Topic 4: Managing Resources

Question 1

What is the carbon cycle?

Answer 1

The carbon cycle describes the movement of carbon between the atmosphere, oceans, biosphere, and geosphere (carbon reservoirs)
If more carbon enters a carbon reservoir than leaves it, it is referred to as a carbon sink (e.g. oceans)
If more carbon leaves a reservoir than enters it, it is referred to as a net carbon source (e.g. combustion of fossil fuels)

Question 2

What is photosynthesis?

Answer 2

Photosynthesis is the chemical process by which plants and some microorganisms use carbon dioxide, water, and energy from sunlight to produce oxygen and glucose
6CO2 + 6H2O energy-> C6H12O6 + 6O2
It is endothermic as it requires the absorption of energy from sunlight

Question 3

What is aerobic respiration?

Answer 3

Aerobic respiration is a series of reactions that occurs in cells that releases energy for metabolic activity
C6H12O6 + 6O2 -> 6CO2 + 6H2O
It is exothermic as it releases energy

Question 4

What are carbon-based fuels?

Answer 4

Carbon-based fuels include fossil fuels and biofuels
They can undergo combustion with oxygen to release chemical energy used primarily in energy production and transport
They are also used as feedstock (raw material) to produce a range of products

Question 5

What are fossil fuels?

Answer 5

Fossil fuels have been formed over hundreds of thousands of years through the decay of organic matter under metamorphic (heat and pressure) geological conditions
Includes coal, petrol, and natural gas
Fossil fuels are relatively abundant, very energy dense, and can be easily extracted and distributed (especially thanks to well-established industries)
However, they are a finite and non-renewable source (the rate at which they are consumed exceeds their rate of formation), and their production and use releases many harmful chemicals into that atmosphere that contribute to climate change

Question 6

What are biofuels?

Answer 6

Biomass fuels are derived from biomass from plants and animal waste matter
Includes bioethanol, biodiesel, and biogas
They provide a renewable alternative to many fossil fuels and are plentiful. They are often described as carbon-neutral as the emissions of carbon dioxide from combustion are offset by the absorption of carbon dioxide by biofuel crops and microbes during photosynthesis
However, they often require larges amounts of land to produce and have little existing infrastructure to produce, transport, and use them

Question 7

What is renewable energy?

Answer 7

Renewable energy is energy that has been generated from sources that can be naturally replenished such as hydropower, wind power, solar energy, geothermal energy, and biofuels
Direct emissions from the use of renewable sources (apart from biofuels) do not significantly contribute to the production of greenhouse gases
However, the establishment, production, distribution, and ongoing maintenance of technologies related to these sources generate a significant contribution to the release of greenhouse gases, which effects global warming

Question 8

What is bioethanol?

Answer 8

An alternative fuel source that is often blended with petrol in varying ratios, or is used as a pure liquid in vehicles that have been designed to accommodate the fuel
Bioethanol is produced by yeasts undergoing fermentation (anaerobic respiration), an exothermic process
C6H12O6(aq) enzymes->2C2H5OH(l) + 2CO2(g)
Higher concentrations of ethanol are obtained through fractional distillation

Question 9

What is biodiesel?

Answer 9

An alternative to petroleum diesel - can be easily incorporated into diesel blends
Derived from triglycerides including fats and oils from plants and algae
Biodiesel is produced through transesterification (displacing one alcohol from an ester with another alcohol) of triglycerides
Methanol (with the aid of a catalyst) reacts with a triglyceride (ester), separating the glycerol and fatty acids by giving its OH to the glycerol and its CH3 to the fatty acid, making it an ester (fatty acid methyl ester)

Question 10

What does a thermochemical equation represent, and what are its components?

Answer 10

A thermochemical equation represents a chemical change and the associated energy change
Shows the correct balanced species, states of matter, and enthalpy change

Question 11

When does complete combustion occur?

Answer 11

Complete combustion occurs when there are enough moles of oxygen available to completely oxidise all carbon atoms (in the fuel) into CO2

Question 12

When does incomplete combustion occur?

Answer 12

Incomplete combustion occurs when there are insufficient moles of oxygen available to completely oxidise all carbon atoms in the fuel, resulting in partial oxidation states, such as C and CO
This is often because it is difficult to maintain the required stoichiometric ratio, so the products include those of both complete and incomplete combustion
Fuels with larger hydrocarbon molecules are more likely to form products of incomplete combustion, as the ratio of carbon to oxygen is larger, limiting the oxygen available to form CO2
Larger molecules also experience stronger dispersion forces, making it more difficult for the fuel to mix with oxygen during combustion

Question 13

How does carbon monoxide affect humans and animals?

Answer 13

CO can bind to haemoglobin much more strongly than oxygen, shifting the position of equilibrium to favour the formation of carboxyhemoglobin, limiting the amount of oxygen that can be carried around the body (via oxygenated haemoglobin), leading to fatigue and possibly loss of consciousness

Question 14

How does soot effect the environment and humans?

Answer 14

Soot is comprised of carbon nanoparticles and various products from incomplete combustion
It causes visual pollution in urban areas, blackening surfaces
When soot covers the leaves of plants, it limits photosynthesis and hence plant growth
When landing on snow and ice, it reduces the Earth’s albedo, resulting in more heat being absorbed by the Earth’s surface
When inhaled, it can lead to decreased respiratory function, and may result in the absorption of carcinogens on the surface of carbon
Soot also absorbs solar radiation, causing localised warming on that causes ice to melt and atmospheric temperatures to increase

Question 15

What is Q in thermochemistry?

Answer 15

Q=mcAT (J) is the quantity of heat released in a combustion reaction, where m is the mass of the heated substance, c is the specific heat capacity of that substance, and AT is the temperature change of the substance

Question 16

What is AH and what does it represent in thermochemistry?

Answer 16

AH = Q/1000xn (KJ/mol) is the molar enthalpy of a chemical reaction and represents the quantity of heat released or absorbed per mole of fuel that reacts, where n is the moles of fuel reacted

Question 17

Explain specific energy and energy density

Answer 17

Specific energy (kJ/g) represents the heat released per gram of fuel
Energy density (kJ/L) represents energy released per litre of fuel undergoing combustion
Both are considered when choosing fuels for vehicles, as it is more economical and efficient to generate more energy whilst carrying and burning less fuel
kJ/mol (/Mr)-> kJ/g (x g/L)-> kj/L

Question 18

How is electricity generated from steam turbines?

Answer 18

Coal and natural gas are combusted to produce high pressure steam, driving turbines linked to a generator, producing electricity
Burning these fossil fuels releases CO2 into the atmosphere, contributing and the heated water can be released to local marine environments, thus affecting surrounding ecosystems

Question 19

How can electricity be generated from photovoltaic cells?

Answer 19

Photovoltaic cells use semiconductor materials to allow electrons to absorb photons of light and shift them from the semiconductor to generate a current (electricity)
Producing photovoltaic cells produces significant carbon emissions

Question 20

What are galvanic cells?

Answer 20

Galvanic cells (aka voltaic cells) are electrochemical cells that rely on spontaneous redox reactions to generate a flow of current, converting chemical energy into electrical energy during the reaction when an electrical current is connected
(A battery is a group of cells)

Question 21

Discuss the two main types of galvanic cells

Answer 21

Typically, the oxidiser and reducer are stored in the cell and are consumed during operation until it is discharged
In a primary cell, one or more reactants become depleted and the cell is disposed of
Secondary (rechargeable) cells can have the redox reactions reversed reforming the reactants, but the generation of reactants is less effective over time

Question 22

What is a fuel cell?

Answer 22

A fuel cell is a type of galvanic cell where the oxidiser and reducer do not need to be stored or regenerated
Instead, fuels such as hydrogen and methanol are fed directly into the cell, and the oxidant is simply oxygen from the air
Electrode reactions are promoted by a metal catalyst, and a selective membrane separates the half-cells

Question 23

What is a flow cell?

Answer 23

A flow cell is a rechargeable fuel cell
Two external tanks contain two electrolytes (anolyte and catholyte), which are pumped into the half cells, separated by an ion-selective membrane
As the cell is discharged, they exchange ions through the membrane, generating electricity
When the cells are depleted, electricity is supplied to create an electrolytic cell, moving the ions back to their original states in their respective electrolyte solutions

The electrolyte does not need to be replaced often
Capacity can be increased by simply increasing the size of the tanks
No emissions of atmospheric pollutants during operation
Components can be laid out in varying configurations, including burying the tanks underground

Question 24

Discuss the advantages and disadvantages of a fuel cell

Answer 24

It uses fuels that are commonly available and renewable (e.g. hydrogen and methanol), which offer high energy density and produce very few, if any, atmospheric pollutants
The components do not need to be replaced if high-quality fuels are used, and are silent during operation
However, hydrogen may be obtained from non-renewable fossil fuels, must be supplied in high purity (electrodes can be easily contaminated), and must be stored safely
The metal catalysts used on the surface of the electrodes are also often expensive and limited in abundance
There is also limited infrastructure surrounding hydrogen transport and refilling

Question 25

What are the five common stages of metal production?

Answer 25

Extraction – an economically viable body of ore is mined from the Earth’s crust Concentration – the ore is crushed into powder, and the mineral is concentrated by removing unwanted minerals and waste rock, reducing the costs associated with transportation Conversion – one or more stages of chemical conversion may be required to convert the mineral to a compound suitable for the reduction stage Reduction – chemical reduction at high temperatures or electrolysis (molten or aqueous) is used to reduce metal ions to the metal Refining – further electrolysis or reactions are undertaken to remove remaining impurities, and the metal may also be alloyed at this stage to improve upon properties

Question 26

Explain electrolytic cells

Answer 26

Electrolytic cells are electrochemical cells that generate non-spontaneous redox reactions by applying an electric current, converting electrical energy to chemical energy Electrolysis is commonly used to reduce metal ions to metals The electrodes have opposite charges (compared to galvanic cells), but electrons still flow form the anode to the cathode (and AnOx RedCat is still true)

Question 27

How is aluminium reduced?

Answer 27

A molten cell to reduce aluminium has a graphite cathode (lining) and a graphite anode (suspended blocks) To create the molten electrolyte, cryolite is melted at ~1000oC, which aluminium oxide (alumina) is dissociated in Electrical current is applied to reduce the aluminium ions at the cathode, and the oxide ions are oxidised to form oxygen at the anode blocks

Question 28

How is zinc reduced?

Answer 28

Zinc is reduced in an aqueous cell, where the electrolyte is zinc sulphate Zinc is reduced at the aluminium cathode, and water is oxidised at the lead anode Zinc can be reduced in an aqueous cell as it is more easily reduced than water, unlike aluminium, which are reduced less easily, hence requiring a molten cell so that water isn’t reduced to produce volatile hydrogen gas (Aqueous cell is preferred to a molten cell as it does not require high temperatures, hence requiring less energy)

Question 29

State the stages of the nitrogen cycle

Answer 29

Nitrogen fixation Nitrification Assimilation Ammonification (mineralisation) Denitrification

Question 30

Explain nitrogen fixation

Answer 30

Nitrogen fixation is when nitrogen molecules (N2) are converted to nitrous acid, nictric acid, ammonium ions, and/or ammonia Atmospheric fixation: Natural phenomena such as lightning, volcanic activity, and bushfires provide energy high enough to allow nitrogen and oxygen to form nitric oxide Nitric oxide is then further oxidised in the atmosphere to form nitrogen dioxide Nitrogen dioxide then combines with water vapour present in the atmosphere to form nitrous and nitric acid N2 + O2 -> 2NO 2NO + O2 -> 2NO2 2NO2 + H2O -> HNO2 + HNO3 However, the majority of natural nitrogen fixation is due to nitrogen-fixing bacteria, which contain the nitrogenase enzyme, allowing them to convert nitrogen and hydrogen in the atmosphere into ammonia and ammonium ions

Question 31

Explain nitrification

Answer 31

Nitrification is when nitrogen-containing compounds are converted to soluble ion forms After atmospheric nitrogen fixation, the nitric and nitrous acid ionise, releasing soluble nitrate and nitrite ions, which then enter the soil during rain HNO3 + H2O -> H3O+ + NO3- HNO2 + H2O <-> H3O+ + NO2- Nitrifying bacteria also convert ammonia and ammonium to nitrate and nitrite ions

Question 32

Explain assimilation

Answer 32

Plants take in nitrogen compounds (e.g. ammonia, ammonium, nitrite ions, and nitrate ions) from the soil via their roots, converting them to amino acids

Question 33

Explain ammonification (mineralisation)

Answer 33

During anaerobic decomposition of remains or waste matter, bacteria convert nitrogen in organic compounds into ammonia and ammonium ions, and aerobic decomposition produces nitrate ions

Question 34

Explain denitrification

Answer 34

Some soils have denitrifying bacteria, which can return nitrates to atmospheric nitrogen in anaerobic conditions

Question 35

Explain eutrophication and the effects caused afterwards (positive feedback cycle)

Answer 35

Eutrophication is the increased nutrient concentration in the environment, which can be caused by: Weathering of rocks and soils Fertiliser run-off Discharge from mining Discharge of detergents Discharge of raw untreated sewage High nutrient concentrations and increased turbidity then stimulate the growth of photosynthetic microbes such as algae, phytoplankton, and cyanobacteria, creating a ‘bloom’ that prevents sunlight from entering the water Aquatic plants beneath the water are then unable to maintain photosynthesis, leading to death and decay, reducing the oxygen available in the water and may produce potentially toxic products The bloom also consumes oxygen in the water, and may also produce toxins that are harmful to certain species As oxygen concentration is depleted, the demand cannot be met for all species, and so some may die, decreasing the diversity of species, often changing the dominant species Decay of these organisms by aerobic bacteria also consumes available oxygen Water then becomes unsuitable for use by humans and animals

Question 36

What are the stages typically applied to treat freshwater in Australia

Answer 36

Coagulation – neutralising the charge on suspended impurities Flocculation – aggregating neutralised particles into floc Sedimentation – the floc settles as sediment and is removed Filtration – remaining solid impurities are trapped and filtered out via screens or sand and charcoal Disinfection – chlorine, chloramines, ozone, UV, etc., are used to kill potentially harmful organisms present in the water Fluoridation – fluoride is added in low concentrations to reduce tooth decay

Question 37

What is coagulation?

Answer 37

Whilst larger particles in water settle eventually, small particles called colloids, including clays, remain on the surface and in suspension due to their small size and because they repel each other with their negative charge, resulting in the turbidity (cloudiness) of the water Coagulation is when chemicals such as metal ions and polymers are used to neutralise the surface charge of colloids, destabilising the suspension

Question 38

What is flocculation?

Answer 38

Flocculation is when the neutralised particles aggregate to form floc, which settles due to its large size and mass, allowing it to be removed as sediment (in sedimentation) Some polymers can also be used to aid in neutralising surface charge and physically entrapping the particles

Question 39

What is hard water, how is it formed, and what does it impact?

Answer 39

Hard water is water that contains a high mineral (naturally occurring chemical compound) content Rainwater and freshwater contain dissolved carbon dioxide, which lowers the pH of the water, allowing it to dissolve calcium and magnesium carbonates, increasing the hardness of the water Hard water inhibits the cleaning ability of soaps as they form precipitates with them (soap scum) Hard water also inhibits hot water systems, dishwashers, and washing machines, as a precipitate of calcium carbonate (scale) is formed when hard water is heated, blocking pipes and drains, thus restricting water flow

Question 40

What are zeolites and how can they be used as water softeners?

Answer 40

Zeolites are hydrated aluminosilicate minerals that have a negative surface charge and cavities (pores) that allow them to accommodate metal cations Cations in water undergo cation exchange with the cations on the surface of the zeolite, allowing hard water ions (calcium and magnesium) to be exchanged with ions such as sodium ions Eventually, all the negative sites are occupied with hard water cations, and the zeolite loses effectiveness, but it can be regenerated by shifting the equilibrium to favour the backward reaction

Question 41

What are the pros and cons to desalination?

Answer 41

Converting saltwater to potable water reduces the demands on fresh water that may be harming ecosystems, and can be done in regions where fresh water is not available However, it is energy-intensive and thus expensive, and produces brine (high concentration of salts) and other chemicals that may cause harm in some environments, the waste heat produced can affect marine ecology, and inlets can drag in and kill aquatic organisms

Question 42

How does reverse osmosis work?

Answer 42

Osmosis is the movement of water from low solute concentration to high solute concentration across a semi-permeable membrane Reverse osmosis is the opposite, where pressure is applied to overcome the osmotic pressure, forcing the water to shift to the other side of the membrane whilst the solute remains on the pressured side

Question 43

How is chlorine gas used as a disinfectant?

Answer 43

Chlorine gas is often used for industrial disinfection (since it is toxic and hence dangerous) Chlorine gas is added to water, which reacts with water to form hypochlorous acid in a pH-dependent equilibrium Cl2(g) ⇌ Cl2(aq) Cl2(g) + 2H2O(l) ⇌ HClO(aq) + Cl-(aq) + H3O+(aq) By adding a base to neutralise the hydronium ions, the forward reaction can be favoured to further increase the concentration of hypochlorous acid An equilibrium is also established between hypochlorous acid (weak acid) and hypochlorite ions HClO(aq) + 2H2O(l) ⇌ ClO-(aq) + H3O+(aq)

Question 44

How are hypochlorites used as a disinfectant?

Answer 44

Hypochlorite salts of calcium, lithium, and sodium are commonly used for disinfection of domestic water supplies and swimming pools They are often used as they are easy to store and handle These salts react with water to form hypochlorous acid in a pH-dependent equilibrium NaClO(s) + H2O(l) ⇌ HClO(aq) + Na+(aq) + OH-(aq) An equilibrium is also established between hypochlorous acid and hypochlorite ions HClO(aq) + H2O(l) ⇌ ClO-(aq) + H3O+(aq) Hypochlorous acid and hypochlorite ions can enter the cell wall of bacteria and oxidise the cell contents, breaking down lipids and oxidising proteins (denaturing them), inhibiting cellular activity and thus killing them Hypochlorous acid is more effective as it carries no charge, so can diffuse through the cell membrane more easily and is a stronger oxidant

Question 45

What are silicates and aluminosilicates?

Answer 45

Silicates make up the vast majority of the Earth’s crust They are based on the SiO44- tetrahedral unit, where each silicon is bonded to four oxygen atoms to form the corners of a tetrahedron Silicate minerals result from the sharing of one or more corner oxygens in tetrahedrons of like units In aluminosilicates, a proportion of the silicon (+4) atoms are substituted with aluminium (+3) (which can be further substituted with calcium (+2) in some cases), because they are of similar size When this change occurs, there is a change in the overall charge of the silicate, increasing the negative charge by one for every aluminium in the formula of the structure

Question 46

What are clays?

Answer 46

Clays are hydrated silicate or aluminosilicate minerals with extremely fine (less than to um) particles They are formed over extended periods of time from chemical weathering and the chemical decomposition of rocks containing silicates Clays are important in the transfer of exchangeable ions as nutrients for plants in soils Clays are composed of phyllosilicates (sheets of silicate tetrahedra), which form parallel sheets with sheets of alumina

Question 47

What is cation-exchange (context of soils)?

Answer 47

Cation exchange occurs between the soil surface and the soil solution, establishing an equilibrium that maintains charge The capacity for a particular soil to exchange cations is called the cation exchange capacity (CEC), which determines how nutrients move through the soil and are retained CEC is related to the clay content and composition in the soil Exchangeable ions are held weakly on the clay surface by secondary interactions, and can be replaced by similarly charged ions Adsorption of these cations provides nutrients to the roots of plants that will not be leached away (cations in the soil solution can be washed away)

Question 48

How is soil acidity important?

Answer 48

When the acidity of soils is decreased, (inc [H+]), a stress is placed on the system that is countered (according to LCP) by shifting the position of equilibrium, favouring the exchange of H+ ions onto the surface of the clays This increases the number of cations in the soil solution, some of which may be toxic (e.g. aluminium in high concentrations), and some may be essential but are then susceptible to leaching during periods of rainfall, resulting in nutrient deficiencies in plants

Question 49

In what conditions does polymerisation occur?

Answer 49

At high temperatures and pressure with the addition of a catalyst

Question 50

What are addition polymers?

Answer 50

Addition polymers are formed by addition reactions, where monomers combine without losing atoms Addition polymers are typically formed from unsaturated monomers containing carbon-carbon double bonds (thus, addition polymers often have a carbon backbone)

Question 51

What are condensation polymers?

Answer 51

Condensation polymers are formed in condensation reactions between monomers, producing a small molecule (often water) Polymerisation occurs in stages, firstly with the formation of dimers (two monomers) which join to form polymers Two classes of condensation polymers are polyesters and polyamides

Question 52

What are polyesters?

Answer 52

Polyesters are formed in condensation of monomers containing carboxyl and hydroxyl functional groups, which form ester groups Polyesters can be formed from a single hydroxycarboxylic acid monomer containing both functional groups, or two monomers, a dicarboxylic acid and a diol

Question 53

What are polyamides?

Answer 53

Polyamides are formed by the condensation of monomers containing carboxyl and amino functional groups They can be formed from aminocarboxylic acid (amino acid) monomers containing both groups, or two monomers, a dicarboxylic acid and a diamine (When identifying monomer/s, remember that (often) water is formed, so you will have to add a H to one end, and OH to another)

Question 54

What are the advantages and disadvantages of synthetic polymers?

Answer 54

Synthetic polymers offer a diverse range of structures and properties, are relatively cheap to manufacture (compared to processed metals and timber), and can mimic natural materials and equal or better many of their physical and chemical properties However, they persist for tens of hundreds of years and can be ingested by wildlife, leach harmful chemicals into the soil and water, release toxins when burnt, and are difficult to recycle, so are often buried as landfill

Question 55

Discuss the properties of polymers

Answer 55

Polymer properties vary widely due to differences in polymer size, monomers used, degree of branching, and the extent of cross-linking between chains, allowing them to be created with various physical and chemical properties The molecular size of polymer chains affects the strength of dispersion forces experienced (larger chain = stronger forces) The functional groups of the monomers affect the secondary interactions between chains, allowing them to experience dipole-dipole interactions and/or hydrogen bonding Branching also affects the ability of chains to pack closely, changing the density of the polymer The extent of cross-linking between chains determines the rigidity of the polymer, allowing them to range from elastic and flexible (light cross-linking) to rigid (extensive cross-linking)

Question 56

What are thermoplastic polymers?

Answer 56

- Thermoplastic polymers exhibit little to no covalent cross-linking (typically linear or branched), and can have their secondary interactions overcome when heated, allowing the chains to slide past one another and flow, but can solidify when cooled This allows them to be recycled

Question 57

What are thermosetting polymers?

Answer 57

Thermosets or thermosetting polymers are extensively cross-linked polymers and do not soften on heating, but rather char and crack This makes them extremely difficult to recycle

Question 58

What are the advantages and disadvantages of polymers produced from petroleum feedstock?

Answer 58

Petrochemicals are relatively abundant and easily extracted (especially thanks to well-established industries), and can be used to produce a wide variety of polymers However, petrochemicals are non-renewable, being consumed at a rate greater than they are produced

Question 59

What are the advantages and disadvantages of polymers produced from biomass?

Answer 59

Biomass for polymer production is relatively abundant and can be easily extracted, and are often by-products or waste products of other industries, and is a renewable feedstock However, there is currently a limited range of polymers that can be produced from biomass, and production of feedstock may compete with crop production

Question 60

How do biodegradable polymers break down?

Answer 60

Biodegradable polymers degrade due to the enzyme-assisted reactions of microorganisms such as bacteria, fungi, and algae Many contain ester and amide groups, which have bonds that readily undergo hydrolysis to break down the polymer

Question 61

How do photodegradable polymers break down?

Answer 61

Photodegradable polymers are designed to become brittle and break down when exposed to sunlight Carbonyl groups (C=O) can be incorporated, which absorb radiation from sunlight and break down, or light-sensitive additives can be incorporated to catalyse the reaction

Question 62

How are polymers recycled?

Answer 62

One of the most labour and energy-intensive stages is sorting the polymer types before recycling Polymers can be separated based on physical and chemical properties such as colour, IR absorption, and density Thermoplastic polymers can be cleaned, ground, melted, and used to form new materials, as the chains can flow easily when heated As the degree and density of cross-linking is increased, the ease of recycling is reduced, as the chains flow less easily and end up decomposing by combustion Some polymers can be depolymerised to reform monomers, which are then isolated through fractional distillation and reused to make polymers

Question 63

Discuss the recycling of metals

Answer 63

More metals are being recycled as resources become scarce, reducing the demand for ore from the Earth’s crust, which reduces environmental impact too The removal of some of the stages associated with metal production also reduces energy requirements (and hence pollution) The stages of metal production afterwards are typically the same as traditional methods, so existing infrastructure can be used

Question 64

What are composite materials?

Answer 64

Composite materials are composed of two or more different materials which often have different properties that complement one another and improve upon them

Question 65

What are modern synthetic composites typically made of?

Answer 65

Modern synthetic composites are typically made of two components: the matrix (binder) and the material acting as the reinforcement (fibres) Many high-performance composites consist of a matrix of thermoplastic or thermosetting polymer and a reinforcement of fibres of carbon, glass, or metal

Question 66

Discuss the recycling of composites

Answer 66

It is difficult to recycle synthetic composites mostly due to the mixing of the resulting material making it hard to separate them It is currently limited due to high associated costs, lower quality of separated components, and lack of incentives and infrastructure

Question 67

What is soil sodicity and how does it affect soils?

Answer 67

Sodic soil is soil that contains too many sodium ions in comparison to other ions The sodium’s +1 charge is unable to effectively neutralise the charge of the clay particle, resulting in clay particles dispersing due to negative charges repelling each other This prevents soils from aggregating to form clumps, resulting in fine, crumbly soil that has very small gaps, making it difficult for nutrients, water, and roots to move through the soil