1、12The general steps to determine the structure of an organic compound34TechniqueAim1.FiltrationTo separate an insoluble solid from a liquid(slow)2.CentrifugationTo separate an insoluble solid from a liquid(fast)3.RecrystallizationTo separate a solid from other solids based on their different solubil
2、ities in suitable solvent(s)4.Solvent extractionTo separate a component from a mixture with a suitable solvent5.DistillationTo separate a liquid from a solution containing non-volatile solutes5TechniqueAim6.Fractional distillationTo separate miscible liquids with widely different boiling points7.Ste
3、am distillationTo separate liquids which are immiscible with water and decompose easily below their b.p.8.Vacuum distillationditto9.SublimationTo separate a mixture of solids in which only one can sublime10.ChromatographyTo separate a complex mixture of substances(large/small scale)The mixture boils
4、 below 100C6If the substance is a solid,its purity can be checked by determining its melting pointIf it is a liquid,its purity can be checked by determining its boiling point734.2 Isolation and Purification of Organic Compounds(SB p.78)The selection of a proper technique depends on the particular di
5、fferences in physical properties of the substances present in the mixture834.2 Isolation and Purification of Organic Compounds(SB p.78)To separate an insoluble solid from a liquid particularly when the solid is suspended throughout the liquid The solid/liquid mixture is called a suspension934.2 Isol
6、ation and Purification of Organic Compounds(SB p.78)The laboratory set-up of filtration1034.2 Isolation and Purification of Organic Compounds(SB p.78)There are many small holes in the filter paper allow very small particles of solvent and dissolved solutes to pass through as filtrateLarger insoluble
7、 particles are retained on the filter paper as residue1134.2 Isolation and Purification of Organic Compounds(SB p.79)When there is only a small amount of suspension,or when much faster separation is required Centrifugation is often used instead of filtration1234.2 Isolation and Purification of Organ
8、ic Compounds(SB p.79)The liquid containing undissolved solids is put in a centrifuge tubeThe tubes are then put into the tube holders in a centrifugeA centrifuge1334.2 Isolation and Purification of Organic Compounds(SB p.79)The holders and tubes are spun around at a very high rate and are thrown out
9、wardsThe denser solid is collected as a lump at the bottom of the tube with the clear liquid above1434.2 Isolation and Purification of Organic Compounds(SB p.79)Crystals are solids that have a definite regular shape smooth flat faces and straight edgesCrystallization is the process of forming crysta
10、ls1534.2 Isolation and Purification of Organic Compounds(SB p.79)To obtain crystals from an unsaturated aqueous solution the solution is gently heated to make it more concentratedAfter,the solution is allowed to cool at room conditions1634.2 Isolation and Purification of Organic Compounds(SB p.79)Th
11、e solubilities of most solids increase with temperatureWhen a hot concentrated solution is cooledthe solution cannot hold all of the dissolved solutesThe“excess”solute separates out as crystals1734.2 Isolation and Purification of Organic Compounds(SB p.79)Crystallization by cooling a hot concentrate
12、d solution1834.2 Isolation and Purification of Organic Compounds(SB p.80)As the solvent in a solution evaporates,the remaining solution becomes more and more concentrated eventually the solution becomes saturated further evaporation causes crystallization to occur1934.2 Isolation and Purification of
13、 Organic Compounds(SB p.80)If a solution is allowed to stand at room temperature,evaporation will be slowIt may take days or even weeks for crystals to form2034.2 Isolation and Purification of Organic Compounds(SB p.80)Crystallization by slow evaporation of a solution(preferably saturated)at room te
14、mperature2134.2 Isolation and Purification of Organic Compounds(SB p.80)Involves extracting a component from a mixture with a suitable solventWater is the solvent used to extract salts from a mixture containing salts and sandNon-aqueous solvents(e.g.1,1,1-trichloroethane and diethyl ether)can be use
15、d to extract organic products2234.2 Isolation and Purification of Organic Compounds(SB p.80)Often involves the use of a separating funnelWhen an aqueous solution containing the organic product is shaken with diethyl ether in a separating funnel,the organic product dissolves into the ether layer2334.
16、2 Isolation and Purification of Organic Compounds(SB p.80)The organic product in an aqueous solution can be extracted by solvent extraction using diethyl ether2434.2 Isolation and Purification of Organic Compounds(SB p.80)The ether layer can be run off from the separating funnel and saved Another fr
17、esh portion of ether is shaken with the aqueous solution to extract any organic products remaining Repeated extraction will extract most of the organic product into the several portions of ether2534.2 Isolation and Purification of Organic Compounds(SB p.80)Conducting the extraction with several smal
18、l portions of ether is more efficient than extracting in a single batch with the whole volume of etherThese several ether portions are combined and dried the ether is distilled off leaving behind the organic product2634.2 Isolation and Purification of Organic Compounds(SB p.81)A method used to separ
19、ate a solvent from a solution containing non-volatile solutes When a solution is boiled,only the solvent vaporizes the hot vapour formed condenses to liquid again on a cold surface The liquid collected is the distillate2734.2 Isolation and Purification of Organic Compounds(SB p.81)The laboratory set
20、-up of distillation2834.2 Isolation and Purification of Organic Compounds(SB p.81)Before the solution is heated,several pieces of anti-bumping granules are added into the flask prevent vigorous movement of the liquid called bumping to occur during heating make boiling smooth2934.2 Isolation and Puri
21、fication of Organic Compounds(SB p.81)If bumping occurs during distillation,some solution(not yet vaporized)may spurt out into the collecting vessel3034.2 Isolation and Purification of Organic Compounds(SB p.81)A method used to separate a mixture of two or more miscible liquids3134.2 Isolation and P
22、urification of Organic Compounds(SB p.82)The laboratory set-up of fractional distillation3234.2 Isolation and Purification of Organic Compounds(SB p.82)A fractionating column is attached vertically between the flask and the condenser a column packed with glass beads provide a large surface area for
23、the repeated condensation and vaporization of the mixture to occur3334.2 Isolation and Purification of Organic Compounds(SB p.82)The temperature of the escaping vapour is measured using a thermometerWhen the temperature reading becomes steady,the vapour with the lowest boiling point firstly comes ou
24、t from the top of the column3434.2 Isolation and Purification of Organic Compounds(SB p.82)When all of that liquid has distilled off,the temperature reading rises and becomes steady later on another liquid with a higher boiling point distils outFractions with different boiling points can be collecte
25、d separately3534.2 Isolation and Purification of Organic Compounds(SB p.82)Sublimation is the direct change of a solid to vapour on heating,or a vapour to solid on cooling without going through the liquid state3634.2 Isolation and Purification of Organic Compounds(SB p.82)A mixture of two compounds
26、is heated in an evaporating dish One compound changes from solid to vapour directly The vapour changes back to solid on a cold surface The other compound is not affected by heating and remains in the evaporating dish3734.2 Isolation and Purification of Organic Compounds(SB p.83)A mixture of two comp
27、ounds can be separated by sublimation3834.2 Isolation and Purification of Organic Compounds(SB p.83)An effective method of separating a complex mixture of substancesPaper chromatography is a common type of chromatography3934.2 Isolation and Purification of Organic Compounds(SB p.83)The laboratory se
28、t-up of paper chromatography4034.2 Isolation and Purification of Organic Compounds(SB p.83)A solution of the mixture is dropped at one end of the filter paper4134.2 Isolation and Purification of Organic Compounds(SB p.83)The thin film of water adhered onto the surface of the filter paper forms the s
29、tationary phaseThe solvent is called the mobile phase or eluent4234.2 Isolation and Purification of Organic Compounds(SB p.83)When the solvent moves across the sample spot of the mixture,partition of the components between the stationary phase and the mobile phase occurs4334.2 Isolation and Purifica
30、tion of Organic Compounds(SB p.83)As the various components are being adsorbed or partitioned at different rates,they move upwards at different ratesThe ratio of the distance travelled by the substance to the distance travelled by the solvent known as the Rf value a characteristic of the substance44
31、34.2 Isolation and Purification of Organic Compounds(SB p.84)TechniqueAim(a)FiltrationTo separate an insoluble solid from a liquid(slow)(b)Centrifugation To separate an insoluble solid from a liquid(fast)(c)CrystallizationTo separate a dissolved solute from its solution(d)Solvent extractionTo separa
32、te a component from a mixture with a suitable solvent(e)DistillationTo separate a liquid from a solution containing non-volatile solutesA summary of different techniques of isolation and purification4534.2 Isolation and Purification of Organic Compounds(SB p.84)TechniqueAim(f)Fractional distillation
33、To separate miscible liquids with widely different boiling points(g)SublimationTo separate a mixture of solids in which only one can sublime(h)ChromatographyTo separate a complex mixture of substancesA summary of different techniques of isolation and purification464734.4 Qualitative Analysis of Elem
34、ents in an Organic Compound(SB p.86)Qualitative analysis of an organic compound is to determine what elements are present in the compound4834.4 Qualitative Analysis of Elements in an Organic Compound(SB p.86)Tests for carbon and hydrogen in an organic compound are usually unnecessary an organic comp
35、ound must contain carbon and hydrogen4934.4 Qualitative Analysis of Elements in an Organic Compound(SB p.86)Carbon and hydrogen can be detected by heating a small amount of the substance with copper(II)oxideCarbon and hydrogen would be oxidized to carbon dioxide and water respectivelyCarbon dioxide
36、turns lime water milkyWater turns anhydrous cobalt(II)chloride paper pink5034.4 Qualitative Analysis of Elements in an Organic Compound(SB p.86)Halogens,nitrogen and sulphur in organic compounds can be detected by performing the sodium fusion test5134.4 Qualitative Analysis of Elements in an Organic
37、 Compound(SB p.86)The compound under test is fused with a small piece of sodium metal in a small combustion tube heated stronglyThe products of the test are extracted with water and then analyzed5234.4 Qualitative Analysis of Elements in an Organic Compound(SB p.86)During sodium fusion,halogens in t
38、he organic compound is converted to sodium halides nitrogen in the organic compound is converted to sodium cyanide sulphur in the organic compound is converted to sodium sulphide5334.4 Qualitative Analysis of Elements in an Organic Compound(SB p.86)ElementMaterial usedObservationHalogens,asAcidified
39、 silver nitrate solutionchloride ion(Cl-)A white precipitate is formed.It is soluble in excess NH3(aq).bromide ion(Br-)A pale yellow precipitate is formed.It is sparingly soluble in excess NH3(aq).iodide ion(I-)A creamy yellow precipitate is formed.It is insoluble in excess NH3(aq).Results for halog
40、ens,nitrogen and sulphur in the sodium fusion test5434.4 Qualitative Analysis of Elements in an Organic Compound(SB p.86)Results for halogens,nitrogen and sulphur in the sodium fusion testElementMaterial usedObservationNitrogen,ascyanide ion(CN-)A mixture of iron(II)sulphate and iron(III)sulphate so
41、lutionsA blue-green colour is observed.Sulphur,assulphide ion(S2-)Sodium pentacyanonitrosylferrate(II)solutionA black precipitate is formed555634.5 Determination of Empirical Formula and Molecular Formula from Analytical Data(SB p.87)After determining the constituent elements of a particular organic
42、 compound perform quantitative analysis to find the percentage composition by mass of the compound the masses of different elements in an organic compound are determined5734.5 Determination of Empirical Formula and Molecular Formula from Analytical Data(SB p.87)The organic compound is burnt in exces
43、s oxygenThe carbon dioxide and water vapour formed are respectively absorbed by potassium hydroxide solution and anhydrous calcium chloride5834.5 Determination of Empirical Formula and Molecular Formula from Analytical Data(SB p.87)The increases in mass in potassium hydroxide solution and calcium ch
44、loride representthe masses of carbon dioxide and water vapour formed respectively5934.5 Determination of Empirical Formula and Molecular Formula from Analytical Data(SB p.87)The organic compound is heated with excess copper(II)oxide The nitrogen monoxide and nitrogen dioxide formed are passed over h
45、ot copper the volume of nitrogen formed is measured6034.5 Determination of Empirical Formula and Molecular Formula from Analytical Data(SB p.87)The organic compound is heated with fuming nitric(V)acid and excess silver nitrate solutionThe mixture is allowed to coolthen water is addedthe dry silver h
46、alide formed is weighed6134.5 Determination of Empirical Formula and Molecular Formula from Analytical Data(SB p.87)The organic compound is heated with fuming nitric(V)acid After cooling,barium nitrate solution is added the dry barium sulphate formed is weighed6234.5 Determination of Empirical Formu
47、la and Molecular Formula from Analytical Data(SB p.87)After determining the percentage composition by mass of a compound,the empirical formula of the compound can be calculated6334.5 Determination of Empirical Formula and Molecular Formula from Analytical Data(SB p.87)The empirical formula of a comp
48、ound is the formula which shows the simplest whole number ratio of the atoms present in the compound6434.5 Determination of Empirical Formula and Molecular Formula from Analytical Data(SB p.87)When the relative molecular mass and the empirical formula of the compound are known,the molecular formula
49、of the compound can be calculated6534.5 Determination of Empirical Formula and Molecular Formula from Analytical Data(SB p.88)The molecular formula of a compound is the formula which shows the actual number of each kind of atoms present in a molecule of the compound6634.5 Determination of Empirical
50、Formula and Molecular Formula from Analytical Data(SB p.88)676834.6 Structural Information from Physical Properties(SB p.89)The physical properties of a compound include its colour,odour,density,solubility,melting point and boiling pointThe physical properties of a compound depend on its molecular s
