ by a large amount (>70C)
-this may be very tedious pocess involving large number of distillationp

Question 10

properties of simple distillation

Answer 10

-simple set up
-fast process
-consumes less energy
-poor separation
-best for relatively pure liquid

Question 11

application of simple distillation

Answer 11

-for purification of organic liquid
-separation of liquid from non-volatile solids- recovery of alcohol in the preparation of dry extracts
-preparation of different substances-ethyl amyl nitrate
-preparation of distilled water
-identification

Question 12

fractional distillation

Answer 12

-one of the most common separation methods when purifying liquid organic samples
-especially to searate miscible volatile liquid having different boiling points ez. mixture of alcohol and water
-it s quite easy to separate a liquid from non-volatile solids by impe distillation but it is very difficult to separate two volatile liquids completely from each other by simple distillation
-the fractional distillation accomplishes the same condensation cycles, by inserting a fractionaing column between distillation flask and the distillation head
-the fractionaing coolumn subjects the mixture to many condensation cycles as the material moves up the column toward distillation head. with each cycle within the column, the composition of th vapor is progessively enriched in the lower boiling liquid. this process continues until most of the the lower boiling compound is removed from the original mixture and condesnsed in the recieving flask

Question 13

process of fractional d

Answer 13

-as the mixture is heated, the temperature rises until it reaches the temperature of the lowest boiling substance in the mixture, while the other components of the mixture remain in ther original phase in the mixture. the resultant hot vapour passes into condenser and is converted to the liquid, which is then collected in a reciever flask
-when the lower boiling liquid is effectively removed from the oiginal mixture, the temperature rises and second fraction containing some of both compounds produced. as the temperature approaches the boiling point of the high boiling point compound the distillate condensing into the third recieving flask is increasingly more pure in the higher boiling point compound

Question 14

principle of fractional distillation

Answer 14

-the principle is based on the estlishment of a large number of theoritical vaporization-condensation cycles
-the apparatus of a simple distillation is modified by inserting a fractioning column between the distillation flask and the distillation head
-the fractioning column provides a large surface area in which the intitial distillate is redistilled and condensed again
-this process continues as the vapours rise up the column until the vapous finally make it into the condenser
-these vapors and the final distillate wll contain a greater percentage of lower boiling liquid
-contineous repition of redistillation process in fractional distillation gives good separation of the volatile liquid components

Question 15

azeotropic mixture

Answer 15

-or constant boiling mixture is one in which composition of the liquid and the vapour in equilibrium with it is the same
-their proportion cannot be altered by simple distillation
-the mixture behaves like a pur liquid and distils without change in composition or boilung pount
such mixture cannot be separated into their pure components by simple distillation
eg) alcohol and water, alcohol and benzene, alcohol and chloroform

Question 16

ternary mixtures

Answer 16

mixtures of three components, which do not for azeotraps may be seprated by fractional distillation

Question 17

properties of fractional distillation

Answer 17

-complicated
-slow
-consumes more enrgy
-better separation
-best for mixtures with close B.P

Question 18

application of fractional disillation

Answer 18

-separtion of two immiscible liquid having different boiling points
-separaition of ternary mixtures
-manufacture of alcohol

Question 19

steam distillation

Answer 19

-special type of distillation for temp sensitive materials like natural aromatic compounds
-many organic compounds tend to decompose at high sustained temp. separation by norma distillation would then not be an option, so water or steam is introduced into the distillation apparatus
-by adding water or steam, the boiling points of the compounds are depressed, allowing them to evaporate at lower temperatures, preferably below the temperatures at which the deterioation of the material becomes appreciable
-steam distillation is used for the distillation of water-immiscible liquid of high boiling points, ex) turpentine, aniline
-by bubbling steam through the liquid the mixture boils at below the nomal boiling point of the either component
-the distllate consists of the two liquids in the sae proportions as in the vapour ex) tupenie has a boiling point of 160C, when mied with water it can be distilled at about 95.6C

Question 20

steam distillation principle

Answer 20

-this method is based on the fact that, total vapor pressure above a mixture of two immiscible liquids is equal to the sum of the vapor pressure of the individual liquids
…….formula
-steam is contineously paused over the impure organic liquid, the steam heats the liquid and gets condensed into water itself
-the resulting mixture of liquid and water begins to boil when the vapor pressye above the mixture becomes equal to the atmospheric pressure
-hence the mixture of the two immiscible liquids will boi at a temperature lower than the normal boilng poits of both the liquid
-the mixture will continue to boil at the same temperature until one of the liquids is completly distilled out
-the distillate, which contains water and the liquid separates out into two layers as both are immiscible
-the two layers can be separated using separated funnel

Question 21

steam distilation process

Answer 21

-the impure compound and water are placed in a distillation flask kept at a sight slant position and heated on a sand bath
-steam is then bubbled through this mixture
-the vapours of the compound,along with steam, leave the flask from the outlet and get condensed in the water condenser
-the condensate collected in the reciever is transferred to a separating funnel
-the liquid compound being immiscible with water forms a separate layers and can be separated

Question 22

solid drying agents

Answer 22

-final traces of water are removed by treating the organic solution with a drying agent
-amount required of drying agent depends on the amount of water in the liquid or solvent solution which you are drying
-when drying is complete you need to remove the dried organic solution from the drying agent. there are several methods by which it can be dose
-if the powder is quite fine (as when using magnesium sulphate) or if the volume is large, gravity filtration is the method of choice
-in case they drying agent is of larger particle size (as when usin sodium sulphate or calcium chloride), decanting is the method of choice

Question 23

small scale steam distillation

Answer 23

-on laboratory scale the apparatus consists of a steam generator filled with a rubber bung/plug having two holes
-through one hole a long safety tube is passed which permits the expulsion of some water if excessive pressure is generated inside the steam distillation
-through the second hole, a bent tube is passed which carries the steam to the flask containing the liquids to be distilled (immiscible liquid +water)
-the bent tube must dip almost to the bottom of the flas
-the steam must touch below the surface of the liquid and heat it up. so that a rapid current of steam passes through the boiling mixture in the flask
-the vapors are allowed to pass through the condenser and the condensed liquid is collected in the florentine reciever

Question 24

florentine flasks

Answer 24

the distillate which form in two layers- one aqeous and the other non-aqeous, are separated from each other as completely as possible. for separation florentine recievers or separating funnel is used. florentine reciever is a specialized reciever for collectin the oil and water in the same reciever

Question 25

applications

Answer 25

-for distillation of water immiscible liquids of high boiling points- turpentine, anilin, phenylalanine, etc
-for extracion of volatile oils from their crude drugs-clove oil, anise oil, and eucalyptus oil from clove, anise, and eucalyptus
-for the purification of volatile substances
-in the manufacture of essential oils, for use in perfumes
-to separet intermediate or final producs during the sysnthesis of complex organic compounds

Question 26

vacuum distillation

Answer 26

-also known as distillation under reduced pressue
-it works on the principle that a liquid boils when its vapor pressure is equal to the atmospheric pressure or the external pressure
-this technique is used for purifying or separating thermally unstable liquid compounds that decompose at their normal boiling points
-liquids which are unstable at their boiling points can be distilled at a much lower temperature than their boiling points under reduced pressue with less likehood of decomposition
-boiling under reduced pressure also increases the rate of distillatin
-under this condition, the compound boil below their normal boiling temperature. hence vacuum distillation is best suited for separation of compounds with higher boiling points (more than 200C) which tend to decompose at their boiling temperaturev

Question 27

vacuum distillation principle

Answer 27

the lowering of pressure on the surface of a liquid lowers its boiling point. at a result og this, a liquid can be boiled and distilled, without any decomposition at temperature much below its normal boiling point. distillation under reduced pressure or vacuum is carried out in a specially designed glass apparatus. a two necked ‘claisens flask’ is used.

Question 28

process of vacuum distillaion

Answer 28

-Distillation under reduced pressure is very commonly used for the evaporation of the menstrum in the preparation of the extracts.
-This special flask has two necks. Through one neck, a thermometer is inserted and is attached to the condenser. Through the other neck a very fine capillary tube is introduced which completely dips in the boiling liquid.
-Bumping readily occurs during the distillation under reduced pressure, but it can be easily prevented by introducing stream of air bubbles passing into the liquid, through the fine capillary tube
-The side tube of the receiver is connected to a vacuum pump to provide the suitable vacuum -In all vacuum distillations, a small pressure gauge (manometer) should be inserted between the receiver and the vacuum pump
-In carrying out the distillation, heating is not commenced until the required vacuum has been attained above the surface of the liquid, otherwise frothing of the hot liquid will result in the receiver.
-Heating of the flask should be done on a water bath or oil bath maintained at about 20°C higher than the boiling point of the liquid under reduced pressure.
-Thin walled glass apparatuses, such as ordinary flat bottomed flasks and conical flasks should never be used for vacuum distillation; otherwise collapsing of such apparatus may result.
-in some cases, persistent foaming occurs during the process of vacuum distillation. This may be overcome by adding capryl alcohol to the liquid to be distilled, or by inserting a second air capillary tube in the thermometer neck of the claisen flask. The stream of air drawn through the tube breaks the
rising foam.

Question 29

advantages of vacuum distillation

Answer 29

-The compounds that decompose on heating to their boiling points can be purified by distillation under reduced pressure. This is because at the reduced pressure, a liquid would boil at a temperature much below its normal boiling point.
-Distillation under reduced pressure is more fuel-economical as it makes the liquid boil at
temperatures well below the normal boiling point.
-Vacuum distillation is used to safely recover higher boiling point solvents.
-It is used to safely recover solvents with boiling points over 300° Fahrenheit.
-Vacuum distillation should not be used on solvents with boiling points below 200° Fahrenheit.

Question 30

applications of vd

Answer 30

-for distillation of thermo labile substances
-for concentration and drying of extracts which get destroyed at high temperature
-for purification of vitamins

Question 31

destructive distillation

Answer 31

-is the term used to describe the decomposition of a substance, usually a natural product, by heat followed by the condensation and collection of the volatile products of decomposition
-it is not a pharmaceuticl process but is used in manufacture of some substances used in medicines