Chemistry

1). Research one biopolymer from given assessment task sheet: ➢ Viscose Rayon Viscose Rayon is an artificial silk which is made from regenerated cellulose, which is usually obtained from cotton or wood pulp. These raw materials are treated to produce sheets of purified cellulose containing 87-98% cellulose. They are then bleached with sodium hypochlorite (NaOCl) to remove natural colour. The obtained cellulose is then subjected to a treatment to turn it into the biopolymer; viscose rayon. The purified cellulose is treated with an 18% sodium hydroxide solution before being shredded (or ‘crumbed’) and ‘aged’ for two or three days under controlled temperature and humidity. Liquid carbon disulfide (CS2) is then added to the ‘crumbs’ to change the cellulose into cellulose xanthate, which is a light orange substance (still in crumb form). It then forms a ‘viscose’ solution after being reacted with more sodium hydroxide (NaOH). To produce the actual rayon filament, the viscose solution is aged, filtered, and vacuum treated, which removes any air bubbles that could cause the filament to weaken and break. It is then pushed through holes in a spinneret into an acid solution (sulphuric acid [H2SO4]); this coagulates the cellulose xanthate to form “regenerated fibres” of 100% cellulose. The freshly formed viscose must then be purified and strengthened. It is thoroughly washed, and treated with a dilute solution of sodium sulphide to remove any sulphur impurities. It may then be bleached to remove a slight yellowness and then it is given a final washing. Because Rayon is made from cellulose, it has many properties similar to many natural cellulosic fibres, such as cotton. Rayon is good at absorbing moisture (even more so than cotton); it is breathable, and easily dyed in many colours. Rayon does not build up static electricity. Rayon is used in clothes due to its properties, and will not pill unless made from short, low – twist yarns (A continuous strand of twisted threads of natural or synthetic material, such as wool or nylon, used in weaving or knitting [www.dictionary.com]). Rayon loses a great deal of strength when it is wet, and because of this it stretches and shrinks more than cotton. Due to rayon being a cellulosic fibre, it can be damaged easily by relatively weak acids. 4) Research the use of ethanol as an alternative fuel. Include the potential the as well as the advantages and disadvantages. Brazil is the country where Ethanol is mostly used just as a fuel, (about 10% of Brazil's total energy usage is provided by ethanol) but it is also used as an octane-enhancing gasoline additive in many countries. Approximately 12% of all U.S. gasoline contains ethanol at a blending percentage of 10%. As a fuel additive, ethanol increases the octane level and adds oxygen that lowers carbon monoxide emissions during the combustion process. As a fuel extender, ethanol replaces gasoline. Many vehicles on the road today can run on blends of ethanol and gasoline—most on lower-level blends such as E10 (10% ethanol and 90% gasoline), and many on higher level blends such as E85 (85% ethanol and 15% gasoline). Studies have shown that compared to reformulated gasoline, E85 emits 80 percent less benzene, 25 percent less nitrogen oxide and 7 percent less carbon dioxide. ➢ Potential One mole of ethanol burns to give three moles of water, two moles of carbon dioxide, and 1409.4 kJ of heat, whereas one mole of octane gives nine moles of water, eight moles of carbon dioxide, and 5470.5 kJ of heat. However, one gram of ethanol only produces 30.6 kJ where one gram of octane produces 42kJ. This means that much larger amount of ethanol need to be produced and transported to achieve the same energy – a massive 40% more fuel makes a big impact, both environmentally and economically. |Advantages |Disadvantages | |Ethanol is a renewable resource. The main sources of ethanol for use in fuel|A much larger amount of ethanol needs to be produced and | |are sugar (obtained from sugar cane), and starch (obtained chiefly from |transported to achieve the same amount of energy that | |corn). So if ethanol was used as a main fuel, it would reduce the use of |octane produces. | |non-renewable fuels such as gasoline (oil). | | |Because it contains oxygen, ethanol can help ensure the complete combustion |It may be difficult to scale up production to the | |of other compounds in a fuel mix. |quantities required for wide-spread use. | |Ethanol has been used successfully on a small scale for many years. |Large areas of land would be required and devoted to | | |growing the crops needed for production. This would lead to| | |soil erosion, salinity, de-forestation etc. | |Ethanol is ‘CO2 Neutral’, which means it is not taking carbon from deep |Disposal of large amounts of waste from fermentation | |underground and adding it to the total amount in circulation in the |process would present environmental concerns. | |atmosphere, but it only generates CO2 that came from plants, only just | | |removed from the atmosphere some months before by the plant. | | . |Cell Features |Dry Cell | |Anode |Zn(s) | | |Zn(s) → Zn2+ + 2e- | |Cathode |C(graphite) +MnO2(s) | | |2MnO2 + 2NH4+ + 2e- → PbSO4 + 2H2O | |Electrolyte |Ammonium chloride & zinc chloride paste | |Energy/Density (KW/Kg) |0.090 | |Cost And Practicality |Inexpensive. | | |Reliable but suffers principally from a low energy density. | | |Best for infrequent use. | | |Used for low energy drain appliances. | | |Easy to store. | | |Non rechargeable but low cost makes it cheap to replace. | | |Zinc anode also forms the container | |Impact On Society |First commercial battery. | | |Widely use as it is suitable for common low drain appliances such as torches, toys and portable | | |radios/CD’s. | | |Short shelf life due to acidic paste attacking the zinc(old batteries may leak their acidic paste into the| | |appliance) | |Environment |Weakly acidic paste and reaction products are not toxic and pose little problems in dumps. | 3. Research the features outlined below for all the following Cells: ➢ Dry Cell ➢ Lead-acid Cell |Cell Features |Lead-acid | |Anode |Pb(s) plates | | |Pb + SO42- → PbSO4 + 2e- | |Cathode |Pb(s) plates covered with PbO2(s) | | | | |Electrolyte |35% (w/w) sulphuric acid | |Energy/Density (KW/Kg) |0.030 | |Cost And Practicality |Expensive due to the cost of lead but it has a long life and is robust and reliable. | | |Capable of high power densities but cells undergo relatively rapid self-discharge. | | |Rechargeable. | | |Its weight makes it suitable for fixed applications or in vehicles. | | |Its level of charge is easily determined using a density hydrometer. | |Impact On Society |Allowed self starters and other convenience devices such as parking lights to be introduced to motor | | |cars. | | |Allowed people in remote locations to use electric lights and refrigerators without having to run | | |mechanical generators. | | |Able to store solar energy when connected to solar panels. | |Environment |Explosive hydrogen gas is released on recharging | | |Recharge the battery using trickle current in a well-ventilated area. | | |Corrosive acid can pollute the environment if spillages occur. | | |Lead is toxic and the electrodes and casings must be recycled. | | |Lead causes anaemia and affects the brain. | ➢ Button Cell |Cell Features |Silver button cell | |Anode |steel cap in contact with powdered zinc | | |Zn(s) + 2OH-(aq) → Zn(HO)2(aq) + 2e- | |Cathode |C/Ag2O paste | | |Ag2O(s) + H2O(l) + 2e- → 2Ag(s) + 2OH-(aq) | |Electrolyte |Potassium hydroxide solution in porous carrier | |Energy/Density (KW/Kg) |0.125 | |Cost And Practicality |Silver is an expensive metal and makes the button cell more expensive than the dry cell. | | |Non-rechargeable. | | |Ideal for applications where small size and light weight are important. | | |Provide considerable amounts of energy at a constant voltage over a long period of time. | |Impact On Society |Allowed miniaturisation of many devices (hearing aids, photo-electric light meters in cameras). | | |Ability to produce a very stable current over longer period of time made it highly suitable for portable | | |electronic devices (watches). | |Environment |Do not produce toxic waste. | | |Expensive silver needs to be recycled. | | |KOH electrolyte is caustic. | ➢ Fuel Cell |Cell Features |Proton exchange membrane fuel Cell | |Anode |Pt coating on porous graphite paper with H2(g) | | |H2(g) → 2H+ + 2e- | |Cathode |Pt, Ag2O on porous graphite with O2 (g). | | |O2(g) +4H+ + 4e- →2H2O | |Electrolyte |Polymer electrolyte membrane (conducting path of H+) | |Energy/Density (KW/Kg) |0.135 | |Cost And Practicality |Expensive as it is a developing technology. | | |High fuel efficiency. | | |High power density, packing more power in a smaller space allowing use in portable electronic devices. | | |Liquid cooling required as cell operates at 85° C. | | |Pure hydrogen required as any impurities poison Pt catalyst. | |Impact On Society |Can enable a transition to a secure, renewable energy future, based on the use of hydrogen; used in spacecraft| | |(Apollo) and space shuttle programs as a source of electrical energy and water. | | |A developing technology for the hydrogen economy that may replace petroleum fuel. | | |Long operating lifetime(50,000 hours) | |Environment |Environmentally friendly since no waste products are produced. | | |Storage of explosive hydrogen required. | ➢ Vanadium redox cell |Cell Features |Vanadium redox cell | |Anode |C(felt) | | |V2+ → V3+ + e- | |Cathode |C(felt) | | |VO2+ +2H + e- → VO2+ +H2O | |Electrolyte |V2+/V3+ in anolyte | | |VO2+/VO2+ in catholyte. | |Energy/Density (KW/Kg) |The energy density of vanadium redox cell is determined be concentration of electrolyte. | |Cost And Practicality |Cost is likely to be high after development stage is complete | | |Inexpensive. | | |Large storage capacities. | | |Low maintenance. | | |Cost per kWh decreases as the energy capacity increases, making large scale applications less costly. | | |Vanadium fuel filling stations will need to be developed to make the battery practical. | |Impact On Society |Lower maintenance and longer life-span than lead –acid batteries. | | |Has a high potential use as power source for electric vehicles; the spent electrolyte can be rapidly | | |replaced by a charged electrolyte. | | |A solar demonstration house built in Thailand has shown that energy self sufficient housing is not far | | |off; implementation in a golf cart shows great promise for specialised traction applications; | | |May eventually lead to electric vehicle applications due to ease in recharging. | | |Storage are tanks are separated from the battery | |Environment |Environmentally friendly since no waste products are produced. | | |The battery releases little explosive hydrogen on recharging. | | |Vanadium solutions are indefinitely recycled and not discarded. | ➢ Lithium Cells |Cell Features |Lithium | |Anode |Lithium | | |Li → Li+ + e- | |Cathode |Steel/I2 polymer | | |I2- + 2e- → 2I- | |Electrolyte |Solid lithium iodide | |Energy/Density (KW/Kg) |0.150 | |Cost And Practicality |Expensive | | |Li/polymer batteries are rechargeable. | | |Deliver high current. | | |Long shelf-life. | | |Very good power to weight ratio. | | |High energy density. | | |Small size and weight makes them more practical for many applications. | |Impact On Society |New lithium ion-polymer batteries are used in mobile phones and laptop computer due to their light weight| | |and high voltage levels(2.8-3.8V) | | |Li/I2 is a lightweight, reliable and long-life battery which is useful in cardiac pacemakers. | | |Supply up to 5 times the power of alkaline batteries. | |Environment |Environmentally friendly; no toxic products. | ➢ Gratzel cell (Liquid Junction Photovoltaic) |Cell Features |Gratzel | |Anode |Ruthenium photosensitive dye/semiconductor (TiO2) | | |dye →dye+ + e- | | |(I- supplies e- to dye+ to allow photovoltaic process to continue) | |Cathode |Glass/SnO2 /Pt | | |I3 + 2e- → 3I- | |Electrolyte |Iodide salt solution | |Energy/Density (KW/Kg) |____ | |Cost And Practicality |80% cheaper to produce and twice as efficient at converting light energy into electrical energy as the| | |currently available cells. | | |Photovoltaic cell is simple construct | |Impact On Society |This important new renewable energy technology has the potential to provide solar power for homes, | | |remote locations and for emergency communication phones. | |Environment |Environmentally friendly; no waste produced; renewable energy. | 4). Write the half reactions for the cells. (Dry to Lithium) • Dry Cell 1) 2 NH4+ + 2 MnO2 + 2e- → Mn2O3 + 2 NH3 + H2O 2) Zn (s) → Zn+2 + 2e- 3) Zn + 2 OH- → ZnO + H2O + 2e- 4) 2 MnO2 + 2e- + H2O → Mn2O3 + 2 OH- • Lead-acid cell 1) H2SO4 → H+ + HSO4- 2) Pb(s) + HSO4-(aq) → PbSO4 (s) + H+(aq) + 2e- 3) PbO2 (S) + 3H +(aq) + HSO4-(aq) + 2e -  → PbSO4 (s)  + 2H2O(aq) 4) Pb(s) + PbO2 (s) + 2H2SO4 (aq) → 2PbSO4 (s) + 2H2O(aq) • Button Cell (Silver Button Cell) 1). Zn(s) + 2OH-(aq) → Zn (HO) 2(aq) + 2e- 2). Ag2O(s) + H2O (l) + 2e- → 2Ag(s) + 2OH-(aq) 3). Zn(s) + Ag2O(s) → ZnO(s) + 2Ag(s) • Fuel Cell (Proton exchange membrane fuel Cell) 1) H2(g) → 2H+ + 2e- 2) O2(g) +4H+ + 4e- → 2H2O • Vanadium redox cell 1) V2+ → V3+ + e- 2) I2- + 2e- → 2I- 3) V2+(aq) + VO2+(aq) + 2H+(aq) → V3+(aq) + VO2+(aq) + H2O(l) • Lithium Cell 1) Li → Li+ + e- 2) I2- + 2e- → 2I- 3) Li(s) + TiS2(s) → Li+(s) +TiS2(s) 5). Bibliography. • http://en.wikipedia.org/wiki/Vanadium_redox_battery • http://answers.com • http://library.kcc.hawaii.edu/external/chemistry/everyday_battery.html • http://hsc.csu.edu.au/chemistry/core/identification/chem924/924net.html#net7 • http://library.kcc.hawaii.edu/external/chemistry/everyday_battery.html • http://en.wikipedia.org/wiki/Dry_cell • http://en.wikipedia.org/wiki/Lead-acid_battery • www.vonwentzel.net/Battery/00.Glossary • http://en.wikipedia.org/wiki/Watch_battery • http://www.fctec.com/fctec_types_pem.asp • http://en.wikipedia.org/wiki/Lithium_battery • http://www.mpoweruk.com/lithiumP.htm • http://www.cheresources.com/solarleaves.shtml • http://www.eere.energy.gov/afdc/altfuel/ethanol.html • http://en.wikipedia.org/wiki/Ethanol_fuel • http://www.hiraeth.com/ytg/qanda/answers/rayon.htm • http://www.swicofil.com/viscose.html • http://www.fibersource.com/f-tutor/rayon.htm • HSC Course Conquering Chemistry by Boland Smith ----------------------- Page | 10