Chemistry HSC
Note: This is not the final revision of my notes (I’m constantly revising them as I do papers), and there may be a few areas of error or unclear explanations. However, I’ve gone through it a number of times, and it should be mostly very accurate and comprehensive. If you find anything wrong, it would be nice if you could tell me on [email protected] so I can either discuss it or change it. Good luck for the HSC guys
Organic Chemistry – the study of compounds containing carbon THIS IS BACKGROUND INFO
Organic chemistry is separate because we can look at all of the included chemical groups in a unifying way, through the bonding properties of carbon.
Study of major groups:
o Oxygen-containing compounds e.g. alcohols o Hydrocarbons e.g. petroleum
o Carbohydrates e.g. sugars
o Nitrogen-containing compounds e.g. amino acids proteins
Etc.
Hydrocarbons
When all bonds are single, they are called alkanes. This is a family of compounds, represented by a general formula CnH2n+2, aka a homologous series. They have similar properties and reactions.
There are ‘straight’ chain alkanes. e.g.
The 109o, zig-zag bonding shape is due to the tetrahedral nature of single bonds. Carbon atoms
always form 4 bonds. If they don’t you’re doing something wrong.
Branched chain (one is attached to at least 3)
Methane, CH4, ethane, C2H6, Propane, C3H8, and Butane, C4H10 are all alkanes.
Physical Properties
C1 to C4 are gases at room temp, C5 to C18 are colourless liquids, others are solids.
The density of alkanes are significantly less than water (1.00g/mL), are non-conductors of electricity and are insoluble in water. The reason for their insolubility is that C-C bonds are non-polar, and C-H bonds are only slightly. This slight polarity is cancelled by symmetry in structure. Weak dispersion forces, relatively low boiling/melting points. Boiling/melting points increase as molecular weight increases, due to stronger dispersion forces (more electrons). Volatility decreases as molecular weight increases.
Alkenes C C C C C C C C C C C C
KMnO4, H+
Contain a double bond between a pair of carbon atoms. Homologous series, formula CnH2n, planar
shape. There are different ways of representing structure:
(2)Full Structural Formula – shows planar geometry around double bond, and tetrahedral around other carbon atom
(3)Intermediate type – infers tetrahedral shape
(4)Condensed structural formula – no attempt to show structure, but enough information is provided
Isomers are different compounds with the same molecular formula but different structural formula. The double bond can be at different positions in the compound.
e.g.
Physical Properties
Straight-chain alkenes similar to alkanes. Densities similar to corresponding alkanes, insoluble in water.
Alkynes
Contain a triple bond between carbons. CnHn-2. As with alkenes, isomers are possible. They are
non-polar, low boiling points and insoluble in water Naming Alkanes, Alkenes and Alkynes
o Stem telling length of carbon chain C1 meth- C4 but- C7
hept-C2 eth- C5 pent- C8
oct-C3 prop- C6
hex-o Lhex-ohex-ok at the lhex-ongest phex-ossible chain, then pick a prefix
o Look for branches, and use a number to denote their position, starting from the closest end e.g. 2,3 – dimethylpentane or 2 - dimethylpentane
o If double or triple bonds present, set this as priority (start counting closest to the bond) and first state branches then double/triple bond e.g. 2– methyl – 1 – propene (methyl on second branch and double bond on first)
o If compound is cyclic, add a cyclo- before the name of the main branch e.g. 1,2,3 - trimethylcyclohexane
Saturated and unsaturated compounds
Alkenes and Alkynes – unsaturated, possible to attach more hydrogen Alkanes – saturated, max no. of H atoms that skeleton can hold Functional Group
The functional group of carbon compounds is the most reactive area of the compound. In alkenes and alkynes, the double/triple bonds are the functional groups. When a hydrogen atom is replaced with a halogen atom, e.g. OH, the halogen becomes the functional group.
Molecules with a particular functional group react similarly, regardless of the attached chains.
KMnO4, H+
Alkanols are alkanes with one H replaced by an OH group. They are named with the ‘e’ replaced by an ‘ol’, and a prefix number to denote the position of the hydroxyl group. This group is the
functional group, and provides high melting/boiling points due to polar bonds.
Primary alcohols have one carbon bound to the carbon w/ OH group, secondary have two and tertiary have three. Extent of hydrogen bonding depends on exposure of OH group, most exposed in primary, highest boiling/melting points etc.
• Construct word and balanced formulae equations of chemical reactions as they are encountered
Types of Organic reactions
Substitution – replacement of one atom or group by another
Addition – adding atoms or groups of atoms to alkenes or alkynes (bond breaks, new atoms are added on)
Elimination – a small molecule breaks off and a double bond is formed in the original (reverse of addition)
Condensation – two molecules react, forming a new compound and a small molecule (usually water)
Hydrolysis – the action of water on a molecule results in two new products
• Identify the industrial source of ethylene from the cracking of the fractions from the refining of petroleum
Ethylene is produced from natural gas or crude oil (mixtures of hydrocarbons, containing mainly alkanes and cycloalkanes and smaller amounts of unsaturated including alkenes), which is called feedstock. The feedstock is refined by fractional distillation to obtain alkenes since alkanes are susceptible to combustion and unreactive (not useful as starting material).
Ethylene is the most versatile, but not found in large quantities in feedstock. Produced from other hydrocarbons in ‘cracking’ (a process where hydrocarbons of higher mol mass are converted to lower mol mass via breaking of chemical bonds). There is greater demand for some fractions than others (e.g. gasoline > heavier hydrocarbons), and fractions from crude oil are not in optimum ratios, hence cracking. Note that air needs to be excluded to prevent combustion. Ethylene is simple and can be synthesised from many different hydrocarbons. Three ways:
1. Thermal cracking – requires very high temps and generally not used. End products hard to control since many places where bonds could break, early method. Accelerates reaction and drives equilibrium to reactants.
2. Catalytic cracking of fractions separated from petroleum. – material is passed over a catalyst at a temperature of about 500oC, and the particles adsorb onto the catalyst and have
their bonds weakened, resulting in decomposition. E.g. C10H22(g) -> C8H18(g) + C2H4(g). Alkane
splits further into smaller alkenes until propene/ethylene formed. Catalysts allow it to be carried out at lower temperatures. Zeolite (by mid 1970’s) is the main catalyst, and is a crystalline substance of Al, Si and O. Usually fine powder (higher surface area for action of catalyst) circulated through feedstock. Zeolite gives greater control over products under different conditions of temperature and pressure (thus increasing yields of desired products) i.e. C18H38(g) ----(zeolite catalyst)---> 4 C2H4(g) + C10H22(g)
3. Steam cracking of ethane and propane – ethane from natural gas deposits fed into
furnaces with steam, heated between 750 – 900oC causing much ethane to be converted to
ethylene
i.e. C2H6(g) -> C2H4(g) + H2(g)
Propane can also be used: C3H8(g) -> C2H4(g) + CH4(g)
Dilute H2So4 cat w/ water KMnO4, H+ Acidified HCl, non aqueous solvent Br 2, non aqueous solvent
• Identify that ethylene, because of the high reactivity of its double bond, is readily transformed into many useful products
Ethylene’s C=C double bond is highly reactive, allowing it to react with molecules to form many useful products
Reaction of alkenes
Characteristic reaction of alkenes is addition reaction. Two new atoms or groups of atoms are added across double bond, one to each carbon. The C=C is converted to a single bond and a saturated hydrocarbon is produced. General eqn:
H2C=CH2 + X-Y => XH2C-CH2Y
1) Addition of hydrogen to ethylene (hydrogenation) - ethylene to ethane by
heating with hydrogen in presence of nickel, platinum or palladium
2) Dibromoethane - Used as a petrol additive - halogen reactions are useful for distinguishing between saturated and unsaturated hydrocarbons. E.g. A non aqueous solution of bromine (e.g. solvent carbon tetrachloride) when added to an alkene causes the solution to lose its colour as bromine becomes incorporated into the alkene:
Alkanes do not react with NA bromine unless exposed to UV. In aqueous
solutions, the reaction may be the same as above, but due to the presence of water products can include:
[CH2=CH2(g) + HOBr(aq) CH2OH-CH2Br]
Hydrogen bromide reaction:
[CH2=CH2(g) + HBr(g) -> CH3 – CH2Br] (What states?)
3) Chloroethene – Monomer for PVC
[2CH2=CH2(g) + Cl2(g) + ½ O2(g) →
+ C
CuCl2 150o
2CH2=CH-Cl(g) + H2O(g?)]
4) Styrene – produces from benzene and ethylene via the intermediate ethylbenzene 5) Ethanol – Used as a fuel in automobiles and as an industrial solvent
[CH2=CH2(g) + H2O(l) → 4 2 ) (dilute H SO CH3-CH2OH(l) ]
6) Ethylene oxide and ethanediol – fumigant (former), manufacture of polymers (polyester fibres and PET) and antifreeze (latter)
[C2H4(g) + ½ O2(g) Ag+C→ o 250 C
2H4O(g)]
[C2H4O(g) + H2O(l) H→+ OH-CH2-CH2-OH]
• Identify the following as commercially significant monomers o Vinyl chloride
o Styrene
By both their systematic and common names Vinyl chloride – chloroethene CH2 = CHCl
Monomer for the production of PVC plastics which are widely used in applications such as electrical insulation, plumbing and garden hoses with various additives to change physical properties
Styrene – ethylbenzene C6H5CH=CH2 (also known as phenylethene)
Production of polystyrene, most stiffened of common plastics due to large phenyl side group. Stable due to presence of C-C and C-H bonds only, minimal chain branching means it can be formed into clear objects. Tool handles, car battery cases, CD cases. Gas can be bubbled through to create foam (foam drink cups), making it soft and light.
• Identify data … to compare the reactivities of appropriate alkenes with the corresponding alkanes in bromine water
Prac – Reactions of hydrocarbons with bromine water Risk analysis:
Bromine water Corrosive, and toxic, can cause skin burns
Wear safety goggles Use small amounts to minimise vapour
Cyclohexane Highly flammable
Eye and skin irritant with severe redness and pain
Wear safety glasses Keep away from hot surfaces, flames or sparks
Toluene Highly flammable, fire
hazard
Eye and skin irritant with severe redness and pain
Keep away from hot surfaces, flames or sparks Polyvinyl gloves
Aim: To compare reactivities of an alkene (cyclohexene), alkane (cyclohexane), and an aromatic hydrocarbon (toluene) in bromine water
Method:
1). Four semi-micro test tubes were half-filled with bromine water, cyclohexane, cyclohexene and toluene respectively, using eye droppers
2). Bromine water was mixed with the other substances by placing a few drops of bromine water in each micro-test tube with a dropper
3). The test tubes were tapped, and observations recorded Results:
Cyclohexane – none
Cyclohexene – forms clear solution Toluene – none
The functional group reacting with bromine is the double bond present in alkenes, this decolourises bromine water. Addition reactions. These reactions are addition reactions: Bromine w/ water ) ( ) ( ) ( ) ( 2 ) ( 2aq H Ol HOBr aq H aq Br aq Br + ←→ − + + + −
Bromine w/ cyclohexene (top)
) ( 2 10 6 ) ( 10 6 ) ( 2aq C H l C H Br aq Br + ←→
Bromine water w/ cyclohexene (bot)
) ( 10 6 ) ( 10 6 ) (aq C H l C H BrOH aq HOBr + →
Toluene did not react as aromatic molecules have delocalised electrons which do something??? ************
Bromine with cyclohexane, this is substitution:
) ( ) ( 11 6 ) ( 12 6 ) ( 2 aq C H l UV C H Braq HBrl Br + → +
Prac – Reaction of lycopene with bromine water
Aim: To determine the effect of bromine water in varying amounts on the spectrum of colours reflected by lycopene
Method:
1). Five semi-micro test tubes were filled halfway with tomato juice
2). An eye dropper was used to place 1, 2, 3, 4 and 5 drops of bromine in each of the test tubes respectively
3). The solutions were stirred with the stirring rod until colour appeared
4). The colours and the corresponding amounts of bromine water in each test tube were recorded Results:
Test tube no. No. of drops of Bromine Colour
1 10 Blue
2 8 Turquoise
3 6 Green
4 4 Khaki
5 2 Orange
Varying amounts of bromine in tomato juice changes the number of delocalised electrons in lycopene molecules, changing the spectrum of colours absorbed and resulting in different reflected visible spectra
• Identify that ethylene serves as a monomer from which polymers are made Polymerisation is the process of bonding monomers together to form long chains.
Polymers are macromolecules consisting of small repeating units called monomers joined by covalent chemical bonds. Polymers can be divided into two categories:
1. Natural polymers – naturally occurring polymers used by humans since ancient times (E.g. cellulose, silk, rubber)
2. Synthetic – more recent man-made polymers. Replacing natural since they do not corrode, are lightweight and relatively cheap. Celluloid was first
commercially manufactured plastic, but highly flammable nature meant it was replaced
Ethylene serves as a monomer due to the reactivity of its double bond. It has a structure that can change to accommodate the additional bond needed to join repeating units together.
• Identify polyethylene as an addition polymer and explain the meaning of this term Polyethylene is an addition polymer, it is created through addition polymerisation.
Def: The monomers add to the chain so that all atoms in monomer are present in polymer. It involves unsaturated monomers (a molecule containing a double or triple bond) joining together. One C=C is broken up and resulting molecules link up, since this provides molecules with extra bonding capacity. E.g. for polyethylene
Addition polymerisation requires a catalyst or initiator to start. Other polymers formed by
addition are Polyvinyl chloride (PVC), polystyrene and Teflon.
• Outline the steps in the production of polyethylene as an example of a commercially and industrially important polymer
General outline: Ethylene can be changed from gas to liquid under high pressure. This liquid ethylene can be heated in the presence of a catalyst to form polyethylene.
Two forms of polyethylene can be produced, each with differing methods and varying properties:
o LDPE (reaction conditions 100 – 300oC, 1500 – 3000 atm) – Polymerisation consists
of three stages
Initiation – organic peroxide catalyst. They produce free radicals (molecules
with unpaired electron), such as H-O. which is a hydroxy radical. This causes
the double bond in ethylene to break and form a bond with the radical. CH2=CH2 +R● RCH2-CH2●
Propagation - The resulting
molecule contains an unpaired electron. Bonds to another ethylene molecule through the same process etc. (Chain propagation reactions).
Backbiting, where the chain curls onto itself and the free electrons takes a hydrogen atom from an existing CH2 group, causes branching.
Termination – at various times, it is possible for two free radical polymers
to react to form a covalent bond, ending propagation (chain terminating reaction).
o HDPE (50 – 75oC, <1 atm) – polymerisation process is same as above, but
Ziegler-Natta catalyst (TiCl4, Al(C2H5)3 used. Ethylene molecules are added to chain on surface
of catalyst, reducing backbiting and branching. Comparison of structures and properties
LDPE HDPE
Higher degree of branching, meaning less dispersion forces between strands, making it softer and more flexible
Lower degree of branching, meaning more dispersion forces within strands,
making it harder and more rigid
Less dense More dense
These products are plastics. Plastics are manufactured materials containing combinations of organic and inorganic elements. They are solid in the finished state but fluid at some stage, and able to be formed into shapes by application of heat and/or pressure.
Factors affecting the properties of polymers:
o Length of chain (no. of monomer units) – those with longer chains are stronger since greater dispersion forces between chains
o Arrangement of chains relative to each other – when chains are unbranched, they are lined up and closely packed creating crystalline areas resulting in stronger and less flexible plastics. Amorphous regions were alignment is more random, produce weaker and softer plastics. Polymer fibres drawn through a small hole aligns them and increases strength
o Function groups in monomer units – polar functional groups increase intermolecular forces between polymer molecules, increasing hardness.
o Cross-linking between polymer chains – covalent links between polymer chains makes polymers very hard and difficult to melt.
o Additives – few polymers are used in pure form, additives improve or extend properties. Additives can include pigments, plasticisers to soften, stabilisers to increase resistances to decomposition etc.
The variable chain length leads to many uses, with shorter lengths for food packaging and milk containers, to longer lengths (800,000 atoms per molecule) for artificial ice rinks.
• Describe the uses of the polymers made from the above monomers in terms of their properties
Polymer Properties Uses
LDPE 1). Resists water and chemicals 2). Electrical insulator
3). Easy and cheap to process 4). Waterproof
5). Non-toxic
1). Pipes for farm and industry
2). Wire and cable sheathing for telephone, coaxial, submarine television and radar 3). Shopping and garbage bags
4). Milk and fruit juice packs, food containers
HDPE 1). Can take high pressures 2). High tensile strength 3). Chemical resistance
4). Durability and toughness
1). Coating in steel pipes in high pressure gas mains 2). Fibres for ropes, fishing nets
3). Moulded into
containers to hold petrol, oil, detergents and acids 4). Children’s toys, plastic buckets, playground equipment
Polyvinyl Chloride
1). Soft and pliable
OR (depending on additives) 2). Rigid
3). Resists burning 4). Low static electricity
1). Wallpaper, clothing upholstery
2). Water pipes, guttering 3). Coatings on materials to make flameproof 4). Flooring; tiles, roll flooring and carpet backing
Polystyrene 1). Rigid and electrical insulator
---As foam:
2). Chemically unreactive 3). Low density
---4). Resists high impact
1). Television backing, hairdryers, washing machines 2). Food containers 3). Marker buoys, surfboards
4). Shoe heels, toys
• Discuss the need for alternative sources of the compounds presently obtained from the petrochemical industry
Petroleum fractions have been the most convenient and economical raw material for synthetic polymers. However, alternatives are being sought since:
1) The current source is non-renewable, and the move to more renewable resources will allow us to continue manufacturing petrochemical products (supplies will run out)
2) Petrochemical products are (non-biodegradable?) and contribute to the degradation of the environment
o A solution is the use of biomass (organic material from living organisms). All living
organisms produce biopolymers, which are naturally occurring polymers made entirely or in large part by living organisms
o They are advantageous since they are renewable, and can be used indefinitely with careful use, and are biodegradable since the bonds within the molecule can be broken down by bacteria and fungi, so they do not contribute to the degradation of the environment.
• Explain what is meant by a condensation polymer
A condensation polymer is a polymer that was produced through the reaction of two different functional groups in which a small molecule (usually water) is eliminated and the two groups become linked together. Condensation reactions involve saturated molecules. Common groups are – COOH (carboxylic acid), –OH (alcohol) and –NH2 (amine) group. Condensation polymers do NOT
require identical monomers
• Describe the reaction involved when a condensation polymer is formed e.g. Condensation polymerisation of nylon
Practical
Aim: to produce nylon using interfacial polymerisation Equipment:
2 x 100 mL beakers Tweezers
Glass stirring rod
20mL of 1,6 – diaminohexane solution 20 mL of 10% sebacoyl chloride in hexane Procedure:
1). 1,6 – sebacoyl chloride was added to a beaker
2). The diamino hexane was run very carefully down the side of the beaker, so that the two solutions mix as little as possible
3). The white material formed between the two layers was clamped using the tweezers
4). The material was drawn away from the beaker and onto the glass stirring rod, being careful to keep away from sides of beaker
5). The material was wound onto the stirring rod, dried and examined Results/Analysis:
A variety of monomers can be used to manufacture nylon, it is simply a generic name for a group of polyamide polymers, the common feature being the repeated –CONH- bond.
This experiment used interfacial polymerisation. It is thus named since the reactants bond together and form nylon at the contact surface between them.
PET (polyethene terephthalate) is also condensation
• Describe the structure of cellulose and identify it as an example of a condensation polymer found as a major component of biomass
Biomass – organic material derived from living organisms Glucose C6H12O6 is a carbohydrate of form:
The presence of five hydroxyl groups allows glucose to form polymers such as starch, cellulose, and glycogen.
Cellulose is a biopolymer, a polymer naturally synthesised by living organism. They are condensation polymers, since water is eliminated from a reactive functional group when glucose units join together.
o Many glucose units linked together (polysaccharides).
o The glucose units come together, causing two hydroxyl groups to react, a hydrogen ion dissociates from one hydroxyl and combines together with the other hydroxyl to form water.
o The leftover oxygen atom then forms a covalent bond between the molecules. These parts are called the functional units
o Cellulose is a linear polymer, producing a fibre-like material. The beta linkages result in flat, ribbon-like strands which are closely packed and have strong hydrogen bonds between them (cellulose strands). This gives cellulose its strength and rigid structure. o It is the main component of plant cell wall and major structural component of woody
plants and natural fibres
o This makes it the most abundant polymer known on earth.
• Identify that cellulose contains the basic carbon-carbon structures needed to build petrochemicals and discuss its potential as a raw material
Cellulose contains three-carbon and four-carbon chains with attached hydrogen and hydroxl groups. Many polymers such as polypropylene are made from three-carbon and four-carbon monomers. If cellulose can be broken down and these chains isolated, it can be used to produce polymers. Large amounts occur naturally such as in plant cell walls, and large amounts left over from agriculture. Use as raw material can be achieved by:
1. Modification of existing biopolymer chains to meet specific applications (e.g. addition of functional groups)
2. Breakdown into smaller molecules which can then be used to build synthetic polymers e.g. thermochemical (steam/acid) pre-treatment followed by hydrolysis using enzyme cellulase. This produces glucose which can be dehydrated to ethene. However, this is more expensive than using hydrocarbon sources.
Rayon is created from regenerated cellulose sourced from waste paper, straw, husks from wheat and corn and wood pulp. The fibres are chemically treated with sodium hydroxide and carbon disulfide to soften and break them down into smaller units.
A potential area is the use of biopolymer-based plastics is food wrappers and disposable containers, since they are used only once. An example is a US company which has made packaging products from corn starch.
• Use available evidence to gather and present data from secondary sources and analyse progress in the recent development and use of a named biopolymer
o Biopol, PHA (polyhydroxyalkanoates) copolymers, a family of microbial energy reserves accumulating as granules within the cytoplasm of cells.
o PHA’s
• polyester thermoplastics
• properties similar to oil-derived polymers (e.g. melting temp 50-180oC)
• mechanical properties can be changed to range from elastic rubber or hard crystalline plastic.
Simplest are PHB’s
Production is carried out by the following process:
o Alcaligenes Eutrophus, a bacteria widely found in soil and water, is fed a precise combination of glucose and propionic acid, producing PHB’s as energy storage o The PHB’s are extracted and can be polymerised to create a plastic with properties
similar to polypropylene
• Excellent flexibility and toughness • Stable in air, humid conditions
• Biodegrades in microbially active environments, bacterial and fungi microorganisms can utilise PHA’s as a source of energy by breaking it down using enzymes
(depolymerases). Potential uses
o Biocompatability - useful in several medical applications such as controlled drug release, medical surtures, bone plates
o Flexibility and toughness - structural materials in packaging products
o Biodegradable – can be used in food packaging, natural breakdown reduces landfill Development
Current work by Metabolix, successfully engineered bio-factories to demonstrate economic production of a broad range of PHA’s. Demonstrated fermentation on a tonnage scale, cost to be under a dollar a pound.
Currently working to produce PHA’s directly in non-food crop plants.
Disadvantage: Current high cost of production as opposed to crude oil sources
• Describe the dehydration of ethanol to ethylene and identify the need for a catalyst in this process and the catalyst used
• 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
Ethanol and is an alkanol. It is tetrahedral about each carbon and bent around oxygen atom (not shown here). Ethylene can be made through dehydration, heating with concentrated sulfuric acid or a porous ceramic catalyst (>350 in industry):
O H CH CH H O CH2 H SO /H PO 2 2 2 3 2 4 3 4 CH − − − → = +
Reverse reaction is hydration, requires dilute aqueous sulfuric acid:
H O CH O H CH CH2 = 2 + 2 H2SO4dilute→CH3− 2 − −
They are general, apply to any alkanol or alkene e.g. 1-pentanol to 1-pentene
• Describe and account for the many uses of ethanol as a solvent for polar and non-polar substances
Risk Analysis
Hazard Risk Control
Iodine Toxic – fatal if swallowed. Corrosive, causes burns and damaging to lungs if
inhaled
Safety glasses, effective ventilation
Oxalic acid Poisonous if swallowed, inhaled or absorbed
through skin
Gloves, avoid generation of dust
Prac – Ethanol as a solvent
Aim: To test the solubility of various materials in ethanol Method:
1). 20 mL of ethanol was poured into each of 10 test tubes using measuring cylinders
2). A rice-grain amount of each solid was placed into successive test tubes, and a few millilitres of each liquid placed into the remaining test tubes using an eye dropper.
3). Each test tube was agitated by tapping and gently shaking 4). Observations were recorded
Results: Solute Solubility Sodium chloride No Napthalene Slightly Cyclohexanol Yes Glycerol Yes
Iodine Yes, dark red
Oxalic acid Yes, purple
Boric acid Yes
Glucose Yes
Wax No
o Ethanol has a single hydroxyl group which is attached to an aliphatic
o Allows it to dissolve substances with polar covalent bonds, hydrogen bonds form o Able to dissolve hydrocarbons and non-polar due to the formation of dispersion forces
with the aliphatic group.
o Widely used as alternative solvent in dissolving medicines, cosmetics, food flavourings, alcoholic beverages, low toxicity so relatively safe
Ionic (sodium chloride): Unable to dissolve since strong ionic bonds holding atoms together, and intermolecular formed inadequately strong to break apart lattice
Polar covalent bonds (cyclohexanol C6H11OH, glycerol C3H5(OH)3, oxalic acid C2O2(OH)2, Boric
acid B(OH)3, Glucose C6H12O6, Urea CO(NH)2) : Polar covalent bonds such as those in hydroxyl
groups allowed ethanol to bond strongly and dissolve them
Macromolecules (Wax C24H50) : Though only held together with weak dispersion forces, its large
size means a larger surface area of contact between molecules and thus more total dispersion forces. Ethanol was unable to dissolve
Non-polar molecules (Iodine, Napthalene, heptane, pentane) – iodine is diatomic and has very weak dispersion forces holding together, but ethanol can form dispersion forces with iodine molecules and pull away. Napthalene is an aromatic hydrocarbon and does not attract strongly, but dissolves in a similar fashion, same for heptane and pentane which are short-chain hydrocarbons.
With 1,2,3 – propanetriol:
• Outline the use of ethanol as a fuel and explain why it can be called a renewable resource Ethanol is a flammable liquid, burning with the reaction:
) ( 2 ) ( 2 ) ( 2 ) ( 5 2H OH l 3O g 2CO g 3H O g C + → +
It is also easily transportable, and was used by hikers and campers. It has thus been proposed as an alternative fuel source, having already been used as an ‘extender’ in world war 2. The purpose of ethanol is to:
1. Reduce greenhouse gas emissions
2. Reduce reliability on non-renewable fossil fuels
Engines would not need any modification to run 10-20% ethanol fuel, and is renewable since synthesised in sugar cane from carbon dioxide, water and sunlight. Burning produces carbon dioxide and water which can then be re-used to produce ethanol, so it follows an almost indefinite material cycle.
It has thus been promoted for motor cars to supplement and replace petrol. • Describe conditions under which the fermentation of sugars is promoted • Summarise the chemistry of the fermentation process
• Present information from secondary sources by writing a balanced equation for the fermentation of glucose to ethanol
o Fermentation requires a carbohydrate as starting material, such as glucose, sucrose or starch
o Disaccharides such as sucrose and polysaccharides such as starch need to first be broken down into monosaccharides such as glucose/fructose by enzymes in the mixture
o This carbohydrate is placed in the presence of yeasts, which produce enzymes that break it down to ethanol and carbon dioxide
C6H12O6(aq) →yeast 2CH3−CH2 −OH(aq) +2CO2(g)
o The optimum conditions are 37oC and anaerobic conditions
o Reaction is exothermic, so temperature needs to carefully controlled
o Fermentation can occur until 15% ethanol, then the yeasts cannot survive and fermentation stops – extra ethanol can be added or distillation used to increase concentration
• Solve problems, plan and perform a first-hand investigation to carry out the fermentation of glucose and monitor mass changes
Prac – Fermentation of glucose
Aim: To investigate the fermentation of glucose Method:
1). One gram of beef extract and 25 grams of glucose and 7 grams of yeast were measured out using an electronic beam balance
2). A test tube with barium hydroxide was weighed on the triple beam balance and its weight recorded
3). The beaker was filled with 300mL of tap water and heated over a bunsen burner until 40oC
4). The beef extract, warm water, yeast and glucose were quickly poured into the conical flask and weighed on the electronic beam balance
5). The apparatus was set up as shown below:
6). After a week, the tubes and stopper were removed, then the fermented solution and test tube with barium hydroxide were weighed on the triple beam balance and analysed 7). Experiment was repeated 2 times
7). Steps 1-6 were repeated without the yeast, to act as a control
Results:
Result Loss in mass of conical flask and contents (g)
Gain in mass of test tube contents (g) 1 8.0 5.9 2 9.8 4.8 3 9.1 5.0 Average 9.0 5.2 Control:
Result Loss in mass of conical flask and contents (g)
Gain in mass of test tube contents (g)
1 0 0
2 0 0
3 0 0
The formation of carbon dioxide was evidenced by the formation of barium carbonate in the test tube. The control showed that the loss in mass, and thus creation of carbon dioxide, was caused by the yeast fermenting glucose.
Equation: ) ( 2 ) ( 2 3 ) ( 6 12 6H O aq 2CH CH OH aq 2CO g C →yeast − − +
Reaction of Barium hydroxide with carbon dioxide:
) ( 2 ) ( 3 ) ( 2 ) ( 2 ) (OH s CO g BaCO s H Ol Ba + → +
Nine grams of carbon dioxide was given off in this experiment (loss in mass of conical flask) the gain in the test tube was not used since some carbon dioxide escaped through holes around the stopper. moles g 20 . 0 2 * ) 00 . 16 ( ) 01 . 14 ( 0 . 9 CO of moles 2 = + =
Through stoichiometry, 1 mole of glucose produced 2 moles of CO2 and ethanol each. Therefore
0.20 moles of ethanol produced
Mass of ethanol = molar mass ethanol x moles produced = 10g (3.3 % w/v)
This reaction did not go to completion, 6 grams of glucose left. This is most likely because the yeast were saturated in ethanol and could no undergo further fermentation, or were no left for sufficient time. Some discrepancy could have been caused by measurement error.
• Process information from secondary sources to summarise the processes involved in the industrial production of ethanol from sugar cane
Industrial production of ethanol from sugar cane 1. Feed preparation
o Crushing – sugar cane is crushed to remove high-quality sugars and molasses, which
are used in fermentation
o Saccharification – bagasse, the other constituents of sugar cane (50% cellulose)
undergo a multi-step hydrolysis process, using an enzyme and sulfuric acid as catalyst to produce glucose compounds
3. Fermentation – yeast and anaerobic conditions ferment glucose compounds to a certain concentration of ethanol (max 15%). (Note: Fermentation less efficient than hydration)
4. Purification of mixture – waste products are removed and distillation is used to concentrate
ethanol
5. Addition of gasoline – varying amounts of gasoline are added to produce a commercial product, ‘gasohol’ or E10 is 10% ethanol 90% gasoline
• Assess the potential of ethanol as an alternative fuel and discuss the advantages and disadvantages of its use
Note: it is more expensive to dehydrate ethanol than it is to purify ethylene from crude oil (this doesn’t really go here, I dunno where to shove it)
Ethanol is flammable liquid that is suitable as a fuel. It can be fermented from biomass such as sugarcane and corn, requires land for agriculture and infrastructure for a fermentation industry to be set up. If these requirements are met adequately, the advantages of ethanol as an alternative fuel are: o Renewable – products of ethanol combustion can theoretically be completely recycled to
produce more ethanol
o Intrinsic anti-knock properties – circumvents the need for toxic anti-knock agents due to presence of oxygen, increases octane of fuel
o Burns more cleanly due to presence of oxygen, , reducing toxic emissions (such as hydrocarbons)
o Reduction of net emission of greenhouse gases due to reuse of carbon dioxide by biomass used to produce ethanol
o Lower blends (<20%) do not require engine modification
o Predicted that household wastes will be recycled to produce ethanol – reduces dumping emissions
Disadvantages are:
o Large areas of arable land needed for agriculture, associated land degradation such as erosion and fertiliser run off
o Blends above 10% shown to be damaging to cars designed for gasoline, including increased carbon deposits on pistons and corrosion of metallic engine components o Greenhouse reductions hindered by use of fossil fuels and emission of toxic waste
products in transportation/production of ethanol
• Process information from secondary sources to summarise the use of ethanol as an alternative car fuel, evaluating the success of current usage
Higher blends of ethanol require special engines suited, lower blends (<20%) do not require this. It is extensively used in some countries, such as Brazil and the US.
o In Brazil, a large portion of cars are currently “flex-fuel”, allowing them to use both ethanol and gasoline, 80% of cars produced in 2005 were flex-fuel
o Government subsidies and rising petroleum prices have successfully encouraged mass-uptake of ethanol use. Pure ethanol and 25% ethanol are available at nearly all gas stations
o Its use has had noticeable improvements on air quality due to more complete combustion o Brazil is approaching self-sustainability in areas of ethanol use due to its large areas of
arable land and tropical climate The Bad:
o There are situations where ethanol cannot replace fossil fuels, such as diesel fuels, and they continue to be burnt
o The popularity of ethanol depends on government subsidies. Production of ethanol requires a large investment of money and energy, and costs more than petroleum to produce
o Requires destruction of rainforest which acts as carbon sink, offsets greenhouse reductions
In Australia:
o Ethanol costs more than petrol to produce, so subsidies are provided to encourage addition of ethanol to petrol
o Ethanol cars are in a small minority
o Public suspicion about fuel, since some independents add excessive ethanol causing engine wear, and claims by manufacturers that blends above 10% will void warranties. Federal government has decided to limit mixtures to max 10% ethanol
o Skepticism about mass-implementation, no reliable studies showing improvements in air quality through ethanol industry and worry about associated environmental costs such as land degradation
o Ethanol uptake is less successful due to lack of arable land for feedstock growth, higher individual wealth and higher costs of labour
Evaluation:
Highly successive in some countries, but less successful in others with less land resources. Usage is hindered economically depending on economic situation, and for some is not economically feasible due to high energy and monetal cost.
• 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 amount of heat energy released when one mole of the substance undergoes a combustion reaction.
Prac – Heat of Combustion of Alcohols
Aim: To measure the amount of energy produced when alcohols are burned and thus calculate their molar heats of combustion
Method:
1). A copper calorimeter and spirit burner were weighed using an electronic beam balance 2). A measuring cylinder was used to pour 100 mL of water into the copper calorimeter 3). The apparatus was set up as show below:
4). The initial temperature of the water was measured using the thermometer
5). The spirit burner was uncapped, lit using a matched then allowed to burn for 30 seconds
6). The spirit burner was capped and the temperature of the water taken again
7). The mass of the spirit burner was weighed on the electronic beam balance 8). Steps 3-7 were repeated for the other alcohols
Results:
Molar heats of combustion Methanol: -410 kJ/mol Ethanol: -640 kJ/mol Propanol: -980 kJ/mol Butanol: -1100 kJ/mol
Butanol produced the most soot since it had the longest carbon chain, increasing tendency for incomplete combustion: energy O H C O OH H C4 9 (l)+2 2(g)→4 (s)+5 2 (l) +
Shorter chain fuels release less energy per molecule and react at an overall slower rate, meaning that the immediate availability of oxygen molecules is adequate to ensure complete combustion. Other fuels react at faster rates due to larger release of energy per molecule, and the rate of oxygen diffusion into the immediate environment of the fuel molecules is inadequate to prevent atoms within the fuel reacting amongst themselves. These latter reactions occurs less readily than complete combustion reactions, but form eventually with adequate particle energy and collision.
o Butanol produced the most heat per gram
o The larger the molecules, the more heat released per gram
o This suggests that the breaking of a CH2 group is more exothermic than breaking off an
‘OH’ group, since one gram of lighter alcohols would contain more hydroxyl groups Ethanol would be the best fuel source since it has the best balance of achieving complete combustion and burning with more heat per gram.
Safety considerations
Danger in transporting spirit burners – carried only while unlit so would not ignite if dropped and shattered
Methanol – vapours are toxic in larger doses, do not open spirit burner Ethanol – skin and eye irritant, wear safety glasses, do not open spirit b urner Errors:
Experimental results differed from theoretical results due to:
o Conduction and radiation of heat from copper calorimeter into surrounding environment, reducing heat of combustion values
o Inaccuracies in measuring equipment This could be remedied by:
o Burning for shorter periods of time, less radiation/conduction of heat
• Explain the displacement of metals from solution in terms of transfer of electrons
• Identify the relationship between displacement of metal ions in solution by other metals to the relative activity of metals
A displacement reaction is where a metal converts the ion of another metal to the neutral atom. o Different metals have different reactivities
o Metals with higher electronegativity or lower reactivities will attract electrons more strongly, or is the stronger oxidant
o When a solid, pure metal is in contact with a solution of another metal’s ions, the metal
with the lower electronegativity, or higher reactivity will displace the other metal in solution, since it has weaker electron pull and loses an electron to the other metal to become a cation
o Electrons are thus transferred from one metal atom to the other, one becoming a neutral atom and depositing out of solution, and the other become a cation going into solution e.g.
A granule of zinc is dropped into a blue solution of copper sulfate, zinc gets covered with reddish-brown copper: ) ( 2 ) ( ) ( 2 ) (s Cu aq Cu s Zn aq Zn + + → + +
Oxidation half-reaction: − + + → Zn e Zn(s) 2 (aq) 2
Reduction half reaction:
) ( ) ( 2 2 s aq e Cu Cu + + − →
The anion is a spectator ion. The activity series can be seen on the table of standard potentials • Account for changes in the oxidation state of species in terms of their loss or gain of
electrons
1. The oxidation of an element in its stable elemental state is 0
2. The sum of oxidation states in an element or compound = 0, and for a polyatomic ion the charge of the ion
3. An increase in oxidation state means a loss of electrons and vice versa.
Examining oxidation states is useful in determining whether a redox reaction has occurred during a chemical reaction. Some elements display multiple oxidation states.
e.g.
In Cu2O (2Cu+, O2-)
Oxidation state of copper is +1
• Outline the construction of galvanic cells and trace the direction of electron flow • Describe and explain galvanic cells in terms of oxidation/reduction equations • Define the terms anode, cathode, electrode and electrolyte to describe galvanic cells A simple galvanic cell requires:
o 2 solid metal pieces to serve as electrodes o 2 containers (e.g. beakers)
o 2 different electrolyte solutions o A salt bridge with electrolyte o Connecting wire
1. Electrodes need to be matched with appropriate electrolyte, optimum metal ion same as metal of electrode. Electrolyte must have greater or equal reactivity than electrode, else displacement will occur
2. Salt bridge needs to be in contact with both solutions, and ions cannot form precipitate otherwise there will be no charge neutralisation (causing opposing emf which impedes current)
3. Conducting wire links both electrodes
The electrode are the conductors of a cell which get connected to an external circuit The anode is the electrode where oxidation occurs
The cathode is the electrode where reduction occurs
The electrolyte is a substance which in solution or molten conducts electricity
Standard conditions are 1M solution and 25oC. Acidic conditions alter the potential difference.
Process:
1. The electrode with lower reactivity attracts electrons from the other electrode through the conductor
2. A redox reaction results:
e.g. Cu(s) +2Ag+(aq) →Cu2+(aq) +2Ag(s)
3. The ion formed goes into solution, and the anion dissolves. The metal ions in solution around the cathode obtain the electron and plate onto the electrode
4. Ions flow from the salt bridge into the electrolyte solutions to neutralise charge and remove opposing potential difference
Detailed purpose of salt bridge If there is no salt bridge:
o As the redox reaction occurs, the electrolyte in contact with anode will have an
increasing excess of positive ions as the electrode dissolves, and the electrolyte in contact with cathode will have an excess of negative ions as positive ions precipitate
o This imbalance of charges produces a potential difference against the direction of electron flow, eventually stopping it
The salt bridge:
o Allows ‘migration’ of charge, and positive ions in the salt bridge move into the negative solution, and vice versa
o This preserves electric neutrality, and eliminates negative potential difference Cell diagrams
Type 1:
Metal/metal ion electrode e.g.
Cu|Cu2+||Ag+|Ag
| = phase separator || = salt bridge
Reaction progresses from left to right Type 2:
Inert substance such as platinum or carbon and equimolar amounts of non-metal and its ion. e.g.
Pt(s) | I2(s)|I-(aq) || Fe2+(aq)|Fe3+(aq) | Pt(s) Reaction progress: 2I -(aq) I2(s) + 2e- (oxidation) Fe3+ + e- Fe2+ (aq) (reduction)
What about gas?
• Perform a first-hand investigation to identify the conditions under which a galvanic cell is produced
• Perform a first-hand investigation and gather first-hand information to measure the difference in potential of different combinations of metals in an electrolyte solution Prac – Galvanic Cells
Aim:
1. to construct a galvanic cell called a Daniell cell and investigate conditions under which it
operates (A)
2. to compare the effect of using different combinations of metals in electrodes (B)
3. to compare the effect of different volumes of electrolytes under otherwise identical
conditions (A) Method A:
1). A zinc strip and copper strip were cleaned with sand paper
2). A half cell consisting of a copper strip resting in a 250 mL beaker half-filled with copper sulfate solution was constructed
3). A similar cell with a zinc strip and zinc sulfate solution was constructed, and these half-cells linked with a piece of filter paper soaked with potassium nitrate solution and folded
4). The copper strip was connected to the positive terminal of a voltmeter, and te zinc strip to the negative terminal
5). The reading and polarity were recorded before quickly disconnecting the voltmeter
6). The beakers were then completely filled with corresponding electrolyte solutions, and the voltage measured again
Results:
Beakers half: 0.20V Current: 0.5 mA Beakers full: 0.25V Current: 0.8 mA Anode: Zinc
Cathode: Copper
At anode (oxidation): Zn(s) -> Zn2+(aq) + 2e
-At cathode (reduction): Cu2+
(aq) + 2e- -> Cu(s)
Overall: Zn(s) + Cu2+(aq) -> Zn2+(aq) + Cu(s)
The salt bridge allows migration of ions into each beaker (cations into cathode solution and vice versa) to neutralise charge buildup and maintain cell voltage.
A larger volume of electrolyte solution means a large surface area of electrolyte in contact with electrodes. This increases the rate at which charged particles are removed from the electrodes, decreasing the internal resistance and thus the current. However, the voltage within the cell is caused by the intrinsic properties of the electrodes (difference in electronegativity), and thus is not
altered significantly. It is affected slightly since a charge buildup generates a slight back emf, which reduces the voltage, and more electrolyte action reduces this. Note: Concentration of electrolyte does affect voltage.
The current output needs to be measured quickly since the ions in salt bridge are being used up, and charge begins to build in half-cells opposing current flow.
Sources of error:
Electrodes not completely polished – reduces effective surface area of action for electrolyte and thus current
Method B:
1). The copper half-cell in A was set up
2). Another half-cell consisting of a magnesium strip in magnesium sulfate solution was set up 3). The electrodes were connected to the terminals of a voltmeter, and voltage reading recorded 4). Steps 2-3 were repeated with:
a. Aluminium in 1M aluminium nitrate solution b. Tin strip in tin(II) nitrate solution
Results:
Test Half-cell Polarity (relative to
Cu/Cu2+) Total cell voltage
Zn/Zn2+ -ve 0.50
Mg/Mg2+ -ve 1.1
Sn/Sn2+ -ve 0.35
Al/Al3+ -ve 0.90
Standard potential Cu – +0.34 V (Oxidation potential -0.34V) Half Reaction (write in
during exam)
Predicted voltage E0 (V) Experimental E0 (V)
Zn -0.76 -0.16
Mg -2.36 -0.76
Al -1.68 -0.56
Sn -0.14 -0.01
The more active the metal, the greater the potential difference.
Note: Oxidation potential is the ability of a substance to oxidise in relation to hydrogen, reductional potential is ability to reduce in relation to hydrogen. E.g. Copper has reduction 0.34 meaning it has higher ability to reduce, but its oxidation is -0.34, it has less ability to oxidise.
• Gather and present information on the structure and chemistry of a dry cell or lead-acid cell and evaluate it in comparison to one of the following:
o Button cell (Silver Oxide cell) In terms of:
o Chemistry
o Cost and practicality o Impact on society o Environmental impact
Structure Chemistry Oxidation Zn(s) -> Zn2+(aq) + 2e -Reduction 2MnO2(s) + 2H+(aq) + 2e- -> Mn2O3(s) + H2O(l)
Hydrogen ions provided by ammonium NH4+<-> NH3(aq) + H+(aq) Overall Zn(s) + 2H+(aq) + 2MnO2(s) -> Zn2+ (aq) + Mn2O3(s) + H2O(l) Oxidation Amalgamated zinc
Zn(s) + 2OH-(aq) -> ZnO(s) +H2O(l) + 2e
-Reduction Silver oxide Ag2O + H2O +2e- -> 2 Ag(s) + 2OH -Electrolyte KOH Overall Zn(s) + Ag2O -> ZnO(s) + 2Ag(s)
Cost and Practicality Adv:
o Inexpensive o Robust
o Easy to store and use Dis:
o Short life
o Voltage not as constant as silver button
(comparison)
o Cannot deliver very high currents
o Cannot be recharged
Adv:
o Compact
o Provides constant voltage over long period of time, since solid reactants and products have fixed
concentration
o Overall long operating life due to solid components
Dis:
o Silver is expensive o Not rechargeable Impact on Society o First commercial
battery, made portable electric devices possible o Used widely in toys,
torches, radios etc.
o Has allowed efficient powering of miniature devices e.g. watches, hearing aids
Environmental
impact o
Manganese readily oxidised to stable
manganese (IV) dioxide, becomes immobilised and not dangerous o Small quantities of
ammonium salts and zinc not harmful
o Not rechargeable, large volume in landfills so space is an issue
o Contains traces of mercury, causes problems with unsafe disposal o Non-rechargeable so takes up space
• Solve problems and analyse information to calculate the potential Eo requirement of
named electrochemical processes using tables of standard potentials and half-equations Eo
Write down half-cell equations, then balance to get overall.
These values are under standard conditions (298K, 1M electrolytes)
A higher concentration of reactants relative to products increases spontaneity of reaction and thus emf.
• Distinguish between stable and radioactive isotopes and describe conditions under which a nucleus is unstable
o The spontaneous emission of radiation by certain elements is called radioactivity
o Some elements have all isotopes radioactive, some only one or some o These particles are thus referred to as radioisotopes
Stable isotopes Unstable isotopes
No radiation emission Emission of radiation
Z ≤ 83 Z > 83
Ratio of neutrons to protons within zone of stability
Ratio of neutrons to protons out of zone of stability
Zone of stability:
A nucleus is unstable when its ratio of neutrons to protons is outside zone of stability. For light elements (Z < 20), 1.0. Stability ratio steadily increases as atomic number increases, up to 1.5 for Z = 83. Past this, all are unstable due to large size of nucleus.
• Describe how transuranic elements are produced Transuranic elements are elements with atomic number above Uranium (92)
o Some isotopes undergo fission when bombarded, others undergo nuclear reactions to form new elements
o When non-fissionable atoms such as Uranium 238 are bombarded with high speed particles, it absorbs the particle to become an unstable atom
o It then rapidly decays to form a new element
There are two machines that are used to produce high speed positive particles to produce transuranics.
Mode Emission Atomic mass Atomic
number α decay 4He 2 -4 -2 β decay 0e 1 − 0 +1 Positron emission e 0 1 0 -1 Electron capture e 0 1 − (absorption) 0 -1 γ emission 0
γ
0 0 0o Linear accelerator – accelerates positive particles in straight line along axes of series of
positive and negative cylinders, accelerating it. Often more than a kilometre in length
o Cyclotrons – accelerates positive particles by passing them through alternating positive
and negative electric fields. A strong magnetic field is used to constrain particles to spiral path, reducing size of machine.
They can also be produced in nuclear reactors, a source of neutrons. Neutrons do not experience electric repulsion like positive nuclei, and thus speeds in nuclear reactors are adequate. These create transuranic elements with a proton deficiency.
e.g. Np e U n U 01 23992 01 23993 238 92 + → →− +
Neptunium, first discovered transuranic element obtained in by chemical separation of nuclear fission reactor products.
This can be further bombarded to create plutonium:
e Pu Np n Np 02 24193 24194 01 239 93 + → → +− Unstable
( )
n Cf Cf C U 126 25098 24698 01 238 92 + → → +423 transuranic elements have been created thus far.
• Process information from secondary sources to describe recent discoveries of elements Recently discovered elements include:
o Ununoctium (118, October 10 2006) – heaviest element discovered to date. It was
indirectly detected by a team of researchers working in Russia at Dubna University’s Joint Institute for Nuclear Research when they detected its decay products after bombarding californium-249 atoms with calcium-48 ions. Very unstable, half-life 0.89ms. Reaction:
o Ununpentium (115, February 2 2004) – Russian scientists at Dubna “…” and
American scientists at Lawrence Livermore National Laboratory announced they
produced 4 atoms of Uup which quickly decayed into Ununtrium (113) in about 100 ms. They bombarded Americium with calcium.
n Uup Ca Am 2048 115288 01 243 95 + → +3
Note these elements are temporarily using IUPAC systematic element names, before they are officially named.
• Identify instruments and processes that can be used to detect radiation
o Photographic film – photographic film darkens in the presence of radiation. Used in
radiation badges worn by laboratory workers handling radioactive substances to determine radiation dosage
o Geiger-Muller tube – Radiation enters window and ionises gas particles inside Geiger
tube (inert gas such as argon), and the resulting charged particles are accelerated to the two plates with a potential difference. They further ionise other argon atoms through
collision creating a cascade effect. This creates a signal which is amplified and converted into an audio signal.
o Scintillation counter – ionizing radiation hits the scintillation crystal (depicted), the
electrons are excited and emit photons which can be detected and amplified by a photomultiplier tube (depicted) to produce a reading.
o Cloud Chamber – contains supersaturated vapour of water or alcohol. Radiation (alpha
or beta particles) ionises it, forming noticeable tracks. Alpha trails are broader and straight, whilst beta tracks are thinner and show more evidence of deflection • Describe how commercial radioisotopes produced
Radioisotopes can be produced by bombardment of high-speed particles. Radioisotopes are commercially produced in:
o Nuclear reactors (proton deficient, neutron enriched) – convenient source of
electrons. Target nuclei are placed in reactor core and are then bombarded by neutrons to produce desired isotope. These are then separated chemically or physically from other substances within reactor.
Currently operating in Australia for this purpose is HIFAR reactor, managed by ANSTO e.g. Creation of technetium:
β
0 1 99 43 99 42 1 0 98 42Mo+ n→ Mo→ mTc+−Technetium decays, releasing gamma ray inside body
o Cyclotron (proton rich, neutron deficient) – neutron deficient isotopes must be
produced in a cyclotron. They are bombarded with a small positive particle such as a helium or carbon nucleus at high speed in order to overcome electrostatic forces of repulsion
National Medical cyclotron e.g.
n Mo p Zn 11 6731 01 68 30 ++ → +2
• Identify one use of a named radioisotope: o In industry
o In medicine
• Describe the way in which the above radioisotopes are used and explain their use in terms of their chemical properties
Technicium-99m (nuclear reactor)
Most widely used in medicine for diagnosis, such as locating brain tumours or studying other parts of the body by being attached to red blood cells.
o Short half-life of 6 hours means patient exposure is minimised
o Versatile chemistry and can be incorporated into range of biomolecules targeting different organs
Iodine-131 –
Produced in cyclotron or nuclear reactor, testing of thyroid function and treatment of thyroid ailments such as overactive thyroid or thyroid cancer (beta decay destroys some thyroid cells)
o Iodine-131 is naturally absorbed by cells in the thyroid gland o Relatively short half life to minimise exposure (8 days) Specific problems:
o Ionising radiation of iodine-131 deals collateral damage to other cells
o Radiation penetrates the body and can damage organic tissue near to the patient
o Transport and production in nuclear reactors requires stringent safeguards, which is problematic
Cobalt-60 – used to measure thickness of materials. With fixed geometry for source and detector, penetration of radiation emitted from radioisotope (beta particles in this case) determines thickness of material. Gamma ray producer
o Long half-life so does not need to be replaced frequently (5.3 years) o Low energy emissions, so absorption is significant and can be detected o Low energy emissions, minimises safety procedures required
Sodium-24
Used to detect leaks in water pipes or underground oil pipes. Dissolved into water source, can be subsequently detected in soil around areas of leakage.
o Dissolves easily into water
o Relatively short half-life to minimise environmental damage (15 hours)
• Use available evidence to analyse benefits and problems associated with the use of radioactive isotopes in identified industries and medicine
Benefits in medicine:
o Created wide range of non-invasive diagnostic procedures otherwise impossible, such as technetium-99m used to identify brain tumours, gallium-67 for cancers, an area very dangerous for surgery
o Allowed radiation therapy to treat many forms of cancer, e.g. iodine-131 for treatment of thyroid cancer
o Ability to make more sensitive, precise and reliable monitoring equipment e.g. cobalt-60 for measuring thickness of materials
o Allows otherwise difficult activities such as detecting leaks in extensive water distribution systems, sodium-24 can be dissolved and radiation detected near leaks Problems:
o Exposure of radiation doses to workers in medicine, industry and research can damage
tissues e.g. ionizing radiation of sodium-24 causes cancer by removing electrons from the biological molecule DNA.
o Extra safety precautions are required for sites with radioactive materials, such as proper
storage facilities and protective clothing e.g. industries dealing with cobalt-60 and technetium-99m need to filter out the fine radioactive dust produced, which can pose a lung cancer risk
o Disposal of radioactive waste requires space, and can be problematic since isotopes such as Cobalt-60 remain radioactive a long time after they are no longer useful, may leak into environment without strict procedures
The Acidic Environment
Definitions and properties of acids/bases
An acid is a substance that produces hydronium ions (H3O+) in solution
A base is a substance containing oxide or hydroxide ions (O2-, OH-) or which in solution produces
the hydroxide ions. A soluble base is an alkali, i.e. one which dissolves or reacts in aqueous solution to produce hydroxide ions. Note that oxygen ion-containers are insoluble or only react.
Common properties of acids: 1. sour taste
2. sting or burn the skin
3. conduct electricity in solution 4. turns blue litmus red
5. React with reactive metals to form salt + hydrogen gas
6. Reacts with carbonates to form CO2, salt and water
7. Reacts with metal oxides/hydroxides to form salt and water Common properties of alkalis:
1. have a soapy feel 2. have a bitter taste
3. conduct electricity in solution 4. turns red litmus blue
5. React with amphoteric metals to produce hydrogen gas
Acids and bases react to form salt and water (there are exceptions). Note that the salt is in aqueous solution, separated as ions and not precipitated. E.g. reaction of sodium hydroxide with
hydrochloric acid:
HCl(aq) + NaOH(aq) -> NaCl(aq) + H2O(l)
Can also be written as: H+
(aq) + NaOH(aq) - > Na+(aq) + H2O(l)
Or
H+ + Cl- + Na+
+ OH- -> H2O(l) + Na+ + Cl
-The chloride and sodium ions are spectator ions. -The net ionic equation is simply H++ OH- -> H
2O(l)
Hydrohalic acids such as HCl, HBr and HI lead to halide salts. Oxyacids (acids containing oxygen attached to an element) e.g. sulfuric acid, nitric acid, phosphoric acid form salts that end in –ate. Nitrous acid (HNO2) and sulphurous acid (H2SO3) create salts that end in ‘ite’. Anions formed from
oxyacids are called oxyanions. Must be familiar with acid formulas. • Classify some common substances as acidic, basic or neutral Acidic:
Vinegar (acetic acid) – used in cooking (~3) Lemon juice (citric acid) (~2.5)
Vitamin C (ascorbic acid) – vitamin supplement
Hydrochloric acid – pH maintenance in swimming pools, clean bricks cement and tiles (~1) Neutral:
Water
Salts (e.g. sodium chloride, copper sulfate) Milk
Basic:
Baking soda (sodium bicarbonate) (NaHCO3) (~8.5)
Oven and drain cleaners (sodium hydroxide) – sodium hydroxide also used in soap, and alumina (~ 13)
Lime (calcium hydroxide) – making mortar (~ 11) Ammonia – used to make fertilisers (~ 12)
• Identify that indicators such as litmus, phenolphthalein, methyl orange and bromothymol blue can be used to determine the acidic or basic nature of a material over a range, and that the range is identified by change in indicator colour
• Identify data and choose resources to gather information about the colour changes of a range of indicators
An indicator is a substance that in solution changes colour depending on the pH of the solution. There are many different indicators, and the range of pH over which these indicators change colour varies. Litmus is the most common and is extracted from lichens. The indicator changes colour in reaction with the pH of a substance, indicating acidity or basicity dependant on the range of the indicator.
Universal indicator is a mixture of several indicators and works over the whole range
• Identify and describe some everyday uses of indicators including the testing of soil acidity/basicity
