Analysing Organic Compounds

Bromine Test

• Use: tests for unsaturation (C=C)

• Reaction: addition reaction

• Positive Test: brown colour of bromine solution fades to colourless

• Negative Test: solution remains brown

• Cons: no information about type or location of unsaturated bonds; can be slow reaction

Silver Mirror Test (Tollens Test)

• Use: tests for -OH in primary alcohols used to differentiate primary and secondary

• Reaction: react a small amount of acidified Cr2O72- (Dichromate) to oxidise alcohol into aldehyde, then mix with Tollens reagent

• Positive Test: silver mirror-like substance

• Negative Test: no change in colour

Bromine Test

• Use: tests for unsaturation (C=C)

• Reaction: addition reaction

• Positive Test: brown colour of bromine solution fades to colourless

• Negative Test: solution remains brown

• Cons: no information about type or location of unsaturated bonds; can be slow reaction

Silver Mirror Test (Tollens Test)

• Use: tests for -OH in primary alcohols used to differentiate primary and secondary

• Reaction: react a small amount of acidified Cr2O72- (Dichromate) to oxidise alcohol into aldehyde, then mix with Tollens reagent

• Positive Test: silver mirror-like substance

• Negative Test: no change in colour

Lucas Test

• Use: tests for -OH

• Reaction: mix Lucas reagent (concentrated HCl and ZnCl2) with alcohol

• Positive Test: cloudy liquid forms

• Negative Test: no change in colour

• Cons: does not differentiate between primary, secondary or tertiary alcohols

Reaction with Metal Carbonate

• Use: tests for -COOH (weak acid)

• Reaction: acid reacts with metal carbonate in neutralisation reaction to produce salt + H2O + CO2

• Positive Test: bubbling

• Negative Test: no change observed

• Confirmation: bubble gas into limewater > forms a cloudy white precipitate if CO2

Baeyers Test

• Use: tests for unsaturation (C=C)

• Reaction: alkaline KMnO4 reacts with C=C

• Positive Test: solution changes from purple to colourless and brown precipitate forms

• Negative Test: solution remains purple

• Cons: only helpful if you know it is a HC (as alcohols and aldehydes would also react); no information on C=C location

Acid-Base Indicator Test

• Use tests for -COOH (weak acid)

• Phenolphthalein: pink to colourless

• Red Litmus Paper: remains red in colour

• Blue Litmus Paper: changes to red in colour

• Universal Indicator: (mixture of indicators: turns green indicator yellow-orange)

Oxidation

• Use tests for -OH in primary or secondary carbon

• Reaction: react acidified MnO4- or Cr2O7-2 with suspected alcohol in oxidation reaction

• Positive Test: solution changes colour from purple to pink (the colourless); or orange to green

• Negative Test: remains purple or orange

• Cons: positive test will occur for aldehydes

Iodine Number

• The iodine number of a fat or oils the mass of Iodine (I2) that reacts with 100g of a substance

• Need to determine the amount (mole) of fat or oil in 100g

• Need to determine the number of C=C bonds present in one molecule

Rinsing Volumetric Analysis Equipment

• Burette: rinse with substance to be placed inside of it (usually the standard solution - do not want to dilute concentration)

• Pipette: rinse with substance to be placed inside of it (usually the analyte - do not want to dilute concentration)

• Conical flask: rinse with deionised H2O

• Volumetric flask: rinse with deionised H2O

Melting Point Determination

• Use: analyse purity of a solid

• Pure: melting point withing a very narrow range (within 0.5-2 Celsius)

• Impure: melting point is lower and across a wider range of temperatures

• Reasoning: impurity disrupts the ordered structure, weakening intermolecular forces between the solid crystals

Mass Spectrometry

• Molecular ion: m/z is indicative of the molar mass of the parent molecule (g mol-1)

• Fragments: provides information about the structure of the molecule

Simple Distillation

• Use: separate and purify liquids based on boiling points (min. difference of 50 Celsius)

• Process:

  1. Heat mixture of liquids, collect vapour

  2. Vapour is cooled, condensed and collected in container (distillate)

  3. Lowest B.P will evaporate first

• Impure: increases B.P and wider range

Chromatography (Qualitative)

• Number of peaks: number of different components in the mixture

• Retention time: can be compared to a bank or database of know Rt values to identify components (conditions of machine must be identical)

• Separates based on relative adsorption to S.P and desorption to M.P (polarity, size)

Fractional Distillation

• Use: separate and purify liquids based on boiling points (less than 50 Celsius difference)

• Process:

  1. Heat mixture of liquids, vapour passes through fractioning column

  2. Vapour is cooled, condensed, collected

  3. Cycle occurs multiple times (purifies)

  4. Lowest B.P will evaporate first (as it gets left in ________ disk)

• Impure: increased B.P and wider range

(B.P are closer together compared to simple distillation)

Chromatography (Quantitative)

• Create standard solutions of the substances

• Run the solutions under identical conditions to the original sample

• Identify peak that matches the substance using Rt and bank of known values

• Record the absorbance of each standard

• Create calibration curve (conc vs abs)

• Determine concentration using absorbance

Infrared Spectroscopy

• Functional groups: determine by the wavenumber (cm-1) and appearance of the absorption bands (data book)

• Fingerprint region: can be compared to a database or bank of spectra for a confirmation of identify

Determining Number of C=C Present

• Can determine the number of C=C by reacting alkene with iodine solution

• If one C=C is present, n(alkene) = n(I2)

• If two C=C is present, n(alkene) = n(I2) x 2

• Experiment is conducted by adding small amounts of I2(aq), which is red-brown in colour, until the colour disappears

Carbon-13 NMR

• Number of peaks: number of chemically distinct carbon environments

• Chemical shift: type of carbon environment (data book)

Esterification

• Use: tests for -OH and -COOH

• Reaction: react suspected alcohol with carboxylic acid (or vice versa) and H2SO4(l); esterification (condensation) reaction will occur to produce ester and water

• Positive Test: sweet-smelling odour formed

• Negative Test: no sweet-smelling odour

• Cons: does not indicate type of alcohol

Proton NMR

• Number of peaks: number of chemically distinct hydrogen environments

• Peak area ratio: number of equivalent hydrogen atoms in each environment

• Splitting pattern (high resolution): number of hydrogen in neighboring environments

• Chemical shift specific type of hydrogen environment (data book)

Explain how the concentration of a substance in a mixture can be determined using hplc

• create standard solution of the substance in question

• run the sample under identical conditions to the original sample

• identify the peak that matches the substance using the retention time and bank of known value

• record the absorbance of each standard

• Create a calibration curve by graphing concentration and absorbance

• determine the conc of the sample using the absorbance and calibration curve

How can chromatography be used to separate the components of a mixture

• Different substances in the mixture will have different polarites, function groups and molecular sizes

• The substances will have different relative attraction to the stationary phase and the mobile phase

• components that are more attracted to the stationary phase will spend more time adsorbed to the stationary phase resulting in a higher retention time, and less time desorbed in the mobile phase

• Molecules with a larger molecule size will form more dispersion forces with stationary phase so will have a higher retention time