1. Fossil Fuels Provide Both Energy and Raw Materials Such As Ethylene for the Production
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Production of Materials
1. Fossil fuels provide both energy and raw materials such as ethylene for the production of other substances Fossil fuels are energy-rich substances having been formed in the Earth’s crust millions of years ago. Under intense heat and pressure, organic remains were gradually converted into petroleum. We can extract and refine these fossil fuels to provide the energy requirements for machinery and to produce other forms of energy such as electricity. In addition, the basic building blocks of these chemicals can be used to create a multitude of more complex materials with different properties and uses. Identify the industrial source of ethylene from the cracking of some of the fractions from the refining of petroleum Petroleum is a mixture of hydrocarbons. It consists of the liquid crude oil and the natural petroleum gas. Both physical can chemical properties can be used to separate out the various compounds. Fractional distillation: Liquid crude oil can be separated into a series of fractions containing molecules of roughly similar molecular weight. Less useful larger molecules can be broken up into smaller and more useful molecules by cracking. This is achieved by breaking the covalent bonds within the larger compounds. Steam/Thermal Cracking High temperature (800oC) Uses steam – inert dilatant Absence of air Just above atmospheric pressure Keeps the concentration of gases low enough so it can flow through the tubes E.g. C3H8 → C2H4 + CH4 Catalytic cracking Crack high molecular weight hydrocarbons to lower molecular weights to increase the output of high demand products (e.g. octane and ethylene) Lower temperatures (500oC) The catalysts commonly used for catalytic cracking are silicon and aluminium oxides, or powdered zeolite. E.g. C10H22 → C8H18 + C2H4 Identify that ethylene, because of the high reactivity of its double bond, it is readily transformed into many useful products Unsaturated hydrocarbons are quite reactive compared to the relatively inert saturated alkanes The double bond in ethylene allows it to react readily with other molecules, thus making it useful as a starting point for many polymerisation reactions The double bond means it readily undergoes addition reactions Alkanes, on the other hand, undergo substitution reactions only under UV light
Addition: adding H2O into ethylene forms ethanol, adding HCl produces chloroethene, vinyl chloride, etc. Identify that ethylene serves as a monomer from which polymers are made The double bond in the ethene molecule can be broken, and when this repeats hundreds and thousands of times, a polymer (polyethylene) is formed Identify polyethylene as an addition polymer and explain the meaning of this term Polyethylene consists of many ethene molecules joined together to form long chains of hydrocarbons The double bond is broken and ethylene radicals are added onto it An addition polymer is a formed by joining molecules together without the loss of any atoms, i.e. the double bond is simply opened and connects with neighbouring molecules Outline the steps in the production of polyethylene as an example of a commercially and industrially important polymer There are mainly two types of polyethylene produced: low density polyethylene and high density polyethylene Steps in making polymers in general Initiation → Propagation → Termination Initiation: an initiator, e.g. peroxide Low Density Polyethylene (LDPE) Uses temperatures, around 300°C, and at very high pressures, around 3000 atmospheres This does not use a catalyst An initiator such as oxygen, or an organic peroxide which contains a –O- O- bond is used Both long and short chains are produced, and at some carbons, the hydrogen is replaced by the alkyl group This means the polymer is unable to pack closely together, reducing density, and the dispersion forces between the chains are weakened, reducing melting point and allows flexibility High Density Polyethylene (HDPE) This process uses lower pressure, only a few times atmospheric pressure, and lower temperature, around 60°C This type of polymerization requires the use of a Zeigler-Natta catalyst, which are usually rare earth metal oxides This polymer is relatively unbranched, allowing the chains to pack closely together in an orderly fashion There are larger crystalline regions which are rigid This reduces the space between molecules, and therefore increases density, and the dispersion forces are stronger, making it more rigid and have a higher melting point Identify vinyl chloride and styrene as commercially significant monomers by both their systematic and common names. Vinyl Chloride Systematic name: Chloroethene Polymer: Polyvinylchloride (PVC) Styrene Systematic name: ethenylbenzene or phenylethene Polymer: Polystyrene Describe the uses of the polymers made from the above monomers in terms of their properties LDPE Uses Cling wrap, plastic bags, milk bottles Properties Flexible - chain branching prevents the molecules from lining up orderly which means the dispersion forces are spread out which means weaker intermolecular bonding. Therefore it is less rigid Lower melting point – chain branching prevents the molecules from lining up in an orderly fashion Chemically inert – After polymerisation, the molecule becomes saturated. Covalent bonds are strong, so chemically, it is very stable HDPE Uses Kitchen utensils, wheelie bins, more rigid toys Properties Hard – virtually no chain branching meaning the molecules fit together in an orderly fashion. This makes HDPE crystalline and very strong High melting points – when the molecules are packed together the strong dispersion forces hold it together hence more energy is required to break these bonds PVC Uses Pipes, wire insulation Properties Hard – The C-Cl bonds are very electronegative, so the intermolecular forces are very strong. This makes PVC very hard Plasticisers and inhibitors prevent UV from attacking the C-Cl bond. It can also soften it up to be used as wire insulation Polystyrene Uses Tool handles, car battery cases, foam cups Properties Very hard – large phenyl side group means very strong intermolecular forces, makes it very rigid Chemically stable – contains only C-C and C-H bonds which are very stable, making it resistant to chemicals and UV Foam can be pumped into it to may polystyrene foam, used in cups 2. Some scientists research the extraction of materials from biomass to reduce our dependence on fossil fuels Discuss the need for alternative sources of the compounds presently obtained from the petrochemical industry Raw materials for making polymers come from crude oil, namely ethylene and propene These are extracted from petroleum, or produced by the cracking of petroleum constituents, e.g. larger hydrocarbon chains The majority of petroleum is used as petrol, and only a small percentage (5-10%) is used in the petrochemical industry There is considerable concern that our oil reserves are going to run out, and diminishing resources will drive the price of petroleum up Hence, there is a need to find a new source of raw materials and fuel Some new sources of these raw materials include glucose and ethanol from agricultural crops. These sugars are to be fermented to produce ethanol, and then this ethanol is dehydrated to form ethylene. Explain what is meant by a condensation polymer A condensation polymer consists of two or more monomer units which are linked together when their functional group reacts, emitting a small molecule in the process. Describe the reaction involved when a condensation polymer is formed Condensation polymers are formed by the elimination of a small molecule, often water, when two monomers are joined together n(HO-C6H10O4-OH) → H-(O-C6H10O4)n-OH + (n–1)H2O Nylon-6 is produced from the monomer unit 6-aminohexanoic acid
H2N-CH2-CH2-CH2-CH2-CH2-COOH The polymerisation equation is
Ra-COOH + H2N-Rb → Ra-CO-NH-Rb + H2O Polyester – A polymer of ethylene glycol and terephthalic acid Describe the structure of cellulose and identify it as a condensation polymer found as a major component of biomass Monomer unit: Glucose During polymerisation, the linkage is a COC bond Each consecutive glucose unit is inverted Biomass is organic material derived from organic matter including animals and plants They produce naturally occurring polymers known as biopolymers Cellulose is the main constituent of plant cell walls, and it is the most abundant polymer in the biosphere The strong hydrogen bonding and linear structure means that it is rigid and very strong Identify that cellulose contains the basic carbon-chain structures needed to build petrochemicals and discuss its potential as a raw material Since glucose contains 6 Carbons chained together, it can be seen as a raw material for other petrochemicals with smaller carbon chains such as ethylene (2 carbons), propylene (3 carbons) Then a chemical process can convert cellulose to a petrochemical Cellulose is broken down into glucose in two different ways Digestion by enzymes Digestion by a strong acid (Moderately concentrated sulphuric acid) Both cases produce a solution of glucose Cellulose → Glucose → Ethanol → Ethylene → Polymer Its potential to be used as a raw material is based on the fact that it is renewable and contains the ethylene monomer within the molecule - it only needs to be separated As the supply of petroleum decreases, alternative sources of petroleum products is required Cellulose is readily available and is the main component of biomass which can be obtained from plants Cellulose can also be obtained from waste products such as sawdust and woodchip, making which means that waste can be reused However, food crops to make raw materials presents ethical problems as there are people starving in the world 3. Other sources, such as ethanol, are readily available from renewable resources such as plants Describe the dehydration of ethanol to ethylene and identify the need for a catalyst in this process and the catalyst used
A H2O molecule is removed from ethanol to form ethylene
A catalyst of concentrated H2SO4 is used
The catalyst speeds up the reaction by sucking the H2O from the glucose CH3CH2OH → CH2CH2 + H2O Describe the addition of water to ethylene resulting in the production of ethanol and identify the need for a catalyst and the catalyst used The addition of water to ethylene to produce ethanol is an addition reaction
The catalyst used is dilute H2SO4 Describe and account for the many uses of ethanol as a solvent for polar and non-polar substances Ethanol contains the –OH radical, and creates a permanent dipole, making the O slightly negative, H slightly positive The intermolecular forces include dispersion forces, dipole-dipole interaction and hydrogen bonding due to the electronegative O This means that ethanol is a polar molecule, and hence will dissolve other polar substances via dipole-dipole interactions and hydrogen bonds The carbon chain means that it is also suitable for dissolving non-polar substances, allowing them to mix through the ethanol via dispersion forces Because of this, it has many applications in industry, as a solvent to mix both polar and non polar substances, e.g. perfume It also has applications in medicine, allowing substances which are insoluble in water to be taken as liquid Outline the use of ethanol as a fuel and explain why it can be called a renewable resource Ethanol undergoes complete combustion quite readily, and the reaction is very exothermic CH3CH2OH + 3O2 → 2CO2 + 3H2O ∆Hc=1367kJ/mol Currently it is being used to “extend” petrol up to 10% It is a renewable resource because it can be made from biomass which can be regrown to replenish the consumed ethanol Process information from secondary sources to summarise the processes involved in the industrial production of ethanol from sugar cane A suitable fruit or grain containing simple sugars such as glucose, sucrose and fructose, or molasses are used as a raw material in producing ethanol Solids are filtered out and the sugar solution is fermented It is fermented by yeast or other similar enzymes A higher concentration is produced by fractional distillation Describe the conditions under which the fermentation of sugars is promoted Anaerobic conditions at about 37oC Yeast is the enzyme which is used Glucose mixture Summarise the chemistry of the fermentation process Enzymes ferment yeast into ethanol in anaerobic conditions C6H12O6(aq) → 2CH3CH2OH(aq) + 2CO2(g) Yeast should be written on top of the arrow Define the molar heat of combustion of a compound and calculate the value for ethanol from first hand data The molar heat of combustion is the amount of energy released when one mole of substance undergoes complete combustion with oxygen at standard temperature and pressure The products will only be water and carbon dioxide
∆Hc=-∆H Assess the potential of ethanol as an alternative fuel and discuss advantages and disadvantages of its use Advantages Renewable: Ethanol can be produced by fermenting biomass, which comes from plants which are renewable since more plants can be grown to replace used ones Burns more completely/cleanly: The oxygen in the ethanol molecule ensures that less oxygen is required to allow the complete combustion of a fuel. As a result, CO and C as by-products are reduced, which is beneficial to the environment as well as the engine 10% ethanol can be added to extend petrol with no modification to engines. This makes petrol supplies last longer. Disadvantages Lower heat of combustion: Ethanol produces less energy per mole than octane, meaning cars can travel further on octane than the same amount of ethanol. Thus, ethanol may be more expensive Engines may get damaged from the water dissolved in ethanol: This is why engines need to be modified for fuels containing >10% ethanol. It is difficult to remove all the water during the distillation of ethanol, and hence the water will corrode engines Large areas of land needed: Large areas of land are required to grow crops for ethanol, so large areas will need to be cleared for this. This may require the clearing of forests and other natural areas. Technical difficulties: Ethanol is carbon theoretically carbon neutral, however, fossil fuels are required to power the process, hence it is somewhat redundant to use fossil fuels to make ethanol as a fuel Ethical problems: growing crops to make ethanol rather than food when there are starving people in the world may seem unethical Judgement Even though there are significant disadvantages, these can be overcome technically, and it maybe inevitable that we will need to use renewable resources such as ethanol. Identify the IUPAC nomenclature for straight chained alkanols from C1 to C8 1: Methanol 2: Ethanol 3-8: [prefix]an-[number]-ol prefix is the length of the carbon chain number is where the –OH group is located 4. Oxidation-reduction reactions are increasingly important as a source of energy Explain the displacement of metals from solution in terms of transfer of electrons A metal displacement reaction is one which a metal converts another metal ion to its neutral atom by transferring one or more electrons The metal ion gains electrons and is reduced The metal which displaces the other metal is oxidised Identify the relationship between displacement of metal ions in solution by other metals to the relative reactivity of metals A list of metals arranged in decreasing ease of oxidation is called the activity series A metal of a more active metal placed in a solution of a less active metal ion will displace it from solution E.g. Zinc is more active than copper 2+ 2+ Zn(s) + Cu (aq) → Zn (aq) + Cu(s) Zn is oxidised (more active) while Cu is reduced K > Na > Mg > Al > Zn > Cr > Fe > Ni > Sn > Pb > H > Cu > Ag > Hg > Pt > Au Perform a first-hand investigation to identify the conditions under which a galvanic cell is produced Why isn’t the voltage produced equal to the theoretical voltage? Impurities in the electrodes will increase electrical resistance and thus the experimental voltage will be less than theoretical If the salt bridge is not soaked sufficiently, the flow of ions is impeded so the voltage is reduced When drawing a salt bridge make sure it is double lined Electrical resistance in wires means the not all of the electricity is measured Account for the changes in the oxidation state of species in terms of their loss or gain of electrons When a species gains electrons it is reduced, the oxidation number is decreased When a species loses electrons it is oxidised, the oxidation number is increased OILRIG: Oxidation is Loss, Reduction is Gain Outline the construction of galvanic cells and trace the direction of electron flow Oxidation and reduction reactions can be used to generate electricity if the reactions are physically separated A wire connected to an external circuit can be used to facilitate the flow of electrons, and thus produces electricity (moving electrons) This is known as a galvanic cell A galvanic cell consists of two half cells Each half cell consists of a conductive metal in ionic solution known as the electrolyte A salt bridge connects the two electrolytic solutions The purpose of the salt bridge is to allow the migration of ions to occur, preventing a build up of electrical charge Electrons flow from the anode to the cathode Define the terms anode, cathode, electrode and electrolyte to describe galvanic cells Anode: The electrode where oxidation occurs Cathode: The electrode where reduction occurs Electrode: The conductors of a cell which is connected to the external circuit Electrolyte: The solution of ions which conducts electricity 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: button cell, fuel cell, vanadium redox cell, lithium cell liquid junction photovoltaic cell (Gratzel cell) in terms of chemistry, cost and practicality, impact on society, environmental impact Lead acid cell Chemistry: 2- - Anode: Pb(s) + SO4 (aq) → PbSO4(s) + 2e Pb is oxidised (0 → +II) Made of lead + 2– – Cathode: PbO2(s) + 4H (aq) + SO4 (aq) + 2e → PbSO4(s) + 2H2O(l) Pb is reduced (+IV → +II) Made of lead dioxide
Concentrated H2SO4 (~5M) electrolyte Cost Lead acid batteries are expensive however, this is counteracted by the fact that they can be recharged many times. Hence the overall cost is lower than many alternative sources Practicality Heavy: not very practical for appliances However, this is not a problem in its most common application, in car batteries since it isn’t moved around that much Contains concentrated sulfuric acid and lead: dangerous to handle Impact on society Used in cars: Huge impact on society because it allows cars to be started much more easily and reliably Therefore allows people to move around and travel long distances Environmental impact The concentrated sulfuric acid is very corrosive and must be disposed of safely Lead is a heavy metal and must be disposed of safely as well However, some car batteries still end up in land fills and the toxic heavy metals seep into the environment Lithium cell Chemistry + - Anode: Li(s) → Li (aq) + e Lithium is oxidised Anode is made of lithium - - Cathode: I2 + 2e → 2I Involves either silver chromate or iodine Anode is made of carbon (graphite) Electrolyte: Lithium iodide Cost They are expensive compared to other batteries, however sometimes there is no substitute possible Practicality Long lasting and have a high voltage (3V compared to 1.5V in alkaline batteries) They are used in mobile phones, computers, cameras and pacemakers Social Impact Allows long lasting, high voltage and reliable supply of electricity to be portable Use in pacemakers which have saved lives Small size allows them to be used in smaller and more portable equipment such as mobile phones. This has greatly improved our ability to communicate Environmental impact Although not a hazard, un-recycled lithium ion batteries contribute significantly to waste due to the large volume of the batteries which is being used 5. Nuclear chemistry provides a range of materials Distinguish between stable and radioactive isotopes and describe the conditions under which a nucleus is stable A stable isotope does not undergo radioactive decay An unstable isotope undergoes radioactive decay in the form of alpha, beta or gamma radiation Alpha decay commonly occurs in large atoms (Z>83) since the electrostatic repulsion by the protons becomes too large for the strong nuclear force to hold it together Emits an alpha particle (Helium nucleus) in the process Beta decay is due to a unbalanced NP ratio A beta particle is either an electron or positrion About 1:1 for smaller nuclei and up to about 1.5:1 in larger ones Too many neutrons = β- decay
Too many protons = β+ decay [neutrinos not required in chemistry] Gamma radiation is emitted from an unstable nucleus. Nuclear transmutation does not occur 99m 99 E.g. Tc → Tc + γ Describe how transuranic elements are produced Transmutation occurs when an atom changes atomic number, such as in alpha or beta decay Transuranic elements can be produced by bombarding heavy atoms with neutrons to induce beta decay 238 1 239 239 239 E.g. U + n → U → Np + -1e → Pu + -1e They can also be produced by bombarding large nuclei or previously made transuranic elements with smaller nuclei Describe how commercial radioisotopes are produced Commercial radioisotopes are made in nuclear reactors called breeder reactors and cyclotrons Breeder reactors The target nuclei is placed into the core of the reactor and is bombarded with neutrons to produce the desired radioisotope Cyclotrons The target nuclei is bombarded with charged particles, often alpha- particles or protons at high speeds This is achieved by accelerating the charged particles with very strong magnetic fields around a large radius Identify instruments and processes that can be used to detect radiation Geiger-Muller counter Scintillation counter Photographic film Cloud Chambers/Bubble Chambers Identify one use of a named isotope In medicine: Technetium-99m Used in diagnostic radiology to diagnose cancers and abnormal organ functionality In industry: Strontium-90 Used in thickness gauges Describe the way in which the named industrial and medical radioisotopes are used and explain their use in terms of their properties Technetium-99m is injected into the blood in a serum and its distribution in the blood as it circulates can be detected by gamma cameras It can detect blood clots, tumours and other abnormalities as these regions often have excessive blood flow, and hence more of the radioisotope will accumulate in that region This is an advantage over x-rays, which can only detect structural damage easily Properties Short half-life (6 hours): Patient and doctors are only exposed to radiation for short amounts of time Also the radiation would be more intense for a shorter period, making it easier to detect Attaches itself to blood cells so it can monitor the circulation of blood Biocompatible: even though radioactivity has nothing to do with chemical properties, radioisotopes behave in the same way as their stable counterparts, hence it must be non-toxic Gamma emission: Alpha and beta radiation are much more ionising, and hence dangerous in the body (especially alpha) Strontium-90 is used in thickness gauges to detect the thickness in production of materials, such as sheets of metal Thickness can be calculated/extrapolated from the amount of radiation it detects. As thickness increases, more is absorbed and vice versa. It is connected to the machine via a feedback loop, and if the thickness deviates, the controller adjusts the machine accordingly to maintain the desired thickness Advantage is that this is very sensitive, allowing a high quality product to be manufactured Properties Long half-life (28 years): Does not need to be replaced often meaning that workers do not need to expose themselves to radiation Low energy emissions means that the material does not become radioactive, and the workers remain safe Beta radiation: Alpha radiation will be blocked entirely, while gamma rays would pass right through the material. Beta particles are only partially blocked, meaning it can be used to detect the thickness Analyse benefits and problems associated with the use of radioactive isotopes in identified industries and medicine Benefits in Medicine More sophisticated diagnosis can provide more details about a patient than conventional x-rays E.g. 3D images can be taken by using gamma cameras from all different angles and can aid diagnosis Able to generate images of the organ over time (few minutes to a few hours), rather than just taking a static image. Multiple x-rays overtime will overdose the patient with radiation Non-invasive method to diagnose cancers and other problems with internal organs. This is not possible otherwise Benefits in Industry Monitoring with radioisotopes is much more sensitive than conventional means, therefore quality control is much better Examining for internal structural faults is not possible without the use of radioisotopes Problems Radiation is dangerous and the ionising ability destroys the complex DNA within cells Causes tissue and genetic damage Can cause cancer and damage to DNA The Acidic Environment 07:15
1. Indicators were identified with the observation that the colour of some flowers depends on soil composition Classify common substances as acidic, basic or neutral Vinegar, lemon juice, etc. are acidic Caustic soda, ammonia, etc. are basic Water, oil, etc. are neutral 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 Litmus pH range: 5-8 Red → Blue Phenolphthalein pH range: 8-10 Colourless → Pink Methyl Orange pH range: 3-4.5 Red → Yellow Bromothymol Blue pH range: 6-7.5 Yellow → Blue Identify and describe some everyday uses of indicators including the testing of soil acidity/basicity Testing soil acidity Barium sulfate is poured on top of the soil sample and allows it to soak up some of the water. The indicator can be used on the white barium sulfate and the colour can be determined The Acidic Environment 07:15
Testing acidity of swimming pool Using in indicator 2. While we usually think of the air around us as neutral, the atmosphere naturally contains acidic oxides of carbon, nitrogen and sulfur. The concentrations of the se acidic oxides have been increasing since the Industrial Revolution Identify oxides of non-metals which act as acids and describe the conditions under which they act as acids Acidic Oxides Reacts with water to form an acid Reacts with bases to form salts Reactions: Acid + metal → Hydrogen + Salt Acid + carbonate → Carbon Dioxide + Water + salt Acid + metal oxide → Water + salt Acid + metal hydroxide → Water + Salt Examples Carbon Dioxide + Water → Carbonic Acid Carbon Dioxide + Sodium Hydroxide → Water + Sodium Carbonate P2O5(s) + 3H2O(l) → 2H3PO4(aq) Basic Oxides Reacts with water to form an alkali Reacts with acid to form water and salt Reactions:
Reacts with amphoteric metals to produce H2 The Acidic Environment 07:15
Dissolves amphoteric metal hydroxides Analyse the position of these non-metals in the Periodic Table and outline the relationship between position of elements in the Periodic Table and acidity/basicity of oxides Acidic oxides are often formed by oxygen-rich non-metals
e.g. CO2, SO3, NO3 Basic Oxides are often formed by metals e.g. Na, Mg, Fe, Cu Neutral oxides are formed by oxygen-poor non-metals
E.g. CO, NO, N2O Amphoteric oxides are formed by semi-metals They have both acidic and basic properties They can behave as a weak base or acid
E.g. BeO, SnO, PbO, Al2O3, Cr2O3 The acidity or alkalinity depend on the electronegativity of the atom bound to the oxygen Define Le Chatelier’s Principle When a system at equilibrium is disturbed, the system adjusts itself to minimise the disturbance Identify factors which can affect the equilibrium in a reversible reaction Temperature Increase temperature = Favours endothermic reaction Decrease temperature = Favours exothermic reaction Partial pressures of gases Partial pressure → concentration The Acidic Environment 07:15
Concentration of products/reagents Changing the concentration of products/reagents will cause the system to act to minimise the change E.g. Products added, system will shift to reduce products Total pressure of volumes Increasing pressure = Decreasing volume Describe the solubility of carbon dioxide in water under various conditions as an equilibrium process and explain in terms of Le Chatelier’s principle
CO2(g) CO2(aq) ∆H<0 [1]
CO2(aq) + H2O(l) H2CO3(aq) ∆H<0 [2] + - H2CO3(aq) H (aq) + HCO3 (aq) [3] - + - HCO3 (aq) H (aq) + CO3 (aq) [4] Pressure Increasing the pressure will be likened to increasing the concentration of
CO2(g), and hence will shift [1] to the right, increasing solubility Increasing temperature will favour the endothermic reaction in [1], shifting the equilibrium to the left and decrease solubility Increasing acidity, will cause [3] and [4] to shift to the left, since, [H+] is
increased. This will in turn shift [2] to the left as [H2CO3] increases and
will shift [1] to the left as [CO2(aq)] increases. Therefore solubility decreases. Adding a base will cause the opposite to happen (increase solubility of
CO2) Assess the evidence which indicates increases in atmospheric concentration of oxides of sulfur and nitrogen Do this later (technology is weak since it only since 1950s)
About 2/3 of the SO2 in the atmosphere comes from volcanos and geothermal hot springs Calculate volumes of gases of some substances in reactions and calculate the masses of substances given gaseous volumes in reactions involving gases at 0oC and 100kPa or 25oC and 100kPa v=nV m=nM The Acidic Environment 07:15
Explain the formation and effects of acid rain
Concentration of CO2 in the atmosphere is about 360ppm, and some of it dissolves in water forming carbonic acid. Hence rain water is naturally slightly acidic Acid rain is defined as a rain with a [H+] higher than 10-5mol/L Since the industrial revolution, oxides of nitrogen and sulfur have been released into the atmosphere Formation
SO2(g) + H2O(l) H2SO3(aq)
SO3(g) + H2O(l) H2SO4(aq)
2NO2(g) + 2H2O(l) HNO3(aq) + HNO2(aq) Effects Increased acidity of bodies of water e.g. lakes Increased acidity can easily kill fish eggs which are sensitive to changes in pH Some fish are sensitive to pH Dissolves the waxy coating of some leaves Erosion of marble structures Marble are carbonates, which is a base so it is neutralised by acid rain Dissolves heavy metals into waterways Toxic heavy metals such as lead bio accumulates and biomagnifies 3. Acids occur in many foods, drinks and even our own stomachs Define acids as proton donors and describe the ionisation of acids in water Acids donate a proton (hydrogen atom) + - E.g. HCl → H + Cl The Acidic Environment 07:15
+ + The H is actually a hydronium ion H3O Acids ionise in water to produce hydronium ions + + H + H2O → H3O Identify acids including acetic (ethanoic), citric (2-hydroxypropane-1,2,3- tricarboxilic acid), hydrochloric and sulfuric acid Acetic acid Weak acid - + CH3COOH CH3COO + H Citric acid Tri-protic Weak acid Stronger than acetic + C6H8O7 C6H5O7 + 3H Hydrochloric acid Strong acid – ionises completely + - HCl → H + Cl Sulfuric acid Diprotic Strong acid (1st ionisation) Weaker 2nd ionisation - + H2SO4 → HSO4 + H - 2- + HSO4 SO4 + H The Acidic Environment 07:15
Describe acids in their solutions with the appropriate use of the terms strong, weak, concentrated and dilute Strong acid – ionises completely Weak acid – does not ionise completely Concentrated acid – When the concentration of acid molecules, whether ionised or not, in solution is high Dilute acid – When the concentration of acid molecules in solution is low Describe the use of the pH scale in comparing acids and bases pH is a measurement of the concentration of H+ ions + Identify pH as –log10[H ] and explain that a change in pH of 1 means a ten-fold change in [H+] + pH = –log10[H ] since it's a log scale to base 10, a pH change of 1 means 10 times more or less hydrogen ions Compare the relative strengths of equal concentrations of citric, acetic and hydrochloric acids and explain in terms of the degree of ionisation of their molecules - + Acetic acid: CH3COOH CH3COO + H + Citric acid: C6H8O7 C6H5O7 + 3H + - Hydrochloric acid: HCl → H + Cl Citric acid is triprotic and weak Acetic is monoprotic and weak Hydrochloric is monoprotic and strong Hydrochloric > Citric > Acetic Why does hydrochloric acid ionise completely? Describe the difference between a strong and a weak acid in terms of an equilibrium between the intact molecule and its ions In a weak acid, not all the acid molecules ionize compelely, but rather they reaction is an equilibrium The Acidic Environment 07:15
HA H+ + A- As H+ ions are formed (Le Chatelier’s principle), the reverse reaction also begins, and eventually the system will reach equilibrium Because of this, not all the acid molecules get ionised This needs more detail 4. Because of the prevalence and importance of acids, they have been used and studied for hundreds of years. Over the time, the definitions of acid and base have been refined Outline the historical development of ideas about acids including those of Lavoisier, Davy and Arrhenius Lavoisier Theorise that acids were substances which contained oxygen The word oxygen was derived from Greek words meaning acid forming This was disproved as many substances containing oxygen such as calcium oxide were, in fact, basic Also, there were many substances such as hydrochloric acid which were acidic and did not contain oxygen Davy Suggested that acids contained replaceable hydrogen That is, the hydrogen could be replaced by metals E.g. when HCl reacts with Zn, the H in HCl would be replaced with Zn,
forming ZnCl2 He stated bases where substances which reacted with acids to form salts and water Arrhenius Proposed that acids were substances which ionised in water to produce hydrogen ions Suggested that a base was a substance which would produce hydroxide ions Limitations:
Metallic oxides were basic e.g. CaCO2, as they neutralised acids, but do not contain hydroxide ions hence did not fit the Arrhenius definition The Acidic Environment 07:15
Does not take into the account the role of the solvent. E.g. HCl is a strong acid when the solvent is water, but a weak acid when the solvent is ethanol
Some substances such as ammonia, NH3, acted as a base even though it contained no hydroxide, and reacts with acid to from salt and water Outline the Brönsted-Lowry theory of acids and bases An acid is a proton donor A base is a proton acceptor Distinguish the relationship between and acid and its conjugate base and a base and its conjugate acid A strong acid has a weak conjugate base A strong base has a weak conjugate acid They always occur in pairs - - E.g. HCl + OH → H2O + Cl The two pairs are: HCl (acid) & Cl- (conjugate base) - OH (base) & H2O (conjugate acid) Identify a range of salts which form acidic, basic or neutral solution and explain their acidic, neutral or basic nature Acidic salts Oxygen-rich non-metal oxides Neutral salts Oxygen-poor non-metal oxides Basic salts Metallic oxides Identify neutralisation as a proton transfer reaction which is exothermic The Acidic Environment 07:15
Neutralisation is the transfer of a proton from an acid to a base Energy is released in the process, hence it is exothermic Describe the correct technique for conducting titrations and preparation of standard solutions An acid-base titration determines the pH of an unknown by calculating how much of it is required to react with a known volume and known concentration Equipment It is important that the equipment is of accurate and analytical grade to ensure accurate measurements. This is because the colour change over the equivalence point happens over less than a drop Volumetric flask The volume stated is when the solution reaches the mark etched onto the side of the flask It is used to prepare standard solutions where the concentration is accurately needed Pipette Used to accurately deliver a specified volume of solution Burette Used to accurately deliver a variable volume of solution Accurate to ±0.05 mL The difference in volume of initial vs final is the amount used in the titration Rinsing Burettes and pipettes are to be rinsed with distilled water initially, and then twice with the solution to be used The thin film of water will dilute the solution inside if it is only rinsed with water Conical and volumetric flasks are just to be rinsed with distilled water as the number of moles of solution is known. Adding water doesn't change this Standard solution Primary standards The Acidic Environment 07:15
A primary standard must have the following properties Obtainable in a pure form with a known chemical formula Is not hydroscopic Relatively high molar mass to reduce weighing errors
Examples include sodium carbonate (NaCO3) and hydrated oxalic acid
(H2C2O4.2H2O) Before sodium carbonate is weighed it is heated in an oven to remove any moisture Secondary standards Sometimes we may need to use some substances which are not suitable
for primary standards such as H2SO4 or NaOH since they are hydroscopic Before these can be used, their concentration must be found by titrating it against a primary standard The resulting solution is known as a standard solution, which should be used rather quickly to avoid changes in concentration due to volatility or absorption of water Choice of indicator An appropriate indicator which changes colour at the equivalence point needs to be chosen. If not, then the results will not be accurate, as the colour change will be either before or after all the reactants have reacted Strong acid – weak base: Methyl red, since the equivalence point is at pH <7 Strong acid – strong base: Bromothymol blue, since the equivalence point is at pH = 7 Weak acid – strong base: Phenolphthalein, since the equivalence point is at pH >7 Weak acid – weak base: generally not performed since rather than a sudden change in colour, it changes over several drops Method Fill burette with the solution of known concentration This solution is called the titrant Record the level of the solution in the burette Place sample to be analysed in a flask under the burette The Acidic Environment 07:15
Add indicator to this sample Place flask on a white tile or paper to see the colour change more clearly Run the solution into the flask, until it starts to change colour When this happens, then slowly add drops of the titrant Wash off any titrant off the side with a bottle of distilled water The end point is reached when there is a permanent colour change The first titration is a rough titration to find out where the equivalence point is Repeat until there are at least three results within ±0.1mL Qualitatively describe the effects of buffers with reference to a specific example in a natural system A buffer is a solution containing a weak acid and large amounts of its conjugate base which is able to maintain a relatively constant pH despite adding significant amounts of strong acids or base to it Buffers are very important in natural systems Some animals are very sensitive to pH range Some enzymes work only in a narrow pH range E.g. Human blood has a pH of about 7.4 Buffers maintain the pH within 7.35 – 7.45 Outside this range, the enzymes in the body start failing The buffer system is a carbonic acid/hydrgogencarbonate system - + H2CO3(aq) HCO3 (aq) + H (aq) If H+ is added then it will shift to the left, reducing its effect Similarly is OH- is added then it will shift to the right, to reduce its concentration Analyse information from secondary sources to assess the use of neutralisation reactions as a safety measure of to minimise damage in accidents or chemical spills The Acidic Environment 07:15
When acids or bases are spilt, they must be neutralised quickly to reduce damage Substances used to neutralise spills should have the following properties Weak acid/base – heat generated from neutralisation with strong acids/bases would be too great since it reacts too fast Safe to use in excess Can neutralise both acids and base Cheap and safe to handle Sodium hydrogencarbonate is often used for this because it is A stable solid which is easy to store Amphoteric so it can neutralise both strong bases and acidic spills Non-toxic and safe to handle in excess, since it is difficult to determine the exact amount of chemicals spilt Cheap and readily available 5. Esterification is a naturally occurring process which can be performed in the laboratory Describe the differences between the alkanols and alkanoic acid functional groups in carbon compounds Alkanols Contain the -OH (hydroxyl) group Soluble in water due to hydrogen bonding However this decreases as the length of the carbon chain increases Much higher MP/BP than alkane with similar molecular weight due to strong intermolecular forces (Hydrogen bonds and dipole-dipole interaction) Alkanoic acids Contain the –COOH (carboxyl) group Soluble in water due to hydrogen bonding The Acidic Environment 07:15
Likewise, this decreases as the length of the carbon chain increases Even higher MP/BP than alkanols due to the more hydrogen bonding in the C=O and O-H groups within the molecule (Alkanols don't have the C=O group) Identify the IUPAC nomenclature for describing the esters produced by reactions of straight-chained alkanoic acids from C1 to C8 and straight- chained primary alkanols from C1 to C8 Alkanols: [prefix]an-x-ol Alkanoic acid: [prefix]anoic acid Explain the difference in melting point and boiling point caused by straight-chained alkanoic acid and straight-chained primary alkanol structures In both cases, the –OH group in the molecule is able to form hydrogen bonds, hence the intermolecular forces are strong, giving them a high MP/BP However in alkanoic acids, there is an additional C=O group where further hydrogen bonding occurs Hence the intermolecular forces are stronger, so more energy is require to separate them This gives them a higher MP/BP than alkanols Identify esterification as the reaction between an acid and an alkanol and describe, using equations, examples of esterification Esterification is the reaction between an alkanoic acid and an alkanol, producing an ester and water The general equation is: Alkanol + Alkanoic acid Ester + water Concentrate sulfuric acid catalyst All products and reactants are liquid The ester is named alkyl alkanoate The alkyl comes from the alkanol The alknanoate comes from the alkanoic acid Describe the purpose of using acid in esterification for catalysts A catalyst speeds up the rate of reaction The Acidic Environment 07:15
Concentrated sulfuric acid is a dehydrating agent and will eliminate the water molecules as they are formed This will shift the equilibrium to the right Explain the need for refluxing during esterification Esterification is carried out at temperatures close to the boiling points of the reagents The reagents are also volatile and may be lost into the atmosphere Hence a condenser is required to condense the vapours so they drip back into the reaction mixture This is known as refluxing This allows the reaction to take place at a higher temperature (and hence higher reaction rate) without losing too much of the reagents Outline some examples of the occurrence, production and uses of esters Apple – methyl butanoate Production of esters Process information from secondary sources to identify and describe the uses of esters as flavours and perfumes in processed foods and cosmetics Perfumes and cosmetics Some esters are used as a solvent e.g. ethyl acetate is used as a common industrial solvent, which can also be used as nail polish remover Perfumes use esters as a solvent to dissolve both polar and non polar substances Processed foods If the ester which is responsible for the flavour can be isolated, it can often be manufactured These artificial flavours are often cheaper than the real flavour and provided that they only use the active ester, therefore have little adverse health affects Chemical Monitoring and Management 07:15
1. Much of the work of chemists involves monitoring reactants and products of reactions and managing reaction conditions Outline the role of a chemist employed in a named industry or enterprise, identifying the branch of chemistry undertaken by the chemist and explaining a chemical principle that the chemist uses Luke the chemist works in the polymer industry which makes polyethylene It is industrial, analytical and petroleum chemistry Role: He is responsible for overlooking the overall production and quality of the polyethylene produced by measuring the quality of the polyethylene, testing for impurities He also monitors the condition such as the temperature and pressure of the reaction vessel Chemical Principles Solubility in gas-liquid chromatography This is used to separate mixtures to their components so they can be measured The different solubility affect how the chemicals separate Identify the need for collaboration between chemists as they collect and analyse data Chemistry is a very diverse field and in areas such as industry, many specialists are needed For example, in an industrial plant may employ: An industrial chemist to maximise yield and reaction rates and reduce costs An analytical chemist to monitor these reaction rates, as well as the quality of the product An environmental chemist to assess the waste products and environmental impacts of the process Hence, collaboration between the chemists are required for the functioning of the plant. Describe an example of a chemical reaction such as combustion where reactants form different products under different conditions and thus would need monitoring Combustion is reaction of a substance with oxygen Often it is a carbon compound containing only hydrogen, carbon and oxygen such as alcohols and hydrocarbons When they react in excess oxygen the reaction is as follows: Chemical Monitoring and Management 07:15
Fuel + Excess Oxygen → Water + Carbon Dioxide 25 E.g. C8H18 (g) + /2 O2 (g) → 9H2O (g) + 8CO2 (g) However, if there is insufficient oxygen, the fuel will still burn, but will yield products that are harmful to the humans or the environment This is called incomplete combustion and the products could include carbon dioxide, carbon monoxide, hydrocarbons and carbon (soot) and water Note, not all the products need to be present (but water is always there) Also, the energy yield from incomplete combustion is much less than the energy released from complete combustion and hence it is more economical For both safety and economical reasons, combustion reactions should be monitored E.g. in a Bunsen burner, complete combustion occurs when there is a light blue flame. It is much hotter than the yellow flame. Incomplete combustion can be observed with the yellow flame, and deposits of soot, a product of incomplete combustion, can form at the base of glassware Gather, process and present information from secondary sources about the work of practicing scientists identifying: The variety of chemical occupations Analytical chemistry – measures concentrations Industrial chemistry – maximise efficientcy Environmental chemistry – monitors pollution Physical chemistry – the physical properties Electrochemistry – making electricity with chemicals Organic chemistry – petroleum products Inorganic chemistry – Minerals and stuff A specific chemical occupation for a more detailed study Analytical chemistry involves the quantitative analysis of chemical reactions These include reaction rates, conditions and concentrations Chemical Monitoring and Management 07:15
Some techniques they use include volumetric analysis, gravimetric analysis, AAS and mass spectroscopy 2. Chemical processes in industry require monitoring and management to maximise production Identify and describe the industrial uses of ammonia Over 80% of ammonia is used in fertiliser It can be directly injected into the soil as liquid or used as a raw material to make other nitrogen based fertilisers It is used to make nitric acid It is also used to make explosives such as TNT and nitroglycerine which are nitrogen based Identify that ammonia can be synthesised from its component gases, nitrogen and hydrogen Describe that the synthesis of ammonia occurs as a reversible reaction that will reach equilibrium Identify the reaction of hydrogen with nitrogen as exothermic Ammonia can be synthesised from its elements in the Haber process
N2(g) + 3H2(g) 2NH3(g) ∆H = -92 kJ/mol This reaction has a negative ∆H, so it releases energy into its surroundings, making it exothermic This is an equilibrium reaction that does not go to completion, hence the reaction must be monitored for maximum production Sources of hydrogen: reaction of steam with methane Sources of nitrogen: Fractional distillation of the atmosphere Explain why the rate of reaction is increased by higher temperatures An increase in temperature gives the molecules more kinetic energy, resulting in more energetic and frequent collisions More frequent collisions lead to faster reactions because of the increased chance of a successful collision In an equilibrium reaction, the equilibrium will be reached faster since both forward and backward reaction rates are increased Explain why the yield of product in the Haber process is reduced at higher temperatures using Le Châtelier’s principle Chemical Monitoring and Management 07:15
According to Le Chatelier’s principle, a system in equilibrium, when disturbed, will react in a way to minimise the disturbance Increasing temperature favours the endothermic reaction, hence in the Haber Process, it will shift the equilibrium to the left, reducing yield Explain that the use of a catalyst will lower the reaction temperature required and identify the catalyst(s) used in the Haber process A catalyst is used to provide an alternative reaction path with a lower activation energy and hence will lower the temperature required for a successful reaction The catalyst used in the Haber process is an iron oxide It allows the reaction to take place at a higher rate, but lower temperature, which means higher yield even at lower temperatures Explain why the Haber process is based on a delicate balancing act involving reaction energy, reaction rate and equilibrium The manufacture of ammonia in the Haber process involves the following reaction
N2(g) + 3H2(g) 2NH3(g) ∆H = -92 kJ/mol An increased temperature will increase reaction rates, but according to Le Chatelier’s principle, the yield will be decreased However, decreasing temperature to maximise yield will decrease the energy of the molecules As a result, the reaction rate so much it becomes uneconomical Hence an compromised between yield and reaction rate must be reached A catalyst is used to speed up the reaction at a lower reaction rate, hence allowing a higher yield as well as reaction rate At a lower temperature, yield is increased because the equilibrium is shifted to the right If the temperature is too high, it will also decompose the iron oxide catalyst Analyse the impact of increased pressure on the system involved in the Haber process Increased pressure will cause the equilibrium to the side with less moles of gas In this case, it will favour the forward reaction, going from 4 moles to 2 moles However, higher pressures are expensive to maintain, requiring very expensive equipment which can deal with these high pressures Explain why monitoring of the reaction vessel used in the Haber process is crucial and discuss the monitoring required Chemical Monitoring and Management 07:15
The Haber process is an industrial process, hence it must be monitored to maintain optimum conditions for maximum production and least possible waste A compromise between favourable reaction conditions and economic factors must be reached to optimise yield Temperature The temperature must be monitored so that it remains between the optimum temperatures of 400-550 ˚C Since the reaction is exothermic, energy will be released and thus the temperature will increase It must be monitored so that production rates are maintained at a high level Also, the catalyst will decompose if the temperature is too high Pressure The optimum pressure of 250-350 atmospheres needs to be maintained for economical and safety reasons If the pressure drops, reaction rate and yield decreases If the pressure increases, then the equipment could get damaged and explode Other conditions Making sure that the reactants are fed into the reaction vessel in the
correct ratio, i.e. the ratio of N2 to H2 is 1:3 Recycling unreacted gases so that it is not wasted Ammonia is constantly removed as a liquid This will shift the equilibrium to favour the production of more ammonia Gather and process information from secondary sources to describe the conditions under which Haber developed the industrial synthesis of ammonia and evaluate its significance at that time in world history Historical context: The Haber process was invented at the beginning of the 20th C, and it was during a crucial time in world history Following the industrial revolution, the world population was growing exponentially and hence the demand for fertilisers to feed its population was increasing Traditional sources of nitrogen for the fertilisers was Chilean saltpetre and Peruvian guano deposits from South America, however these were soon depleted Chemical Monitoring and Management 07:15
Hence there was a high demand for an alternative source of nitrogen Furthermore, during WWI, the Allies had blockaded the German ships from accessing Chilean saltpetre, preventing the Germans from a source of nitrogen for explosives and fertiliser Bosch had later industrialised the Haber process and mass produced ammonia for the German war effort Evaluation: It is predicted that the Germans would have lost the war by 1916 if the Haber process did not get industrialised, as they would have run out of fertiliser to feed its people Hence it is arguable that the Haber process may have changed the course of history if Germany had won the war Today, its significance is still prevalent, as the Haber process produces ammonia to feed about a third of the world population 3. Manufactured products, including food, drugs and household chemicals are analysed to determine or ensure their chemical composition Deduce the ions present in a sample from the results of tests Cations [Pb2+, Ba2+, Ca2+, Fe2+, Fe3+, Cu2+] If we know that only one ion is in the sample then we perform the HCl,
H2SO4, NaOH test White precipitate with HCl = Pb2+ Reacts with I- to form yellow precipitate 2+ 2+ Precipitate with H2SO4 = Ba or Ca Ba2+ will not precipitate with F- ions apple green flame test Ca2+ Will precipitate with F- ions forming a white precipitate Brick red flame test Precipitate with NaOH = Fe2+, Fe3+ or Cu2+ Chemical Monitoring and Management 07:15
Fe2+ Green precipitate with OH- but may decompose into Fe3+ and turn brown Decolourises acidified potassium permanganate solution 2+ 4– H+ 3+ 2+ 5Fe (aq) + MnO (aq) + 8 (aq) → 5Fe (aq) + Mn (aq) + 4H2O(l) Fe3+ Brown precipitate with OH- Forms a blood red mixture with SCN- Fe3+(aq) + SCN–(aq) Fe(SCN)2+(aq) Cu2+ Forms a blue precipitate with OH- 2+ Reacts with ammonia to form the deep blue complex ion, Cu(NH3)4 Blue-green flame test When multiple ions are present, then the tests must be performed in a specific order: HCl→ H2SO4→NaOH so that the tests do not upset the results for a following test 2+ 2+ E.g. if Pb and Ba are both present, then adding H2SO4 will precipitate both cations, then they become indistinguishable
The solubility of certain compounds, in particular PbCl2 and CaSO4 means that if the concentration of the substances are too low, then no precipitate will be formed even if it is present 2- 2- - 3- Anions [CO3 , SO4 , Cl , PO4 ] 2- CO3 Solution has a pH of about 8-11 Effervescence when reacts with acid - HNO3 used because the NO3 ion is soluble 2- SO4 When added to a solution of acidified Ba2+, there will be a thick white
precipitate of BaSO4 Can be confirmed with Pb2+ which will also precipitate Cl- Acidify to remove carbonates then add Ag Forms AgCl which is a white precipitate This darkens in the presence of UV light AgCl also dissolves in ammonia 3- PO4 3- Make the solution alkaline to produce more PO4 ions It shifts the following equilibrium to the right using Le Chatelier’s principle, as the base will remove the hydronium ions 2- + 3- HPO4 + H2O H3O + PO4 Then add Ba2+ to precipitate Acidify then add ammonium molybdate Forms a blue complex ion 07:15
1. Industrial chemistry processes have enabled scientists to develop replacements for natural products 07:15
Discuss the issues associated with shrinking world resources with regard to one identified natural product that is not a fossil fuel, identifying the replacement materials used and/or current research in place to find a replacement for the named material. Define Natural Product A natural product is a product produced directly from something found in nature with little or no modification. E.g. metal ores and guano fertiliser There are two types of natural resources: Inexhaustible and Exhaustible Inexhaustible natural resources are unlimited and are not likely to be exhausted by human activities. E.g. solar energy, wind Exhaustible resources are limited and can be depleted by human activities e.g. forests, animals, fossil fuels Need For Replacements Humans exploit their surroundings for resources Due to the population boom following the Industrial Revolution about 250 years ago the demand for natural resources has exponentially increased with the population. We cannot generate more of a natural resource to satisfy this demand, since natural regeneration is slower than consumption Hence replacements are needed Type of replacements Synthetise the same material: find another way to obtain the same product E.g. drug synthesis Replace natural product with an alternative material which, although chemically different, have the same desired physical properties E.g. Synthesis of ammonia to replace guano Almost every material → plastics Ammonia [Basically this is how answer to the question] Define natural resource Rapid population growth following the Industrial Revolution meant that natural fertilisers such as animal dung was not sufficient to fertilise crops to feed the population 07:15
Alternative sources of nitrogen such as guano deposits on many islands on the Pacific Coast were completely depleted before the end of the 19th Century Nitrogen sources were used to make fertilisers so that nitrogen would be presented in a form which would be usable by plants. Hence without an alternative source, there would not be enough fertiliser to grow food for a growing population Due to the Allie’s embargo on the trade of saltpetre from Chile, the Germans had to find a new way of producing a nitrogen based fertiliser The Bosch-Haber Process solved this problem by securing food supply by production of ammonia which would be used in fertilisers Briefly describe the Haber Process The Haber Process solved the problem in the early 20th century, but the process is very costly due to high pressures and temperatures Future options include genetic engineering Some algae and bacteria can absorb atmospheric nitrogen and convert it into organic nitrogen via intermediate ammonium ions. The bacteria could be engineered to absorb nitrogen and release it into the soil as ammonia Some micro-organisms have a gene known as the NIF-gene and create the enzyme nitrogenase which is able to fix atmospheric nitrogen to synthesis ammonia. This gene could be inserted directly into plants, allowing it to use the nitrogen in the air 2. Many industrial reactions involves manipulation of equilibrium reactions Explain the effect of changing the following factors on identified equilibrium reactions Pressure Only affects gases Partial pressure is the pressure exerted on the vessel if only that gas is present Equilibrium is only affected when the partial pressure of the gas is changed Partial pressure can be likened to concentration Increasing pressure will favour the reaction to less moles Volume Concentration Temperature Increased temperature favours the endothermic reaction 07:15
Decreased temperature favours the exothermic reaction Identify that temperature is the only factor that changes the value of the equilibrium constant (K) for a given equation The equilibrium constant is constant for a given temperature 3. Sulfuric acid is one of the most important industrial chemicals Outline three uses of sulphuric acid in industry Source of sulphate in the production of superphosphate fertilisers and ammonium sulfate It is often used as a strong acid to clean the oxide layer off iron before galvanising or electroplating Manufacture of detergents, to make alkylbenzene sulfonates Used as a catalyst (such as manufacture of esters) Dehydrating agent (such as dehydration of ethanol Describe the processes used to extract sulfur from mineral deposits, identifying the properties of sulfur which allow its extraction and analysing potential environmental issues that may be associated with its extraction Frasch Process Superheated water is pumped into underground sulfur deposits at about 165°C, which melts the sulfur which has a melting point of 119°C Hot compressed air is pumped into the deposit to force it to the surface out the third pipe This sulfur and water emulsion can be separated easily since sulfur insoluble in water Environmental concerns Forms cavities in the ground which may cause landslides These need to be “backfilled”, which is very difficult to do Sulfur is easily oxidised to sulfur dioxide and reduced to hydrogen sulphide which are both pollutants 4. The industrial production of sodium hydroxide requires the use of electrolysis Explain the difference between galvanic cells and electrolytic cellsin terms of energy requirements 07:15
Galvanic cells produce electricity, electrolytic cells require energy Outline the steps in the industrial production of sodium hydroxide and describe the reaction in terms of net ionic and full formulae equations Blah blah Distinguish between the three electrolysis methods used to extract sodium hydroxide by describing each process and analyse the technical and environmental difficulties involved in each process Mercury process Diaphragm process Membrane 5. Saponification is an important organic industrial process blah blah blah 6. The Solvay process has been in use since the 1860s Identify the raw materials used in the Solvay process and name the products Raw materials Brine (concentrated NaCl solution) Ammonia (reused) Calcium Carbonate Products Calcium Chloride Sodium Carbonate Ammonia