BTEC National Applied Science student B2 past paper PDF

T AF R D Principles and Applications of...

T AF R D Principles and Applications of Science II 5 M05 BTEC National Applied Science Student B2 XXXXX.indd Page 1 08/05/17 9:17 PM f-0314 /122/PE02858/BTEC_Applied_Science/NA/SE/Applied_Science/G1/XXXXXXXXXX/Layout/Inte...  UNIT 5 Getting to know your unit Science technicians need to be able to use and apply key science concepts Assessm ent to work efficiently and safely in science and science related organisations. Chemists, for example, need to understand how the uses of chemical You will be assesse d products relate to their physical and chemical properties. Scientists in through a written exam the pharmaceutical and medical industries need to understand how the which is set and marke d human body works. They need to know how diseases can be diagnosed by Pearson. and treated. Engineers need to understand the properties and behaviour of different materials to ensure that the materials are fit for purpose. When designing machines, they need to understand how materials will behave under different conditions. They also need to understand how energy is transferred in order to make efficient machines and engines. How you will be assessed T The external assessment for this unit will be split into three sections. ▸▸ Section A – Chemistry (Properties and uses of substances, Structures, Reactions AF and properties of commercially important organic compounds, Energy changes in industry) ▸▸ Section B – Biology (Organs and systems, Ventilation and gas exchange to the lungs, Urinary system structure and function, Cell transport mechanisms) ▸▸ Section C – Physics (Thermal physics, Materials, Fluids in motion). The assessment will contain a range of question types, including multiple choice, calculations, short answer and open response. These question types, by their very nature, generally assess discrete knowledge and understanding of the content in R this unit. You need to be able to apply and synthesise knowledge from this unit. The questions will be contextualised in order for you to show that you can do this. Throughout this unit you will find assessment practices that will help you prepare for D the assessment. Completing each of these will give you an insight into the types of questions that will be asked and, importantly, how to answer them. Unit 5 has four Assessment Outcomes (AOs). These are: ▸▸ AO1: Demonstrate knowledge of scientific facts, terms, definitions and scientific formulae Command words: describe, draw, explain, identify, name, state ▸▸ AO2: Demonstrate understanding of scientific concepts, procedures, processes and techniques and their application Command words: calculate, describe, draw, explain, give, show, state ▸▸ AO3: Analyse, interpret and evaluate scientific information to make judgements and reach conclusions Command words: analyse, comment, describe, explain, give, state ▸▸ AO4: Make connections, use and integrate different scientific concepts, procedures, processes or techniques Command words: calculate, comment, explain 2 Principles and Applications of Science II M05 BTEC National Applied Science Student B2 XXXXX.indd Page 2 08/05/17 9:17 PM f-0314 /122/PE02858/BTEC_Applied_Science/NA/SE/Applied_Science/G1/XXXXXXXXXX/Layout/Inte...  Getting to know your unit UNIT 5 Principles and Applications of Science II Command word Definition – what it is asking you to do Add/label This requires you to add labelling to a stimulus material given in the question, for example labelling a diagram or adding units to a table. Assess You need to give careful consideration to all the factors or events that apply and identify which are the most important or relevant. You need to make a judgement on the importance of something and come to a conclusion where needed. Calculate You will obtain a numerical answer, showing relevant working. If the answer has a unit, you must include it. Comment on This requires you to synthesise a number of variables from data/information to form a judgement. More than two factors need to be synthesised. Compare This asks you to identify the main factors of two or more items and point out their similarities and differences. You may need to say which are the least important or most important. The word Contrast is very similar. Complete This requires you to complete a table/diagram. Criticise Here you need to inspect a set of data, an experimental plan or a scientific statement and consider the elements. Look at the merits and/or faults of the information presented and back up the judgements that you make. Deduce Here you draw/reach conclusion(s) from the information provided. Derive Here you combine two or more equations or principles to develop a new equation. T Describe You need to give a full account of all the information, including all the relevant details of any features, of a topic. Determine Your answer must have an element that is quantitative from the stimulus provided, or must show how the answer can be reached quantitatively. To gain maximum marks there must be a quantitative element to the answer. Devise Discuss AF You plan or invent a procedure from existing principles/ideas. Here you write about the topic in detail, taking into account different ideas and opinions. Draw You produce a diagram either using a ruler or using freehand. Evaluate Here you bring all the relevant information you have on a topic together and make a judgment on it (for example on its success or importance). Your judgment should be clearly supported by the information you have gathered. Explain You make an idea, situation or problem clear to your reader, by describing it in detail, including any relevant data or facts. R Give a reason why This is when a statement has been made and you only need to give the reasons why. Give/state/name These generally require you to recall one or more pieces of information. Identify This usually requires you to select some key information from a given stimulus/resource. D Plot You need to produce a graph by marking points accurately on a grid from data that is provided and then drawing a line of best fit through these points. You must include a suitable scale and appropriately labelled axes if these are not provided in the question. Predict You give an expected result. Show that You prove that a numerical figure is as stated in the question. The answer must be to at least one more significant figure than the numerical figure in the question. Sketch You produce a freehand drawing. For a graph this would need a line and labelled axes with important features indicated. The axes are not scaled. State and justify/ You make a selection and justify it. identify and justify State what is Here, you give the meaning of a term but there are different ways in which this meaning can be described. meant by Write Here the question asks for an equation. 3 M05 BTEC National Applied Science Student B2 XXXXX.indd Page 3 08/05/17 9:17 PM f-0314 /122/PE02858/BTEC_Applied_Science/NA/SE/Applied_Science/G1/XXXXXXXXXX/Layout/Inte...  Getting started This unit builds on prior knowledge. Look at the topics for each section of the exam. Write down two things you already know about each of those topics. Suggest what you are expecting to learn about when studying those topics. A Properties and uses of substances Relating properties to uses Other aluminates can form depending on the conditions. Hot concentrated sodium hydroxide will give sodium and production of substances tetrahydroxoaluminate, 2NaAl(OH)4. You will not be expected to know all aluminates that may form. Scientists need to know the different chemical properties of substances. They can use this knowledge to make new, In general, aluminium oxide is chemically inert except T useful materials. under certain conditions, e.g. when a hot acid or base is present. This means it has a lot of uses including filler, Metal oxides and metal hydroxides paint, sunscreens, and glass. The amphoteric nature of alumina means it can be used as a medium for Alumina is the common name for aluminium oxide. One AF property of alumina is that it is amphoteric. This means chromatography as a basic, acidic or neutral medium. It is also an effective desiccant and can be used at a range that it will act as an acid or a base depending on the conditions. If an acid is present it will react as a base. of basic and acidic pHs. It is stable over pH range 2–13. If a base is present it will act as an acid. This also makes it suitable for environmental clean-up and separation applications. Group 1 and group 2 metal oxides are basic. If they Key terms R dissolve in water, then they will react with the water to Amphoteric – substance that can act as both an acid form metal hydroxides. This forms an alkali solution. For and a base. example: Acid – a compound containing hydrogen that Na2O + H2O S 2NaOH dissociates in water to form hydrogen ions. D CaO + H2O S Ca(OH)2 Base – a compound that reacts with an acid to form a salt and water. Key term Alkali – a base that dissolves in water to form hydroxide ions. When aluminium oxide reacts with an acid it reacts in the same way as other metal oxides, such as magnesium oxide, that are bases. The oxide ion is a very strongly basic anion due to its very small size and high (2−) charge. The oxide ion in the Aluminium oxide reacts with hot hydrochloric acid to give metal oxide reacts with water to produce hydroxide ions, aluminium chloride and water. The aluminium chloride is because a hydroxide ion is the strongest base that can soluble so you get aluminium chloride solution. persist in water. Al2O3 + 6HCl S 2AlCl3 + 3H2O Calcium oxide (quicklime) reacts with water to form Aluminium oxide will react with bases such as sodium calcium hydroxide (lime). This can then be used by farmers hydroxide to form aluminates. For example: to raise the pH of acidic soil. Al2O3 + 6NaOH + 3H2O S 2Na3Al(OH)6 Magnesium oxide can be used as a desiccant when (sodium aluminate) preserving books in a library. Some papers produce acidic 4 Principles and Applications of Science II M05 BTEC National Applied Science Student B2 XXXXX.indd Page 4 08/05/17 9:17 PM f-0314 /122/PE02858/BTEC_Applied_Science/NA/SE/Applied_Science/G1/XXXXXXXXXX/Layout/Inte...  Learning aim A UNIT 5 sulfur oxides when oxidised in air. Although magnesium Figure 5.1 shows the electrolysis of molten sodium chloride. Principles and Applications of Science II oxide is not a very good desiccant, it is used because due Sodium is produced at the cathode (positive electrode) and to its basic nature it will neutralise the acidic sulfur oxides chlorine is produced at the anode (negative electrode). produced and so help to preserve the book. e2 e2 Sodium hydroxide, which is produced when sodium Inert Inert oxide reacts with water, is an important compound in the Electrode Battery Electrode chemical industry as well as in everyday life. For example, it is used in some processes to make plastics and soaps. It Cl2(g) is used in food processing in many ways. Some examples are to peel fruits and to process cocoa and chocolate. It is found in drain cleaner or in oven cleaner. These uses all rely on the basic properties of the compound. Cl2 Na1 Magnesium hydroxide, Mg(OH)2, is also known as ‘milk of magnesia’ and is used for treating acid indigestion. It raises Anode Cathode the stomach pH due to its basic nature. Calcium hydroxide, Ca(OH)2, is used in the treatment of ▸▸ Figure 5.1 Electrolysis of molten sodium chloride acidic effluent. Factories that produce or use sulfuric acid T will also produce acidic liquid effluent which may have The only ions present are sodium and chloride ions and to be treated before being released to the environment, so only sodium and chlorine can be produced by this especially if it has high acid content. Impurities are reaction. precipitated and removed. The acidic liquid can be neutralised using calcium hydroxide, lime. This reaction occurs. AF Figure 5.2 shows the electrolysis of sodium chloride solution. H2SO4 + Ca(OH)2 S CaSO4 + 2H2O e2 e2 Inert Inert The calcium hydroxide is a base and a neutral calcium Electrode Battery Electrode sulfate is formed. Calcium sulfate is a salt. Although other bases are available, calcium hydroxide is cheap and simple Cl2(g) H2(g) R to use. Key term Salt – a compound formed by an acid–base reaction Cl2 H2O D where the hydrogen in the acid has been replaced by a metal (or other positive) ion. Anode Cathode ▸▸ Figure 5.2 Electrolysis of sodium chloride solution Electrolysis When the sodium chloride is dissolved in water, hydrogen Electrolysis breaks down compounds into simpler and hydroxide ions are present as well as the sodium and substances. It is used in some industrial processes (see chloride ions. In this case, the chlorine is still produced at page 9). Ionic substances are decomposed by an electrical the anode but hydrogen gas is produced at the cathode charge being passed through them during electrolysis. rather than sodium. It is only possible for one type of ion The ions must be free to move for this to work so the to discharge at each electrode. The ion which is selected to compound must either be molten (reduced to liquid form discharge at an electrode depends on a number of factors. by heating) or in solution. The position of the ion in the electrochemical series affects its ease of discharge at an electrode. When metals react, Key term they lose electrons to become positive ions. If a metal is Electrolysis – the decomposition of a compound using placed in water, then the metal atoms will tend to lose electricity. electrons to the water and become positive. This in turn 5 M05 BTEC National Applied Science Student B2 XXXXX.indd Page 5 08/05/17 9:17 PM f-0314 /122/PE02858/BTEC_Applied_Science/NA/SE/Applied_Science/G1/XXXXXXXXXX/Layout/Inte...  attracts the negative electrons back to the metal. This is an containing the chloride ion, the chloride ion will be example of an equilibrium process. discharged rather than the hydroxide ion, even though the hydroxide ion is more easily oxidised. For example, magnesium in water will have the following equilibrium reaction. Assessment practice 5.1 Mg2+(aq) + 2e− Mg(s) { Explain the products of the electrolysis of brine. A piece of copper in water will behave in the same way. Cu2+(aq) + 2e− Cu(s) { Transition metals As copper is less reactive than magnesium, it will form ions Transition metals are the d block elements found less easily so the equilibrium for copper in water is further between group 2 and 3 on the periodic table. They are to the left than that for magnesium in water. used in a variety of industrial processes and transition For both the metals, there is a potential difference metals and their compounds have a wide number of between the negative charge on the metal and the uses. Transition metals have incomplete d-sub-shells as a positive charge of the solution around it. The potential stable ion. difference is bigger for magnesium than it is for copper. If we look at the transition elements in period 4, across the This potential difference can be measured as a standard period, from scandium to zinc, the 3d-orbitals are being electrode potential and then the metals can be placed T filled. The pattern is regular. (Except for chromium and in order of the standard electrode potentials (E°) in the copper, which do not follow the principle of completely electrochemical series. filling the lowest energy levels first.) The sub-shell energy Hydrogen is also included in the electrochemical series levels in the third and fourth energy levels overlap. The (see Table 5.1). AF 4s-sub-shell fills before the 3d-sub-shell. When they react, transition element atoms lose electrons ▸▸ Table 5.1 Part of the electrochemical series to form positive ions. Transition metals lose their 4s Equilibrium half equation E° (volts) electrons before their 3d electrons. They form ions with more than one stable oxidation state. They can all form Li+(aq) + e− −3.03 { { Li(s) compounds with metal ions in the +2 oxidation state. K+(aq) + e− K(s) −2.92 In solution, transition metal compounds form complex R Na+(aq) + e− −2.71 ions. A complex ion consists of a central metal ion { Na(s) −2.37 surrounded by ligands. A ligand is a molecule or ion that Mg2+(aq) + 2e− { { { { { Mg(s) donates a pair of electrons to the central transition metal Al3+(aq) + 3e− Al(s) −1.66 ion to form a dative covalent bond. D Zn2+(aq) + 2e− Zn(s) −0.76 Figure 5.3 shows the complex ion [Fe(H2O)6]2+. Each of the 2H+(aq) + 2e− H2(g) 0 six H2O ligands forms one dative covalent bond with the central metal ion. Cu2+(aq) + 2e− Cu(s) +0.34 ½ CI2(aq) + e− S CI−(aq) +1.36 OH2 21 H 2O OH2 The lower the metal is in the electrochemical series, the Fe more likely it is to be discharged. So in a solution of copper H2O OH2 sulfate, the copper ions will be discharged to form copper atoms rather than the hydrogen ions. In a solution of OH2 sodium chloride, hydrogen gas is given off at the cathode ▸▸ Figure 5.3 Complex metal ion rather than sodium metal. Other complex ions include [Cu(H2O)6]2+, [Al(H2O)6]3+, and The concentration of the ions in solution will also have an [CuCl4]2−. effect on which ion is discharged. The most concentrated ion tends to be discharged, no matter where the ions are Transition metals, oxides of transition metals and transition in the electrochemical series. So in a concentrated solution metal complexes are all used as industrial catalysts. 6 Principles and Applications of Science II M05 BTEC National Applied Science Student B2 XXXXX.indd Page 6 08/05/17 9:17 PM f-0314 /122/PE02858/BTEC_Applied_Science/NA/SE/Applied_Science/G1/XXXXXXXXXX/Layout/Inte...  Learning aim A UNIT 5 So the vanadium(V) oxide catalyst takes part in Principles and Applications of Science II Key terms the reaction and is changed in the reaction but Complex ion – a transition metal ion bonded to one or remains chemically unchanged by the end of the more ligands by dative covalent bonds. reaction. Ligand – a molecule or ion that can donate a pair of 3 The sulfur trioxide is converted into sulfuric acid. electrons to the transition metal ion to form a dative Adding sulfur trioxide to water is too uncontrollable bond. to be the method used. First sulfur trioxide is dissolved Catalyst – a substance that speeds up a reaction. It can in concentrated sulfuric acid. This produces fuming take part in the reaction but is left unchanged at the sulfuric acid which can then be added safely to water end of the reaction. to produce more concentrated sulfuric acid. H2SO4 (l) + SO3 S H2S2O7 (l) Platinum and rhodium are used in catalytic converters in H2S2O7 (l) + H2O(l) S 2H2SO4 (l) car exhausts. They convert carbon monoxide and nitrogen monoxide emissions into carbon dioxide and nitrogen gas. Iron is used as the catalyst in the Haber process for the These gases are not polluting. Manganese dioxide acts as synthesis of ammonia. Nitrogen reacts with hydrogen a catalyst in the decomposition of hydrogen peroxide into to produce ammonia. water and oxygen. N2(g) + 3H2(g) 2NH3(g) T { The contact process uses vanadium(V) oxide as a catalyst for the production of sulfuric acid. There are four stages in The iron catalyst speeds up the reaction by lowering this process. the activation energy so that the N2 bonds and H2 bonds can be broken more readily. 1 Sulfur reacts with oxygen to produce sulfur dioxide. S(s) + O2(g) S SO2(g) AF Key term Or sulfur dioxide is produced by reacting sulfide ores Activation energy – the minimum amount of energy with excess air. needed by the reactants for collisions to result in a reaction taking place. 4FeS2(g) + 11O2 S 2Fe2O2(s) + 8SO2(g) The sulfur dioxide produced is mixed with excess air for R use in stage 2. Case study 2 Sulfur dioxide is converted into sulfur trioxide in a reversible reaction. The Haber Process 2SO2(g) + O2(g) 2SO3(g) { The iron catalyst lowers the energy demands of D Vanadium(V) oxide catalyses this stage. The following the Haber Process. This means that the costs reactions occur. of the process are reduced and also helps the environment. Less fuel is needed to be burned The overall reaction is: to generate the energy needed. This means           V2O5 fossil fuels are conserved and there are fewer carbon dioxide emissions. The Haber Process SO2 + ½O2 SO3 is an important industrial reaction because it Vanadium(V) oxide can act as a catalyst due to the produces ammonia. This is used as the basis for ability of vanadium to change its oxidation state. Sulfur making fertilisers which improve crop yield. This dioxide is oxidised to sulfur trioxide by the vanadium(V) becomes more important each year as we need oxide. So the vanadium(V) oxide is reduced to to feed the world’s population, which is increasing vanadium(IV) oxide. every year. SO2 + V2O5 S 2SO3 + V2O4 Check your understanding 1 How does the use of iron in the Haber Process The vanadium(IV) oxide is then oxidised with the oxygen: lower environmental and financial costs? V2O4 + ½O2 S V2O5 7 M05 BTEC National Applied Science Student B2 XXXXX.indd Page 7 08/05/17 9:17 PM f-0314 /122/PE02858/BTEC_Applied_Science/NA/SE/Applied_Science/G1/XXXXXXXXXX/Layout/Inte...  PAUSE POINT List all the different chemical substances discussed so far in this unit. Hint Compete a table with the headings metals, metal oxides and metal hydroxides. Extend Give one use for each of the substances based on its chemical properties. to help the sedimentation process. The bauxite residue Assessment practice 5.2 is transferred to the washing tanks to recover the caustic Describe how vanadium(V) oxide acts as a catalyst in soda, which is reused in the digestion process. the contact process. Include any relevant equations. Key terms Flocculants – substances that causes particles to clump Purification, extraction and and so settle out of a liquid. manufacture of useful substances Sedimentation – small solid particles settling at the bottom of a liquid. Alumina (aluminium oxide) is a material that retains its strength at high temperatures. It is chemically and physically stable at these high temperatures. It is a refractory material. Further separation of the pregnant liquor (the sodium T It can be used in linings for furnaces, kilns and reactors. It can aluminate remains in the solution) from the bauxite residue also be used in acidic reactions as it does not react. is performed using a series of filters to ensure that the final product is not contaminated with impurities present in the residue. Key term Refractory material – material that is physically AF Precipitation is used to recover the alumina by crystallisation from the liquor, which is supersaturated in and chemically stable at very high temperatures, for sodium aluminate. The liquor is cooled, resulting in the example, over 3000°C. formation of small crystals of aluminium trihydroxide (Al(OH)3), which then grow and form larger crystals. Alumina and aluminium extraction The spent liquor is heated through a series of heat exchangers Alumina is extracted from bauxite ore using the Bayer and subsequently cooled in a series of flash tanks. The R process. The bauxite is crushed to form grains. It is then mixed condensate formed in the heaters is re-used in the process, with liquor from the later precipitation stage and crushed e.g. for washing bauxite residue. The remaining caustic soda is again to make a slurry. Bauxite can have a high level of silica washed and recycled back into the digestion process. present so it may have to go through a desilication process to remove this. Hot caustic soda (NaOH) solution is used to The gibbsite crystals formed in precipitation are classified D dissolve the aluminium-bearing minerals, gibbsite, böhmite into size ranges. This is normally done using cyclones or and diaspore, in the bauxite, to form a sodium aluminate gravity classification tanks. supersaturated solution (liquor). This is called ‘digestion’. The filter cakes are fed into calciners where they are heated to temperatures of up to 1100°C to drive off Key terms moisture. This produces alumina solids. The following Bauxite – aluminium ore. equation describes the calcination reaction: Slurry – semi-liquid mixture containing fine solid 2Al(OH)3 S Al2O3 + 3H2O particles. Alumina, a white powder, is the product of this step and Conditions for this change due to the composition of the the final product of the Bayer Process. bauxite ores. Those with a high gibbsite content need about 140°C, while those with a high böhmitic content Key terms need a higher temperature between 200 and 280°C. Condensate – liquid collected by condensation. After digestion, the slurry is cooled to around 106°C. It Calcination – heating to high temperature to remove is then clarified to separate the solids from the liquor via free and chemically bonded water. sedimentation. Chemical additives, flocculants, are added 8 Principles and Applications of Science II M05 BTEC National Applied Science Student B2 XXXXX.indd Page 8 08/05/17 9:17 PM f-0314 /122/PE02858/BTEC_Applied_Science/NA/SE/Applied_Science/G1/XXXXXXXXXX/Layout/Inte...  Learning aim A UNIT 5 Aluminium is extracted from alumina using the Hall- react with the hydroxide ions in solution to form sodium Principles and Applications of Science II Héroult process. Alumina is dissolved in molten cryolite, hydroxide. The chlorine and the hydrogen gases are Na3AlF6 (an aluminium ore), and electrolysis is used to kept separate as a mixture of these gases will explode on extract the aluminium. Aqueous aluminium oxide is not exposure to heat or light. used because the aluminium is readily oxidised by the The chlorine will also react with the sodium hydroxide hydrogen ions present in the solution. Alumina has a solution formed to produce a mixture of sodium chloride melting point of over 2000°C and so it is not practical to and sodium hypochlorate. This mixture can be used as use molten alumina. However, if the alumina is dissolved in bleach. However, specialised cells are need if the desired molten cryolite, then the melting point is a lot lower (about products are chlorine and sodium hydroxide. There are 1000°C) and so electrolysis is possible. Aluminium fluoride two types of cell that can be used: is also added to the mixture and this lowers the melting ▸▸ a diaphragm point even further. ▸▸ a membrane cell. The aluminium sinks to the bottom of the cell and is syphoned off. Carbon dioxide is produced at the anode The diaphragm cell has a diaphragm in the centre. This along with hydrogen fluoride from the cryolite. is made of a porous mixture of asbestos and polymers. The brine is added on one side of the diaphragm and the Electrolysis of brine aqueous sodium hydroxide is removed on the other side. Brine is aqueous sodium chloride. As you saw on page 5, The level of liquid on the side where the brine is added is T the electrolysis of brine produces sodium hydroxide, always higher than the side where the aqueous sodium hydrogen and chlorine, all of which are industrially useful hydroxide is removed, so that the brine does not flow back chemicals. Sodium hydroxide is used in food processing to mix with the chlorine produced. and removing pollutants during paper manufacture. AF Hydrogen is used in the production of hydrochloric acid and as a fuel. Chlorine is a disinfectant and is also used in The membrane in a membrane cell is made from a polymer that only allows positive ions to pass through it. So the sodium ions can pass through but the chloride ions making plastics. Figure 5.4 shows electrolysis of brine using cannot. So the sodium hydroxide that forms in the right a Hoffman voltameter. hand compartment does not mix with sodium chloride solution. The chlorine produced in diaphragm and membrane cells will mix with any oxygen produced at the anode but can R be purified by liquefying it under pressure. Under pressure, the oxygen will stay a gas. chlorine hydrogen Titanium extraction Cl2(g) H2(g) D Titanium can be obtained by extraction from its ore, TiO2, called rutile. The titanium cannot be extracted electrolyte using carbon, as titanium carbide (TiC) will form and the sodium chloride presence of this carbide makes the titanium very brittle. NaCl(aq) There are two stages in the extraction process. It is a batch platinum electrodes process so only small amounts are made at one time. It is also expensive due to the two steps, the conditions and 1 anode 2 cathode the use of chlorine and magnesium. The magnesium has to be extracted from its ore before being used for this process. battery 1 Conversion of titanium(IV) oxide to titanium(IV) 1 2 dc supply chloride ▸▸ Figure 5.4 Hoffman voltameter TiO2(s) + 2Cl2(g) + 2C(g) S TiCl4(g) + 2CO(g) 2 Titanium chloride is then reduced using magnesium to Inert platinum electrodes are used to prevent reaction produce titanium. with the gases produced. Chlorine is collected at the anode TiCl4(g) + 2Mg(l) S Ti(s) + 2MgCl2(s) and hydrogen is collected at the cathode. The sodium ions 9 M05 BTEC National Applied Science Student B2 XXXXX.indd Page 9 08/05/17 9:17 PM f-0314 /122/PE02858/BTEC_Applied_Science/NA/SE/Applied_Science/G1/XXXXXXXXXX/Layout/Inte...  The magnesium is put into a steel reactor and the titanium It is important to understand that products are used based chloride is pumped in. The reactor is sealed and heated to on the properties they have. These can be physical or 1200°C. The reaction is carried out in an argon atmosphere chemical properties. Their production is also dependent as the titanium produced would react with any oxygen on their properties. For example, aluminium is very or water present. Any oxygen or nitrogen present in the reactive, so is extracted by electrolysis because it cannot reactor would make the metal brittle. The reactor is left be extracted using the cheaper reduction with carbon sealed for two to three days before the titanium can be method. Titanium can be reduced but magnesium is removed. A large reactor will only produce about 1 tonne needed to do this as using carbon would cause the metal of titanium a day, which is a relatively small amount. to be brittle. PAUSE POINT Draw a mind map of all the production methods discussed in this unit. Hint Link each to purification, extraction and manufacture methods. Extend Link each production method to the properties of the substances. Structures, reactions and properties Key terms T of commercially important organic Aliphatic – a hydrocarbon with carbon atoms joined compounds together in straight or branched chains. Alicyclic – a hydrocarbon with carbon atoms joined Organic chemicals are carbon based compounds. They are compounds found in living organisms, e.g. amino AF acids, fatty acids, etc. They are also used in industry and together in a ring structure. Aromatic – a hydrocarbon containing at least one in everyday products. Clothes, plastics, and food are a few benzene ring. examples of where organic chemicals are used. IUPAC nomenclature – system of the International Union of Pure and Applied Chemistry for naming There are different families of organic compounds. These organic compounds. families are called homologous series. The alkanes found in crude oil are a few of the organic compounds found in Saturated compound – contains single bonds only. R the alkane homologous series. Alkenes and alcohols are two more homologous series. All members of a homologous The general formula for an alkane is CnH2n + 2. Table 5.2 series have the same functional group and differ only by shows the first ten alkanes, their name, formula and the number of CH2 units present. Organic compounds can structure. D be classified as aliphatic, alicyclic or aromatic. ▸▸ Table 5.2 Alkanes Alkanes and alkenes Name Molecular formula There are millions of organic compounds. All scientists Methane CH4 use the same system to name them. This is the IUPAC nomenclature. Scientists follow the rules of Ethane C2H6 this nomenclature to name compounds. Alkanes are Propane C3H8 aliphatic saturated compound hydrocarbons. They only Butane C4H10 have single bonds and only contain carbon and hydrogen atoms. Methane is an alkane. The ‘ane’ part of the name Pentane C5H12 shows it is an alkane. The first part of the name, ‘meth’ Hexane C6H14 shows how many carbons are present in the chain. Heptane C7H16 Key terms Octane C8H18 Homologous series – family of organic chemicals. Nonane C9H20 Functional group – group of atoms responsible for the characteristic reactions of a substance. Decane C10H22 10 Principles and Applications of Science II M05 BTEC National Applied Science Student B2 XXXXX.indd Page 10 08/05/17 9:17 PM f-0314 /122/PE02858/BTEC_Applied_Science/NA/SE/Applied_Science/G1/XXXXXXXXXX/Layout/Inte...  Learning aim A UNIT 5 Some alkanes are cyclic. These have rings of carbons. For carbons along the chain so that the functional group Principles and Applications of Science II example, cyclohexane has a ring structure with six carbons. has the lowest number possible (e.g. butan-1-ol, butan- Cyclic alkanes have a general formula of CnH2n. 2-ol, but-1-ene and but-2-ene). Alkenes are organic compounds containing a double bond 4 If there is more than one functional group, they are and have the general formula CnH2n. They have similar written in alphabetical order. names to alkanes with the same number of carbon atoms Table 5.3 shows common functional groups. but the name ends in ‘–ene’. ▸▸ Table 5.3 Common functional groups Naming organic compounds Functional group Formula Prefix Suffix Scientists follow these rules when naming an organic Alcohol OH Hydroxy- -ol compound. Aldehyde CHO -al 1 The stem is the main part of the name and comes Alkane C C -ane from the longest carbon chain or parent chain in the compound. Alkene C C -ene 2 The suffix is the end of the name. This identifies the Carboxylic acid COOH -oic acid most important functional group, e.g. ‘ane’ in alkanes. Ester COO -oate 3 The prefix is the front part of the name and identifies T Haloalkane F, Cl, Fluoro-, chloro-, other functional groups. The number of the carbon Br, I bromo-, iodo- atom they are attached to is given. You count the AF Ketone C CO C -one Worked example Name the following organic compounds. H CH3 H 1 H C C C H H OH H R Stem – the longest chain contains 3 carbon atoms and so the stem is prop-. There are two functional groups: i. alcohol OH, ii. alkyl (methyl-) CH3 They are both on the second carbon in the chain. OH becomes the suffix. -2-ol D CH3 is the prefix 2-methyl- The name of the compound is 2-methylpropan-2-ol. 2 H3C CH CH2 CH CH2 CH3 Br Cl Stem – the longest chain contains 6 carbons so the stem is hex-. The suffix is –ane, and there are halogens bromine and chlorine present, as this is a haloalkane. There are two functional groups, bromine and chlorine. These are both prefixes. Remember, if there is more than one prefix they are written in alphabetical order. So bromine is first. This means you count the carbons from the end nearest the bromine as above. The name of this compound is 2-bromo-4-chlorohexane. Key term Haloalkane – alkane where at least one hydrogen is replaced by a halogen. 11 M05 BTEC National Applied Science Student B2 XXXXX.indd Page 11 08/05/17 9:17 PM f-0314 /122/PE02858/BTEC_Applied_Science/NA/SE/Applied_Science/G1/XXXXXXXXXX/Layout/Inte...  Types of organic formulae Key terms A displayed formula shows the relative positions of all atoms Organic compound – compound based on a carbon in a molecule and the bonds between them. For example, structure. ethanoic acid has the formula CH3COOH. Sometimes the functional group is shown as —COOH. However, in a Isomers – two or more compounds that have the same displayed formula you must show all the bonds H  O and atoms. molecular formula but a different arrangement of atoms in the compound and so have different properties. The displayed formula for ethanoic acid is H C C. H  O H Butane and 2-methyl propane both have the molecular Organic compounds are not two-dimensional. It is often formula C4H10. They are chain isomers. important to draw the structure of an organic compound to show its three-dimensional structure. Methane can H H H H H H C C C C H be shown as H C H. This does not show how the H H H H H Butane hydrogen atoms are arranged in space around the carbon. H To see the spatial arrangement, we use wedge and dashed H C H T H H H lines. C H The solid lines are in line with the plane H H C C C H  H H H H backwards and the wedge shows the bond is angling AF of the paper. The dashed line shows the bond is angling forward. It is easier to see the different bond angles when 2-methyl propane Chain isomers occur in all carbon compounds with four a compound is drawn in this way. or more carbons. The longer the chain, the more possible A symmetrical alkene has the same groups attached chain isomers there are. to each of the carbons in the double bond. Ethene is a Butane and 2-methyl propane are both alkanes so have symmetrical alkene because both carbons in the double similar chemical properties but their boiling points are different. R H H bond are attached to two hydrogens. C C Positional isomers are molecules with the same carbon H H chain and functional groups but the functional groups But-2-ene can exist in two distinct geometric forms which are on different carbons within the chain. For example, have different types of symmetry. Both carbons in the butanol has the molecular formula C4H10O. It has two D double bond have a methyl group and a hydrogen atom positional isomers where the OH functional group is 1 4 either on the first or the second carbon in the chain. H3C CH3 2 3 attached. C C has a mirror plane symmetry. Functional group isomers have the same molecular   H H formula but different functional groups, so they belong But exchanging the positions of the methyl group and the to different organic families. For example, propanal is an hydrogen attached to carbon atom 3 results in another aldehyde with the molecular formula C3H6O. Propanone structure which has a centre of two-fold rotational symmetry. has the same molecular formula but it is a ketone. Stereoisomerism is caused by a double or triple bond. Isomers Optical isomers are also a form of stereoisomerism. These two forms of but-2-ene are called isomers. Isomers Stereoisomers are compounds that have the same are two or more compounds that have the same general structural formula but the arrangement of their atoms in formula but a different arrangement of atoms in the space is different. Atoms can rotate around a single bond. compound and so have different properties. However, this rotation is restricted around a double or Substances with the same molecular formula but different triple bond. For example, ethene C2H4 has a double C C structural formulae are called structural isomers. There are bond. If a methyl group is added to each carbon, replacing three types of structural isomer; chain isomers, positional a hydrogen atom, stereoisomers form. These are called cis isomers and functional group isomers. and trans-isomers. Figure 5.5 shows these stereoisomers. 12 Principles and Applications of Science II M05 BTEC National Applied Science Student B2 XXXXX.indd Page 12 08/05/17 9:17 PM f-0314 /122/PE02858/BTEC_Applied_Science/NA/SE/Applied_Science/G1/XXXXXXXXXX/Layout/Inte...  Learning aim A UNIT 5 H3C CH3 H3C H In alkanes such as methane, the carbon 2s and 2p atomic Principles and Applications of Science II orbitals make four hybrid orbitals called sp3 orbitals. (This C C C C notation is a result of hybridisation of the one s and three H H H CH3 p orbitals in the second energy level.) One sp3 orbital from cis–but–2–ene trans–but–2–ene each carbon overlap to produce a C C bond. The others (Z)–but–2–ene (E)–but–2–ene overlap with 1s orbitals in each of the hydrogen atoms, ▸▸ Figure 5.5 (Z)-but-2-ene and (E)-but-2-ene forming C H σ-bonds. The bonding in the double bond in alkenes is slightly E/Z and cis/trans are two different methods of classifying different. A σ-bond forms between the two carbon geometric isomers. If something is the cis-isomer, then atoms in the same way as in a single bond. A pi-bond its name is cis-but-2-ene; if it is the E isomer, then its (π-bond) is formed by the electrons in adjacent p-orbitals name is (E)-but-2-ene. E/Z isomerism is different as it overlapping above and below the carbon atoms. The applies a priority to each group attached to the double- π-bond can only form if a σ-bond has already formed. The bonded carbon and compares the position of those with π-bond restricts movement around the double bond. This highest priority. Alkenes showing cis/trans isomerism will means the region around the double bond in a molecule is also show E/Z isomerism, but the opposite is not true. flat. Double bonds are ‘planar’. The π-bond is the reactive For example, 1-bromo-1-chloropropene will have E/Z part of the molecule because there is a high electron isomerism but not cis/trans isomerism. density around it. Figure 5.6 shows the bonding in ethene. T Sigma and pi bonds Carbon has four electrons in its outer shell. These form Bond length and bond shape four covalent bonds by pairing with electrons on other Bond length and bond shape in molecules can be AF atoms. The electron clouds from each electron in a bond overlap. This is called a sigma bond (σ-bond). C C bonds and C H bonds are examples of σ-bonds. The overlap of explained by the hybridisation of orbitals (see Table 5.4). A bond is formed by the overlap of atomic orbitals. Hybridisation is when atomic orbitals fuse to form two s orbitals or two p orbitals forms σ-bonds. newly hybridised orbitals. Pi bond made from overlap of lobes of p orbital R H H H Sigma bonds C C D H H H H H C C H H Planar structure ▸▸ Figure 5.6 Bonding in ethene ▸▸ Table 5.4 Hybridised orbitals Hybrid type Bond angle Arrangement Example C C bond strength C C bond (kJ mol−1) length (nm) sp3 109.5o tetrahedral ethane 347 0.147 sp2 120o Trigonal planar ethene 612 0.135 13 M05 BTEC National Applied Science Student B2 XXXXX.indd Page 13 08/05/17 9:17 PM f-0314 /122/PE02858/BTEC_Applied_Science/NA/SE/Applied_Science/G1/XXXXXXXXXX/Layout/Inte...  For example, methane contains four C H bonds. Carbon The bonds between the carbons in the benzene ring have has the electronic configuration 1s2 2s2 2p2, so only the two a length of 0.140 nm which is between that of a C C bond p electrons are unshared. This would mean only two bonds and a C C bond. The bond strength is about 518 kJ mol−1, are possible. However, we know four bonds are formed. which is between the bond strengths of the C C bond The one s and three p orbitals combine to form hybrid and the C C bond. orbitals which have 25% s character and 75% p character. In order to show the delocalised electrons in benzene These are sp3 hybridised orbitals. This makes all four bonds when representing it in an equation, you draw a hexane in methane equivalent to each other, giving equal bond ring with a circle inside to represent the delocalised angles of 109o and methane a tetrahedral shape. electrons, as shown in Figure 5.7. In ethene, a π-bond is required for the double bond. This uses sp2 hybridised orbitals. The 2s orbitals mix with two of the three available 2p orbitals forming three sp2 orbitals with a remaining p orbital. The type of bond affects the length and strength of the bond. This is shown in Table 5.5. ▸▸ Table 5.5 Bond strength and length T Bond Number of Bond Bond length electrons strength ▸▸ Figure 5.7 The skeletal structure of benzene Single 2 Weakest Longest Double 4 AF Boiling points As the chain length of the alkanes increases, so does the Triple 6 Strongest Shortest boiling point. The relative molecular mass also increases as the chain length increases. The larger the molecule, the As the number of electrons shared between two atoms more surface area is available for contact with adjacent increases, the bond strength increases. The distance molecules. This means the number of induced dipole- between the nuclei decreases and so you get a stronger, dipole forces increases (van der Waals forces; see Unit 1). R shorter bond. So the double C C bond in ethene So the longer the chain, the stronger the intermolecular is stronger and shorter than the single C C bond attraction and so more energy is needed to overcome this in ethane. for the molecule to change state. The bond strengths and lengths in the benzene ring of an Structural isomers of alkanes will have different boiling D aromatic hydrocarbon are different than those in a straight points. This is because they are branched chains and chain alkene. so have a smaller surface area than their straight chain equivalents. Therefore there is less surface area for The formula for benzene is C6H6. All the bond lengths contact, and so fewer induced dipole-dipole attractions. between each carbon are identical. This is because it has So branched-chain isomers will have a lower boiling point a delocalised electron structure. Each carbon atom in than the straight-chained isomer. benzene donates on electron from its p-orbital, forming a ring of delocalised electrons above and below the plane Pentane has a boiling point of 31.6°C. 2,2-dimethylpropane of the molecule. The electrons move freely within the ring only has a boiling point of 9.5°C. They are structural and do not belong to any one carbon. isomers of each other. PAUSE POINT Produce a table showing the name formula and structural formula of the organic compounds discussed in this unit. Hint You have studied alkanes, alkenes and haloalkanes as well as aromatic compounds. Extend Choose two different organic molecular formulas and draw out all the isomers for each. 14 Principles and Applications of Science II M05 BTEC National Applied Science Student B2 XXXXX.indd Page 14 08/05/17 9:17 PM f-0314 /122/PE02858/BTEC_Applied_Science/NA/SE/Applied_Science/G1/XXXXXXXXXX/Layout/Inte...  Learning aim A UNIT 5 Reactions of organic compounds The free radical substitution mechanism has three stages: Principles and Applications of Science II 1 Initiation – formation of radicals. Alkanes are not very reactive. This is because a large amount of energy is needed to break the covalent bonds 2 Propagation – steps that build up the desired product in the molecules. (The bonds have high bond enthalpy— in a side reaction. see next page). The electronegativities of carbon and 3 Termination – two free radicals collide. hydrogen are very similar and so the C H bond is not These reactions are unpredictable and difficult to control. very polar. A mixture of products is formed and these will need to be Alkanes are often used as fuels as complete combustion separated by fractional distillation or chromatography. The releases large amounts of energy. When there is plenty of reaction is shown in Table 5.6. air, or excess oxygen, all alkanes will completely combust ▸▸ Table 5.6 Free radical substitution to form carbon dioxide and water. The word equation for the combustion of alkanes is: Step Equation Description Initiation Cl2 S 2Cl UV light or 300°C alkane + oxygen S carbon dioxide + water Propagation CH4 + Cl S Step 1 generates an alkyl radical Methane is the fuel used in a Bunsen burner. The equation CH3 + HCl and hydrogen chloride. for the combustion of methane is: CH3 + Cl2 S Step 2 generates the desired CH4 + 2O2 S CO2 + 2H2O CH3Cl + Cl product and regenerates the T chlorine radical. If oxygen supply is limited, for example, when the hole in Termination 2Cl S Cl2 A mixture of products is the Bunsen burner is closed, incomplete combustion will produced by the random 2 CH3 S C2H6 occur. collisions between free radicals. 2CH4 + 3O2 S 2CO + 4H2O AF CH3 + Cl S CH3Cl The desired CH3Cl needs to be separated from the rest of the products. Termination is Many organic reactions take several steps to gain the final product. These steps are called the reaction mechanism. the result of any two radicals colliding. Key term As there are chlorine radicals present in the mixture, the Reaction mechanism – the step by step sequence chloromethane produced could react with these to form R of reactions that lead to an overall chemical change other chloroalkanes with chlorine attached to more than occurring. It shows the movement of electrons in the one carbon. process. Assessment practice 5.3 D Free radical substitution Alkanes react with halogens to form haloalkanes. For Write out the three steps for the free radical example, chlorine will react with methane to form substitution of ethane, C2H6, by bromine, Br. chloromethane. The reaction needs ultraviolet light or temperatures of about 300°C. Halogenation happens by homolytic fission of the halogen molecule forming free Electrophilic addition in alkenes radicals. A hydrogen atom in the alkane is substituted with Alkenes are more reactive than alkanes. This is due to the a halogen atom. If the reaction conditions remain then all C C double bond. the hydrogens can be substituted with a halogen. The mean bond enthalpy for C C is +347 kJ mol−1. Key terms So you might expect the mean bond enthalpy for C C to be double that, +694 kJ mol−1. In fact, it is only Halogenation – addition of halogen such as bromine +612 kJ mol−1. This means that the π-bond only uses or chlorine to an alkane. 265 kJ mol−1 of energy to break the bond. The π-bond is Homolytic fission – formation of a free radical by weaker than the σ-bond and so breaks more easily and splitting a bond evenly so each free radical has one of reacts first. the two available electrons. The double bond is an area of high electron density so Free radical – atom with a single unpaired electron. electrophiles such as Br2 and HBr are attracted to it.