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CHEMISTRY MODULE 7

Organic Chemistry

CHEMISTRY MODULE 7 – ORGANIC CHEMISTRY

NOMENCLATURE

Inquiry question: How do we systematically name organic chemical compounds?

● investigate the nomenclature of organic chemicals, up to C8, using IUPAC conventions, including simple methyl and ethyl branched chains, including: (ACSCH127) – alkanes – alkenes – alkynes – alcohols (primary, secondary and tertiary) – aldehydes and ketones – carboxylic acids – amines and amides – halogenated organic compounds

● explore and distinguish the different types of structural isomers, including saturated and unsaturated hydrocarbons, including: (ACSCH035) – chain isomers – position isomers – functional group isomers

HYDROCARBONS

Inquiry question: How can hydrocarbons be classified based on their structure and reactivity?

● construct models, identify the functional group, and write structural and molecular formulae for homologous series of organic chemical compounds, up to C8 (ACSCH035) : – alkanes – alkenes – alkynes

● conduct an investigation to compare the properties of organic chemical compounds within a homologous series, and explain these differences in terms of bonding (ACSCH035)

● analyse the shape of molecules formed between carbon atoms when a single, double or triple bond is formed between them

● explain the properties within and between the homologous series of alkanes with reference to the intermolecular and intramolecular bonding present

● describe the procedures required to safely handle and dispose of organic substances (ACSCH075)

● examine the environmental, economic and sociocultural implications of obtaining and using hydrocarbons from the Earth

PRODUCTS OF REACTIONS INVOLVING HYDROCARBONS

Inquiry question: What are the products of reactions of hydrocarbons and how do they react?

● investigate, write equations and construct models to represent the reactions of unsaturated hydrocarbons when added to a range of chemicals, including but not limited to:

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 1 OF 65 – hydrogen (H2) – halogens (X2) – hydrogen halides (HX) – water (H2O) (ACSCH136)

● investigate, write equations and construct models to represent the reactions of saturated hydrocarbons when substituted with halogens

ALCOHOLS

Inquiry question: How can alcohols be produced and what are their properties?

● investigate the structural formulae, properties and functional group including: – primary – secondary – tertiary alcohols

● explain the properties within and between the homologous series of alcohols with reference to the intermolecular and intramolecular bonding present

● conduct a practical investigation to measure and reliably compare the enthalpy of combustion for a range of alcohols

● write equations, state conditions and predict products to represent the reactions of alcohols, including but not limited to (ACSCH128, ACSCH136): – combustion – dehydration – substitution with HX – oxidation

● investigate the production of alcohols, including: – substitution reactions of halogenated organic compounds – fermentation

● investigate the products of the oxidation of primary and secondary alcohols

● compare and contrast fuels from organic sources to biofuels, including ethanol

REACTIONS OF ORGANIC ACIDS AND BASES

Inquiry question: What are the properties of organic acids and bases?

● investigate the structural formulae, properties and functional group including: – primary, secondary and tertiary alcohols – aldehydes and ketones (ACSCH127) – amines and amides – carboxylic acids

● explain the properties within and between the homologous series of carboxylic acids amines and amides with reference to the intermolecular and intramolecular bonding present

● investigate the production, in a school laboratory, of simple esters

● investigate the differences between an organic acid and organic base

● investigate the structure and action of soaps and detergents

● draft and construct flow charts to show reaction pathways for chemical synthesis, including those that involve more than one step

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 2 OF 65 POLYMERS

Inquiry question: What are the properties and uses of polymers?

● model and compare the structure, properties and uses of addition polymers of ethylene and related monomers, for example: – polyethylene (PE) – polyvinyl chloride (PVC) – polystyrene (PS) –

polytetrafluoroethylene (PTFE) (ACSCH136)

● model and compare the structure, properties and uses of condensation polymers, for example: – nylon – polyesters

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 3 OF 65

IUPAC

NOMENCLATURE

OUTCOMES

● investigate the nomenclature of organic chemicals, up to C8, using IUPAC conventions, including simple methyl and ethyl branched chains, including: (ACSCH127) – alkanes – alkenes – alkynes – alcohols (primary, secondary and tertiary) – aldehydes and ketones – carboxylic acids – amines and amides – halogenated organic compounds

● analyse the shape of molecules formed between carbon atoms when a single, double or triple bond is formed between them

HYDROCARBONS

Hydrocarbons are compounds that contain only carbon and hydrogen. They are the main constituents of natural gas and crude oil.

Hydrocarbons can be saturated (in hydrogen) or unsaturated, depending on whether they contain just single bonds or double/triple bonds, respectively.

ALKANES

- Contain only C-C single bonds in backbone - Saturated hydrocarbon - General formula for straight chained and branched alkanes = CnH2n+2

Alkanes are called saturated hydrocarbons because no more hydrogen atoms can be added to the carbon atoms.

Alkanes are a homologous series: family of compounds that can be represented by one general molecular formula.

Name Molecular Formula MP BP

methane -182 -164

ethane -183 -89

propane -190 -42

butane -138 0

pentane -130 36

hexane -95 69

heptane -91 98

octane -57 126

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 4 OF 65 MOLECULAR STRUCTURE OF ALKANES

BRANCHED ALKANES

Branched alkanes are alkane compounds containing alkyl side

groups.

Alkyl Groups Molecular Formula

Methyl

Ethyl

Propyl

Butyl

Pentyl

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 5 OF 65 STEM NOMENCLATURE

Longest Carbon Chain Prefix Number of identical groups Prefix

1 Meth- 5 Pent-

2 Eth- 6 Hex-

3 Prop- 7 Hept-

4 But- 8 Oct-

NAMING BRANCHED CHAIN ALKANES

1) Find the longest continuous chain of carbon atoms. Assign a parent name based on this number. 2) Find whatever groups that are not part of the longest continuous chain. Name these as prefixes and put

them in alphabetical order. 3) Assign numbers to groups by counting from one end of the chain. A chain has two ends, and the end we

start from is the one that gives the lowest set of numbers to the groups.

eg: 3-methylhexane

NAMING ALKANES WITH MULTIPLE ALKYL GROUPS

Number of identical groups Prefix Number of identical groups Prefix

2 Di 5 Penta

3 Tri 6 Hexa

4 Tetra 7 Hepta

LOWEST SET OF NUMBERS

To determine the lowest set of numbers:

1) Work out the numbers for the two possible names (going along the longest carbon chain in both directions) 2) List the numbers in each name in increasing order 3) Compare the first number of each name

a. If there is a difference, the name with the lower number is correct b. If the numbers are the same, move onto the second number and so on until there’s a difference

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 6 OF 65 ALKENES

- Contains at least one C=C double bond in backbone - Unsaturated hydrocarbons - General formula = CnH2n

Carbon atoms with double and triple bonds can accept more hydrogen therefore alkenes and alkynes are unsaturated hydrocarbons.

The double bond carbon atoms are called functional groups because they are sites of chemical activity.

- A functional group is an atom, or group of atoms, which give a compound some characteristic physical and

chemical properties.

It is necessary to assign a number to describe the location of the double bond. The bonds are numbered much like carbons. The lowest number is assigned to the bond.

ALKYNES

- Contain at least one C≡C triple bond in backbone - Unsaturated hydrocarbons - General formula = CnH2n−2

SHAPE

Bonds around Carbon Angle between Bonds Number of VSEPR groups aroun

Shape

Four Single Bonds 109.5 4 Tetrahedral

Two single bonds and one double bond

Trigonal planar Two Double bonds or one riple bond and one single

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 7 OF 65 EXTENSION: CYCLIC HYDROCARBONS

Hydrocarbon compounds in which the carbon atoms have joined to form closed ring structures are called cyclic (or alicyclic) hydrocarbons. They may also be saturated or unsaturated:

- Those that contain only C-C bonds are called cycloalkanes. - Those that contain C=C bonds or C≡C bonds are called cycloalkenes and cycloalkynes respectively.

Due to the extra C-C bond that closes the ring structure, there are always two less hydrogen atoms

than the respective straight chain. Cyclohexane 3-methylcycloheptene EXTENSION: AROMATIC HYDROCARBONS

A unique type of cyclic structure is the aromatic hydrocarbons. These structures contain a ring of carbon atoms linked together such that they have delocalised electrons. Delocalised electrons are not held within bonds but are free to move around a structure.

Benzene

- The electrons of the double bond are free to move around the entire ring, forming a “cloud” of delocalised

electrons above and below the plane of the ring. - The delocalisation is shown by drawing a circle around the inside of the ring. This depiction represents the

equivalent nature of the six carbon-carbon bonds.

The delocalisation of the electrons in aromatic compounds gives them significantly different properties to alkenes. They have much greater stability and are often unreactive.


PHYSICAL PROPERTIES

OUTCOMES

● conduct an investigation to compare the properties of organic chemical compounds within a homologous series, and explain these differences in terms of bonding (ACSCH035)

● explain the properties within and between the homologous series of alkanes with reference to the intermolecular and intramolecular bonding present

PROPERTIES OF HYDROCARBONS

Members of the same homologous series have:

- A similar structure and the same general formula and functional group (each member of a homologous

series differs by a −CH2 − unit from the previous member) - A pattern to their physical properties - Similar chemical properties

MELTING AND BOILING POINTS

The melting and boiling points are measures of the thermal energy required to overcome intermolecular forces.

- As ↑ intermolecular forces → ↑ Eheat → ↑ MP and ↑ BP

The packing of molecules also affects the boiling and melting

point.

- Packing depends on molecular shape. Molecules that are small, symmetrical or unbranched tend to be able

to pack more closely together. This results in stronger intermolecular forces. - The effect of packing on intermolecular forces strength is more significant for molecules in solid states

(melting point).

MELTING AND BOILING POINTS OF ALKANES

Alkane molecules are nonpolar, the only intermolecular force is dispersion forces. As the length of the carbon chain increases, the overall force of attraction between molecules also increase. (Dispersion forces is proportional to molar mass). Because boiling and point is determined by the strength of intermolecular forces, boiling point increases as alkane chain length increases.

Molecular shapes also influence the strength of dispersion forces. Straight-chained alkanes are able to fit together more closely and tend to have higher boiling points than their corresponding chain isomers.

Melting point is affected by the strength of the dispersion forces, size and shape of the molecule.

Melting points of hydrocarbons follow the same general patterns as boiling points, with a few exceptions. The melting points of straight-chain hydrocarbons increase as the number of carbon increases. However, there are deviations in this trend, relating to whether the molecules have an even or odd number of carbon atoms.

Chains with even numbers of carbon atoms pack slightly more efficiently in the solid state than chains with odd numbers. The more efficient packing requires more energy to melt the compound resulting in a higher melting point.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 9 OF 65 Name Molecular Formula Molecular Mass (g/mol) MP (°C) BP (°C)

methane 16.04 -182 -164

ethane 30.07 -183 -89

propane 44.09 -190 -42

butane 58.12 -138 0

pentane 72.15 -130 36

hexane 86.17 -95 69

heptane 100.2 -91 98

octane 114.2 -57 126

- BP (C1 − C4) < 25°C ∴ Gaseous at RTP - BP (C4 − C8) > 25°C ∴ Liquids at RTP - Generally, as ↑ molecular mass → ↑MP, however methane and ethane’s BP > propane. This is because

ethane and methane’s shapes allow them to pack tighter relative to propane, increasing IMF and hence MP.

BOILING POINTS OF ALKENES AND ALKYNES

Alkenes and alkynes, like alkanes, are nonpolar hydrocarbons. Their molecules are also nonpolar so the forces of attraction between them are only weak dispersion forces. Members of these homologous series have relatively low boiling points similar to those observed for alkanes with the same number of carbon

atoms.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 10 OF 65 As with alkanes, the boiling points of alkenes and alkynes increase with molecular size as the strength of dispersion forces between molecules increase.

- The boiling points of alkenes are slightly lower than alkanes with the same number of carbon atoms. - Alkynes have higher boiling points than both alkenes and alkanes that have the same number of carbon

atoms. This is due to the increase packing because of its linear shape.

Since alkenes have lower molecular mass compared to alkanes with the same number of carbon atoms, the strength of the dispersion forces is weaker. Hence the boiling points are lower.

MELTING POINTS OF ALKENES AND ALKYNES

Alkenes, alkynes and haloalkanes follow the similar pattern to alkanes. As the length of the carbon chain increases, the melting point increases. The alkenes ethene, propene and butene are all gases at room temperature, alkenes with 5-14 carbons are liquid, and longer-chained molecules are solid.

Alkynes follow the same general trend for melting points seen in alkanes and alkenes. The position of the triple bond can greatly affect the melting points as the shape of the molecule changes.

SOLUBILITY (LIKE DISSOLVE LIKE)

The solubility of a substance depends on the strength of the IMF within the solute and within the solvent (cohesive forces), in comparison to the IMF between the solute and solvent (adhesive forces).

The generalisation is that polar compounds tend to only dissolve well in polar compounds and non-polar compounds only dissolve in non-polar compounds.

Hydrocarbons are soluble in each other as well as in non-polar organic compounds such as benzene, diethyl ether and carbon tetrachloride (tetrachloromethane). This is because the cohesive forces within the solvent are also weak dispersion forces that are similar in strength to the dispersion forces within hydrocarbons.

DENSITY

The density of a substance is a measure of its mas per unit volume. (g/mL or g/cm3)

Alkane Formula Density (g/cm3 at 20°C) Molecular Mass (g/mol)

Pentane C5H12 0.626 72.15

Decane C10H22 0.730 142.3

Pentadecane C15H32 0.768 212.4

Isosane C20H42 0.789 282.6

Alkanes are immiscible with water (cannot mix). When mixed, two layers form and the alkane will float on water. This occurs as the density of all alkanes < water.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 11 OF 65 VOLATILITY

Volatility is the ability of a liquid (or solid) to escape and form a vapour. ↑ BP → ↑ IMF Strength → ↑ Volatility

Volatility is measured by vapour pressure, which is a measure of concentration in the gas phase above the liquid. It is constant at a constant temperature.

Hydrocarbons are non-polar and hence have dispersion forces as their only intermolecular force. Since the intermolecular forces are relatively weak, their bonds are easily overcome and hence the BP is relatively low. Therefore, hydrocarbons will be volatile.

↑ Molecular Mass → ↑ Strength of dispersion forces → ↑ Eheat → ↓ Volatility at a constant temperature.

VISCOSITY

Viscosity refers to a substance’s resistance to fluid flow. Liquids with a relatively high resistance to flow

have high viscosity. For a substance to flow, particles must flow over each other. Viscosity depends on:

- Strength of intermolecular forces. ↑ IMF → ↑ Viscosity - Size of molecules. ↑ Size → ↑ Viscosity - Temperature. ↑ Temperature → ↓ Viscosity

Viscosity decreases with increasing temperature. At higher temperatures, molecules have greater kinetic energy. Thus, the molecules move around more which increases the space between molecules. This causes the intermolecular forces to be weaker and hence viscosity decreases.


FUNCTIONAL GROUPS

OUTCOMES

● investigate the nomenclature of organic chemicals, up to C8, using IUPAC conventions, including simple methyl and ethyl branched chains, including: (ACSCH127) – alcohols (primary, secondary and tertiary) – aldehydes and ketones – carboxylic acids – amines and amides – halogenated organic compounds

FUNCTIONAL GROUPS

A functional group is an atom or group of atoms which give a compound some characteristic physical and chemical property.

A homologous series is a family of organic compounds with the same general formula or functional groups with similar chemical properties.

ALCOHOLS (ALKANOLS)

Alcohols are formed when a H atom on a hydrocarbon has been replaced with an -OH group.

For naming:

1) Find longest continuous chain of carbon atoms that contain the functional group. Assign a stem name and

use the suffix “-ol”. 2) Name the substituents as prefixes in alphabetical order. 3) Number the chain so that the functional group at the end of the name gets the lowest possible number.

eg: 2-ethylbutan-1-ol

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 13 OF 65 Alcohols can also be classified according to the number of carbon atoms attached to the carbon bearing the -OH group.

- A primary (1°) alcohol is one in which the carbon bearing the -OH group is bonded to one other carbon

atom. - A secondary (2°) alcohol is one in which the carbon bearing the -OH group is bonded to two other carbon

atoms. - A tertiary (3°) alcohol is one in which the carbon bearing the -OH group is bonded to three other carbon

atoms.

These three types of alcohols have different physical and chemical properties.

Butan-1-ol Hexan-3-ol 2-methylpentan-2ol Primary Alcohol Secondary Alcohol Tertiary Alcohol

ALDEHYDES AND KETONES (CARBONYLS)

A carbonyl functional group consists of carbon attached to an oxygen atom by a double bond.

The difference between aldehydes (alkanals) and ketones (alkanone) is the position of the carbonyl group along the carbon chain:

- If the carbonyl group is on a terminal carbon (at the end of a chain), it is called an aldehyde, which is given

the suffix “-al”. - If the carbonyl group is in the middle of the carbon chain, it is called a ketone, which is given the suffix “-

one”.

Aldehyde: Ketone:

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 14 OF 65 - When the aldehyde is the suffix, the aldehyde carbon is assigned the number 1. Since it is always carbon 1,

“1” (terminal carbon) is omitted from the name. (“-al”) Eg. 2-methylbutanal

- When the ketone is the suffix, the carbon chain is numbered so that the ketone is assigned the lowest

number. (“-one”) eg. Pentan-3-one.

CARBOXYLIC ACIDS (ALKANOIC ACIDS)

Carboxylic acids contain the carbonyl group, C=O, connected to a hydroxyl group. The carboxyl group is abbreviated as -COOH, and is given by the suffix “-oic acid”.

- Since the carboxylic acid uses up 3 bonds on the carbon atom, it must be situated at the end of the chain

(terminal carbon).

Eg: 2,2,3-trimethylbutanoic acid

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 15 OF 65 IUPAC Name Common Name

Methanoic acid (HCOOH) Formic acid

Ethanoic acid (CH3COOH) Acetic acid

Propanoic acid (CH3CH2COOH) Propionic acid

Butanoic acid (CH3CH2CH2COOH) Butyric acid

Pentanoic acid (CH3CH2CH2CH2COOH) Valeric acid

2-Hydroxypropanoic acid (HC3H5O6) Lactic acid

2-Hydroxypropane-1,2,3-tricarboxylic acid (H3C6H5O7) Citric acid AMINES AND AMIDES

Amines and amides both contain nitrogen. Amides contain the group. They use the suffix “-amine” or the prefix “amino-”.

Amides are carboxylic acids where the OH group has been replaced with an amine. They use the suffix “amide”. When they quoted as the prefix, the carbonyl and the amine are named separately (using the prefixes “oxo” and “amino” respectively).

Eg. 3-methylpentan-2-amine

Eg. 5-amino-3-methyl-oxopentanoic acid

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 16 OF 65 HALOGENATED ORGANIC COMPOUNDS

Halogenated organic compounds have hydrogen atoms replaced with a halogen (Group 17 element).

The halogen functional groups are named using prefixes placed in front of their name of the alkane:

• Br: bromo

• Cl: chloro

• F: fluoro

• I: iodo

Eg. 1,2-dibromo-3,4-difluoropentan-3-one

DIFFERENT FUNCTIONAL GROUPS

The highest priority functional group takes the suffix, and the other functional groups are placed earlier in the name.

Aldehyde > Ketone > Alcohol > Alkyne = Alkene

Name Structure Suffix Prefix

Carboxylic Acid (Alkaonic acid) -oic acid

Amide -amide oxo- & amino- (The carbonyl & amine groups are named as if

they were separate)

Aldehyde (Alkanal) -al oxo-

Ketone (Alkanone) -one oxo-

Alcohol (Alkanol) -ol hydroxy-

Amine -amine -amino

Alkene -ene -en-


STRUCTURE ISOMERS

OUTCOMES

● explore and distinguish the different types of structural isomers, including

saturated and unsaturated hydrocarbons, including: (ACSCH035) – chain isomers – position isomers – functional group isomers

ISOMERS

Structural isomers are molecules that have the same molecular formula, but their atoms are arranged in different ways, giving rise to different structural formulae.

Although isomers have the same molecular formula, they are different compounds with different chemical and physical properties, as well as different names.

CHAIN ISOMERS

Chain isomers involve rearrangement of the carbons in the backbone, resulting in a different number of carbons in the longest chain or different branching in the carbon chain.

EXAMPLE – HEXANE

An alkane with the molecular formula C6H14 has 5 chain isomers. Each isomer has the same molecular formula but has a different arrangement and a different name.

Hexane

2-methylpentane 3-methylpentane

2,2-dimethylbutane 2,3-dimethylbutane

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 18 OF 65 POSITION ISOMERS

Position isomers result when molecules have the same carbon chain but the functional group is at a different location.

Position isomers only exist for molecules that contain functional groups, where the chain is long enough for the functional group to occupy different positions. (Eg. Not possible for ethene or ethane).

EXAMPLE – BUTENE

But-1-ene But-2-ene

FUNCTIONAL GROUP ISOMERS

Functional group isomers result when the atoms in the molecules are arrange in different ways that lead to the isomers having different functional groups.

EXAMPLE

Propanoic acid and 1-hydroxypropan-2-one are functional group isomers as both molecules have the formula C3H6O2, but propanoic acid contains a carboxyl functional group while 1-hydroxypropan-2-one contains carbonyl and hydroxyl functional groups.

Propanoic acid 1-hydroxypropan-2-one

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 19 OF 65 GEOMETRIC ISOMERS

Two atoms joined by a single bond can rotate freely around the single bond. Geometric isomers can occur when there is restricted rotation somewhere in the molecule. Restricted rotation can occur about a C=C or a ring.

HYDROCARBON REACTIONS

OUTCOMES

● investigate, write equations and construct models to represent the reactions of unsaturated hydrocarbons when added to a range of chemicals, including but not limited to: – hydrogen (H2) – halogens (X2) – hydrogen halides (HX) – water (H2O) (ACSCH136) COMBUSTION REACTIONS

All combustion reactions are exothermic. It may be complete or incomplete.

For complete combustion to occur, excess oxygen must be readily available, and the products are always carbon dioxide and water.

C8H18(l) + 252 O2(g)

→ 8CO2(g)

+ 9H2O

(l)

Incomplete combustion occurs when there is insufficient oxygen. The products are water and three different oxidations of carbon, soot, carbon monoxide and carbon dioxide.

Incomplete combustion results in less energy being produce per mole of fuel combustion, making it less efficient. This is due to the reduction of C=O bonds being formed. The formation of C=O releases a large amount of energy.

Alkenes and alkynes tend to burn with a more sooty flame compared to alkanes due to the higher percentage of carbon atoms. Some of the carbon may not combine with oxygen.

- Standard molar heat of combustion is the energy released. Therefore, it is positive. - Standard enthalpy of combustion is always negative as combustion is exothermic. It is the change in

enthalpy.

REACTIONS OF UNSATURATED HYDROCARBONS

STABILITY OF CARBON BONDS

The bond energies dictate the overall reactivity of hydrocarbon compounds. Subsequent carbon-carbon bonds in a multiple bond are less stable and weaker than the original single covalent bond.

- This means that double and triple bonds are highly reactive and can break open more easily and allow

atoms to join (saturate). - This makes the alkenes and alkynes highly reactive compared to alkanes. - Alkenes and alkynes are able to react with a number of chemical reactions called addition reactions.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 21 OF 65 ADDITION REACTIONS OF ALKENES

HYDROGENATION

Alkenes react with hydrogen gas in the presence of a metal catalyst to form a saturated alkane.

Alkene + H2(g)

Saturated Alkane

HALOGENATION (BROMINATION AND CHLORINATION)

Bromine adds to almost all alkenes very rapidly at RTP to give a compound that has two bromines on adjacent carbons. The reaction occurs spontaneously at RTP.

This is used as in indicator for alkenes and alkynes.

ADDITION OF HX (HYDROHALOGENATION)

Any of the hydrogen halides (HF, HCl, HBr and HI) can add to the double bond of an alkane to give the corresponding alkyl halide. The double bond is converted into a single bond.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 22 OF 65 PREDICTING A MAJOR PRODUCT

When an asymmetric reagent, such as HBr is added to an asymmetric alkene, more of one isomer is produced than the other.

- The predominant isomer is called the major product and the other isomer(s) is called the minor product(s). - In some reactions, only the major product will be formed.

The major product obtained from an addition reaction can be predicted using Markovnikov’s rule.

In addition reactions involving unsymmetrical alkenes, the hydrogen atom will predominantly bond to the carbon atom bearing the greater number of hydrogen atoms.

ADDITION OF WATER (HYDRATION)

Water alone does not react with alkenes, but if an aqueous acid catalyst (eg. Dilute H2SO4) is added and the mixture is heated, water adds to the C=C double bond to give an alkanol.

ADDITION REACTIONS OF ALKYNES

Alkynes undergo addition reactions in a similar fashion to alkenes.

- One of the three bonds in the triple bond is broken, and two new bonds form. The original triple bond is

converted into a double bond. - The second addition reaction can be stopped by controlling equivalents of reagent used or by using a

specialised reagent.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 23 OF 65 HYDRATION OF ALKYNES

The addition of water to alkynes is different.

- Alkynes do not react with water with only an acid catalyst. A mercury(II) catalyst, such as mercury(II) sulfate,

must also be present. - A carbonyl (ketone or aldehyde) is produced instead of an alcohol. The alcohol forms as an intermediate

which quickly rearranges to form the carbonyl.

SUBSTITUTION REACTIONS OF ALKANES

A substitution reaction occurs when an atom or functional group in a molecule is replaced or substituted

by another atom or group.

Alkanes are far less reactive than alkanes and alkynes as C-C single bonds are relatively strong. However, their hydrogen atoms can be substituted by halogens. These reactions do not occur spontaneously at RTP.

Substitution of alkanes can only be carried out with chlorine and bromine (fluorine reacts too explosively, and iodine does not react) and required energy in the form of ultraviolet (UV) radiation.

Chloromethane is called the substitution product of this reaction.

OUTCOME

● describe the procedures required to safely handle and dispose of organic substances (ACSCH075)

All organic waste should be discarded into appropriately labelled waste containers.


PHYSICAL PROPERTIES OF ALCOHOLS

OUTCOMES

● investigate the structural formulae, properties and functional group including: – primary – secondary – tertiary alcohols

● explain the properties within and between the homologous series of alcohols with reference to the intermolecular and intramolecular bonding present

INTERMOLECULAR AND INTRAMOLECULAR BONDING IN ALCOHOLS

Alcohols contain a highly electronegative oxygen atom. This creates a polar bond in the molecule.

- The hydrocarbon chain of the alcohol is non-polar (alkyl chain) and can form dispersion forces. It is

hydrophobic (repelled from water). - The -OH functional group is polar and can form hydrogen bonds, dipole-dipole and ion-dipole bonds. It is

hydrophilic (attracted to water).

As the chain length of an alcohol increases, the strength of the dispersion force increases. However, the extent of hydrogen bonding does not change.

- The strength of the hydrogen bonding depends primarily on the molecule’s shape and the number of

hydrogen bond donors and acceptors available.

Thus the length of the hydrocarbon chain influences the properties within the homologous series of alcohols, and the hydroxyl group influences the differences in properties between alcohols and other homologous series.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 25 OF 65 MELTING AND BOILING POINT OF ALCOHOLS

Alkanol Molecular Mass (g/mol) Melting Point (°C) Boiling Point (°C)

Methanol 32.04 -98 65

Ethanol 46.07 -114 78

Propan-1-ol 60.09 -126 97

Butan-1-ol 74.12 -90 118

Pentan-1-ol 88.15 -79 138

Hexan-1-ol 102.17 -52 157

Heptan-1-ol 116.20 -34 176

Octan-1-ol 130.22 -16 195

- ↑ Chain length → ↑Molecular mass → ↑ Strength of dispersion forces → ↑BP and ↑ MP - However, the shape of ethanol and methanol allow them to pack more closely together than propan-1-ol,

thus resulting in stronger intermolecular forces and a higher MP.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 26 OF 65 The position of the hydroxyl group within the molecule can also affect the melting and boiling points of alcohols.

For example, three alcohols with the same molecular formula: C4H9OH

Type of

Alcohol P (°C)

Primary Butan-1-ol 118

Secondary Butan-2-ol 100

Tertiary 2-methylpropan-2-ol 82

Secondary and tertiary alcohols have lower boiling points than primary alcohols with the same number of carbon atoms.

- Since the three alcohols are isomers, their dispersion forces will be the same. - However, the hydrogen bonding is weaker in secondary and tertiary alcohols. The alkyl group adjacent to

the OH group hinders the OH groups from getting closer together, restricting their ability to form strong hydrogen bonds. - Hence the lower boiling points arise from weaker hydrogen bonding in secondary and tertiary alcohols.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 27 OF 65 ALKANES VS ALKANOLS

- Hydrogen bonding allows the alkanols to have a higher boiling point than similar molecular mass alkanes.

SOLUBILITY IN WATER Alkanol Solubility in Water at RTP (g/100mL)

Methanol Miscible

Ethanol Miscible

Propan-1-ol Miscible

Butan-1-ol 7.9

Pentan-1-ol 2.3

Hexan-1-ol 0.59

Small alcohols dissolve well in water. However, solubility in water decreases with increasing carbon chain length.

The solubility of alcohols in water is dictated by size because the opposing effects of the polar and non-polar portions of the molecule.

- The polar hydroxyl group is hydrophilic (“water loving”) and the non-polar hydrocarbon chain is

hydrophobic (“water-hating”)

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 28 OF 65 Water molecules cannot solvate the large non-polar carbon chains in long alcohols.

- The -OH group can form hydrogen bonds with water, allowing solvation of this portion of the molecule. - However, to solvate the large non-polar carbon chain, many strong hydrogen bonds between water

molecules need to be broken. Since the alkyl chain has no strong attraction to water, these cohesive hydrogen bonds cannot be broken. - Thus, the alkyl end remains unsolvated, and solubility in water is drastically decreased.

A very general rule for solubility in water, if it has less than a 4:1 carbon : oxygen ratio, it is soluble.

Small alcohols are good solvents for dissolving both polar and non-polar substances due to the presence of both polar and non-polar areas in the molecule.

- The polar hydroxyl group can form polar interactions such as ion-dipole, hydrogen bonding and dipole-

dipole forces with other polar and ionic substances - The non-polar hydrocarbon chain can form dispersion forces with other non-polar substances.

SOLUBILITY IN ORGANIC SOLVENTS

Alcohols become more soluble in non-polar organic solvents such as hexane, benzene and toluene, as the length of the carbon chain increases.

- The large alkyl chain can form strong dispersion forces with other non-polar substances. These are strong

enough to disrupt hydrogen bonds holding the alcohol together. - Therefore, the alcohol molecules separate and disperse throughout the solvent.


REACTIONS OF ALCOHOLS

OUTCOMES ● write equations, state conditions and predict products to represent the reactions of

alcohols, including but not limited to (ACSCH128,

ACSCH136): – combustion – dehydration – substitution with HX – oxidation

● investigate the products of oxidation of primary and secondary alcohols

DEHYDRATION

When alcohols are heated with concentrated sulfuric or phosphoric acid as a catalyst, an OH and a H atom on the adjacent carbon will be eliminated from the alcohol to give an alkene and water.

The reactivity and rate of reaction varies depending on the type of alcohol.

- Tertiary alcohols are the most reactive and always react the fastest. Dehydration occurs readily at room

temperature. - Primary and secondary alcohols require higher temperatures. Primary alcohols are less reactive and react

slower than secondary alcohols.

SUBSTITUTION REACTION OF HALOALKANES

Alcohols undergo substitution in the presence of a hydrogen halide (HCl, HBr, HI) to give the corresponding alkyl halide and water.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 30 OF 65 The trend in reactivity is the same as for dehydration. For primary alcohols, the rate of reaction is also dependent on the hydrogen halide used. HCL is the slowest whilst HI is the fastest.

OXIDATION

Alcohols can be oxidised with strong oxidising agents, such as acidified solutions of permanganate (MnO4-) or dichromate (Cr2O72-) to give carbonyl compounds. A change in oxidation states can be seen for the carbon atoms.

OXIDATION OF PRIMARY ALCOHOLS

Primary alcohols are oxidised into carboxylic acids.

- The oxidation of alcohols is driven by a simultaneous reduction reaction, usually of inorganic reagents.

Either acidified permanganate (MnO4- purple in colour) or dichromate (Cr2O72- orange in colour) can be used as the oxidant. - The oxidation occurs stepwise: the alcohol is first oxidised to the aldehyde, which is then oxidised into the

carboxylic acid.

Aldehydes are very reactive and the second oxidation generally occurs too rapidly for it to be separated practically.

MnO4- : Purple → colourless

Cr2O72- : Orange → green

OXIDATION OF SECONDARY ALCOHOLS

Secondary alcohols can be oxidised to produce ketones.

- Either acidified permanganate (MnO4- purple in colour) or dichromate (Cr2O72- orange in colour) can be used

as the oxidant. - Since there are no hydrogen atoms attached to the ketone carbon, no further oxidation can occur. - Secondary alcohols are generally less reactive than primary alcohols, thus require higher temperatures and

longer reaction times to be oxidised.

Slower decolourisation of the acidified oxidants.


OXIDATION OF TERTIARY ALCOHOLS

Tertiary alcohols cannot be oxidised to give any carbonyl compound. The carbon bearing the hydroxyl group has no hydrogen atoms, thus it cannot be oxidised.

COMBUSTION

Alcohols can readily combust in the same manner as hydrocarbons. They can undergo complete and incomplete combustion.

Alcohols are good fuels as the combustion of alcohol is highly exothermic and since they are already oxygenated, they are more prone to complete combustion.


PRODUCTION OF ALCOHOLS

OUTCOMES

● investigate the production of alcohols, including: – substitution reactions of halogenated organic compounds – fermentation

PRODUCTION BY ADDITION (HYDRATION)

Water alone does not react with alkenes, but if an aqueous acid catalyst (eg. Dilute H2SO4) is added and the mixture is heated, water adds to the C=C double bond to give an alkanol.

PRODUCTION BY SUBSTITUTION

Alcohols can also be prepared from substitution reactions of haloalkanes.

This reaction occurs by heating the haloalkane with a solution of sodium hydroxide or potassium hydroxide. The hydroxide ion from the aqueous base replaces the halogen atom to generate an alcohol and halide salt.

X: Cl, Br, I. Fluoroalkanes will not react as the C-F bond requires too much energy to break.

This reaction occurs due to the highly polarised carbon-halogen bond, which produces a partial positive charge on the carbon atom.

- The partially positive carbon atom can be easily “attacked” by a negatively charged hydroxide ion. - This results in the formation of a covalent carbon-oxygen bond. In the process, the negative

charge is

donated to the electronegative halogen atom, which leaves as a halide ion.

The rate of this reaction is dependent on the type of haloalkane and the halogen atom that leaves the molecule.

- Haloalkanes can be categorised as primary, secondary and tertiary. The reactivity is highest for primary,

followed by secondary and then tertiary. - This is because the presence of alkyl groups greatly hinders the ability of the hydroxide ion to approach the

partially positive carbon and thus slows the reaction.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 33 OF 65 The type of halogen atom leaving the molecule also has an effect on the rate. The reaction occurs the fastest with iodide, followed by bromide and then chloride. This is because the carbon-halogen bonds are of different strengths.

Bond Average Energy (kJ/mol)

C-F 485

C-Cl 338

C-Br 276

C-I 238

- The lower the bond energy, the easier it is to break the bond.

It is also possible for haloalkanes to undergo substitution reactions with water to form alcohols. This reaction occurs much more slowly, and the reactivity is highest for tertiary.

PRODUCTION BY FERMENTATION

Fermentation is a process that involves the conversion of carbohydrates into simple alcohols by the action of enzymes. This is a natural process used by microorganisms to extract energy.

Carbohydrates have the molecular formula of: Cx(H2O)y. Carbohydrates are abundant in plant material. They are also called saccharides.

- The simplest carbohydrates are monosaccharides. They are the building blocks of more complex

carbohydrates, such as disaccharides like sucrose and polysaccharides like cellulose.

The fermentation of monosaccharides, such as glucose and fructose is the simplest form of fermentation which process ethanol and carbon dioxide.

This process relies on the presence of zymase, an enzyme found in yeast.

CONDITIONS FOR FERMENTATION

1) Zymase is present – found in yeast 2) Warm temperatures (30 − 40°C but depends on the yeast strain) 3) Anaerobic environment (oxygen limited environment) 4) Aqueous solution of sugar

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 34 OF 65 - Fermentation of monosaccharides must be catalysed by zymase. Since zymase is a biological catalyst, it is

sensitive to temperature. - Yeast can produce ethanol to concentrations up to only about 15%

v/v. This is due to ethanol being toxic

and around 15% v/v, yeast will start to die. - To produce higher alcohol contents, it is necessary to distil the liquid:

- If the aqueous mixture from a fermentation process is subjected to fractional distillation, 95%

ethanol can be obtained. - To obtain 100% ethanol, more elaborate procedures such as molecular sieving are required.

ENVIRONMENTAL IMPACTS OF HYDROCARBONS

OUTCOMES

● examine the environmental, economic and sociocultural implications of obtaining and using hydrocarbons from the Earth

SOURCES OF HYDROCARBONS

The primary source of hydrocarbons is from petroleum. Petroleum is a mixture of hundreds and thousands of different alkanes, ranging from methane up to alkanes with 40 or more carbons.

- The mixture of gases found in petroleum is called natural gas and the mixture of liquid components is called

crude oil. - Petroleum is found within pores of rocks deep in the ground.

The complex mixture is separated into fractions according to their boiling points using fractional distillation.

- The petroleum is heated to about 400°C to produce hot liquid/vapour mixture that enters the fractioning

tower. - Inside the tower are horizontal trays, each which contains many bubble caps upon which alkanes condense - Fractions which have lower boiling points will rise higher in the column before condensing. Fraction which

have higher boiling points will not rise as high and will condense towards the bottom of the column.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 36 OF 65 Differences in physical and chemical properties of each petroleum fraction mean that they are suitable for different purposes. Generally, light fractions (LPG, petrol, naphtha) are more useful and are in higher demand than heavy fractions (heavy fuel oil, lubricating oil, wax and asphalt).

Some of the longer alkanes are further processed through cracking, which involves heating alkanes to high temperatures in the absence of oxygen. This causes them to split and form shorter, more useful alkanes as well as alkenes.

- A zeolite catalyst, which consists of Al, Si and O, may be employed to allow this reaction to be carried at

lower temperatures.

USES OF HYDROCARBONS

The major use of petroleum is transport. Hydrocarbons are excellent fuels and the combustion of hydrocarbons is the primary source of energy production globally.

Unsaturated hydrocarbons are highly reactive and can undergo addition reactions. This makes them extremely important as raw materials for the production of other organic chemicals, such as haloalkanes and alcohols, and commercially valuable goods such as plastic.

THE PROBLEMS WITH USING PETROLEUM

Petroleum deposits in the ground are formed by the burial and decomposition of prehistoric living organisms over millions of years. Thus, petroleum is a finite and non-renewable resource.

As the world’s crude oil diminishes, there will be enormous negative economic and sociocultural consequences. Such as the instability of world markets and increase costs of goods.

Another huge problem that arises is that the combustion of petroleum releases huge amounts of carbon dioxide into the atmosphere.

- Carbon dioxide is a greenhouse gas, so it absorbs infrared radiation from the atmosphere and keeps our

Earth warm. - The extra carbon dioxide produces through combustion is a major contributor to the enhanced greenhouse

effect which causes global warming. - The consequences for global warming include rising sea levels which in the long term will result in land loss and flooding, more frequent and intense extreme weather events, warming of the oceans and disruptions to the feeding behaviour of wildlife.

The higher concentrations of carbon dioxide has also resulted in the acidifications of oceans which is threatening the survival of aquatic life.


BIOFUELS OUTCOMES ● compare and contrast fuels from organic sources to biofuels, including ethanol ALTERNATIVE FUEL SOURCES A possible solution to the reliance on non-renewable crude oil is to use biofuels. Biofuels are fuels derived from biomass, which is biological material from living or recently living organisms such as wood, crops, wet waste and animal waste. BIOETHANOL Bioethanol is ethanol produced from the fermentation of monosaccharides such as glucose and fructose. Monosaccharides are the building blocks of more complex carbohydrates which make up plant material. Thus monosaccharides can be sourced from: - Sucrose based feedstock (eg. Sugarcane and fruits) - Starch based feedstock (eg. Grains like wheat and corn) - Cellulose based feedstock (eg. Wood residues) Fermentation usually involves mashing up grains, sugarcanes or fruits with water to create an aqueous solution of sugar to which yeast is added. - Sucrose (C11H22O11) and starch are readily hydrolysed into monosaccharides during the fermentation process as yeast contains the necessary enzymes required to catalyse the breakdown. -

Hydrolysis: C11H22O11(aq) + H2O(l) → 2C6H12O6(aq)

- Fermentation: C6H12O6(aq)

yeast → 2C2H5OH(aq) + 2CO2(g) - Cellulose is difficult to break down to its component sugars as the enzyme cellulase is not readily available

for industrial use. Bioethanol has been developed as a substitute for petroleum-based ethanol and as an alternative to petrol. It has the potential to be used as standalone fuel to completely replace petrol but is usually used as an additive to petrol. - In Australia, most cars post-1986 can use up to 10% ethanol (E10 fuel). BIOGAS Biogas consists of mixtures of gases, such as methane, carbon monoxide and hydrogen, released from the natural breakdown of organic matter by anaerobic bacteria. - The organic matter is sourced from natural wastes from agriculture and households, such as manure, human sewage, food processing wastes and crop wastes. - To produce biogas, the waste is placed in a large enclosed tank, called the digester, containing anaerobic bacteria. The gas released from the decay is collected by gas outlets. The biogas collected can be combusted as a fuel to generate electricity or to heat boilers from industrial processes and for cooking and heating water in homes. CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 38 OF 65

The biofuel production represents a carbon cycle, where plants absorb carbon dioxide during growth,

recycling the carbon dioxide released during combustion.

The use of biogas also helps reduce the enhanced greenhouse effect as methane is a greenhouse gas that has a larger effect than carbon dioxide. By collecting it and using it to produce electricity, less is released into the atmosphere. Another environmental benefit is that bioethanol and biodiesel are cleaner fuels than petroleum fuels.

- They are oxygenated, so complete combustion is more likely to occur and they do not contain sulfur

impurities. - They are non-toxic and biodegradable, thus do not pose as severe a threat to the environment in the event

of a spill.

OBSTACLES IN THE PRODUCTION OF BIOFUELS

In Australia, biomass sources currently being used are waste residues.

- Bioethanol is made from sugar cane molasses (waste) and waste from starch and red sorghum production. - Biogas is generated from the treatment of waste water - Biodiesel is produced from waste vegetable oil from restaurants and industrial food producers

However, this only produces a small percentage of Australia’s fuel needs. It is not possible to manufacture enough biofuel from these sources to replace all petroleum fuels used today.

1) Large amounts of fertile land would be required to grow the crops.

a. This requires clearing of forests and bushland which will contribute to an increase in carbon dioxide

levels in the atmosphere and to habitat loss. Fertile land is also limited thus it competes with food crops, resulting in increase in food prices. 2) Intensive farming can lead to land degradation and erosion. 3) A large amount of fertiliser would be required to replace the nutrients taken from the ground 4) A large amount of water would be required 5) There is also a large amount of energy required for harvesting of crops and processing biofuels, energy that

is currently derived from fossil fuels. 6) Large scale commercial agriculture leads to the reduction of biodiversity due to the loss of important

organic matter from that crop.

The potential of biofuels lies in making it financially viable compared to conventional petroleum-based fuels.


ORGANIC ACIDS AND BASES

OUTCOMES

● investigate the differences between an organic acid and organic base

CARBOXYLIC ACID

Organic acids are acids that have a carbon-based structure. The most common type of carboxylic acids are alkanoic acids. They occur abundantly in nature.

- Propanoic acid is found in cheese - Methanoic acid is produce in ant venom - Lactic acid is in milk - Citric acid is in citric fruits

All carboxylic acids are weak acids thus they will partially ionise in water to produce hydrogen or hydronium ions.

- Each carboxylic acid group is monoprotic - The covalent bond between oxygen and hydrogen is highly polar. The bonding electrons are strongly

attracted to oxygen so the hydrogen can be drawn easily by a base, leaving behind a negative charge on the oxygen, - If more than one carboxylic acid group is present in the molecule, these acids will be polyprotic. For

example, citric acid is triprotic (H3C6H5O7).

Different carboxylic acids will have different strengths, ionising to different extents. Their strengths can be compared by comparing their acid dissociation constant Ka.

Acid Formula Ka1 Ka2 Ka3

Methanoic HCOOH 1.8 × 10−4

Ethanoic (acetate) CH3COOH 1.8 × 10−5

Propanoic CH3CH2COOH 1.3 × 10−5

Fluoroethanoic CH2FCOOH 2.2 × 10−3

Citric H3C6H5O7 7.4 × 10−4 1.7 × 10−5 4.1 × 10−7

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 40 OF 65 The strength of a carboxylic acid is influenced by the length and substitution of the hydrocarbon chain.

- As the chain length increases, the strength of the acid decreases. - This is because the alkyl groups

are capable of donating electron density. Carbon is more electronegative, so

it pulls electron density towards itself and away from hydrogen. The additional electron density allows carbon to “donate” additional negative charge to neighbouring carbon atoms. - This increases the negative charge on the -COO- group, making it more attracted to the H+.

- Substituting a highly electronegative atom, such as a halogen, onto the hydrocarbon chain increases the

strength of the acid. The strong electron-withdrawing power of the substituent helps weaken the oxygen- hydrogen bond. This makes it easier for the hydrogen to be dissociated.

- As the number of electronegative atoms increases, so does the strength of the acid. - Fluorine has the biggest electron-withdrawing effect, then chlorine, bromine and iodine.

AMIDES (WEAK B/L BASES)

Organic bases are organic compounds that are characterised by the presence of an atom with a lone pair of electrons that can accept an H+.

- Nitrogen containing compounds such as amines are the most common organic bases.

Many amine bases exist in nature. The most important being the four nitrogenous DNA bases: adenine, cytosine, guanine and thymine, and the 20 natural amino acids used to make proteins in living organisms.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 41 OF 65 Amino acids are molecules that contain both a carboxylic acid and a basic amine group.

Simpler amines are made by substitution reactions of haloalkanes with ammonia.

Amines act as a base in an analogous manner to ammonia. The lone pair of electrons on the nitrogen can accept a proton, forming an ammonium ion. Like ammonia, they are weak bases.

The base dissociation constant Kb can be used to compare the strength of different amine bases.

Base Formula Kb

Ammonia NH3 1.8 × 10−5

Methylamine CH3NH2 4.4 × 10−4

Ethylamine CH3CH2NH2 5.4 × 10−4

Propylamine CH3CH2CH2NH2 6.9 × 10−4

- ↑ Chain length → ↑ Partial negative → ↑ H+ acceptor → ↑ Base strength

Alkyl groups are capable of donating electron density. This results in a build-up of partial negative charge on the electronegative nitrogen atom, allowing it to pick up H+ more readily and also stabilise the positive charge on the ammonium ion. The longer the chain, the greater the electron density donate.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 42 OF 65 Amides are also nitrogen containing compounds with a lone pair of electrons.

- Amides are neutral compounds. The presence of the highly electronegative oxygen atom in the C=O group

pulls electron density away from the nitrogen atom, which makes it more difficult to accept a H+

and stabilise a positive charge if nitrogen was to accept it.

REACTIONS OF CARBOXYLIC ACIDS AND AMINES

- Carboxylic acid + reactive metal → salt + hydrogen gas - Carboxylic acid + metal hydroxide/oxide → salt + water - Carboxylic acid + metal carbonate/bicarbonate → salt + carbon dioxide + water - Amine + acid → ammonium salt

When carboxylic acids react with amines, the product formed will depend on the conditions. At low temperatures, a proton transfer (neutralisation reaction) proceeds between the carboxylic acid and amine, forming a carboxylate ion (acid) and an alkyl (base).

At higher temperatures or in the presence of a suitable catalyst, an amide is produced with the elimination of water (condemnation reaction), which forms the OH group on the acid and a hydrogen from the amine.

- Condensation reaction: Where two or more molecules combine to form a larger molecule with the

simultaneous elimination of a small molecule such as water or methanol.


PHYSICAL PROPERTIES OF CARBOXYLIC ACIDS, AMINES AND

AMIDES

OUTCOMES

● explain the properties within and between the homologous series of carboxylic acids amines and amides with reference to the intermolecular and intramolecular bonding present

● investigate the structural formulae, properties and functional group including: – aldehydes and ketones (ACSCH127) – amines and amides – carboxylic acids

BOILING POINT

Carboxylic acids, amines and amides are all polar molecules. They can form hydrogen bonds with other molecules.

- ↑ Alkyl chain → ↑ MM → ↑ Dispersion forces → ↑ BP

Amides do not exhibit a linear relationship between boiling point and molecular weight. This is because the hydrogen bonding exhibited by the amides is extensive and are more complex.

Amides exhibit the highest boiling points compared to carboxylic acids and amines. Carboxylic acids have higher boiling points than amines.

- Carboxylic acids and amines have less atoms that can form hydrogen bonds. Each carboxylic acid molecule can form two hydrogen bonds with another acid molecule through the double bonded oxygen and OH group, forming a dimer (existing in pairs).

- Each amine molecule can only form one hydrogen bond with another amine molecule.


Amines and amides can be classified into primary, secondary and tertiary depending on the number of alkyl groups attached to the nitrogen.

- Primary amines have the highest boiling points, followed by secondary and then tertiary amines. The same

trend occurs with amides.

SOLUBILITY

Small amines, amides and carboxylic acids dissolve completely in water. However, solubility decreases as the hydrocarbon chain increases.

- ↑ Carbon chain length → ↑ Non-polar nature of compound → ↑ Dispersion forces domination → Water

cannot solvate the long hydrocarbon chain due to cohesive bonds → ↓ Solubility

Similar to alcohols, the trend is reversed for their solubility in organic solvents.


ESTERS OUTCOMES ● investigate the production, in a school laboratory, of simple esters FORMATION OF ESTERS Esters are organic compounds with the functional group −COO −. Esters are formed from the reaction of a carboxylic acid and an alcohol. The OH group on the acid is replaced with an OR group from the alcohol. This reaction is called esterification (a condensation reaction). The reaction is extremely slow. Concentrated H2SO4 (dehydrating agent) is used to remove the water and catalyse the reaction. Because it is all liquids, it has a equilibrium constant: Keq = [H

2O][ester]

[alkanoic acid][alkanol]

Esters are everywhere in nature and are used in a number of industrial applications. - Short chain esters are known for their distinctive, fruit like odours and many occur naturally in fruits and the essential oils for plants. - Due to their pleasant odours, they are commonly used as flavouring (banana lollies) agents in processed foods, as well as fragrances in perfumes and cosmetics. - Fats and oils are also naturally occurring triesters derived from glycerol and fatty acids. IUPAC NOMENCLATURE OF ESTERS 1) The alkanol is changed to “alkyl” and is the first word of the esters name 2) The alkanoic acid becomes the alkanoate and is the second word of the esters name CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 46 OF 65

For example, an ester that smells like banana.

pentanol + ethanoic acid → pentyl ethanoate + water

ESTERIFICATION

To increase rate of reaction:

- ↑ Temperature - ↑ Acid catalyst

To increase yield:

- Remove water - Concentrated H2SO4 (catalyst and dehydrating agent)

REFLUX

Esterification must be carried out under reflux.

Reflux is a technique that involves heating a reaction mixture in a vessel fitted with a cooling condenser so that the volatile reactants and products are returned to the reaction mixture without any loss.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 47 OF 65 PURPOSE OF REFLUXING

Component Purpose

Reaction flask Contains volatile reactants and products

Condenser Prevents the volatile reactant or product from escaping before the reaction has reached equilibrium by cooling the reactant vapour into a liquid. Water enters at the base and leaves from the top

Boiling chips To provide a surface upon which bubbles form, promoting even boiling

Open top To avoid dangerous pressure build-up inside the apparatus


SOAP

S

OUTCOMES


STRUCTURE OF SOAPS

Soaps are surfactants which, when dissolve in water, help to remove dirt, oil and foreign matter from surfaces.

Soaps are salts of fatty acids

- Fatty acids are carboxylic acids with long hydrocarbon chains (10+) - The salt of a fatty acid consists of a negatively charged carboxylate ion (called the head) with a long

hydrocarbon chain (called the tail) and a positively charged ion.

In water the sodium or potassium ions float free and do not play a part in the cleaning actions of soaps. It is the negatively charged fatty acid ion which is responsible for the cleaning action.

- The charged head is hydrophilic (water loving) due to its polar nature - The tail is hydrophobic (water hating) due to its non-polar nature

SAPONIFICATION

Soaps are produced from the hydrolysis of fats and oils (lipids) in a basic solution such as NaOH.

Fats and oils are known as fatty esters, triglycerides or triesters.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 49 OF 65 When esters are heated in the presence of a strong base such as NaOH or KOH, the ester is broken down to give the alcohol and a carboxylate ion.

- This reaction is known as saponification. It is a type of hydrolysis reaction, involving the breaking of a

chemical bond by the addition of water

The general reaction for saponification of a triglyceride is:

HOW SOAPS WORK

Soap is a surfactant (surface active agents)

- This means it functions by reducing the surface tension of water and binding to grease and dirt to emulsifies

them.

The hydrophobic part of the soap molecule is long, non-polar hydrocarbon chain. It is strongly repelled by water molecules.

When soap molecules are added into water, they form an oriented monolayer (with tails sticking out of the water) at the surface in order to satisfy the interaction of both the hydrophobic and hydrophilic portions of the soap molecule. This effectively breaks the hydrogen bonding between molecules of water and thus reduces the surface tension of water.

The components self-assemble into the most stable arrangement, which consists of spherical structures with the carboxylate groups forming a negatively-charged spherical surface, with the hydrocarbon chains inside the core of the sphere.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 50 OF 65 The spheres are called micelles. The hydrophobic tails are shielded from the water by the polar heads, which minimises the repulsive forces in the system.

1. DISSOLUTION

Soap molecules must be first dissolve in water. The hydrophilic head of a soap ion interacts with water molecules via ion-dipole interactions and hydrogen bonding.

2. ADSORPTION

Grease and oil consists of non-polar molecules.

- The hydrophobic tails of the soap ions dissolve in the grease due to dispersion forces and orientates

themselves.

Surfactant molecules continue to absorb into the grease, decreasing the surface tension of water at the interface between the grease and water.

The hydrophilic heads interacting with water via ion-dipole forces effectively pull the grease off the surface.

3. EMULSIFICATION

With agitation, the grease layer breaks into smaller, spherical droplets (micelles), with the hydrophilic surfactant head groups interacting with the water via ion-dipole forces, and the hydrophobic surfactant tails adsorbed into the grease. This forms a dispersion of grease droplets in water (an emulsion).

The negative charged heads on the soap repel each other, preventing the grease and dirt from joining together and keeping them dispersed throughout the solution. Therefore, the grease and oil can be simply rinsed away, leaving a clean surface.


SYNTHETIC DETERGENTS

OUTCOMES


PROBLEMS WITH SOAP

- The soap ion must be dissolved in water to have a cleaning effect - As salts of weak acids, in low pH, soaps are converted into uncharged fatty acids

CH3(CH2)16COO− Na+(aq) + HCl

(aq) → CH

3(CH

2)16

COOH (s)

+ NaCl(aq)

Soluble fatty acid ion + acid → Insoluble fatty acid molecule + ionic salt

- Soaps can also form insoluble salts (scum) in hard water (water with high concentration of divalent metal

ions such as Ca2+ and Mg2+)

2CH3(CH2)16COO− Na+(aq) + Mg2+(aq)

→ [CH3(CH

2)16

COO−]2Mg 2+(s) + 2Na+(aq)

Soluble fatty acid ion + divalent metal ion → insoluble salt + sodium or potassium ion

SYNTHETIC DETERGENTS

- All such synthetic surfactants are known as detergents - They have a similar structure to soaps, with a long non-polar hydrocarbon tail and a polar head. However,

they vary in the structure of the polar head group.

ANIONIC DETERGENTS

All anionic detergents have a negatively charged polar head.


The main structural difference between anionic detergents and soap is the presence of a sulfate (R − SO2 − O−) or sulfonate group (R − O − SO2 − O−) instead of a carboxylate (R − COO−).

EFFECTIVENESS IN HARD OR ACIDIC WATER

Anionic detergents don’t form insoluble precipitates. They form salts that are all soluble. However, the effectiveness is still reduced in hard and acidic water. The positive ions in hard water/acidic water will attract the negative head of the detergent.

Phosphate is an example of a builder that can be added to soften the water.

CATIONIC DETERGENTS

All cationic detergents have a positively charged polar head. The positive head is usually a quaternary ammonium ion. They are also known as fatty amine salts.

Generally cationic detergents are not very good cleaning agents due to the strong attraction of cationic detergents to negatively charged surfaces. (Most surfaces are negatively charged).

This attraction however can be beneficial in certain situations.

- Many fabrics acquired acquire a negative charge when they become wet. - Cationic detergents are used in fabric softeners and hair conditioners.

The strong attraction of cationic detergents to negatively charged surfaces can be detrimental in other situations.

- Cationic detergents are particularly toxic to microorganisms. They are attracted to the negative surface of

bacteria and damage or kill bacteria that are involved in their decomposition. They therefore have very low biodegradability.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 54 OF 65 NON-IONIC DETERGENTS

All non-ionic detergents have uncharged polar heads. The polar heads consists of polar groups such as ethoxylates. Although these surfactants are uncharged, the polar head groups are still attracted to the highly polar water molecules forming numerous hydrogen bonds.

Non-ionic detergents don’t foam as much as other detergents. Hence, they can be used in dish washers.

ENVIRONMENTAL IMPACTS OF SURFACTANTS

Detergents are synthetic, whereas soaps are made from naturally occurring biological materials (fats and oils). Thus detergents are less biodegradable.

- The enhanced stability of detergents means they persist in the environment, causing damage to the mucus

membrane in wildlife and resulting in excessive frothing in the water ways. This leads to less sunlight penetration. - Toxic to aquatic life.

Anionic detergents often contain builders such as sodium triphosphate (Na5P3O10).

- The builders react with minerals in hard water and form soluble molecules. - High levels of phosphates entering the rivers and waterways can lead to eutrophication (turning a lake into

swamp, algae etc)


REACTION PATHWAYS

OUTCOMES

● draft and construct flow charts to show reaction pathways for chemical synthesis, including those that involve more than one step

FLOWCHART OF REACTIONS

[Deleted sorry. Mod 8 might have some flowcharts for rxns]


POLYMER

S

OUTCOMES

● model and compare the structure, properties and uses of addition polymers of ethylene and related monomers, for example: – polyethylene (PE) – polyvinyl chloride (PVC) – polystyrene (PS) – polytetrafluoroethylene (PTFE) (ACSCH136)

● model and compare the structure, properties and uses of condensation polymers, for example: – nylon – polyesters

POLYMER

A polymer is a long chain molecule made up of repeating units, called monomers joined by covalent bonds. The process of linking monomer units is called polymerisation.

Polymers may be natural or synthetic:

- Natural polymers are made by living organisms. Eg. Hair, starch, cellulose, DNA and silk - Synthetic polymers are manufactured. Eg. Plastics like polyethylene, polyvinyl chloride and nylon.

ADDITIONAL POLYMERS

Addition polymers are polymers made by adding unsaturated molecules to each other, without the elimination of any atoms.

- Additional polymerisation is a type of addition reaction, in which one of the bonds in the C=C double bond is

broken to form two new single bonds.

A simple way of representing polymers is by writing the repeat units in square brackets followed by the subscript n where n is the number of monomer units in the polymer.

Addition polymers are all synthetic, they do not exist in nature.

CONDENSATION POLYMERS

Condensation polymers are polymers formed through the condensation reaction of difunctional monomers with the elimination of a small molecule such as water or methanol in the process.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 57 OF 65 - Monomers used to synthesise condensation polymers usually contain groups such as alcohol, carboxylic and

amine.

Condensation polymers are found everywhere in nature.

- Polysaccharides such as cellulose and starch are condensation polymers made from glucose monomers.

POLYESTERS

Polyesters are condensation polymers in which the repeating units are joined by ester

links.

Polymers made from two different monomers are called copolymers.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 58 OF 65 POLYAMIDES

Polyamides are condensation polymers in which the repeating units are joined by amide links.

The nylon class refers to polyamides that have linear carbon chains in the repeating units.

PROPERTIES OF POLYMERS

Physical properties of polymers are important in determining their uses. These include:

- Melting point (softening point) - Mechanical strength - Flexibility.

This is due to the chemical structure of the polymers which leads to different strengths of intermolecular forces that is dependent on:

- Molecular weight or chain length - Extent of chain branching - Presence of side groups (eg. -OH)

CHAIN LENGTH

Polymers are extremely large covalent molecules. The dominant intermolecular force is dispersion.

The length of a polymer (and its molecular weight) depends on the number of monomers the polymer contains. The melting point, rigidity and hardness of a polymer increases with an increase in chain length.

CHAIN BRANCHING

Polymers are able to form branched and unbranched chains. Unbranched chains are able to pack more closely in an orderly fashion, forming a rigid crystalline solid.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 59 OF 65 Branched polymer chains are unable to align with each other, forming an amorphous solid that has weak intermolecular forces between the chain.

CRYSTALLINITY AND AMORPHOUS

If the polymer chains have few branches, as in the case with HDPE, the molecules can sometimes line up in a regular arrangement, creating crystalline regions. The regular arrangements brings the polymer chains closer together. The IMF between closely packed chains are stronger, and the presence of crystalline regions strengthens the material overall.

Crystalline regions in a polymer prevents the transmission of light through the material, making it appear cloudy or opaque.

Amorphous region will form where the polymer chains are randomly tangled and unable to pack very closely. In some polymer materials, the entire solid is amorphous. Amorphous polymers are usually more flexible and weaker and are often transparent. (LDPE) Increasing the percentage crystallinity of a material makes it stronger and less flexible. This also makes the material less transparent because crystalline regions scatter light. There are more crystalline regions in unbranched polymers

There are crystalline and amorphous regions in all polymers.

SIDE GROUPS

Side groups can be introduced to make a material more rigid and brittle. This results in a harder polymer.

CROSS-LINKING

Polymer chains are held together by intermolecular forces or they can be linked by covalent bonds called cross-links to form a large extended network.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 60 OF 65 Polymers with only intermolecular forces between their chains are called thermoplastic polymers. They soften when heated as the intermolecular forces are relatively weak and easily broken to allow the chains to move between one another. This property allows polymers to be remoulded

Polymers with cross-links are called thermosetting polymers. Since covalent bonds are very string, cross links limit movement between polymer chains, making the polymer more rigid, hard and heat resistant. These polymers cannot be remoulded (like XLDPE).

TYPES OF POLYMERS

POLYETHYLENE (PE)

Polyethylene (polyethene) is the most popular plastic in the world. It has a very simple structure.

Ethene is an unsaturated molecule because a double carbon-carbon bond. When ethene polymerases, the double bond breaks and new covalent bond are formed between carbon atoms on nearby monomers. The polyethene formed does not contain any double bonds.

Ethene is one of the most simple and versatile monomers. It is easily able to undergo addition polymerisation

LOW DENSITY POLYETHYLENE (LDPE) (4)

LDPE is produced under high temperatures and pressures. Under these harsh conditions, the polymer is formed too rapidly for the molecules to be neat and symmetrical. The products usually contain too many small chains (branches) that divide off the main polymer.

The molecules in the polymer cannot pack closely together thus reducing the dispersion forces.

The arrangement of the polymer molecules can be described as disordered or non-crystalline.

- Flexible, chemically inert, good elongation - Low melting point/thermoplastic - Lightweight, good puncture resistance - Waterproof

Used in: Milk carton lining, bowls, flexible water pipes, bottles

HIGH DENSITY POLYETHYLENE (HDPE) (2)

Highly specialised transition metal catalyst, known as Ziegler-Natta catalysts are used to avoid the need for

high pressure. Due to the polymer being produced under a lower pressure, the conditions are milder and there are fewer branches.

The lack of branches allows the molecules to pack together tightly increasing the density and the hardness of the polymer formed. The arrangement of the polymer molecules is more ordered, resulting in crystalline sections.

Used in: Food packaging, dustbins, crates, drums, water pipes

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 62 OF 65 POLYVINYL CHLORIDE (PVC)

PVC (polychloroethene) is made out of vinyl chloride monomers. The chlorine atoms introduce dipoles into the long molecules. This increases the IMF between molecules, which leads to a higher melting point. A PVC item burning in a flame will not continue to burn when it is removed from the flame. It is used in products such as conveyor belts, cordial bottles, water pipes and the covering of electrical wires.

Pure PVC is very hard and brittle. Additives are incorporated into PVC to improve its flexibility, thermal stability and UV stability. In a fire, PVC decomposes to form toxic and corrosive hydrogen chloride.

POLYSTYRENE (PS)

First commercial production by IG Farben; used in disposable household products, plastic model kits, laboratory containers, insulation and packaging.

Benzene rings are covalently bonded to every second carbon atom in the polymer chain. This causes polystyrene to be a hard but quite brittle plastic with a low density. It is used to make food containers, picnic sets, refrigerator parts, and CD and DVD cases. Polystyrene is made from styrene (ethylbenzene monomers).

Polystyrene (polyethylbenzene) is commonly manufactured as a foam. Foamed polymers are formed by blowing a gas through melted polymer materials. Foaming can drastically change the physical properties of a polymer material. 95-98% air

Polystyrene foam is produced by introducing pentane into melted polystyrene beads. The beads swell up to produce the lightweight, insulating, shock-absorbing foam that is commonly used for takeaway hot drink containers, bean bag beans, packaging materials and safety helmet linings. Once polystyrene has been converted to a foam, it is difficult to recycle.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 63 OF 65 POLYTETRAFLUOROETHYLENE (PTFE)

Polytetrafluoroethene is used in cookware fabrics, wiper blades, nail polish, industrial coatings. (aka Teflon, or Fluon). Made out of tetrafluoroethene monomers.

Tetrafluoroethene is formed when all the hydrogen atoms in ethene are replaced by highly electronegative fluorine atoms.

It has quite exceptional properties that are very different from those of polyethene. It can be used to make non-stick frying pans, medical implants, gears and clothing. The electronegative fluorine atoms reduce the

strength of intermolecular bonds with other substances.

- Non-stick - Heat resistant - Chemical resistant - Good mechanical properties - Low friction coefficient - Flame resistant - High melting point

POLYETHYLENE TEREPHTHALATE (PET)

Polyesters are a class of polymers that are formed through the process of condensation polymerisation. Polyesters are formed by combining monomers that contain carboxylic acid and hydroxyl functional groups. They are typically formed by reacting a dicarboxylic acid monomer with a diol monomer.

This is the most often polymer used to make polyester fabric. PET is synthesised by reacting benzene-1,4-dioic acid monomers with ethane-1,2-diol monomers.

PET has a range of uses including recyclable drink bottles and food packaging. PET is a strong material because the ester groups are polar, so that there are dipole-dipole attractions between the polymer chains. Benzene rings make it stiff and strong, resistant to deformation.

CHEMISTRY MODULE 7: ORGANIC CHEMISTRY PAGE 64 OF 65 NYLON 6,6

Nylon stockings created shopping frenzy in the USA in the 1940s. It is also used in clothing, parachutes, kitchen utensils, toothbrushes, fishing lines, guitar strings, seatbelts.

Nylon is formed when a monomer containing an anime group on each end reacts with a monomer with a carboxyl group on each end, a polyamide can form.

The term ‘nylon’ refers to the group of polyamides, in which the monomers are linear carbon chains. A common example is nylon-6,6 which is named so because the dicarboxylic acid monomer has a chain of 6 carbons and the diamine monomer also has a chain of 6 carbon atoms.

Nylon can be easily drawn into fibres that have high tensile strength. These fibres are used to produce strong lightweight material for clothes.

CHEMISTRY MODULE 8

Applying Chemical Ideas

CHEMISTRY MODULE 8 – APPLYING CHEMICAL IDEAS

ANALYSIS OF INORGANIC SUBSTANCES

Inquiry question: How are the ions present in the environment identified and measured?

● analyse the need for monitoring the environment

● conduct qualitative investigations – using flame tests, precipitation and complexation reactions as appropriate – to test for the presence in aqueous solution of the following ions: – cations: barium (Ba2+), calcium (Ca2+), magnesium (Mg2+), lead(II) (Pb2+), silver ion (Ag+), copper(II) (Cu2+),

iron(II) (Fe2+), iron(III) (Fe3+) – anions: chloride (Cl–), bromide (Br–), iodide (I–), hydroxide (OH–), acetate (CH3COO–), carbonate (CO32–),

sulfate (SO42–), phosphate (PO43–)

● conduct investigations and/or process data involving: – gravimetric analysis – precipitation titrations

● conduct investigations and/or process data to determine the concentration of coloured species and/or metal ions in aqueous solution, including but not limited to, the use of: – colourimetry – ultraviolet-visible

spectrophotometry – atomic absorption spectroscopy

ANALYSIS OF ORGANIC SUBSTANCES

Inquiry question: How is information about the reactivity and structure of organic compounds obtained?

● conduct qualitative investigations to test for the presence in organic molecules of the following functional groups: – carbon–carbon double bonds – hydroxyl groups – carboxylic acids (ACSCH130)

● investigate the processes used to analyse the structure of simple organic compounds addressed in the course, including but not limited to: – proton and carbon-13 NMR – mass spectroscopy (ACSCH19) – infrared spectroscopy (ACSCH130)

CHEMICAL SYNTHESIS AND DESIGN

Inquiry question: What are the implications for society of chemical synthesis and design?

● evaluate the factors that need to be considered when designing a chemical synthesis process, including but not limited to: – availability of reagents – reaction conditions (ACSCH133) – yield and purity (ACSCH134) – industrial uses (eg pharmaceutical, cosmetics, cleaning products, fuels) (ACSCH131) environmental, social

and economic issues

CHEMISTRY MODULE 8: APPLYING CHEMICAL IDEAS PAGE 1 OF 48

ION IDENTIFICATION

OUTCOMES

● analyse the need for monitoring the environment

CHEMICAL MONITORING AND MANAGEMENT

Chemical monitoring and management are needed to ensure the health and wellbeing of both plants and animals. Monitoring also allows for more effective management.

For example, the destruction of UV-protective ozone, caused by widespread use of chlorofluorocarbons (CFCs)

- Hazardous ions in the environment such as mercury have also been identified and monitored using chemical

techniques. - Nutrients required by humans and other living organisms have also been discovered through environmental

monitoring.

OUTCOMES

● conduct qualitative investigations – using flame tests, precipitation and complexation reactions as appropriate – to test for the presence in aqueous solution of the following ions: – cations: barium (Ba2+), calcium (Ca2+), magnesium (Mg2+), lead(II) (Pb2+), silver ion (Ag+), copper(II) (Cu2+),

iron(II) (Fe2+), iron(III) (Fe3+) – anions: chloride (Cl–), bromide (Br–), iodide (I–), hydroxide (OH–), acetate (CH3COO–), carbonate (CO32–),

sulfate (SO42–), phosphate (PO43–) QUALITATIVE ION ANALYSIS

- Precipitate: Insoluble ionic salt formed when 2 ionic solutions are mixed together. - Qualitative analysis: Identification of the constituents of components in a sample. - Quantitative analysis: Measurement/determination of the amount (expressed in a concentration) of the

constituent. - Destructive testing: Test that irreversibly alter the composition of a sample.

CHEMISTRY MODULE 8: APPLYING CHEMICAL IDEAS PAGE 2 OF 48 PRECIPITATION REACTIONS SOLUBILITY RULES Precipitation reactions are useful for the rapid identification of ions. - Solutions of specific ions are added to the unknown aqueous sample. - The formation or absence of a precipitate can be used to determine the ion present. Rule Exceptions

All Group 1 (Li+, Na+, K+, Rb+, Cs+) and ammonium (NH4+) are soluble NONE All nitrate (NO3-) and acetate (CH3COO-) salts are soluble NONE All chloride (Cl-) and bromide (Br-) salts are soluble Ag+, Pb+ (Hg+) All iodide (I-) salts are soluble Ag+, Pb+, Hg+

All sulfate (SO42-) salts are soluble Ag+, Pb2+, Ba2+, Ca2+, Sr2+, Hg+

All hydroxide (OH-) salts are insoluble Group 1 and NH4+ salts are soluble. Ba2+, Ca2+ are slightly All carbonate (CO32-) and phosphate (PO43-) are insoluble Group 1 and NH4+ salts are soluble

Ba2+

Solution PO4 2− SO4 2− CO3 −2 OH− Cl− Br− I− CH3COO−

Colourless White insoluble White insoluble

White soluble White soluble White soluble

White soluble Ca2+ White insoluble White

insoluble White soluble White soluble White soluble

White soluble Mg2+ White insoluble

White soluble White insoluble White insoluble White soluble White soluble White soluble

White soluble Pb2+ White insoluble White insoluble

White insoluble White insoluble Bright Yellow

White soluble Cu2+ Blue Blue insoluble Blue soluble Green insoluble

Blue insoluble Blue soluble Blue soluble

Not stable Blue soluble Fe2+ Pale green Green insoluble

Green soluble Grey insoluble

Green insoluble Green soluble Green soluble Green soluble

Green soluble Fe3+ Yellow Pink insoluble

Yellow soluble Not stable

Brown insoluble Brown soluble Brown soluble

Not stable Brown soluble Ag+ Colourless Yellow insoluble

White insoluble Yellow insoluble

Not stable White insoluble

Pale yellow insoluble White soluble

- Ag+ halides precipitates decompose with exposure to light to form Ag(s). This is observed

as darkening of the solid. CHEMISTRY MODULE 8: APPLYING CHEMICAL IDEAS PAGE 3 OF 48

COMPLEXATION REACTIONS

Complexation reactions are commonly used to identify transition metal cations (due to their d orbitals).

- This includes Ag+, Cu2+, Fe2+, Fe3+ and Pb2+

A complexation reaction occurs when a coordination compound or complex forms.

- These consist of a central metal ion (typically a transition metal) coordinated to molecules or ions (polar &

lone pair of electron molecules). - The coordinating species are called ligands. They are typically neutrally or negatively charged. (E.g.

H2O,NH3,Cl−,CN−)

Coordination complexes are usually coloured and are indicated by the formula being enclosed in square brackets. E.g. [Cu(OH2)6]

2+ and [CuCl4]2−.

COMPLEXATION REACTIONS AND ION IDENTIFICATION

HYDRATED TRANSITIONAL METAL ION

When transition metal ions dissolve in water, a complexation reaction occurs:

FeCl2(aq) + 6H2O(l) → [Fe(OH2)6] (aq) 2+ + 2Cl (aq) −

- Water molecules (ligands) coordinate to the transition metal centre - Charge stays the same as the original cation - Hydrated transition metal centres often have characteristic colours that can be used to identify them.

IDENTIFICATION WITH COMPLEXATION

Complexation reactions can be also used in conjunction with precipitation reactions to identify ions.

Sliver halides can be distinguished due to their different complexation reactions with ammonia:

- AgCl is soluble in dilute ammonia: AgCl(s) + 2NH3(aq) ⇌ [Ag(NH3)2] (aq) + + Cl (aq) − - AgBr is

soluble in concentrated ammonia: AgBr(s) + 2NH3(aq) ⇌ [Ag(NH3)2] (aq) + + Br (aq) − - AgI is insoluble in any concentration of ammonia

This test can be used to distinguish between Ag+ and Pb2+. (PbCl2 does not dissolve in ammonia)

CHEMISTRY MODULE 8: APPLYING CHEMICAL IDEAS PAGE 4 OF 48 Complexation reactions can also be used as confirmatory tests:

- Iron (III) ions react with thiocyanate (SCN-) to produce blood red [Fe(SCN)]2+ - Copper (II) ions react with ammonia to form pale blue Cu(OH)2(s) which then dissolves to form deep blue

[Cu(NH3)4]2+

o Ammonia initially reacts with water to produce the OH-: NH3(aq) + H2O(l) → NH4 (aq) + + OH (aq) −

FLAME TESTING

A flame test is used to qualitatively identify some metal ions in a sample. It can be used to distinguish between cations that undergo similar precipitation reactions. For example, Ba2+ and Ca2+ or Group 1 metals. However, not all metals produce a diagnostic flame colour.

ATOMIC EMISSION

The flame colour arises from atomic emissions of the metal.

- The heat of the flame excites electrons into higher energy

levels - Atomic emission occurs when an electron in a higher energy

level returns to a lower energy level (relaxation) - During relaxation, a wavelength of light matching the energy

difference between the levels is emitted.

Wavelength is inversely proportional to energy:

E = hcλ

- The greater difference → shorter λ

The colour of the flame produced in the flame test results from a combination of the most intense wavelengths emitted in the visible regions.

Metals that do not produce a characteristic flame colour typically have atomic emissions that fall outside the visible region.

CHEMISTRY MODULE 8: APPLYING CHEMICAL IDEAS PAGE 5 OF 48 CHARACTERISTIC FLAME COLOUR

Metal Ion Colour

Ba2+ Yellow-green (apple green)

Ca2+ Orange-red (brick red)

Mg2+ No characteristic flame colour

Pb2+ Grey-blue

Cu2+ Green (halide = blue green)

Fe2+/Fe3+ Orange-brown

Ag+ No characteristic flame colour

LIMITATIONS OF THE FLAME TEST

- Flame tests are only useful for some metal cations. - Destructive - Can be ambiguous which metal ion is present

o The flame colours may be similar (e.g. Rb and Cs produce the same colour as K) o Different oxidation states of the same metal cannot be distinguished (e.g. Fe3+ and Fe2+) - Inconclusive results

can be caused by interference created by other metal ions present in the sample. (e.g.

Ba flame masks Cu, Li and Sr)

o Interference can sometimes be removed by using coloured glass filters. For example, blue cobalt

glass can be used to filter out the bright yellow light produced by Na, a common impurity.

ADDITIONAL TESTS FOR ION IDENTIFICATION

SOLUTION PH

Conjugates of strong acids/bases will dissolve to produce a solution with neutral pH. Conjugate bases of weak acids/bases will produce a non-neutral pH.

Basic Ion (pH > 7) Neutral Ion (pH = 7)

Hydroxide (OH-) Chloride (Cl-)

Acetate (CH3COO-) Bromide (Br-)

Carbonate (CO32-) Iodide (I-)

Phosphate (PO43-) Sulfate (SO42-)

ACID CARBONATE REACTION

Carbonate anions (CO32-) can be identified through the addition of an acid. Bubbles will be observed. A lime water test can be used to confirm the presence of CO2(g).

2H (aq) + + CO3 (aq) 2− → H2O(l) + CO2(g)

CHEMISTRY MODULE 8: APPLYING CHEMICAL IDEAS PAGE 6 OF 48 FLOWCHARTS

- To create a flowchart effectively, go from least soluble to most soluble. - It is important to include ‘in excess’ for flowcharts with more than 1 ion in a sample.

o Include filtering out precipitates as well.

CATIONS

GRAVIMETRIC ANALYSIS

OUTCOMES

● conduct investigations and/or process data involving: – gravimetric analysis

WHAT IS GRAVIMETRIC ANALYSIS

Gravimetric analysis uses the mass of product (precipitate) formed through a precipitate reaction to quantify a target ion. It is used in applications such as monitoring water quality, determining the mineral composition of soil and product testing.

Gravimetric analysis is typically performed with the following steps:

1) A known quantity of sample is dissolved in water 2) The target ion is precipitated from the solution using a suitable reagent 3) The precipitate is collected by filtration, then washed, dried and weighed

The reagent used in the precipitation reaction must react selectively with the target ion and form a highly insoluble precipitate in order to give accurate results. The selective reagent can be chosen using the solubility rules, while the solubility of the resulting precipitate can be found by examining the solubility product constant (Ksp).

Undesired precipitation reactions can be prevented through experimental design.

The amount of the target ion present is usually expressed as a mass percentage of the original sample.

GRAVIMETRIC ANALYSIS ASSUMPTIONS (VALIDITY)

- Only the target ion precipitates out

o Selective reagent o Remove or prevent the precipitation of other salts - All the target ion precipitates out

o Selective reagent (Highly insoluble precipitate, really small Ksp) o Added in excess

CHEMISTRY MODULE 8: APPLYING CHEMICAL IDEAS PAGE 9 OF 48 - All of the precipitate is collected and in a pure form o Filtration (quantitative filter paper) o Wash precipitate with warm distilled water multiple times o Ensure it is dry when measuring its mass SULFATE CONTENT OF FERTERLISER Fertilisers (a solid mixture) commonly contain ammonium sulfate (NH4)2SO4, as a sulfur source for plants. The sulfate content of fertiliser can be determined gravimetrically through the addition of Ba2+ to form a highly insoluble BaSO4. Barium can precipitate with CO32-, Cl-, PO43- and OH- anions as well. To precipitate out: - CO32-: Add acid in excess - PO43 and OH-: Acidify solution (Don’t use H2SO4) - Cl-: Add AgNO3

in excess If other anions precipitate with Ba, the mass of the residue collected will increase. Therefore, a higher w/w % will be calculated than actually present. EXAMPLE QUESTION 1 The following results were obtained for the gravimetric analysis of sulfate ions in several fertiliser samples Sample A B Mass of fertiliser sample used (g) 13.5 1.5 Mass of BaSO4 collected (g) 1.642 0.0870 There are two methods:

A m(BaSOn(BaSOn(SOm(SO% of 44SO) ) = 4= 4 4) ) in n(BaSO= 0.679520932 = fertiliser

0.00703663719 1.642 4) g

= = 0.00703663719 g m(SO13.5 mol 4)

= 5.01%

mol

B m(BaSO% m(SO% of of 4SOSO) 4 = 4 4) in in 0.0870 = BaSOfertiliser 0.0870 4 × = 41.17% g

mm(BaSO= mm(SOm(SO1.5 = 40.035814768 4) 4) ) = = 2.4%

233.37 96.07

= 41.17%

g PROS AND CONS OF GRAVIMETRIC ANALYSIS ADVANTAGES - It is very accurate, if the gravimetric analysis is carefully designed (assumptions) and conducted. - It does not require speciality equipment to perform. - It does not require the construction of a calibration curve, which can be time consuming DISADVANTAGES - The target ion of interest must be able to form a sufficiently insoluble precipitate for accurate results (A limitation of the technique) CHEMISTRY MODULE 8: APPLYING CHEMICAL IDEAS PAGE 10 OF 48

- The precipitate must be highly pure o Impurities can be adsorbed to the surface of the precipitate or trapped within the precipitate,

resulting in increased mass and inaccurate results - It is extremely time consuming compared to modern analytical techniques - Concentration of the target ion must be high enough to produce a precipitate that can be accurately

weighed.

PRECIPITATION TITRATIONS

OUTCOMES

● conduct investigations and/or process data involving: – gravimetric analysis – precipitation titrations

TITRATION

Precipitation titration are commonly used in the quantification of halides (Cl-, Br-, I-). In these procedures, silver ions are usually the titrant and consequently they are known as argentometric titrations.

The main three titrations used are:

- Mohr’s method - Volhard’s method - Fajan’s method

MOHR’S METHOD (DIRECTION TITRATION)

Mohr’s method quantifies chloride, bromide and cyanide ions using direct titration with a standard silver nitration solution.

Ag (aq) + + X (aq) − → AgX(s)

Yellow potassium chromate (K2CrO4) is used as the indictor:

- Silver preferentially precipitates with halide ions - When excess silver is added, it will react with chromate ions to produce a reddish-brown precipitate

Ag2CrO4(s)

2Ag (aq) + + CrO4 (aq) 2− ⇌ Ag2CrO4(s)

LIMITATIONS OF MOHR’S METHOD

The presence of multiple anions in a sample can lead to invalid results. Carbonate and phosphate ions will precipitate with silver.

2Ag (aq) + + CO3(aq) 2− → Ag2CO3(s)

3Ag (aq) + + PO4(aq) 3− → Ag3PO4(s)

CHEMISTRY MODULE 8: APPLYING CHEMICAL IDEAS PAGE 11 OF 48 The conical flask must be thoroughly stirred during the titration to ensure the Ag+ ions are evenly distributed, so AgCrO4 will not precipitate early.

The titration must be conducted at a pH 6.5-9.0

- At pH < 6.5, the chromate ion (a weak base) accepts H+ to become HCrO4-, so there will not be enough

chromate in solution to produce the end point colour change. HCrO4- is also bright orange, which obscures the endpoint. - At pH > 9.0, the concentration of OH- is too high. It will form a precipitate with Ag to produce AgOH which is

a brown precipitate. It also obscures the endpoint and increases the silver needed to reach it.

Mohr’s method is suitable for the analysis of chloride and bromide ions, but not iodide or thiocyanate ions. This is because the chromate ions are strongly adsorbed to the surface of AgI and AgSCN precipitates, making the endpoint indistinct.

In this precipitation titration, the concentration of the indicator used is quite low as adding too much chromate indicator will lead to an intense yellow colour which masks the end point. Hence the excess titrant required to cause a colour change is relatively large.

- 2Ag (aq) + + CrO4(aq) 2− ⇌ Ag2CrO4(s) - Small concentrations of CrO42- means that equilibrium lies towards the LHS. To shift equilibrium towards the

RHS, a relatively large amount of Ag+ needs to be added.

This excess silver required to reach the end point leads to a systematic error, which can be corrected using a blank titration.

- The same quantity of chromate indictor is to be used in the titration is added to a suspension of calcium

carbonate (which imitates the white AgX precipitate). - AgNO3 is added to the solution until a colour change occurs. - The volume of AgNO3 required to cause the colour change in the blank is the excess volume required. This

volume is subtracted from the titration volumes.

VOLHARD’S METHOD (BACK TITRATION)

Volhard’s method quantifies anions used in back titration procedure.

- A known excess quantity of AgNO3 is added to the sample to precipitate all of the analyte anions:

o Ag (aq) + + X (aq) − → AgX(s) - The excess AgNO3 is determined by back titration against KSCN(aq) standard solution

o Ag (aq) + + SCN (aq) − → AgSCN(s) - A small amount of Fe3+ is added as the indictor.

When excess SCN- is present, there will be a permanent

colour change.

o Fe (aq) 3+ + SCN (aq) − → [Fe(SCN)] (aq) 2+

LIMITATIONS OF VOLHARD’S METHOD

The Volhard titration must be performed in low pH to prevent the precipitation of Fe3+ indictor as Fe(OH)3. At low pH, there is a relatively low [OH-], therefore the precipitate Fe(OH)3 will not form.

The Volhard method is less valid if the first precipitate formed is more soluble than AgSCN.


- For example, AgCl (Ksp = 1.77 × 10−10) is more soluble than the AgSCN (Ksp = 1.03 × 10−12). This means that AgCl can dissolve during the titration leading to a greater titration volume required.

To avoid this problem, the procedure can be modified.

- The first precipitate can be removed via filtration before titration. However, this can lead to inaccuracies

and is less convent . - A dense organic liquid like nitrobenzene or chloroform can be added to the conical flask to act as a barrier

between the precipitate and aqueous layer.

FAJAN’S METHOD (DIRECT TITRATION AND ADSORPTION INDICATOR)

In the analysis of chloride, an anionic dye is added to the sample.

- A standard solution of AgNO3 is added and the precipitation occurs:

o Ag (aq) + + Cl (aq) − → AgCl(s) - Before the equivalence point, a small excess of chloride ions is incorporated into the precipitate, so it carries

a negative charge. The dye is repelled and remains in solution. - After the equivalence point, there is a small excess of silver ions. Therefore, the precipitate becomes slightly

positively charged, and the dye adsorbs onto it, resulting in a precipitate colour change.

The most suitable indicator depends on the analyte.

PROS AND CONS OF FAJAN’S METHOD

The Fanjan’s method relies on a large precipitate surface area, to allow sufficient dye to adsorb so the colour change is easily visible.

- Dextrin (starch) can be added to prevent silver halide precipitates from aggregating - A high concentration of spectator ions can also caused aggregation, so this method cannot be used with all

samples. - The analyte must also be concentrated enough, as the colour will not be seen if there is too little precipitate.

The pH of the titration reaction must be carefully controlled as anionic dye indicators are conjugate bases of weak acids. This means it will react with free H+ and will not adsorb onto the surface of the precipitate.


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