HSC Chemistry Topic 1

HSC topic 1 Production Of Materials HSC topic 1 Production Of Materials

1. Fossil fuels provide both energy and raw

1. Fossil fuels provide both energy and raw materials such as ethylene, for materials such as ethylene, for the production of otherthe production of other substances.

substances.

Construct word and balanced formulae equations of chemical reactions as they are

Construct word and balanced formulae equations of chemical reactions as they are encounteredencountered Basic reactions to remember:

Basic reactions to remember: 1. Element+ oxygen

1. Element+ oxygenelement oxideelement oxide  4Na (s) + O (g)

 4Na (s) + O (g) 2NaO (s)2NaO (s) 2. Element + hydrogen

2. Element + hydrogenelement hydrideelement hydride N (g) + 3H (g)

N (g) + 3H (g)2NH (g)2NH (g) 3. Metallic Oxide + water

3. Metallic Oxide + water hydroxidehydroxide NaO (s) + HO (l)

NaO (s) + HO (l) 2NaOH (aq)2NaOH (aq) 4. Non metallic oxide + water

4. Non metallic oxide + wateracidacid SO (g) + HO (l)

SO (g) + HO (l)HSO (aq)HSO (aq) 5. Metal + water

5. Metal + waterhydroxide + hydrogen gashydroxide + hydrogen gas 2K(s) + 2HO (l)

2K(s) + 2HO (l)2KOH (aq) + H (g)2KOH (aq) + H (g) 6. Metal + acid

6. Metal + acidsalt + watersalt + water Mg (s) + 2HCl (aq)

Mg (s) + 2HCl (aq)MgCl (aq) + H (g)MgCl (aq) + H (g) 7. Acid + base

7. Acid + base salt +watersalt +water HNO (aq) + NaOH (aq)

HNO (aq) + NaOH (aq) NaNO (aq) + HO (l)NaNO (aq) + HO (l) 8. Acid + Carbonate

8. Acid + Carbonatesalt + carbon dioxide + watersalt + carbon dioxide + water HCl (aq) + CaCO (s)

HCl (aq) + CaCO (s) CaCl (aq) + CO (g) + HO (l)CaCl (aq) + CO (g) + HO (l) 9. Carbonate + heat

9. Carbonate + heatoxide + carbon dioxideoxide + carbon dioxide CaCO (s) + heat

CaCO (s) + heatCaO (s) + CO (g)CaO (s) + CO (g) 10. Metallic oxide + heat

10. Metallic oxide + heat metal + oxygenmetal + oxygen 2HgO (s) +heat

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11. Hydroxide +heat

11. Hydroxide +heatwater + oxidewater + oxide Mg(OH) (g) + heat

Mg(OH) (g) + heatHO (l) + MgO (s)HO (l) + MgO (s) 12. Metallic Oxide + acid

12. Metallic Oxide + acid salt + watersalt + water MnO (s) + 2HCl (aq)

MnO (s) + 2HCl (aq) MnCl (aq) + HO (l)MnCl (aq) + HO (l) 13. Non metallic oxide + base

13. Non metallic oxide + basesalt + watersalt + water CO (g) + 2 NaOH (aq)

CO (g) + 2 NaOH (aq) NaCO (aq) + HO (l)NaCO (aq) + HO (l) 14. Carbon dioxide + water+ UV rays

14. Carbon dioxide + water+ UV rays glucose + oxygenglucose + oxygen 6CO + 6HO (l) +UV

6CO + 6HO (l) +UVCHO(s) + 6O (g)CHO(s) + 6O (g) Complete

Complete combustioncombustion:: Hydrocarbon

Hydrocarbon + + oxygen oxygen water water + + carbon carbon dioxidedioxide Displacement

Displacementreactionsreactions:: Y

Y + + X X ((aanniioonn) ) X X + + Y Y ((aanniioonn)); ; wwhheerre e Y Y > > X X oonn activity seriesactivity series.. y

y  Alk  Alk ene/aene/alk lk ane reactions:ane reactions:

 ± 

 ± 

CCrackingrackingof pentaneof pentane::

 pentane pentane ethylene ethylene + + propanepropane

 CC55HH12 (g)12 (g) CC22HH4 (g)4 (g)+ C+ C33HH8 (g)8 (g)

 ± 

 ± 

HHydrogenationydrogenationof ethyleneof ethylene::

 ethylene ethylene + + hydrogen hydrogen ethaneethane

 CC22HH4 (g)4 (g)+ H+ H22 (g)(g) CC22HH6 (g)6 (g)

 ± 

 ± 

HHydrationydrationof ethyleneof ethylene::

 ethylene ethylene + + water water ethanolethanol

 CC22HH4 (g)4 (g)+ H+ H22OO(l)(l) CC22HH55OHOH(l)(l)

 ± 

 ± 

HHalogenationalogenation(more (more specificallspecifically,y,CChlorinationhlorination) of ethylene) of ethylene::  ethylene ethylene + + chlorine chlorine 1,2-dichloroetha1,2-dichloroethanene

 CC22HH4 (g)4 (g)+ Cl+ Cl2 (g)2 (g) CC22HH44ClCl2 (l)2 (l)

 ± 

 ± 

HHydrohalogenationydrohalogenation(more specifically,(more specifically,HHydrofluorination) of ethyleneydrofluorination) of ethylene::  ethylene ethylene + + hydrogen hydrogen fluoride fluoride fluoroethanefluoroethane

11. Hydroxide +heat

11. Hydroxide +heatwater + oxidewater + oxide Mg(OH) (g) + heat

Mg(OH) (g) + heatHO (l) + MgO (s)HO (l) + MgO (s) 12. Metallic Oxide + acid

12. Metallic Oxide + acid salt + watersalt + water MnO (s) + 2HCl (aq)

MnO (s) + 2HCl (aq) MnCl (aq) + HO (l)MnCl (aq) + HO (l) 13. Non metallic oxide + base

13. Non metallic oxide + basesalt + watersalt + water CO (g) + 2 NaOH (aq)

CO (g) + 2 NaOH (aq) NaCO (aq) + HO (l)NaCO (aq) + HO (l) 14. Carbon dioxide + water+ UV rays

14. Carbon dioxide + water+ UV rays glucose + oxygenglucose + oxygen 6CO + 6HO (l) +UV

6CO + 6HO (l) +UVCHO(s) + 6O (g)CHO(s) + 6O (g) Complete

Complete combustioncombustion:: Hydrocarbon

Hydrocarbon + + oxygen oxygen water water + + carbon carbon dioxidedioxide Displacement

Displacementreactionsreactions:: Y

Y + + X X ((aanniioonn) ) X X + + Y Y ((aanniioonn)); ; wwhheerre e Y Y > > X X oonn activity seriesactivity series.. y

y  Alk  Alk ene/aene/alk lk ane reactions:ane reactions:

 ± 

 ± 

CCrackingrackingof pentaneof pentane::

 pentane pentane ethylene ethylene + + propanepropane

 CC55HH12 (g)12 (g) CC22HH4 (g)4 (g)+ C+ C33HH8 (g)8 (g)

 ± 

 ± 

HHydrogenationydrogenationof ethyleneof ethylene::

 ethylene ethylene + + hydrogen hydrogen ethaneethane

 CC22HH4 (g)4 (g)+ H+ H22 (g)(g) CC22HH6 (g)6 (g)

 ± 

 ± 

HHydrationydrationof ethyleneof ethylene::

 ethylene ethylene + + water water ethanolethanol

 CC22HH4 (g)4 (g)+ H+ H22OO(l)(l) CC22HH55OHOH(l)(l)

 ± 

 ± 

HHalogenationalogenation(more (more specificallspecifically,y,CChlorinationhlorination) of ethylene) of ethylene::  ethylene ethylene + + chlorine chlorine 1,2-dichloroetha1,2-dichloroethanene

 CC22HH4 (g)4 (g)+ Cl+ Cl2 (g)2 (g) CC22HH44ClCl2 (l)2 (l)

 ± 

 ± 

HHydrohalogenationydrohalogenation(more specifically,(more specifically,HHydrofluorination) of ethyleneydrofluorination) of ethylene::  ethylene ethylene + + hydrogen hydrogen fluoride fluoride fluoroethanefluoroethane

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 CC22HH4 (g)4 (g)+ HFl+ HFl(g)(g) CC22HH55FlFl(g)(g)

 ± 

 ± 

RReaction of cyclohexeneeaction of cyclohexene withwith bromine waterbromine water::

 cyclohexene cyclohexene + + bromine bromine + + water water 2-bromo-1-cyclo2-bromo-1-cyclohexanol hexanol + + hydrogen hydrogen bromidebromide

 CC66HH10 (l)10 (l)+ Br+ Br2 (aq)2 (aq)+ H+ H22OO(l)(l) CC66HH1010BrOHBrOH(l)(l)+ HBr+ HBr(aq)(aq) y

y F F ermentation and other ethanoermentation and other ethanol-l-based reactions:based reactions:

 ± 

 ± 

DehydrationDehydrationof ethanolof ethanol::

 ethanol ethanol ethylene ethylene + + waterwater

 CC22HH55OHOH(l)(l) C2C2HH4 (g)4 (g)+ H+ H22OO(l)(l)

 ± 

 ± 

CCombustionombustionof ethanolof ethanol::

 ethanol ethanol + + oxygen oxygen carbon carbon dioxide dioxide + + waterwater

 CC22HH55OHOH(l)(l) + 3O+ 3O2 (g)2 (g) 2CO2CO2 (g)2 (g)+ 3H+ 3H22OO(g)(g)

 ± 

 ± 

FermentationFermentationof glucoseof glucose::

 glucose glucose ethanol ethanol + + carbon carbon dioxidedioxide

 CC66HH1212OO6 (aq)6 (aq) 2C2C22HH55OHOH(aq)(aq)+ 2CO+ 2CO2 (g)2 (g) y

y E E l l ectrochemistry:ectrochemistry:

 ± 

 ± 

DisplacementDisplacementof copper from solution due to zincof copper from solution due to zinc::  zinc zinc + + copper copper sulfate sulfate zinc zinc sulfate sulfate + + coppercopper

 ZZ_{nn(s)(s)+ CuSO+ CuSO4 (aq)4 (aq)} ZZ_{nSOnSO4 (aq)4 (aq)+ Cu+ Cu(s)(s)}

 ± 

 ± 

IIonic equationonic equationof this reactionof this reaction::

 zinc zinc + + copper(II) copper(II) ion ion + + sulfate sulfate ion ion zinc(II) ion zinc(II) ion + + sulfate sulfate ion ion + + coppercopper

 ZZ_{n + Cun + Cu}2+2+_{+ SO+ SO44}2-2- ZZ_nn2+2+_{+ SO+ SO44}2-2-_{+ Cu+ Cu}

 ± 

 ± 

NNet ionic equationet ionic equationof this reactionof this reaction::

 zinc + copper(II) ionzinc + copper(II) ion zinc(II) ion + copperzinc(II) ion + copper

 ZZ_{nn(s)(s)+ Cu+ Cu}2+2+_(aq)(aq) ZZ_nn2+2+_{(aq)(aq)+ Cu+ Cu(s)(s)}

 ± 

 ± 

HHalf-equationsalf-equationsof this equationof this equation::  ZZnn ZZnn2+2++ 2e+ 2e¯¯

Identify the industrial source of ethylene from the cracking of

Identify the industrial source of ethylene from the cracking of some of the fractions from the refining some of the fractions from the refining of of  petroleum

petroleum

Petroleum (crude oil) is a complex mixture

Petroleum (crude oil) is a complex mixture of hydrocarbons consisting mainly of alkanes andof hydrocarbons consisting mainly of alkanes and

cycloalkanes, with smaller quantities of unsaturated hydrocarbons including alkenes. For the crude oil to cycloalkanes, with smaller quantities of unsaturated hydrocarbons including alkenes. For the crude oil to be used as a fuel or as a raw material

be used as a fuel or as a raw material for the petrochemical industry, it must be refined. To refine thefor the petrochemical industry, it must be refined. To refine the crude oil, the process used is called fractional distillation which is separated based on

crude oil, the process used is called fractional distillation which is separated based on different boilingdifferent boiling pts of the hydrocarbons. Ethylene (CH) is one of

pts of the hydrocarbons. Ethylene (CH) is one of the most useful substances in the petrochemicalthe most useful substances in the petrochemical industry. To obtain ethylene we must crack these larg

industry. To obtain ethylene we must crack these larg e hydrocarbon chains formed from the fractionale hydrocarbon chains formed from the fractional distillation of crude oil. Cracking is the process of brea

distillation of crude oil. Cracking is the process of brea king large hydrocarbon molecules into smallerking large hydrocarbon molecules into smaller length chains, using heat or a

length chains, using heat or a catalyst. Each fraction of the hydrocarbon has a catalyst. Each fraction of the hydrocarbon has a different volatility, Boilingdifferent volatility, Boiling Pt and Mr. The proportions of

Pt and Mr. The proportions of different fractions obtained by the fractional distillation of different fractions obtained by the fractional distillation of petroleumpetroleum usually do not match the demands of

usually do not match the demands of the market. There is the market. There is greater demand for some fractions than forgreater demand for some fractions than for others.

others.

However, the ethylene produced by the crude oil is no

However, the ethylene produced by the crude oil is no t enough to match the gt enough to match the global demand for thelobal demand for the substance.

substance. Therefore other products formed from the fractional distillation of crude oil must be crackedTherefore other products formed from the fractional distillation of crude oil must be cracked to produce ethylene.

to produce ethylene.

E.g. The cracking of pentane into ethylene and propane E.g. The cracking of pentane into ethylene and propane:: Thermal cracking of petroleum fractions

Thermal cracking of petroleum fractions This method of breaking down larger

This method of breaking down larger fractions of hydrocarbons is a non catalytic process in fractions of hydrocarbons is a non catalytic process in which awhich a mixture of alkanes with steam is passed through very hot metal tubes (700-1000°C) and at just above mixture of alkanes with steam is passed through very hot metal tubes (700-1000°C) and at just above atmospheric pressure to decompose the alkanes completely into small alkanes such as ethylene, atmospheric pressure to decompose the alkanes completely into small alkanes such as ethylene, propene and butene. Some hydrogen gas may be produced as

propene and butene. Some hydrogen gas may be produced as well.well. E.g.1.

E.g.1. CH (g) CH (g)   4CH 4CH (g) (g) + + CH CH (g) (g) + + H H (g)(g) E.g.2.

E.g.2. CH (g)CH (g)CH=CH (g) + H (g)CH=CH (g) + H (g)

However, thermal cracking had many disadvantages. However, thermal cracking had many disadvantages. 1. It was very

1. It was very expensive because of the energy required to maintain these high temperatures.expensive because of the energy required to maintain these high temperatures. 2. It was also

2. It was also difficult to control the production of the rdifficult to control the production of the r esultant products as there are many differentesultant products as there are many different places where the breaking of bonds could occur.

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Catalytic cracking of petroleum fractions

This process involves the use of a catalyst to break down feedstock into smaller hydrocarbon molecules. The main catalysts for the catalytic cracking of petroleum fractions are a group of silicate minerals called zeolites.Z_{eolites are crystalline substances composed of aluminium, silicon and oxygen. The catalyst is} usually in the form of a fine powder that is circulated with the feedstock in the catalytic cracker. Z_eolite crystals have a three dimensional network structure containing a l arge number of tiny pores or

channels. The reactant molecules are adsorbed in these pores where their reactions are catalysed. It is possible to synthesis zeolites with pores of different sizes to control the end products formed. Note:The zeolite crystal allows the reaction to occur at a much lower temperature range.

This image shows a portion of the zeolite catalyst.

Identify that ethylene, because of the high reactivity of its double bond, is readily transformed into many useful products

An alkane and an alkene with comparable molecular weights will have similar physical properties because both are non-polar substances and display the same type of intermolecular forces namely dispersion forces.

Alkenes however are much more reactive than alkanes due to the presence of the covalent double bond in its structure. Ethylene is an alkene and can undergo additional reactions by opening out its double bond for two other atoms in a diatomic molecule to be added in.

Hydrogenation:Hydrogen is reacted with ethylene, using a platinum catalyst at 150°C. The product is ethane.

Hydration: Ethylene is reacted with water, using dilute phosphoric acid as a catalyst, to produce ethanol. This is an industrially important reaction.

Halogenation:R_{eactive molecules from the halogen group (Fl2, Cl2and Br2) can all react with ethylene.} EG:_{Chlorine molecule reacting with ethylene forms 1,2-dichloroethane.}

Hydrohalogenation: In this reaction, a hydrohalogen (such as HCl or HFl) and ethylene react to form a halo-ethane. EG:_{HFl reacting with ethylene forms fluoroethane.}

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Identify that ethylene serves as a monomer from which polymers are made

A monomer is a small versatile molecule which consists of a carbon double bond that is capable of  linking up with other such molecules to form a macromolecule. A polymer is a natural occurring or synthetic compound consisting of large molecules made up of a linked series of repeated simple monomers.

Polyethylene is an additional polymer because when its monomer (ethylene) goes under the process of  hydrogenation, no additional molecules are produced (e.g. water)  there is no gain or loss of electrons, the double bond just simply opens and monomers att ach.

From this diagram of polyethylene, we can clearly see that no additional molecules are produced. Outline the steps in the production of polyethylene as an example of a commercially and industrially important polymer

Polyethylene is used both commercially and industrially. There are two methods for its production:

High Pressure Method:_{In this process, ethylene is subjected to high pressures and temperatures of}  300°C. A molecule, called the initiator, is introduced, usually a peroxide. The peroxide starts off a chain reaction, creating the polyethylene macromolecule.

This process creates branched chains of polyethylene that cannot be packed together tightly. Thus branched polyethylene is called low-density polyethylene (LPDE).

Ziegler-Natta Process:_{This process uses only a few at mospheres of pressure and temperatures of about} 60°C. An ionic catalyst is used:_{it is a mixture of titanium (III) chloride and a trialkylaluminium compound.} This process creates unbranched chains of polyethylene that can be packed together very densely. Thus unbranched polyethylene is called high-density polyethylene (HDPE).

The steps taken to produce LDPE and HDPE are the same, but the initiator molecule is different.

Initiation

The initiator molecule (peroxide radical- an oxygen compound with a free electron) is added to the ethylene container. The initiator reacts with one ethylene molecule, breaking its double bond, and attaches to only one bonding site, creating an ethylene- initiatorR_{ADICAL. The dot represents a free,} highly reactive electron.

Propagation

The ethylene radical then attaches to another ethylene monomer, opening another bonding site, then another attaches, and so on. This rapidly increases the length of the chain.

Leading to:

Termination

The reaction terminates when two such chains collide and the two radicals react, forming a longer chain. This is a random process, so the length of polyethylene chains can vary greatly. Note:_{The peroxide} initiator is engulfed by the reaction and is no longer present.

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Identify the following as commercially significant monomersby both their systematic and common names

Common name:_{VinylChloride Systematic name}:_Chloroethene Molecular formula:_CHCl

This molecule is produced by the substitution of hydrogen for a chlorine atom in an ethylene molecule. This can then undergo polymerisation to form a very important polymer known as polyvinyl chloride (polychloroethene):

Common name:_{Styrene Systematic name}:_{Phenylethylene} Molecular formula:_CH

Styrene is an ethylene molecule with one of its hydrog en atoms replaced by a benzene ring. Note:_{A benzene ring is a six- carbon ring with alternating} double bonds. These double bonds within benzene are not reactive. This substance can undergo polymerisation to form polystyrene (polyphenylethene).

Describe the uses of the polymers made from the above monomers in terms of their properties

Polymer Uses Properties for the use

Low-density polyethylene Cling wrap

Disposable shopping bags Milk bottles

Flexible, clear, non-toxic, permeable to O& CO but not water allow the food to be kept fresh and prevent it from drying out

High-density polyethylene Pipes to carry natural gas R_{ubbish bins}

Kitchen utensils

High chemical resistance thus HDPE can be moulded to hold petrol, oil, detergents, acids and solvents. It is rigid, slightly flexible and hard. Strong and non-toxic

PVC Garden hoses

Pipes and guttering

With the addition of certain additives, PVC may improve its flexibility and thermal stability. It is very rigid and hard, and un-reactive

Crystal Polystyrene CD cases and cassette tapes Screw driver handles

Clear, hard, rigid, easily shaped and is a good insulator. Very durable and strong, hard and inflexible.

Expanded Polystyrene 

polystyrene foam aka Styrofoam is produced by blowing gas through liquid polystyrene until it froths up into a foam which is then allowed to cool down and solidify

Packaging and disposable cups Sound proofing

It is light (full of air), cheap, thermal insulator. It is a shock absorbent material, light, easily shaped

Factors affecting the properties of polymers

1. The length of the chain (number of monomer units)  Plastics composed of longer polymer chains are stronger than those with shorter chains due to the greater amount of dispersion forces between them. 2. The arrangement of the chains- When the molecules are lined up and closely packed, they form

crystalline regions resulting in a stronger, less flexible polymer. Amorphous (no distinct shape) regions in which the polymers have a random arrangement produce weaker and softer plastics.

3. The degree of branching- More branching restricts t he orderly packing arrangement and therefore reduces the density and hardness of the polymer but increases its flexibility.

4. The inclusion of additives- certain additives are included to improve or extend the properties of the polymer.

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Practical: _{Identify data, p}l an and perform a first -hand investigation to compare the reactivities of  appropriate alk enes with the corresponding alk anes in bromine water 

AIM:To determine the difference between the reactivity of alkanes and alkenes . MATERIALS:

y Bromine water y Pure cyclohexane y Pure cyclohexene y Molecular model kits y Test tubes

y Measuring cylinders y Beakers

DISPOSAL:Place in an organic waste bottle, rinse the test tube and place rinse in an organic waste bottle

RISKASSESSMENT:

Chemical Risk Management

Bromine Water Highly toxic if ingested and slightly corrosive Use eye and skin protection

Cyclohexane

Toxic by all routes of exposure, highly flammable and vapour moderately toxic

Use in a fume cupboard and eye skin protection or use in small amounts in a well ventilated area

Cyclohexene

Toxic by all routes of exposure, highly flammable and vapour moderately toxic

Use in a fume cupboard and eye skin protection or use in small amounts in a well ventilated area

METHOD:

1. Place 3mL of Br water into 2 test tubes.

2. To one of the tubes add 3 drops of cyclohexane and shake the tube by flicking it briskly. 3. To the other tube, add 3 drops of cyclohexane and shake the tube by flicking it briskly. 4. Draw to diagram to illustrate observations.

5. Construct a model of cyclohexane and cyclohexene molecule, with a model kit. VARIABLES:

Controlled variables:

y Amount of Br water y Amount of Cyclohexane

y Amount of Cyclohexene y Concentration of Br water y Temperature of surroundings y Air Pressure

y Humidity of surroundings

y Method of mixing chemicals (Flicking 3 times)

o Dependent variable:

y The amount of Br water required

o Independent variable:

y The alkane and alkenes

IMPROVING VALIDITY: y Repetition

y Using a range of different Alkanes and Alkenes

 Note: _{Cyclohexene and Cyclohexane were used, instead of ethylene or propene because C1} to C4 are gases at room temperature, and would be hard to manage; cyclohexene/ane are liquid at room temperature.

 Also cyclohexene/ane was used instead of hexene/ane because cyclic hydrocarbons are more stable than their linear counterparts

IMPROVING RELIABILITY: y Repetition

y Improving measurements

o Using a pipette to measure out the amount of bromine water, rather then a measuring

cylinder RESULTS:

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DISCUSSION:Alkenes are more reactive than alkanes due to the presence of their double bond. Alkenes go through what is called an addition reaction. It is where in an alkene; a double bond is broken and replaced with two new covalent bonds added across double bond where a foreign element/compound attaches itself.

E.g. Ethene +Bromine 1,2  dibromoethane

As mentioned above this is described as an addition reaction because extra elements are being added to the hydrocarbon and breaking the double bond. Alkanes go through a process called a substitution reaction. The substitution needs the presence of UV light to go through. An example is shown below:

 +++&O ,,89,, (J+&&+&O+&&++&O ,,,, ++++

When for example Ethane and Bromine undergo a sub stitution reaction the compound HBr is formed. This is due to one of the Br being substituted with an H on the hydrocarbon. Therefore Br2is broken into two, one atom goes and joins the hydrocarbon and the H which the Br replaces attaches on to the free Br to make HBr.

CONCLUSION:Alkenes are more reactive than alkanes as seen in the results of this experiment due to the presence of their double bond.

Practical _: Anal yse information from secondary sources such as computer simul ations, mol ecul ar model  k its or mul timedia resources to model the pol ymerization process

 ± 

In this experiment, molecular modelling kits were used to show how polyethylene is produced

through the polymerisation of ethylene.

 ± 

The class was divided into groups, and each group was provided with a kit.

 ± 

3 ethylene monomers were created by each group, with bl ack balls representing carbons and

smaller, white balls representing hydrogen.

 ± 

Then the monomers were polymerised: each group combined their monomers with every

other group until a large chain was created  a section of polyethylene.

 ± 

JUSTIFYthe method:

 The models created a 3D representation of the chemical process, which led to greater understanding of polymerisation.

 The use of ball-and-stick models, depicting the double-bond with flexible rubber rods, greater increased understanding of the process.

 ± 

LIMITATIONSof the method:

 The model only provided a very limited section of a polyethylene molecule, as there were limited numbers of kits.

 The use of catalysts (such as Zeigler-Natta catalysts) was not shown in the process, and thus it was not completely accurate.

2. Some scientists research the extraction of materials from biomass to reduce our dependence o n fossil fuels

Discuss the need for alternative sources of the compounds presently obtained from the petr ochemical industry

The petrochemical industry is one of the largest in the world, and provides fuels such as petrol, diesel and the raw materials used to make polymers. The source of petrochemicals is the fossil fuel petroleum (crude oil) or natural gas, which are non-renewable resources as they are being consumed at a far

greater rate than produced. The demand for petroleum in recent times has increased, and will continue to increase due to the demands of developing countries such as China and India. Currently Australia has petroleum reserves that will last about ten years and natural gas reserves that will last about one

hundred years.

It will eventually run out, and if energy and material needs are to be met in the future, renewable alternatives need to be found.R_{enewable alternatives that have been suggested include biomass} (organic matter produced by living things):_{Vegetable oils as a possible substitute for diesel fuel, and} ethanol (produced from the fermentation of sugars) as a possible substitute for petrol.

There are also concerns that most polymers produced by the petrochemical industry are non-biodegradable and cause environmental problems. Natural polymers are more likely to be biodegradable, and cause less problems.

The main problem at present is the high cost of these alternatives. However, it is likely that as

petrochemicals become scarcer and therefore more e xpensive; these alternatives will become more economically viable.

Explain what is meant by a condensational polymer

A condensational polymer is a high molecular height substance formed when many simple molecules (monomers) chemically joined by eliminating a small molecule usually water.

E.g. Natural polymers such as cellulose, starch, protein, DNA, and manufactured polymer fabrics such as silk, polyester and nylon.

A n d r e w N g u y e n P a g e | 15

Condensational polymerisation involves a reaction between two different functional groups in which a water molecule (or some other small molecule) is eliminated and the two functional groups become linked together. Condensation polymerisation usually involves a reaction between two different monomers, but can occur where a molecule contains t wo different functional groups.

Note:_{There is no double bond that opens (as in addition); the functional groups of the two monomers} react together, forming a new bond and water.

E.g. Cellulose

Cellulose is a natural polymer formed through the polymerisation of glucose

ß-Glucose (CHO) is the monomer for cellulose. It forms a beta 1,4-glycosidic bond which links each glucose molecule in the growing chain.

The reaction sites are the hydroxyl (OH) groups on the first and fourth carbons. Each glucose molecule has 2 reaction sites; that is why they can polymerise. One C-OH bonds to another C-OH, forming a C-O-C bond (glycosidic bond). The left over H+and OH-combine, forming water.

Describe the structure of cellulose and identify it as an example of a condensation polymer found as a major component of biomass

Cellulose is a natural occurring condensational biopolymer (a biopolymer). It is the most abundant polymer on Earth, making up to 50% of the total biomass of the planet (biomass is the mass of all organisms in a given area).

There are two structural forms of glucose called alpha and beta glucose. It is the beta glucose that leads to cellulose formation. Ultimately up to 10000 glucose units will form the long, unbranched cellulose chain.

Diagram of Beta Glucose

This alternating arrangement maintains a linear structure in the polymer. Cellulose is insoluble in water because its structure

exposes few OH groups to the water molecules in the environment.

Identify that cellulose contains the basic carbon-chain structures needed to build petrochemicals and discuss its potential as a raw material

The basic carbon-chain structures that are used to make petrochemicals are short-chained alkenes such as ethylene (2C), propene (3C) and butene (4C). Glucose, the basic structure in cellulose, is a 6C molecule. Hence it has to potential to be transformed i nto the above compounds.

The Potential of Cellulose as a Raw Material:

Although theoretically, cellulose can provide limitless amounts of renewable raw materials, this is currently too expensive and impractical.

This is because in order to derive ethylene, etc., from cellulose, firstly, cellulose must be broken into glucose (using either bacterial digestion or acidic decomposition), then fermented (with yeast) into ethanol and then dehydrated (using H2SO4) into ethene; this is a lengthy and expensive process.

Hence, cellulose has great potential, but is currently not economical.

Report:_{Use avai} l abl e evidence to gather and present data from secondary sources and anal yse progress in the recent devel opment and use of a named biopol ymer. This anal ysis shoul d name the specific enzyme used or organism used to synthesise the material and an eval uation of the use or potential use of  the pol ymer produced rel ated to its properties

Name of Biopolymer:_Biopol

It is made of  pol yhydroxybutyrate(PHB) and pol yhydroxyval erate(PHV). Organism Used:

Alcaligenes eutrophus (a bacterium).

A n d r e w N g u y e n P a g e | 17

In industrial production, A. Eutrophus is grown in an environment  favourabl e to its growth to create a very large population of bacteria (such as high nitrates, phosphates and other nutrients).

When a sufficiently large population has been produced, the environment is changed to one that is high in gl ucose, high in valeric acid and low in nitrogen.

This unnatural environment induces the production of the polymer by the bacterium; the polymer is actually a natural fat storage material, created by the A Eutrophus in adverse conditions.

Large amounts of a chlorinated hydrocarbon, such as trichl oromethane are added to the bacteria/polymer mix; this dissolves the polymer.

The mixture is then filtered to remove the bacteria.

The polymer is extracted from the hydrocarbon solvent as a powder, which is then melted or treated further to create a usable polymer.

Properties:

-It is BIODEGR_{ADABLE and BIOCOMPATIBLE}

-It is non-toxic, insoluble in water, permeable to oxygen, resistant to UV light, acids and bases, high melting point, high tensile strength

Uses in Relation to Properties:

-It has many medical applications (e.g. biocompatible stiches that dissolve or are absorbed by the body) -Disposable containers for shampoo, cosmetics, milk bottles, etc., as it only takes 2 years to decompose back into natural components

-Disposable razors, cutlery, rubbish bags, plastic plates, etc.

Advantages:

-It is biodegradable, unlike polyethylene and other petroleum derived plastics, and so will help to reduce levels of rubbish in land fills

-It is compatible with organisms (biocompatible); it is not rejected by the bodys immune system and so can be used safely

-It is a renewable resource

-It is currently very expensive, and currently the demand is not high enough for it to be economically viable

Future Developments:

-R_{ecently, the gene for producing Biopol polymer strands from the Alcaligenes Eutrophus bacteria was} extracted and implanted into E. coli using genetic engineering techniques. E. coli bacteria are much easier to grow than other bacteria, and thus are cheaper

-Nutrient sources are starting to be derived from waste materials, such as molasses and other agricultural wastes. This greatly reduces costs.

3. Other resources, such as ethanol, are readily available from renewable resources such as plant s Describe the dehydration of ethanol to ethylene and identify the need for a catalyst in this process and the catalyst used

Before ethylene became readily available through the catalytic cracking of petroleum fractions, it was mainly produced from ethanol. This involved heating ethanol vapour

over a catalyst at 350°C.

Ethanol ethylene + water

CHOH CH (G) + HO (L)

An acid catalyst (concentrated sulphuric acid) is needed because the acid breaks the C-OH and C-H bonds, allowing the formation of a double  bond and water. It also reduces the activation energy.

Describe the addition of water to ethylene resulting in the production of ethanol and identify the need for a catalyst in this process and the catalyst used

The hydration of ethylene is the chemical process whereby a water molecule is added to ethylene, forming ethanol.

Ethylene + water ethanol

CH (G) + HO(L) CHOH (L)

Note that a diluted acid is required to open the double bond, allowing water to attach to it, forming ethanol.

A n d r e w N g u y e n P a g e | 19

Practical  _{ Process information from secondary sources such as mo}l ecul ar model  k its, digital 

technol ogies or computer simul ations to model the addition of water to ethy l ene and the dehydration of  ethanol :

Molecular modelling kits were used to model:

The addition of water to ethylene (hydration) and the removal of water from ethanol (dehydration) Ball-and-stick kits were used, where bl ack balls represented carbons, smaller, white balls representing hydrogen, and red balls represented oxygen.

Firstly, and ethylene molecule was created, and a water molecule created: Then, the water molecule was split into a H+ion and an OH-ion

The double-bond of ethylene was opened, and the ions were attached where there were free bonding sites; the resultant molecule was ethanol

Secondly, a separate ethanol molecule was created:

The hydroxide group (OH-) and a hydrogen was removed from the ends

They were combines, and water was formed; the two open bonding sites of the ethanol were joined, and ethylene was formed.

J_USTIFYthe method:

The models created a 3D representation of the chemical process, which led to greater understanding of  dehydration and hydration processes.

The use of ball-and-stick models, depicting the double-bond with flexible rubber rods, greater increased understanding of chemical reactions.

LIMITATIONSof the method:

Both were severely simplified representations of chemical processes, which had many multiple steps and consisted of a series of aqueous (dilute sulfuric acid) or solid catalysts.

Describe and account for many uses of ethanol as a solvent for polar and non-polar substances

A POLAR _{covalent bond is a bond where one of the atoms in it is more electronegative than the other,} and so the bond has a slight charge.

Electronegativity is the ability of an atom to attract electrons; the more electro-negative an atom, the stronger it will hold onto electrons in a chemical bond .

The order of electronegativity, from most electronegative to least, for relevant atoms is: _{f l uorine,} oxygen, chl orine, nitrogen, carbon and then hydrogen.

For example, a bond between oxygen and hydrogen is a polar bond because oxygen holds onto negative electrons stronger; thus, in this bond, oxygen is slightly negative. Solubility Rules:

- Polar substances dissolve other polar substances: _{This is because the slightly negative end is attracted} to the slightly positive end of another polar bond, forming a slight intermolecular bond.

- Non-polar substances dissolve other non-polar substances: _{This is due to very weak dispersion forces} between molecules.

Ethanol is a very useful solvent. A range of substances including polar, non-polar and some ionic

compounds dissolve readily in ethanol. The solubility of ethanol in both water (a polar compound) and hexane (a non-polar compound) are due to its molecular structure. The ethanol molecule consists of two parts, the polar hydroxyl end (OH) and the non-polar alkyl end (CHCH-) end. The ability of ethanol to act as a solvent for polar substances is due to the polar nature of the O-H bond. This end of the ethanol molecule interacts with other polar molecules via dipole-dipole forces or hydrogen bonds.

The alkyl chain, although short, is essentially non-polar and this allows ethanol to act as a solvent for some non-polar substances including some hydrocarbons, oils and resins. The non-polar alkyl chain forms dispersion forces with non-polar solutes, similar to the intermolecular forces between solute molecules. This tends to favour the solubility of non-polar solutes in ethanol.

Outline the use of ethanol as a fuel and explain why it can be called a renewable resource

As supplies of petroleum dwindle, the use of renewable energy sources has become more attractive. Ethanol is one such renewable fuel that has received much attention. Ethanol can be produced from the starch or sugars present in sugar cane, corn, wheat, maize and other cereal crops. Although no

commercially viable method of obtaining ethanol from cellulose is currently available, large-scale production by fermentation of starch and sugars has been carried out for decades.

A n d r e w N g u y e n P a g e |21

CHOH (L) + 3O2(G) 2CO (G) + 3HO (G)

Despite its short chain, ethanol is a liquid (due to strong polar bonds). Describe conditions under which fermentation of sugars is promoted

Fermentation is the biochemical process in which glucose is turned into ethanol and carbon dioxide by the action of enzymes produced by microbes (esp. yeast).

Glucose ethanol + carbon dioxide Yeast

CHO (aq)2CHOH (aq) + 2CO (G)

R_{aw materials and conditions for fermentation}

1. Source of glucose is needed e.g. suitable g rains and/ or fruits are mashed with water 2. Yeast is added

3. Exclude oxygen (anaerobic conditions) to avoid the oxidation of ethanol 4. Temp:_{body temperature = 37°C}

The max concentration of ethanol obtained directly from fermentation is 15% v/v. This is because as the concentration of ethanol is greater than 15% v/v, the yeast will be intoxicated. To obtain a higher

concentration of ethanol, distillation is required.

Research_{-Process information from secondary sources to summarise the p rocesses invol ved in the}

industrial production of ethanol from sugar cane

Ethanol/Petrol Mixtures: _{Significant quantities of 10% ethanol are sold in some parts of Australia;} however, there has not been much success as the public holds suspicions about the effect of ethanol on their engines.

However, in other countries, ethanol/petrol mixtures are very successful. In the United States, many states require a minimum of 10% ethanol in all fuel sold. In Sweden, 85% ethanol mixtures are common. Brazil requires that ALL car engines are able to accept at least 25% ethanol. Thus in certain countries, use of ethanol as a fuel is quite successful.

Pure Ethanol Fuels: _{Pure ethanol is ethanol with AT MOST 1% water. It is a very clean fuel. Engines} must be modified to deal with such high levels of ethanol. It is currently being used in Brazil and Argentina as a complete alternative to gasoline. A quarter of all Brazilian cars run on pure ethanol. It has proven to be a very efficient fuel.

Ethanol Fuel-Cells: _{This is still in an experimental stage; it is the proposition that fuel cells be used to run} cars; success of such a scheme is still not known.

Inf o-Present information from secondary sources by writing a bal anced equation for the fermentation of  gl ucose and monitor mass changes

Fermentation of glucose

Summarise the chemistry of the fermentation process

Fermentation is composed of a series of chemical reactions whereby complex organic compounds are split into more simple ones.

Cane sugar, such as molasses, is rich in sucrose (C12H22O11), however, it is uneconomic to separate. Hence, water and yeast are added, which react with the sucrose to produce glucose and fructose, both of which have the molecular formula C6H12O6.

The glucose/fructose can then be converted to carbon dioxide and yeast via the anaerobic respiration of  yeast (fermentation).

C6H12O6(s)2 CO2(g) +2 C2H5OH(l)

Practical _{-Sol ve probl ems, pl an and perform a first -hand investigation to carry out the fermentation of} 

gl ucose and monitor mass changes

In this experiment, sucrose solution was fermented to form ethanol and carbon dioxide. The yeast cells first split sucrose into two glucose molecules using the invertase enzyme.

A n d r e w N g u y e n P a g e |23

- A 250 mL side-arm conical flask with a rubber stopper was used. A plastic hose was connected to the side arm, and the end of the hose was placed in another conical flask in a solution of  l imewater . No gas was allowed to escape the apparatus:

- 100 ml of 0.15 M sucrose solution was placed in the conical flask. ONE gram of  active yeast  was placed into the sucrose, along with a pinch of sodium biphosphate (Na2HPO4) as a yeast nutrient. This was mixed thoroughly.

- The stopper firmly put on, and the flask was WEIGHED with an electronic scale.

The apparatus was then set up as shown, with the yeast beaker in a water bath at a constant temperature (37°C).

Both flasks were weighed daily for 5 days. RESULTS:

1. The yeast flask turned foamy and smelt clearly of alcohol, while the limewater turned cloudy; this proved that CO2and ethanol were produced, and that fermentation occurred.

2. The mass of the yeast flask also steadily decreased by about half a gram each day; this is due to the carbon dioxide escape; the limewater flask also gained approximately the same mass.

J_USTIFYthe method:

1. A closed system (where no gas was allowed to escape) was used to ensure an accurate experiment. 2. Limewater was employed to prove CO2was produced.

3. The water bath ensured that the most optimal fermentation occurred.

LIMITATIONSof method:

- The combined masses of both flasks steadily decreased as well; this was due to inevitable leakages of  gas.

- The atmosphere in the flasks was not anaerobic (oxygen-free) and this could have hampered the fermentation process.

Define the molar heat of combustion of a compound and calculate the value for ethanol from first-hand data

The molar heat of combustion is the heat energy released when one mol eof a substance undergoes complete combustion with oxygen at a pressure of 101 .3 kPa (or 1 atmosphere), with the final products being CO2and H2O

Formula for change in heat:

For the calculation of the molar heat of combustion of ethanol, the following first hand values, were used (from 2001 HSC, Q17):

In this case, the formula for H is applied to the water (the system): T = 59  19 = 40 K

A n d r e w N g u y e n P a g e |25

m = 250 g = 0.25 kg

C = 4.18 x 103J kg-1K-1 (This value is a constant; given in exams) Therefore: _{H = -0.25 x 4.18 x 10}3_{x 40}

= -41800 joules = -41.8 kilojoules (kJ)

But the change in mass of the burner was 2.3 grams, therefore only 2.3 grams of ethanol was combusted.

Moles = mass / molar mass = 2.3 / 46 = 0.05 mol Therefore, -41.8 kJ/0.05 mol = -836 kJ/mol

Assess the potential of ethanol as an alternative fuel and discuss the advantages and disadvantages of  its use

Advantages of Use 

Renew abl _{e Resou}rc _{eThe chemical energy in ethanol is produced in plants/biomass such as sugarcane,}

corn and potatoes, via photosynthesis, and is therefore renewable. Plants can be renewed through agriculture as the ethanol becomes deplete:

6CO2+ 12H2O + light energyC6H12O6+6O2+6H2O

Therefore, unlike fossil fuels it will not run out.

Greenhouse gas neutral  The combustion of ethanol is considered Carbon Dioxide neutral if derived from biomass. Unlike ethanol derived from petroleum, it does not take carbon dioxide locked deep underground, but from the atmosphere as part of photosynthesis by the plants. Therefore, use of  ethanol as fuel would reduce carbon dioxide emissions compared with combusting fossil fuels.

Lower Emissions  Combusting ethanol produces lower levels of toxic hydrocarbons, carbon monoxide, benzene, toluene and xylenes. Up to 26% less CO is released when compared with petrol.

Improved human health  Half burned hydrocarbons produced when combusting petrol in engines, e.g. chrysene and Buckminster fullerene are carcinogenic, and have an adverse effect on human health. Ethanol produces less of such hydrocarbons than petrol. The reduction in CO emissions by up to 26% will reduce the pollution-related malaise common in urban areas where there a lots of motor vehicles. It is a simple, non-toxic and economically viable replacement as an octane-enhancer for MTBE, which is a toxic compound known to contaminate ground water and t herefore dangerous to human health.

Expense  Ethanol is expensive to produce. The energy required to distil ethanol is half the energy produced when ethanol is combusted. The energy and cost of fermentation and distillation are almost twice that of mining and refining petroleum. Despite rising oil prices and depletion of fossil fuels, and development of technology that reduces the cost of ethanol production, it still remains too impractical a prospect in terms of cost and energy to be taken up by fuel companies

Large land area needed  Large areas of arable land need to be cleared in order to grow the biomass necessary for the production of ethanol. Although this appears less destructive than an oil field, such mass production of crop will result in a mono-culture that would be disastrous for the biodiversity in the region. The need for land could also result in the clearing of irreplaceable natural ecosystems, such as the clearing of tropical rainforests in Queensland.

Potential for engine corrosion  Ethanol absorbs water. Blends of ethanol that are a round 25% (E-25) or higher absorb enough water to cause corrosion and damage of the fuel lines in engines.

Benefits of emission reductions and effect on greenhouse gases are small  Presently, much of the energy used to power the growing, harvesting and processing of crop to produce ethanol is derived from fossil fuels, which makes the net reduction of carbon dioxide gas emissions much smaller.

Increased levels nitrogen oxides in exhaust gases  While combustion of ethanol reduces the amount of  carbon dioxide, monoxide and other toxic gases, it rel eases more nitrogen oxides than petrol, leading to an increase in smog and acid rain.

Research-Process information from secondary sources to summarise the use of ethanol as an al ternative car fuel  , eval uating the success of current usage

It is a renewable resource and so would reduce the use of non-renewable fossil fuel (provided less fossil fuel was used to make the ethanol than was saved by using the ethanol in cars). It could reduce

greenhouse gas emissions (if the amount of CO2 not released from oil because of the use of ethanol in cars was greater than the CO2 released from the fossil fuels used to make the ethanol).

The disadvantages are:

Large areas of agricultural land would need to be devoted to growing suitable crops with consequent environmental problems such as soil erosion, deforestation, fertiliser runoff and salinity.

Disposal of the large amounts of smelly waste fermentation liquors after removal of ethanol would also present major environmental problems.

The current situation inAustralia:

1. Ethanol costs more than petrol to produce so the federal government has set up subsidies and excise concessions to encourage the production of ethanol (from crops) to be added to petrol (presumably to reduce oil consumption).

2. Car manufacturers accept that up to 10% ethanol in petrol has no detrimental effect on vehicles but have opposed higher concentrations.

A n d r e w N g u y e n P a g e |27

3. Significant quantities of petrol with 10% ethanol in it are available in some parts of Australia, but there is considerable public suspicion of this blended fuel, largely because of incidents involving some petrol suppliers who put excessive amounts of ethanol in their petrol (to gain from the government subsidies), and because of car manufacturers who have widely claimed that amounts above 10% could damage car engines and may void warranties.

4. There are no reliable studies to show whether ethanol as made in Australia from wheat or molasses produces less greenhouse gas in total than does the petrol it replaces.

Identify the IUPAC nomenclature for straight-chained alkanols from C1-C8

Alkanols are a group of alkanes where one or more hydrogens have been replaced by the hydroxy l (OH) functional group

When naming alkanols, there are specific rules:

The number of carbons determines the prefix of the name:

#Cs 1 2 3 4 5 6 7 8

Prefix methane- ethane- propane- butane- pentane- hexane- hepane-

octane-If there is only ONE hydroxyl group, the e is dropped from the prefix and the suffix  -ol is added. The carbon the hydroxyl is on must also be stated; this is written before the prefix with a dash. The carbons, depending on how long the chain is, are numbered from 1 to 8.

E.G. This alkanol has 5 carbons, but only one hydroxyl, so its prefix is pentan-, and its suffix is -ol. Also, the hydroxyl is on the 2ndcarbon (the number is taken either from the left OR _{the right; the SMALLE}R _number must be taken).

HENCE this alkanol is 2-pentanol.

INCORR_{ECT naming would be 4-pentanol.}

No. of OHs 1 2 3 4

Suffix -ol -diol -triol -tetraol

For more than one carbon, the e at the end of the prefix is NOT dropped. The positions of the OH groups must be stated. If there are 2 hydroxyls on the same carbon, then the number is written twice, with a comma in between:

E.G. This alkanol has 6 carbons, and 3 hydroxyl groups so its prefix is hexane- and its suffix is -triol. Also, one hydroxyl is on the 1stcarbon, while the other 2 are on the 3rdcarbon. HENCE, the IUPAC name for this alkanol is 1,3,3-hexanetriol.

INCORR_{ECT naming would be 4,4,6-hexanetriol}

Practical _{-Identify data sources, choose resources and perform a first -hand investigation to determine}

and compare heats of combustion of at l east three l iquid alk anol s per gram and per mol e The 3 alkanols used were:_{methanol, ethanol, and 1-propanol}

Each alkanol was placed in a spirit burner; the original mass recorded, and then was used to heat 200 mL of water (at 25°C) in a tin can.

A thermometer was used to stir the water as well as m easure the temperature

Once the temperature rose by 10 degrees (Kelvin or Celsius, it doesnt matter; they both use the same scale) the spirit burner was capped and immediately reweighed.

RESULTS:

- The H (change in heat) was calculated for each alkanol by using the formula H = -mCT. This was then calculated per gram, and then per mole, to give the heat of combustion per gram, as well as the molar heat of combustion.

- Methanol has the lowest value, followed by ethanol, and then 1-propanol.

NOTE: _{This is not because of the extra bonds in longer hydrocarbon chains, but rather more bonds need} to be created in the products (H2O and CO2); recall that:

- creating bonds releases energy. -breaking bonds absorbs energy.

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J_{USTIFYthe method}:

- A tin can was used as it is a better thermal conductor than a glass beaker

- Methanol, ethanol and 1-propanol were used as they are the shortest alkanols and thus are the most likely to undergo complete combustion

LIMITATIONSof method:

- Molar heat of combustion refers ONLY to complete combustion; the yellow flames and soot formed indicated that the combustion was incomplete. Thus the experimental data gathered is inaccurate. - Also, much heat was lost to the air, as there was not 100% efficiency of heat transfer from flame to tin can.

Heat was also radiated from the can to the air; insulation would reduce this.

4. Oxidation reduction reactions are increasingly important as a source of energy Explain the displacement of metals from the solution in terms of transfer of electrons

A displacement reaction is a reduction-oxidation reaction in which a more reactive product changes a less reactive products ions into solid or gaseous atoms . In other words, the less reactive products ions are displaced out of a solution and neutralised into atoms.

E.g. the reaction between zinc and copper sulphate is an example of an oxidation-reduction reaction. Chemical equation-Z_{n(s) + CuSO (aq)}Z_{nSo (aq) + Cu (s)}

Ionic equation Z_{n + Cu²}+_{+ SO²}Z_n²+_{+ SO² + Cu} Net ionic equation- Z_{n + Cu²}+_Z_n²+_{+ Cu}

These equations symbolise the transfer of electrons, where one substance donates electrons to another. Half equations

These half equations is the net ionic equation split into two halves. E.g. From above

Z_nZ_{n² + 2e Oxidation} Cu² + 2eCu R_eduction

Oxidation R_eduction

Said to be oxidised Said to be reduced

Is the reducing agent Is the oxidising agent

Is the reductant Is the oxidant

Loses electrons Gains electrons

Increase in oxidation state/number Decrease in oxidation number/state

Note:OIL-RIG, where Oxidation Is Loss,Reduction Is Gain There are many types of redox reactions:

Displacement reactions; e.g. magnesium and silver nitrate: Mg(s)+ 2AgNO3 (aq) Mg(NO3)2 (aq)+ 2Ag(s)

Mg + 2Ag++ 2NO3- Mg2++ 2NO3-+ 2Ag

Mg + 2Ag+ Mg2++ 2Ag (2NO3-is the spectator ion) Mg Mg2++ 2e¯(Oxidation)

2Ag++ 2e¯ 2Ag (R_eduction)

Acid/Metalreactions; e.g. sulfuric acid and zinc: H2SO4 (aq)+Zn(s) ZnSO4 (aq)+ H2 (g)

2H++ SO42-+Zn Zn2++ SO42-+ H2

2H++Z_n Z_n2+_{+ H2(SO4}2-_{is the spectator ion)} Z_n Z_n2+_{+ 2e}¯_(Oxidation)

2H++ 2e¯ H2 (Reduction)

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2Na(s)+ Cl2 (g) 2NaCl(s)

2Na + Cl2 2Na++ 2Cl-(No spectator ion in this case) 2Na 2Na++ 2e¯ (Oxidation)

Cl2+ 2e¯ 2Cl- (Reduction)

Alkali metal/waterreactions; e.g. reacting potassium and water: 2K(s)+ 2H2O(l) 2KOH(aq)+ H2 (g)

2K + 2H2O 2K++ 2OH-+ H2 2K 2K++ 2e¯(Oxidation)

2H2O + 2e¯ 2OH-+ H2(Reduction)

This is slightly different as there are TWO elements in the reduction half. Metal combustionreactions; e.g. burning magnesium in oxygen:

2Mg(s)+ O2 (g) 2MgO(s) 2Mg + O2 2Mg2++ 2O

2-2Mg 2Mg2++ 2e¯ (Oxidation) O2+ 2e¯ 2O2-(R_eduction)

Identify the relationship between displacement of metal ions in solution by other metals to the relative activity of metals

Metals were ranked in order of reactivity by comparing their reactivities with oxygen, water and acids. They can also be arranged into an activity series by their ability to displace one another from solution. If a strip of copper is placed in a solution of zinc sulphate, no reaction occurs. This is because Z_{n² ions} have a lesser tendency to gain electrons (reduced) than Cupper ions. As a result, Cu atoms will not giv e up electrons to Z_{n² ions. However, if a piece of copper is placed in a solution of silver ions, the copper} metal displaces silver ions from the solution. Therefore Ag² ions have a greater tendency to gain electrons than Cu² ions.

These experiments allow us to arrange these three me tal ions in increasing order of ease to be reduced: Z_{n² < Cu² < Ag.}

Or we can arrange them in order of the tendency to be oxidised: Z_{n > Cu > Ag} The metal activity series

Note:reactive metals will tend to be oxidised, the unreactive metals ions will tend to be reduced. Account for the changes in the oxidation state of species in terms of their loss or gain of electrons Rules of oxidation number

1. O.N of all elements in free forms (uncombined forms) is zero E.g. Ca, H, O, F, Na, Fe

2. O.N of fluorine in all compounds/polyatomic ions is -1 E.g. NaF¹

3. O.N of oxygen in most compounds/ polyatomic ions is -2 E.g. KCO²

4. O.N of hydrogen is +1 in most compounds (except when it reacts with reactive metals from group 1 or 2)

E.g. HCl

5. O.N of the alkaline metals (group 1) is +1 O.N of the alkaline Earth metals (group 2) is +2 6. The total sum of the O.N in a compound is zero

7. The total sum of the O.N in a polyatomic ion is the charge it carries 8. The O.N of a monatomic ion is the charge of that ion

The oxidation state provides a useful way of determining whether an oxidation-reduction reaction has taken place. An increase in oxidation number represents oxidation whilst a decrease in oxi dation number represents a reduction.

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R_{elating this back to the metal displacement reactions}: Z_n Z_n2+_{+ 2e}¯ _(Oxidation)

Cu2++ 2e¯ Cu (R_eduction)

It can be seen that the oxidation state of  zinc changes from (0 +2); this increase signifies an oxidation, while the oxidation state of copper changes from (+20); this decrease shows it is a reduction.

Thus, relating this back to transfer of electrons:

- An increase in oxidation number means that electrons have been lost, and the oxidation number is increasing (moving towards the positive numbers) due to the loss of negative electrons.

- A decrease in oxidation number means that electrons have been gained, and the oxidation number is decreasing (moving towards the negative numbers) due to a gain of negative electrons.

Describe and explain galvanic cells in terms of oxidation/reduction reactions

A galvanic cell is a device or apparatus that converts the chemical energy of a spontaneous redox

reaction into electrical energy. Electricity is simply a flow of electrons. Thus redox reactions are electron-transfer reactions; if this electron flow can be exploited, electricity could be produced.

There are two half cells; oxidation takes place in one and reduction takes place in the other.

A conducting wire and salt bridge connects the two half-cells and completes the circuit; as electrons have to flow from the oxidation cell to the reduction cell, a flow of electrons is produced in the wire, and hence electricity is produced.

Outline the construction of galvanic cells and trace the direction of electron fl ow

A galvanic cell consists of two half-cells. Each half-cell consists of an electrode, which is a conductive metal or graphite strip in contact with an electrolytic solution. These solutions are joined by a salt bridge containing an electrolytic solution such as KNO. The salt bridge may consist of a filter paper saturated with KNO solution or a U-tube containing KNO solution in an agar jelly. The salt bridge completes the circuit and allows ions to move between each half cell.

Galvanic cell setup:

There are two cells, each containing a solution of the metal-sulfate; one cell contains zinc sul  fate, the other cell copper sul  fate. In the zinc sulfate, there is a solid zinc electrode, connected by a wire to a solid copper electrode, which is in the copper sulfate solution. A salt bridge, soaked in   potassium nitrate solution, connects the two cells.

In the zinc-sulfate cell, oxidation is occurring, as SOLID zinc is oxidised to zinc IONS, which then flow into the zinc sulfate solution. The electrons that are released flow into the wire:

Z_n Z_n2+_{+ 2e}¯_(Oxidation)

In the copper-sulfate cell, reduction is occurring, as copper IONS are reduced to SOLID copper, when then build up on the copper electrode. Electrons are received through the wire, which then reduce the ions:_Cu2+_{+ 2e}¯ _{Cu (}R_eduction)

NOTE: The oxidation and reduction cells can be on the left OR _{the right, it does not matter, although} oxidation is conventionally on the right.

As the zinc is slowly oxidised, and more zinc ions build-up, the zinc sulfate solution builds up in POSITIVE charge (moreZ_n2+_{than SO4}2-_).

Similarly, as the copper ions are reduced, the copper sulfate solution builds in NEGATIVE charge (more SO42-than Cu2+).

However, this will affect the flow of electrons; electrically neutral solutions are needed for optimal electricity production. Hence the role of the salt bridge :

- The salt bridge completes the circuit, but also has another function.

- The salt bridge maintains electrical neutrality; this means that it keeps the charges in both the half-cells at zero, by allowing the flow of ions.

- The salt bridge is soaked in potassium nitrate solution:_{Thus, as the positive charge builds up in the left} cell, NEGATIVE nitrate ions migrate towards the cell to neutralise the charge; as the negative charge builds up in the right cell, the POSITIVE potassium ions move towards the cell to neutralise it as well.

This type of galvanic cell is called a Daniell cell.

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Define the terms anode, cathode, electrode and electrolyte to describe galvanic cells

Electrode- anything through which electric current passes; in the context of galvanic cells, they are the metal conductors placed in the electrolytes (solution)

Types of electrodes

1. Metal-metal electrodes Cu(s)l Cu²ll Agl Ag(s) 2. Metal-Inert electrodes Cu(s) l Cu² ll Fe²(aq) l Pt 3. Inert-Inert electrodes

Pt l Cl(g), Cl ll Fe²(aq), Fe³(ag) l Pt

Electrolyte- a substance which dissociates in solution to form ions, and i s therefore electrically conductive

Anode- the negative electrode in which electrons come up from the cell and oxidation occurs (loses electrons)

Cathode- the positive electrode in which electrons enter the cell and reduction occurs (gains electrons)

Practical -Perform a first -hand investigation to identify the conditions under which a gal vanic cell is  produced 

A galvanic cell was produced in the lab in the same set-up as above; that is, in the form of a DANIELL CELL

A 2 cm strip of zinc and copper were cut from metal strips. Using wire leads and crocodile clips, the zinc strip was connected to the NEGATIVE terminal of a voltmeter, and the copper strip connected to the POSITIVE terminal

The zinc was then placed in 50 mL of 1M solution of zinc sulfate, and the copper in 50 mL of 1M solution of copper sulfate.

A strip of filter paper was soaked in potassium nitrate; the two cells were then connected using this salt bridge

RESULTS: _{The voltmeter showed a reading of 0.4 volts. When more electrolyte was added, the voltage} stayed at 0.4 volts; thus the voltage is determined ONLY by the metals used, and has nothing to do with the amount of copper or zinc.

J_{USTIFYthe method}:

- Copper and zinc were used as they are readily available, non-toxic metals - 1M solution was used as the ratio of moles of the salts was 1:₁

- A potassium nitrate salt bridge was used as potassium and nitrate ions do not react with zinc, copper of  sulfate ions.

Practical _{-Perform a first -hand investigation and gather first -hand information to measure the difference}

in potential of different combinations of metal s in an el ectrol yte sol ution

Report -Gather and present information on the structure and chemistry of a dry cell or l ead -acid cell and  eval uate it in comparison to one of the foll owing:-button cell  , fuel cell  , vanadium redox cell  ,l ithium cell  ,

l iquid junction photovol taic device ( E _{.g. the Gratzel cell)in terms of chemistry, cost and practical ity,}

impact on society and environmental impact 

Dry cells and lead-acid batteries are extremely useful and cost effective sources of portable power. The DRYCELL(or Leclanché Cell):

STR_UCTUR_E:

The dry cell is made of a carbon rod surrounded by a mixture of  manganese (IV) oxide and carbon (in the form of  graphite); this is the cathode. This is then surrounded by a paste of ammonium chloride which acts as the electrolyte. All of this is contained in a zinc shell, which is the anode.