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

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

Petroleum is a mixture of crude oil and natural gas Crude oil is separated into fractions using fractional distillation. Each fraction contains a

mixture of molecules that have a specified range of boiling points.

Long-chain hydrocarbons can be broken down into smaller chains by a process called cracking. Thermal cracking and catalytic cracking are the two procedures commonly used. Ethylene is one of the important products made by the process of cracking.

Thermal (steam) cracking

Thermal cracking produces a high yield of ethylene. Steam and the long-chain hydrocarbons are pumped into a furnace containing long pyrolysis coils which generate conditions of high temperature (750-900oC) and pressure just above atmospheric. Thermal cracking involves three main steps:

Initiation: The C-C bonds are broken from the conditions of high temp. and pressure – giving rise to radical species

Propagation: The radical species fragment into short chain alkenes (e.g. ethylene) and alkyl radicals.

Termination: Occurs through a combination of two alkyl radicals to form a stable alkane.

Catalytic cracking

Catalytic cracking generates a high yield of petrol-type alkanes and a smaller yield of alkenes. The hydrocarbon vapour is heated at moderate temperatures (500oC) and pressures just above atmospheric in the presence of a zeolite catalyst (composed of aluminium silicate).

The acidic surface of the catalyst takes hydrogen atoms from the hydrocarbons. The unstable, positively charged hydrocarbon ions which result (carbocations) subsequently decompose to yield the intended products.

The catalyst can be tuned to generate a higher proportion of a desired product (e.g. more petrol or more alkenes)

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

An addition reaction is a reaction that involves breaking the double bond of an alkene to form two single bonds.

A substitution reaction is reaction that causes one atom in a molecule to be replaced by another atom/group of atoms.

Alkenes (e.g. ethylene) are more reactive than alkanes due to the high electron density of the double bond. Electronegative elements (such as bromine, chlorine and oxygen) are attracted to the double bond with the electrons being transferred as they react.

Alkenes commonly react with molecules such as chlorine, bromine, hydrogen, chloride and water via addition reactions.

Hydration

Alkenes will react when heated with water and an acid catalyst. The final product is an alkanol.

Bromination

When an alkene is mixed with a solution of bromine in an organic solvent, the bromine molecule reacts with the double-bond and bromine atoms add across to form a ‘dibromoalkane’.

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

Polymers are large molecules (macromolecules) made up of repeating sub-units (monomers).

Monomers are small molecules which can react with itself (or similar monomers) to generate a polymer.

Ethylene and propylene are common monomers:

Monomer Polymer

Identify polyethylene as an addition polymer and explain the meaning of this term

Polyethylene is a member of a class of polymers known as addition polymers. These polymers are produced when alkene monomers are reacted together through addition reactions (double bonds of alkenes are broken up to form single bonds with neighbouring molecules)

Outline the steps in the production of polyethylene as an example of a commercially and industrially important polymer

Polymerisation with an initiator

The polymerisation of ethylene can be induced by adding a molecule called an initiator.

Low-density polyethylene (LDPE) is produced using an initiator at a high pressure (100-300 MPa) and high temperature (300oC)

The polymerisation process with an initiator involves three steps:

Initiation/Activation: the initiator molecule is decomposed (by laser light or heat) to reactive free radicals. The free radicals then react with ethylene molecules to form activated ethylene radicals.

Propagation: activated monomers react with (non-activated) ethylene monomers to dimer radicals, which then react with other (non-activated) ethylene monomers to form trimer radicals, and so on (chain length continues to increase).

Termination: Chain growth terminates when two free radicals (of variable chain length) come into contact and the two unpaired electrons unite to form a single bond. Alternatively, the use of inhibitors or lowering the temperature/pressure can also stop polymerisation.

Polymerisation using a surface catalyst

Certain compounds can act as surface catalysts to produce addition polymers.

High density-polyethylene (HDPE) is manufactured using a surface catalyst method called the Ziegler-Natta method. This method uses relatively low temperatures (60oC) and low pressure. It employs a solid, heterogeneous catalyst (made from titanium chloride and triethylaluminium) called the Ziegler-Natta catalyst.

The ethylene molecules bond to the titanium atoms, weakening the double bond and leading to polymerisation. Polymerisation terminates when the monomer runs out or by addition of inhibitors.

Properties and uses of LDPE and HDPE

LDPE HDPE Produced in high temp/pressure, free

radical polymerisation (uses initiator) Relatively high proportion of amorphous

regions (due to side branching from ‘back-biting’)

Thermoplastic (melted/reshaped easily) These amorphous regions have weaker

dispersion forces, leading to LDPE being less rigid/more flexible and having a lower MP

Amorphous regions are also transparent. This results in LDPE polymers being more transparent

Overall, LDPE is soft, flexible and is not particularly strong. This makes it suitable for making glad wrap, disposable shopping bags, flexible toys, and soft bottles.

Formed through Ziegler-Natta catalyst with low temp/pressure in an alkane solvent

Relatively high proportion of crystalline regions (80-95%) due to lack of side branching.

Thermosetting (cannot be heated and reshaped hard to recycle)

Crystalline regions have stronger dispersion forces, meaning HDPE is more rigid and generally has a higher MP

Crystalline regions scatter/refract light. This results in HDPE polymers bring translucent or opaque

Overall, HDPE is harder and stronger than LDPE. It is widely used to make kitchen utensils/containers, rigid toys, piping, ‘wheely’ bins and milk crates.

Identify the following as commercially significant monomers (vinyl chloride and styrene) by both their systematic and common names

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

Vinyl chloride

Common name: Vinyl chloride

Systematic name: Chloroethylene or chloroethene

Vinyl chloride is formed when ethylene reacts with chlorine in the presence of oxygen (150oC temp. and with a copper (II) chloride catalyst). The reaction involved is a substitution reaction.

Polymerisation process:

Polyvinyl chloride

Properties UsesHard and inflexible due to the presence of large chlorine molecules.

Household items, Outdoor furniture, credit cards, drainage/sewage pipes. (For outdoor uses, an inhibitor is added to the PVC, otherwise UV light would attack the C-Cl bonds)

Soft (after addition of non-volatile plasticisers) Electrical insulation and garden hoses

Styrene

Common name: Styrene

Systematic name: Phenylethene, ethenylbenzene

Styrene is formed when ethylene reacts with benzene (C6H6). The reaction requires an aluminium catalyst at high temperature and pressure. The reaction involved is an addition reaction. This product then has to undergo dehydrogenation to produce styrene.

Polymerisation process:

Note: there are two major types of polystyrene: crystal polystyrene and expanded polystyrene

Crystal Polystyrene

Properties UsesClear (amorphous polymer)Strong, rigid/stiff (twisted configuration due to large phenyl groups)

Car battery cases, handles for screwdrivers, CD cases

Expanded Polystyrene (Styrofoam)

Styrofoam is produced by blowing gases through molten polystyrene then allowing it to cool.

Properties UsesLight-weight, rigid Protective layer in packaging (absorbs shock),

foam cups (insulator)

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

Discuss the need for alternate sources of the compounds presently obtained from the petrochemical industry

Fossil fuels such as natural gas, coal and petroleum are limited, non-renewable resources, as they take hundreds of millions of years to accumulate. At present, we are facing a future in which these fossil fuels will eventually run out; this would dramatically increase the cost of products made of petroleum. Based on current usage statistics, petroleum reserves could be completely used up within a few decades. In addition, there is increasing pressure to reduce the use of petroleum due to the greenhouse effect.

The major use of petroleum is as a fuel for vehicles (cars, trains, planes) and to produce plastics in the petrochemical industry.

Therefore, due to the above reasons, alternative sources of carbon compounds must be developed Potential alternative sources include cellulose and the ethanol used in agriculture (which could be used as a source of ethylene). Although currently it is more cost effective to use petroleum to supply energy, many argue that as the supplies diminish, it would become more cost effective to use these alternative fuel sources.

Explain what is meant by a condensation polymer

A condensation polymer is one formed through condensation polymerisation. Condensation polymerisation is sometimes called ‘step-growth’ polymerisation. The important aspect of this type of polymerisation is:

Monomers combine with the elimination of small molecules (e.g. water) at each step

Describe the reaction involved when a condensation polymer is formed

Polyester PolyamideFormation of monomer

Esterification – an alcohol molecule reacts with a carboxylic acid to form a larger molecule (ester). Water is eliminated in the process

Amidation – when an amine molecule reacts with a carboxylic acid they form a larger molecule (amide). Water is eliminated in the process

Polymerisation To produce a polyester, one monomer must be a dicarboxylic acid (two COOH groups) and the other monomer must be a diol (two OH groups)

Dicarboxylic acid + diol ester dimer + water

To produce a polyamide, one monomer must be a dicarboxylic acid and the other must be a diamine (two amine groups)

Dicarboxylic acid + diamine amide dimer + water

Dimers are formed in the first step. The chain grows as monomers (dicarboxylic acid, diol or diamine) condense onto the ends of the dimer (with water being eliminated at each step).Dimer Trimer tetramers etc.

Ester: an organic molecule containing the COO functional group

Amine: an organic molecule containing the NH2 functional group

Carboxylic acid: an organic molecule containing the COOH functional group

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

Biomass is organic matter derived from living organisms. All living organisms produce natural polymers called biopolymers (e.g. cellulose), which are all condensation polymers.

Cellulose is a biopolymer formed by the condensation polymerisation of glucose monomers. It forms a large proportion of the world’s biomass.

There are two structural forms of glucose: alpha-glucose and beta-glucose. It is the beta form that leads to cellulose formation. The β-(1,4)-glycosidic bonds in cellulose result in a linear structure of the polymer (with the CH2OH groups alternating on opposite sides). The strong hydrogen bonds give strength and rigidity to the molecule, and so it is used as structural support in plants and used to make ropes.

OR

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

Cellulose contains the basic carbon chain structures needed to build the compounds currently needed and obtained from the petrochemical industry (through processing petroleum). The main advantage associated with using cellulose is that biomass is renewable.

Glucose molecule: Cellulose:

The use of plant material (cellulose) as a source of raw material can be achieved by:

1) Modifying the existing biopolymer chains into cellulose acetate, which can be converted into ester groups

2) The biopolymer could be broken down into smaller molecules by using bacteria (which produce cellulose enzymes that break down cellulose to glucose). The glucose produced can be fermented to form ethanol and then dehydrated to yield ethylene (an important starting material in the petrochemical industry)

Plastics made of biopolymers are biodegradable as the bonds within the molecule can be broken down by bacteria/fungi. Therefore, plastics designed to be used once could be made of cellulose-based plastics (e.g. cellophane used in food packaging)

Problems

1) Cost – fossil fuels are currently much cheaper to produce and utilise than biomass fuels2) Suitable land – a large amount of fertile land is required to grow these energy crops (which is

not always available.

3. Other resources, such as ethanol, are readily available from renewable resources such as plants

Describe the dehydration of ethanol to ethylene and identify the need for a catalyst in this process and the catalyst used

Ethanol can be converted to ethylene in a process called dehydration. The ethanol is heated with concentrated sulphuric acid (H2SO4), the acid acts as both a dehydrating agent (removes H2O) and a catalyst.

C2H5OH (l) C2H4 (g) + H2O (l)

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

Ethylene and steam is passed over a silica gel/zeolite surface impregnated with phosphoric acid (which acts as the catalyst) at high pressure (1-9 MPa) and about 330 oC. Recycling the unreacted vapours and condensing out the ethanol/water as it forms compensates for the low yield of 4% per run. Eventually 97% conversion can be achieved.

C2H4 (g) + H2O (l) C2H5OH (l)

Generally, dilute acid favours the reaction from ethylene to ethanol whilst concentrated acid favours the reaction from ethanol to ethylene.

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

Ethanol is a clear, colourless liquid that has a lower BP than water. It is also volatile and its vapours form combustible mixtures with air.

Ethanol is a good solvent for both polar and non-polar substances due to the presence of the polar OH group and the non polar CH3CH2 group. Ethanol and ethanol water mixtures are used as solvents in cosmetics, toiletries, medications and antiseptics, as it easily dissolves ingredients and readily evaporates from the skin. In addition, it is used as an industrial solvent for lacquers, paints, resins etc.

Ethanol is a very polar molecule due to its hydroxyl (OH) group – allowing solutes with polar functional groups (esters, carboxylic acids, glucose) to dissolve in it. The high electronegativity of the oxygen also allows hydrogen bonding with some substances – increasing ethanol’s ability to dissolve such substances. The hydrogen bonding also allows ethanol to dissolve in water in all proportions.

The non-polar ethyl group (CH3CH2) can form weak dispersion forces with other non-polar substances – thus allowing ethanol to dissolve non-polar molecules also.

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

Ethanol can be used as a fuel as it is a liquid which readily burns:

Ethanol is an easily transportable liquid, and is often used as portable fuel in camping stoves, and as a ‘petrol extender’ (being added to petrol to about 10% ethanol without any detrimental effects on the engine or fuel efficiency)

It is a renewable source as it can be manufactured from glucose that is produced by photosynthesis in plants. When ethanol is burnt, it is released as carbon dioxide and water, which can then be reused by other plants and subsequently converted back to ethanol. In this way, ethanol can be generated renewably.

Describe conditions under which fermentation of sugars is promoted

Fermentation is a biochemical process in which sugars are converted (broken down) into ethanol and carbon dioxide by the action of enzymes present in yeasts.

Anaerobic conditions – yeasts are aerobic organisms but when deprived of oxygen it will respire the sugars anaerobically. If oxygen or air is present, the yeast uses the sugars and oxidises them to carbon dioxide and water.

Temperature is kept at 35-39oC for optimum enzyme activity. At temperatures above 40oC the enzymes will denature

Addition of alcohol tolerant yeast Low pH level – prevents pathogens from growing The fermentation is an exothermic reaction and heat must be dissipated (via heat

exchangers) to ensure the yeast doesn’t die

C2H5OH (l) + 3O2 (g) 2CO2(g) + 3H2O (g)

Summarise the chemistry of the fermentation process

The fermentation process depends on the presence of yeast microorganisms which produce enzymes that catalyse the conversion of glucose to ethanol and carbon dioxide according to the equation:

When deprived of oxygen, yeasts respire the sugars anaerobically. Any oxygen present is quickly used up by the reproducing yeast cells and conditions change back to anaerobic. As anaerobic fermentation continues, the bubbles of carbon dioxide escape from the fermenting mixture. Fermentation stops once the available sugars are metabolised.

Under normal conditions, the fermentation can proceed until the ethanol concentration reaches about 15% (v/v). Distillation (ethanol BP is 78oC) can be used to produce higher alcohol contents (92% purity)

To obtain pure ethanol, the partially purified ethanol is mixed with a dehydrating agent (e.g. CaO) and redistilled, giving pure (99% +) ethanol.

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

Molar heat of combustion is the energy liberated per mole of fuel undergoing complete combustion (ie. combustion in the presence of excess oxygen).

Molar heat of combustion for ethanol : 1360 kJ/mol (accepted value)

Experimental results: 488.82 kJ/mol

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

Advantages of using ethanol as a fuel Disadvantages of using ethanol as a fuel It is a renewable source It is relatively carbon neutral, as the CO2

produced from combustion is absorbed by the energy crops. In this way it could reduce greenhouse gas emissions ( if the amount of CO2 that would be released from oil is greater than CO2 released from the manufacture of ethanol)

Burns more efficiently and completely than octane (i.e. producing less greenhouse emissions when combusted) This is due to the presence of the OH in ethanol. A considerably larger amount of oxygen is needed for the complete combustion of octane.

Most costly to produce than petrol made mostly of octane

Large areas of agricultural land would be needed to be devoted to growing suitable crops. This could lead to environmental problems such as soil erosion, deforestation and fertiliser run-off

The disposal of large amounts of smelly waste fermentation liquors after removal of ethanol

Flash point of ethanol is higher than petrol. Therefore, ignition of ethanol vapour is harder in cold climates.

Ethanol produces less energy per mole

C6H12O6 (aq) 2CH3CH2OH (aq) + 2 CO2 (g) + heat

Glucose Ethanol + Carbon Dioxide + heat

Mixtures of ethanol and petrol boost the rating of the fuel (meaning the fuel burns efficiently and is better for the engine)

than petrol. However, a 10% ethanol blend provides a similar amount of energy as petrol with octane.

The usage of petrol with higher concentrations of ethanol requires engine modifications, which are extremely expensive.

Currently, it is not feasible to have ethanol as a stand-alone fuel source. However, research is being conducted to reduce economic costs and environmental impact (it is not carbon neutral due to energy being make crop fertiliser, as well as the distillation of ethanol)

As petroleum resources diminish in size, other sources such as ethanol will be required to meet energy demands. Because it is a renewable source, ethanol will undoubtedly be a viable source of energy in the future.

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

1) Identify the number of carbon atoms present. Select the correct stem to name the parent alkane. Remove the ‘e’ and replace it with the suffix ‘-ol’.

2) For chains with three of more carbon atoms, number the chain from the end giving the alcohol group the lowest locant possible.

3) Insert the locant of the alcohol group in front of the ‘-ol’ suffix

Process information from secondary sources to summarise the processes involved in the industrial production of ethanol from sugar cane

Sugarcane is grown to produce sugar (sucrose). A by-product of the sucrose production is a concentrated solution called molasses, which can be fermented to produce ethanol.

The process is as follows:

1) The harvested sugarcane is crushed to extract the juices containing sucrose. The remaining liquor (molasses) contains a high percentage of sucrose.

2) Water is added to the molasses syrup (reducing sucrose concentration to 40%). Acid is also added to prevent bacterial growth.

3) The mixture is placed in the fermentation tank and adjusted to the appropriate temperature (32-37oC) and alcohol tolerant yeast (Saccharomyces cerevisiae) is added.

4) Fermentation begins. After about 2 days, the fermentation process is complete and there is 8-12% ethanol. The mixture is purified through rectifying columns.

5) Final mixture is distilled – producing approx. 96% ethanol. Steam produced from the combustion of sugarcane waste (bagasse) is used to heat the distillation vessel.

Process information from secondary sources to summarise the use of ethanol as an alternative car fuel, evaluating the success of current usage

Currently, ethanol costs more than crude oil to produce and only proportions are added to petrol to use as fuel.

Car manufacturers accept that up to 10 percent ethanol in petrol has no detrimental effect but have opposed higher concentrations (claiming it could damage car engines and void warranties)

No reliable studies indicating whether ethanol made in Australia from wheat/molasses produces less greenhouse gas in total than the petrol it replaces.

4. Oxidation-reduction reactions are increasingly important as a source of energy

Explain the displacement of metals from solution in terms of transfer of electrons

Electron transfer reactions are all known as redox reactions because one species is always reduced and another oxidised. Oxidation refers to the loss of electrons; reduction refers to the gain of electrons.

A displacement reaction is a reaction in which a metal concerts the ion of another metal to the neutral atom.

For example, if a piece of zinc were placed in a copper sulphate solution, it would quickly dissolve and be covered by reddish-brown metallic copper. In terms of the electrons, zinc transfers its valence electrons to the copper ions. Thus, zinc is oxidised and copper is reduced.

Zn(s) Zn2+(aq) + 2e-

Cu2+(aq) + 2e- Cu(s)

The reaction of metals with the hydrogen ions in dilute acids is also a special type of displacement reaction, as the metal displaces the hydrogen gas from its solution of hydrogen ions.

Mg(s) + 2H+(aq) Mg2+

(aq) + H2 (g)

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

The reactivity of a metal refers to its ability to lose electrons. The more reactive it is, the more easily it will lose electrons.

In displacement reactions, the metal that goes into solution is the one that is more easily oxidised (i.e. more reactive). In other words, the more reactive metal is the one which will displace the other metal from a solution of its ions.

Account for changes in the oxidation state of species in terms of their loss or gain of electrons

The oxidation state of an element is a measure of the number of electrons lost or gained relative to the native element, and is expressed as the charge on the ion (including the sign). An increase in the

oxidation state corresponds to loss of electrons (oxidation) and a decrease in oxidation state is the gain of electrons (reduction).

It is important to note that elements in their elemental state have an oxidation state of 0, as they have not lost or gained electrons. Elements in compounds all have non-zero oxidation states as they have either lost or gained electrons.

For monatomic ions, the oxidation state refers to the formal atomic charge. For polyatomic ions, if the charge is not zero, the sum of the atomic charges equals to the total charge.

In molecules, we pretend that all of the bonds are ionic rather than covalent, and apply the same thing as for polyatomic ions (except that molecules are always neutral charged). Oxygen is usually -2, hydrogen is usually +1.

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

We can make redox reactions generate electricity by arranging for the oxidation and reduction half reactions to occur at different locations, and by providing a wire for the electrons we use. A galvanic cell is essentially a device which harnesses the positive redox potential between two redox couples to generate an electric current.

For example, if we had two beakers, one of zinc metal in zinc sulphate solution and the other of copper metal in copper sulphate solution – once the wire is connected and salt bridge is attached, the zinc metal would be oxidised and the released electrons would flow through the wire to reduce the copper ions in the other beaker. Consequently, this would generate an electrical current.

Outline the construction of galvanic cells and trace the direction of electron flow

A strip of copper metal is suspended in a beaker of copper nitrate solution and a silver wire suspended in silver nitrate solution in another beaker. A conducting wire is attached to the copper metal and silver wire (to allow electron flow). The two solutions are connected by a U-tube (salt bridge- facilitates flow of ions to maintain electrical neutrality without mixing the two half cells. It completes the circuit and allows current to flow). In order to make electrical contact the U-tube must contain some conducting substance such as a solution of potassium nitrate.

The electrons flow from the anode (electrode getting oxidised) to the cathode (electrode getting reduced). Typically, the anode is drawn to the left, and the cathode drawn to the right.

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

Electrodes are the conductors of a cell which get connected to the external circuit

Electrolyte is a substance which conducts electricity in solution

Anode is the electrode where oxidation occurs, and in galvanic cells, is the negative terminal (electrons flow out from the anode).

Cathode is the electrode where reduction occurs, and in galvanic cells, is the positive terminal (it draws the electrons back into the cell)

Solve problems and analyse information to calculate the potential Eo requirement of named electrochemical processes using tables of standard potentials and half equations

NOTE: look in book for further detail (diagrams etc.)

Standard conditions are electrolyte concentration: 1mol/L, standard temp and pressure (25oC, 100kPa)

The standard cell potential (Eo) is defined as the sum of the standard half-cell reduction potential and the standard half-cell oxidation potential.

o The standard EMF of the oxidation half equation is MINUS the corresponding reduction electrode potential.

o Since, the standard cell potential is a measure of energy per electron, it does not matter how many electrons are in the reaction. In other words, do not multiply the EMF if charges need to be balanced.

o If the Eo total is negative, the reaction is not spontaneous

Galvanic cell notation

Gather and present information on the structure and chemistry of a dry cell or lead-acid and evaluate it in comparison to one of the following: button cell, in terms of chemistry, cost and practicality, impact on society and environmental impact

The dry cell is one of the most common and reliable sources of portable electric power in modern society. It is also relatively cheap to make. The silver button cell is used in appliances that require small cells with stable voltages during operation.

Dry cell: Silver button cell:

Chemistry The negative anode is the zinc casing of the cell. The central, positive cathode is an inert graphite rod surrounded by graphite and manganese dioxide powder. Between the two electrodes is an aqueous electrolyte paste containing ammonium chloride.

The negative anode is zinc powder whilst the positive cathode is graphite with some silver oxide paste. The two electrodes are separated by a KOH paste in a porous carrier.

Equations Zn(s) Zn(aq) 2+ + 2e-

2MnO2 (s) + 2NH4+

(aq) + 2e-Zn(s) + 2OH-

(aq) Zn(OH)2 (s) + 2e-

Ag2O(s) + H2O(l) + 2e- 2Ag(s) + 2OH-

Eo = E reduction + E oxidation

H2O (l) + Mn2O3 (s) +2NH3 (aq) (aq)

Cost and practicality

The materials needed to make a dry cell are relatively cheap and easy to obtain. However, the dry cell is non-rechargeable and voltage falls during use as the electrolyte concentration around the cathode drops. It also has a short shelf life as zinc is attacked by the ammonium paste. Small and portable

The silver button cell is expensive to make due to the high cost of silver. It is non-rechargeable and so needs to be recycled to recover the expensive silver. It has a relatively long shelf life compared to the dry cell and produces a stable voltage over the life of the cell. Small and portable.

Impact on society

The dry cell was the first commercially developed battery and had a significant impact on society; allowing the development of portable electrical appliances. Nowadays it is used in low-drain appliances such as torches, remote controls, LCD calculators and battery powered toys.

The development of the silver button cell allowed use of miniature electrical appliances (e.g. watches). Currently it is used in watches, cameras, hearing aids, calculators and other appliances that require a stable voltage over time.

Effect on environment

Battery components are weakly acidic but non-toxic. There are few environmental consequences upon disposal.

The components are non-toxic but KOH is caustic (highly basic) and can cause burns.

5. Nuclear chemistry provides a range of materials

Distinguish between stable and radioactive isotopes and describe the conditions under which a nucleus is unstable

The stability of the nucleus is related to the forces holding the nuclear particles together (known as the strong nuclear force). The most important indicator of nuclear stability is the neutron to proton ratio.

A plot of the neutron to proton ratios of various isotopes indicates that stable nuclei are found in an area of the graph known as the ‘zone of stability’.

- Lighter elements (Z<20) tend to be stable when the n:p ratio is approximately equal to 1

- Heavier elements need more neutrons than protons (i.e. n:p ratio is greater than 1) in order to reduce proton-proton repulsions.

An isotope is radioactive (i.e. nucleus is unstable) when the n:p ratio lies outside the zone of stability or if the atomic number (Z) is greater or equal to 93 (transuranic elements)

- Isotopes with too many neutrons are beta emitters- Isotopes with too few neutrons are alpha emitters

Unstable nuclei spontaneously emit radiation whilst stable nuclei do not emit radiation. All isotopes of elements with Z>83 are unstable and radioactive. (Bismuth- Z=83 is the last

stable element)

Types of nuclear decay

Alpha particle:consists of two protons and two neutrons (helium nucleus)

Beta particle: the electron released when a neutron decays into a proton and electron

Gamma radiation: a type of electromagnetic radiation (high frequency, short wavelength). Note that gamma radiation doesn’t change atomic or mass number.

Alpha particle Beta particle Gamma radiationWritten as:

Mass 4 amu Approx. 0.0005 amu Virtually no massCharge 2+ -1e UnchargedIonising power

High Moderate Low

Penetrating power

Low Moderate High

Effect of Magnetic Field

Moderate deflection Strong deflection No deflection

Effect of electric field

Moderate deflection Strong deflection No deflection

Describe how transuranic elements are produced

Transuranic elements are elements that have atomic number greater than 92. All isotopes of these elements are radioactive and are artificially synthesised.

There are numerous ways of producing transuranic elements:

Neutron bombardment can be used to produce neptunium (Z=93)

Alpha bombardment can be used to produce an isotope of curium (Z=96) from plutonium-239

Ion accelerators are used to produce transuranic elements with higher atomic numbers. It involves firing accelerated particles (usually ions) into a target. Ion accelerators are either a linear accelerator or heavy ion synchrotron.

Generally, only the long-lived transuranic elements have any real use (e.g. plutonium is used as nuclear fission fuel; americium is used in household smoke detectors).

Describe how commercial radioisotopes are produced

Today, radioisotopes are produced using particle accelerators (cyclotrons) and nuclear reactors. They are used in medicine, industry and research.

Nuclear reactors are sources of neutrons and can be used to make radioisotopes through neutron bombardment. Target nuclei are placed in the reactor core where they are bombarded by neutrons to produce the required isotope. Cobalt-60 (used in cancer treatment) is made by placing normal cobalt-59 in a reactor where it captures a neutron.

Cyclotrons can be used to produce certain radioisotopes used in medicine. A target nucleus with is bombarded with a small positive particle such as a helium nucleus (alpha particle) or carbon nucleus. Fluorine-18 is prepared by bombarding nitrogen with an alpha particle.

Identify instruments and processes that can be used to detect radiation

Geiger Muller (GM) counter – the radiation enters the GM tube through a window and hits a gas molecule (usually argon) and ionises it by releasing electrons. As these electrons accelerate due to the high voltage, they cause more ionisations - leading to a cascade of electrons arriving at the anode. An amplified electrical pulse is created at the anode which is measured by generating clicks in an audio amplifier or by a digital counter.

Scintillation counter – when certain substances are hit by radiation, they emit a flash of light which is collected and amplified in a photomultiplier. The electrical signal generated then operated by a counter.

Cloud chamber – a chamber containing a cold saturated vapour (e.g. alcohol). Cloud trails are produced in the path of the ionising radiation.

Radiation dosage badges are worn by workers in the nuclear industry to monitor radiation exposure. There are several types of badges, including:

Film badges – the amount of darkening of the film indicates the amount of radiation the worker has received.

Thermoluminescent dosimeters (TLDs) – Thermoluminescent material traps ionising radiation, and then releases it upon heating as visible light. The brighter the light, the higher the ionising effect.

Identify one use of a named radioisotope: in industry, in medicine

Describe the way in which the above named industrial and medical radioisotopes are used and explain their use in terms of their chemical properties

Iodine-123 (used in medicine)

Iodine-123 is a radioisotope used in imaging of the thyroid gland. It can be ingested by capsule or an oral solution, and it travels through the bloodstream to the thyroid gland where it concentrates. It releases gamma radiation as it decays, which is then detected by gamma cameras to create images of the thyroid gland.

It is a gamma-emitter which means that radiation has enough penetrating power to reach the detector (gamma camera) without ionising too much tissue along the way (safety). It also has a short half-life (13.2 hours) so the patient is only exposed to the radiation for a short period of time. Although it is weakly ionising, it can still damage cells so dosage needs to be kept low.

Strontium-90

In industry, many materials are produced as sheets which need to have uniform thickness. The beta particles released by the decay of strontium-90 are used to monitor the thickness of sheeting as it emerges from rollers. A strontium-90 source is placed on one side of the sheet whilst a radiation detector is placed on the other side. Changes in the levels of beta particles that pass through the sheeting are automatically monitored. The proportion of beta particles that reach the detector is proportional to the thickness of the sheet.

Stronium-90 has a relatively long half-life (28 years), meaning that samples used in industry can last a long time. However, it isn’t long lived as to create long term environmental problems upon disposal. Beta radiation is also optimal for thickness gauges as alpha particles are not sufficiently penetrating and gamma rays are too penetrating. An issue with using strontium is that its chemical similarity with calcium causes it to accumulate in bones; and so, constant monitoring of workers is important.

Process information from secondary sources to describe recent discoveries of elements

Between 1943 and 1953, the team at Lawrence Berkley National Laboratory (LBNL) discovered: americium, curium, berkelium, californium, einsteinium, fermium, mendelevium and nobelium.

In 1999, a research team at Dubna in Russai discovered element 114. It’s half-life was 30 seconds, considerably lower than that of the half-lives of other superheavy nuclei (elements with ridiculously large and unstable nucleus), which are typically measured in milliseconds.

- It was created by colliding a calcium-48 ion into a plutonium-244 target using a heavy ion accelerator

Use available evidence to analyse benefits and problems associated with the use of radioactive isotopes in identified industries and medicine

Benefits Problems Used to make equipment in industry –

radioisotopes can be used in tracers, detectors and thickness gauges which are more sensitive, precise and reliable than earlier equipment. It can also be used to examine buildings and machinery for structural faults.

Diagnostic purposes –For example, radioactive iodine-131 is similar to nonradioactive iodine which concentrates in the thyroid gland; and thus iodine-131 used to diagnose thyroid disease.

Radiation therapy – Radioactive isotopes can be used to treat many forms of cancer, however, the ionising radiation source must be carefully administered to minimise damage/exposure to surrounding tissue

Radiation dosage - nuclear radiation is dangerous to living tissue; continuous exposure can lead to burns, cancer, and even genetic damage. Scientists working with radioisotopes have regular health checks conducted on them.

Radioactive waste – the products of radioactive decay are often radioactive themselves. The radioactive wastes produced at nuclear power plants must be disposed of correctly; otherwise it may easily contaminate the surrounding environment as it can spread through wind, groundwater and organisms. For this reason, waste is often stored underground in stable, geological structures.

Chemical similarities – radioactive isotopes often have the same chemical properties as non-radioactive isotopes. This could pose health problems; for example, Strontium-90 could bio accumulate in bones (due to its chemical similarity with calcium) and radiate surrounding tissue – potentially leading to cancer.