CARBON COMPOUNDS Let’s study L 5 CHAPTER t*OUSPEVDUJPOUPDBSCPODPNQPVOET t)ZESPDBSCPOT tAlcohol t'BUT t1BMNPJM Name two natural carbon compounds that are Malaysia’s exports which contribute significantly to the economy. What makes oil palm special compared to other products, such as soya bean, as a source of cooking oil? 140
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Carbon dioxide in the atmosphere Are eaten by Form Photosynthesis Burning of fuels Fossil fuels (petroleum, natural gas, coal) Respiration Respiration Decay Dead Organisms Green plants Carbon Compounds in Nature Carbon compounds are compounds which contain the element carbon, C. Carbon compounds can be divided into two groups, namely organic carbon compounds and inorganic carbon compounds (Figure 5.1). 5.1 Introduction to Carbon Compounds Figure 5.1 Organic carbon compounds and inorganic carbon compounds Living things Non-living things Inorganic carbon compounds Organic carbon compounds originate from originate from Carbon compounds Petroleum, silk, charcoal Limestone, carbon dioxide Carbon Cycle The carbon cycle shows how carbon elements are recycled through the formation or decomposition of carbon compounds in living things and organic substances in the environment through processes such as respiration, combustion, decomposition and photosynthesis (Figure 5.2). Figure 5.2 Carbon cycle Carbon dioxide in the atmosphere Are eaten by Form Photosynthesis Burning of fuels Fossil fuels (petroleum, natural gas, coal) Respiration Respiration Decay Dead Organisms Green plants BRAIN TEASER If compound X contains the carbon element, is compound X an organic carbon compound or an inorganic carbon compound? 142 5.1.1 5.1.2
Carbon dioxide Oxygen Light energy Photosynthesis Photosy Photosyn hotosynthesis ynthesis (happens i appens i n chlorophyll) chlorophyll) Glucose Water Figure 5.3 Photosynthesis Photograph 5.1 Smoke from petrol combustion Photograph 5.2 Smoke from forest fire Carbon dioxide is released into the atmosphere through three main processes: (a) Respiration Carbon dioxide is a carbon compound which is released into the atmosphere through the respiration of all living things including animals, plants and microorganisms. (b) Combustion Burning of fossil fuels releases carbon dioxide into the atmosphere. Natural phenomena such as volcanic eruptions and forest fires also release carbon dioxide into the atmosphere. (c) Decomposition During the process of decomposition by decomposers such as bacteria and fungi, carbon dioxide is released into the atmosphere. Carbon dioxide is absorbed by green plants from the atmosphere to carry out photosynthesis (Figure 5.3). The importance of photosynthesis includes: • enabling green plants to make their own food • providing food to animals • increasing the oxygen content in the air • removing excess carbon dioxide from the air to maintain the carbon dioxide content in the air 143 Chapter 5 Carbon Compounds 5.1.2
Activity 5.1 21 Century Skills st • ICS • Project-based activity 1. What is organic carbon compound? 2. What is inorganic carbon compound? 3. Give two examples of inorganic carbon compounds. 4. What is carbon cycle? 5. State the importance of carbon cycle. To illustrate the carbon cycle in the form of a diagram Instructions 1. Complete the carbon cycle diagram in Figure 5.4. Figure 5.4 2. Present and display your illustration of the carbon cycle to the class. 3. Justify the enhancements or changes made to your group’s illustration of the carbon cycle. Plant Animal Rubbish SOYA SOYA OS YA KICAP Factory Algae and aquatic animals Formative Practice 5.1 144 5.1.2
Remains of dead marine life buried in the seabed. Over millions of years, these remains are buried deeper and deeper into the seabed under thick layers of rock and mud. The combined effects of pressure exerted by the layers of sand and mud, heat absorbed from the surroundings, and decomposition caused by bacteria changes the buried remains into petroleum and natural gas. Natural gas Petroleum Mud and stone Sea Sea Seabed Figure 5.5 Formation of petroleum and natural gas Figure 5.6 Formation of coal Millions of years ago, the remains of dead plants were naturally buried underground. Over millions of years, the remains become buried deeper and deeper into the ground under thick layers of rocks. The combined effects of pressure exerted by the layers of rock, heat absorbed from the surroundings, and decomposition caused by bacteria changes the buried plant fossils into coal. Coal Sea Seabed Fossils of animals and plants Hydrocarbon compounds are organic carbon compounds made up of only carbon and hydrogen elements. Hydrocarbon Compounds from Natural Sources The formation of hydrocarbon compounds from natural resources are shown in Figures 5.5 and 5.6. 5.2 Hydrocarbons 145 Chapter 5 Carbon Compounds 5.2.1
Activity 5.2 Fractional Distillation of Petroleum Petroleum is a mixture of hydrocarbons. This mixture of hydrocarbons needs to be separated through the fractional distillation process before the petroleum fractions can be used. Fractional distillation is used because the petroleum fractions have different boiling points. Fractional distillation in a distillation tower at an oil refinery and uses of different petroleum fractions. http://buku-teks.com/sc5146 To separate crude oil into four different petroleum fractions using fractional distillation Materials Crude oil, wooden splinter, ice, water and glass wool Apparatus Measuring cylinder, boiling tube, retort stand, test tubes, test tube rack, beaker, rubber stopper with delivery tube, thermometer (0oC – 360oC), Bunsen burner and evaporating dishes Instructions 1. Fill a boiling tube with 10 cm3 of crude oil. 2. Prepare the apparatus set-up (Figure 5.7). Figure 5.7 Fractional distillation of petroleum Science 21 Century Skills st • TPS • ISS Thermometer (0°C – 360°C) Retort stand Boiling tube Crude oil Glass wool Heat Delivery tube Test tube Ice Distillate • Wash your hands with soap and water if you get crude oil on your hands. • Heating crude oil releases petroleum vapour which is highly flammable. Safety Precautions CAUTION! • Use crude oil only. • Do not substitute crude oil with any other fuel. 146 5.2.1
3. Heat the crude oil in the boiling tube gently from room temperature to 80ºC. 4. Stop heating the crude oil when its temperature reaches 80ºC. Continue the heating process when its temperature drops below 80ºC. 5. When there is about 1 cm3 of distillate collected in the test tube, replace the test tube with another empty test tube. 6. Label the distillate collected from room temperature to 80ºC as Fraction 1. 7. Repeat step 3 to collect three more fractions of petroleum at the following ranges of temperatures: (a) 80ºC – 150ºC with the collected distillate labelled as Fraction 2 (b) 150ºC – 230ºC with the collected distillate labelled as Fraction 3 (c) 230ºC – 250ºC with the collected distillate labelled as Fraction 4 8. Observe and record the colour of each of the fractions labelled 1, 2, 3 and 4. 9. Pour each petroleum fraction into separate evaporating dishes. 10. Observe and compare the rate of flow or viscosity of each petroleum fraction. 11. Record the viscosity of each petroleum fraction obtained. 12. Ignite each petroleum fraction with a burning splinter. Compare and record how flammable each fraction is. Observation Fraction 1 2 3 4 Range of boiling points 30oC – 80oC 80oC – 150oC 150oC – 230oC 230oC – 250oC Colour Viscosity Flammability Questions 1. Name the method of separation used in this activity. 2. Is petroleum a compound or a mixture? Give your reasons. 3. Based on the information from Science Info on page 146, name the distillate obtained from the fractions labelled as follows: (a) Fraction 1: (b) Fraction 2: (c) Fraction 3: (d) Fraction 4: 4. What characteristic of the petroleum fractions is applied in the fractional distillation of petroleum? 147 Chapter 5 Carbon Compounds 5.2.1
Figure 5.8 Hydrocarbon compounds Homologous Series In organic chemistry, a homologous series is made up of a specific group of organic compounds which have similar chemical properties. Examples of homologous series are the alkane and the alkene. Alkane Alkanes are saturated hydrocarbon compounds. Each carbon atom in an alkane molecule forms single covalent bonds with other carbon atoms (Figure 5.9). As alkane is a homologous series, each member of the alkane homologous series can be represented by the general formula Cn H2n+2 where n = 1, 2, 3, … Alkene Alkenes are unsaturated hydrocarbon compounds. Each alkene molecule has at least one double covalent bond between two carbon atoms (Figure 5.10). As alkene is a homologous series, each member of the alkene homologous series can be represented by the general formula Cn H2n where n = 2, 3, … Saturated and Unsaturated Hydrocarbons Figure 5.8 shows two types of hydrocarbon compounds, namely saturated hydrocarbons and unsaturated hydrocarbons. Hydrocarbon compounds Saturated hydrocarbons Unsaturated hydrocarbons Have single covalent bonds between carbon atoms (C–C) Have at least one double covalent bond (C C) or triple covalent bond (C C) between carbon atoms H HHH H H H CCC H H HHH H CCC H Example: Alkane Example: Alkene Figure 5.9 Alkane H HHH H H H CCC H Single covalent bond Figure 5.10 Alkene Double covalent bond H H H H H CCC H 148 5.2.2
Activity 5.3 21 Century Skills st • ICS, ISS • Project-based activity The names of the first six members of alkane and first five members of alkene are given in Table 5.1. Table 5.1 Names of alkanes and alkenes Number of carbons, n Alkane Alkene 1 Methane – 2 Ethane Ethene 3 Propane Propene 4 Butane Butene 5 Pentane Pentene 6 Hexane Hexene To build and name molecular models of alkane and alkene Materials Environmental-friendly materials for building model such as waste paper and wooden splinters Instructions 1. Carry out this activity in groups. 2. Build and name models of the following alkane and alkene molecules using used materials: (a) first 6 members of the alkane homologous series (b) first 5 members of the alkene homologous series 3. Present your built models to the class. Alternative Energy and Renewable Energy Sources in Daily Life Fossil fuels such as petroleum, coal and natural gas are non-renewable energy sources which are fast depleting. As such, alternative energy sources are becoming increasingly important in supplying the energy for daily life. Alternative energy sources are sources of energy that will not deplete easily such as nuclear energy or other renewable energy sources. Examples of renewable energy sources are as follows: • solar energy • wind energy • hydroelectric energy • biomass energy • geothermal energy • tidal energy • wave energy Many countries, including Malaysia, have the potential to build nuclear power stations to obtain energy. The advantages and disadvantages of building nuclear power stations should be taken into consideration before any decision is made. 149 Chapter 5 Carbon Compounds 5.2.2 5.2.3
Activity 5.4 To produce methane gas from school canteen food waste Instructions 1. Carry out this activity in groups. 2. Gather information related to alternative energy and renewable energy sources in daily life. 3. Read and understand the following information: Rubbish disposal sites release carbon dioxide and methane gases as a result of organic waste decay. There are some countries which use methane gas to generate electrical energy. 4. Gather and analyse ways to produce methane gas from food waste from the Internet. 5. Plan and carry out a project using the STEM approach to produce methane gas from the decay of food waste in your school canteen. 6. Present your group project to the class. 1. What is hydrocarbon? 2. State one similarity and one difference between saturated and unsaturated hydrocarbons. 3. Name one gas which is produced from food waste decay to generate electrical energy. Alcohol is an organic carbon compound which contains carbon, hydrogen and oxygen elements. Alcohol is prepared through the fermentation process by using the action of yeast on food containing glucose or starch such as sugar, grapes, apples, sugarcane, rice, wheat, potato and barley. 5.3 Alcohol 21 Century Skills st • ICS, ISS, TPS, STEM • STEM project-based activity CAUTION! Methane gas is highly flammable. Formative Practice 5.2 Be careful when collecting the methane gas. Safety Precautions 150 5.2.3 5.3.1
Activity 5.5 21 Century Skills st • TPS • Inquiry-based activity Alcohol Preparation Process In the fermentation process, the zymase in yeast converts glucose into ethanol and carbon dioxide as in the following equation: Zymase (enzyme in yeast) Glucose Ethanol + Carbon dioxide To prepare ethanol through fermentation Materials Distilled water, yeast, sugar, starchy substances such as bread and rice, fruits such as banana and apple, porcelain chips and limewater Apparatus Beaker, glass rod, conical flask, measuring cylinder, delivery tube with stopper, test tube, distillation flask, Liebig condenser, thermometer, Bunsen burner, tripod stand and wire gauze Instructions 1. Carry out this activity in groups. 2. Your teacher will instruct each group to prepare either apparatus set-up A, B or C as follows: Apparatus set-up A Procedure Conical flask Sugar solution + yeast Test tube Limewater Figure 5.11 (a) Put 100 g of sugar and 50 cm3 of distilled water into a beaker. Stir the mixture with a glass rod until it forms a sugar solution. (b) Add 10 g of yeast into the sugar solution and pour the mixture into a conical flask. (c) Prepare the apparatus set-up (Figure 5.11). Apparatus set-up B Procedure Conical flask Mixture of bread, yeast and distilled water Test tube Limewater Figure 5.12 (a) Place 100 g of starchy substance like bread and 50 cm3 of distilled water in a beaker. Stir the mixture with a glass rod. (b) Add 10 g of yeast into the mixture and pour the mixture into a conical flask. (c) Prepare the apparatus set-up (Figure 5.12). 151 Chapter 5 Carbon Compounds 5.3.1
Apparatus set-up C Procedure Conical flask Test tube Limewater Mixture of banana, yeast and distilled water Figure 5.13 (a) Place 100 g of fruits such as mashed bananas and 50 cm3 of distilled water in a beaker. Stir the mixture with a glass rod. (b) Add 10 g of yeast into the mixture and pour the mixture into a conical flask. (c) Prepare the apparatus set-up (Figure 5.13). 3. Keep apparatus set-ups A, B and C in the laboratory for a week. Observe and record changes in the conical flask mixture and the limewater in the test tube. 4. After one week, filter the mixture into a conical flask and pour the filtrate into a distillation flask. 5. Distill the contents in the distillation flask using the apparatus set-up shown in Figure 5.14. 6. Collect the distillate at a temperature of 78ºC. 7. Observe and record the colour and smell of the collected distillate in the table. Observation Substance Observation Beginning of activity End of activity Mixture in apparatus set-up A, B or C Limewater Distillate – Colour: Smell: Questions 1. What product turns the limewater cloudy? 2. What is the purpose of the distillation process in this activity? 3. What is the principle used to separate ethanol from the products of fermentation through distillation? xxxxxxxxxxxxxxxxxxxxx Thermometer Water outlet Water bath Water inlet Filtrate Porcelain chips Distillate Liebig condenser Heat Figure 5.14 152 5.3.1
Activity 5.6 To study the physical and chemical properties of ethanol Materials Ethanol, ethanoic acid, concentrated sulphuric acid, limewater, dry cobalt chloride paper, matches and water Apparatus Boiling tube, measuring cylinder, delivery tube, dropper, evaporating dish, test tube holder, filter funnel, beaker, test tube, retort stand, connecting tube and Bunsen burner Instructions A. Physical properties of ethanol Observe and record the following physical properties of ethanol: • colour • state of matter at room temperature • smell • solubility in water B. Combustion 1. Measure 2 cm3 of ethanol using a measuring cylinder and pour into an evaporating dish. 2. Ignite the ethanol in the evaporating dish (Figure 5.15). 3. Observe and record the colour of the flame. 4. Test the gas released with limewater. 5. Test the droplets of liquid formed on the filter funnel with dry cobalt chloride paper. C. Esterification 1. Measure 2 cm3 of ethanol and 2 cm3 of ethanoic acid using a measuring cylinder and pour both liquids into a boiling tube (Figure 5.16(a)). Shake the boiling tube. Delivery tube Test tube Ethanol Limewater Evaporating dish Filter funnel Connecting tube Figure 5.15 The Physical and Chemical Properties of Alcohol The physical properties of alcohol are as follows: • colourless • liquid at room temperature • has a distinctive smell • the boiling point increases when its number of carbon atoms increases • the solubility in water decreases when its number of carbon atoms increases Apart from these physical properties, carry out Activity 5.6 to study the physical and chemical properties of alcohol. Photograph 5.3 Use of alcohol as an antiseptic which is applied before an injection 21 Century Skills st • CPS, ISS • Inquiry-based activity 153 Chapter 5 Carbon Compounds 5.3.2
Ethanoic acid Ethanol Dropper Concentrated sulphuric acid Test tube holder Heat Water (a) (b) (c) (d) Figure 5.16 6. Add five drops of concentrated sulphuric acid into the boiling tube mixture (Figure 5.16(b)) in a fume chamber. Shake the boiling tube. 7. Heat the mixture for several minutes (Figure 5.16(c)). 8. Pour the mixture into a beaker filled with water (Figure 5.16(d)). Observe and record the characteristics of the product. Observation A. Physical properties of ethanol Physical property of ethanol Observation Colour State of matter at room temperature Smell Solubility in water B. Combustion Characteristic Observation Colour of flame Change(s) to limewater Change(s) to dry cobalt chloride paper C. Esterification Characteristic Observation Smell of product Solubility of product in water Questions 1. What is produced from the combustion of alcohol? 2. (a) What is produced from the reaction between ethanol and ethanoic acid? (b) What are the physical properties of the product of the reaction between ethanol and ethanoic acid? 3. What is the function of sulphuric acid in the process of esterification? CAUTION! Concentrated sulphuric acid is very corrosive. Its use is limited within the fume chamber. 154 5.3.2
Photograph 5.4 Uses of industrial substances which contain alcohol and ester in daily life Uses of Alcohol in Daily Life Alcohol is widely used in various fields in daily life as follows: Fuel Alcohol is a good fuel because this organic carbon compound is highly flammable, burns with a blue flame and produces a complete and clean combustion without soot. For example, alcohol is used as a biofuel for motorised vehicles in the Philippines. Medicine Alcohol is used as an antiseptic and disinfectant to kill microorganisms and it is also used as a solvent for various types of medicine. Cosmetics Alcohol is also used as a solvent for various cosmetics such as perfume, lotion and lipstick. Industry Alcohol is normally used as a solvent in industry because it can dissolve organic substances that are used to prepare various types of industrial substances such as liquid cleaners and food. Alcohol is also a reactant in the formation of ester which is used in food processing, cosmetics, paint and other industries. Ethanediol, on the other hand, is a type of alcohol used as an antifreeze in industries. 155 Chapter 5 Carbon Compounds 5.3.3
Effects of Excessive Alcohol Consumption Alcohol consumption, especially in excess, causes addiction. Alcohol addiction normally causes social problems in families and social crimes that disrupt societal peace. A person who is drunk as a result of excessive alcohol consumption normally causes various problems such as dangerous driving and altercations. Expectant mothers who consume excessive alcohol can cause defects in their baby known as foetal alcohol syndrome. Babies with foetal alcohol syndrome have small-sized head and brain, abnormal face and stunted growth. Table 5.2 Adverse effects of excessive alcohol consumption on health Part of the body Adverse effects of excessive alcohol consumption Brain Damage to brain cells as well as compromised coordination and nervous system cause disruptions to body balance and difficulty in estimating distance Eyes Blurred vision Lungs Increased rate of breathing Heart • Increased rate of heartbeat • High blood pressure Stomach Irritation to stomach wall causes bleeding and ulcers Liver • Damage to liver cells • Liver cells die and harden • Cirrhosis • Liver cancer Kidney Kidney damage due to overactive elimination of waste substances Urinary bladder Frequent urination Click@Web Scientific studies on effects of alcohol consumption http://buku-teks.com/sc5156 156 5.3.4
Milk Meat Butter Coconut oil Groundnut Activity 5.7 5.4 Fats Fat is a type of organic carbon compound which contains carbon, hydrogen and oxygen elements. What is the importance of fats as a class of food for humans? Photograph 5.5 shows various sources of fats in the human diet. Photograph 5.5 Sources of fats To produce posters or pamphlets or a scrap book on the effects of excessive alcohol consumption on health Instructions 1. Carry out this activity in groups. 2. Gather information from various sources about the effects of excessive alcohol consumption on health. 3. Discuss the information gathered. 4. Prepare posters or pamphlets or a scrap book based on the outcome of your group discussion. 5. Present and display the posters or pamphlets or a scrap book on the science notice board in your class or science laboratory. 1. What is alcohol? 2. How is alcohol prepared? 3. What is the purpose of distillation in the process of alcohol preparation through glucose fermentation? 4. State two uses of alcohol in daily life. 5. Why is drunk driving caused by the excessive intake of alcohol a serious traffic offence? 21 Century Skills st • ICS • Project-based activity Formative Practice 5.3 157 Chapter 5 Carbon Compounds 5.3.4 5.4.1
Figure 5.17 Similarities and differences between saturated fats and unsaturated fats Effects of Eating Food Containing Excessive Fats on Health Fats represent an important component of a balanced diet in human nutrition. Eating of food containing excess fats especially saturated fats will increase the level of cholesterol in the blood and affect our health. Saturated fats from animal sources such as cheese, eggs, butter and meat contain high levels of cholesterol. The importance of cholesterol in the human body includes building of cell membranes, synthesising bile and sex hormones, and producing vitamin D in skin that is exposed to sunlight. Fats exist in two states, solid and liquid. Solid fats at room temperature usually originate from sources of animal fats. For example, chicken, cow, goat and fish. Fat in the form of liquid is known as oil. Oil normally originates from plants. For example, palm oil, coconut oil and soya bean oil. As in hydrocarbons, fats can be divided into saturated fats and unsaturated fats. The similarities and differences between saturated fats and unsaturated fats are shown in Figure 5.17. Similarities Differences Saturated fats Unsaturated fats Source State at room temperature Melting point Number of hydrogen atoms in the molecule Addition of hydrogen atoms to molecule Plants Liquid Low Not maximum Possible Animals Solid High Maximum Not possible t Organic compounds containing carbon, hydrogen and oxygen t Do not dissolve in water t Important source of fatty acids in the body 158 5.4.2 5.4.3
Activity 5.8 However, excessive cholesterol in the blood can affect human health as follows: (a) Gallstones and jaundice Excessive cholesterol in the blood can form gallstones which block the bile duct. Blocked bile duct can cause jaundice. (b) Cholesterol deposited in the inner wall of arteries and atherosclerosis Cholesterol that accumulates and deposits on the inner artery walls causes the artery lumen to become narrow. This narrowed artery can disrupt or block flow of blood in a condition known as atherosclerosis (Figure 5.18). Normal Lumen lumen Cholesterol build-up Figure 5.18 Cross section of healthy artery and effect of atherosclerosis on artery Atherosclerosis can cause hypertension or high blood pressure, stroke (burst or blocked artery leading to the brain) and fatal heart attack. Steps to avoid health problems caused by excessive cholesterol in blood include: • reducing the intake of saturated fats in nutrition • consuming unsaturated fats which can lower the cholesterol level in blood Click@Web Information on cholesterol http://buku-teks.com/sc5159 To gather information on fats Instructions 1. Carry out this activity in groups. 2. Gather information from the Internet, print media and other electronic media on the following: (a) fat content of various sources in daily life (b) saturated and unsaturated fats (c) effects of excessive fat intake on health 3. Discuss the information gathered. 4. Present the outcome of your group discussion to the class using a multimedia presentation. 21 Century Skills st • ICS • Discussion 159 Chapter 5 Carbon Compounds 5.4.3
Activity 5.9 To observe the structure of the oil palm fruit and identify the quantity aspect of oil from pulp and kernel Materials 10 oil palm fruits Apparatus Forceps, knife, magnifying glass, press, Bunsen burner, tripod stand, wire gauze and white tile Instructions 1. Place an oil palm fruit on a white tile. Hold the oil palm fruit using forceps and make a cross-sectional cut on the oil palm fruit using a knife (Figure 5.19). 5.5 Palm Oil Structure of Oil Palm Fruit Observe the structure of the oil palm fruit in Photograph 5.6. The oil palm fruit is made up of three parts, namely: • pulp (mesocarp) which contains the most palm oil • kernel which contains the best quality palm kernel oil • shell (endocarp) which does not contain oil Photograph 5.6 Structure of oil palm fruit Pulp Shell Kernel 1. What are fats? 2. Give one example of fats and the source. 3. State one similarity and one difference between saturated fats and unsaturated fats. 4. State three health problems caused by food intake which contains excess fats. Formative Practice 5.4 21 Century Skills st • TPS • Inquiry-based activity 160 5.4.3 5.5.1 5.5.2
2. Observe and sketch the structure of the oil palm fruit and label the parts in the structure of the oil palm fruit. 3. Wash all the oil palm fruits with water. 4. Put the oil palm fruits into a beaker filled with water and boil the water and the oil palm fruits for 20 minutes (Figure 5.20). 5. Remove the oil palm fruits from the beaker using forceps. 6. Separate the pulp from the shell of the oil palm fruit (Figure 5.21). 7. Put the pulp into a press to be squeezed. Collect the palm oil extracted from the pulp in a beaker (Figure 5.22). 8. Cut open the shell and remove the kernel. 9. Repeat step 7 by replacing the pulp with the kernel. 10. Compare and contrast the quantity of oil extracted from the pulp and kernel. Record the quantity of oil collected in the beaker. Observation Sketch and label a cross section of the oil palm fruit. Oil extracted from Quantity of oil collected Pulp Kernel Questions 1. What is the aim of boiling the oil palm fruits? 2. What is the difference in the quantity of oil extracted from the pulp and the kernel? 3. State the difference in colour of the oil extracted from the pulp with the oil extracted from the kernel. Figure 5.19 Figure 5.22 Figure 5.20 Figure 5.21 xxxxxxxxxxxxxxxxxxxxx Boiling water Oil palm fruit Pulp Shell Heat Press Palm oil Knife Oil palm fruit 161 Chapter 5 Carbon Compounds 5.5.1 5.5.2
Figure 5.23 Sequence of the industrial extraction process of palm oil Sequence in the Industrial Extraction Process of Palm Oil The sequence in the industrial extraction process of palm oil is shown in Figure 5.23. Bunch of oil palm fruits Pure PO Pure PKO Sterilisation Threshing Digestion The oil palm fruits are detached from their bunches in a threshing machine. The whole bunch of oil palm fruits is sterilised with steam at a high pressure and temperature. The heat from the steam kills microorganisms such as bacteria and fungi which can spoil the oil palm fruits. Steam also softens the pulp of the oil palm fruits and makes it easier to remove the fruits from the bunches. The oil palm fruits are reheated at a high temperature and pounded by rotating beater arms to separate the pulp from the shell. The pulp and shell which contain the kernel are then processed separately. Pulp (Extraction of palm oil (PO)) The pulp is squeezed with a hydraulic or spindle press to extract PO. Kernel (Extraction of palm kernel oil (PKO)) The shell which contains the kernel is steamed at a high pressure. Then, the kernel is separated. The kernel is dried and PKO is extracted from it with a hydraulic or spindle press. Filtration The pulp fibres are separated from the PO through filtration. Filtration The kernel is separated from the PKO through filtration. Purification t Steam is flowed through the PO to remove odour and eliminate acid which causes the PO to become sour. t PO flows through activated carbon to be decolourised. PO – Palm oil PKO – Palm kernel oil 162 5.5.3
Activity 5.10 Activity 5.11 Components of Palm Oil Palm oil is made up of two parts, namely glycerol and various types of fatty acids (Figure 5.24). Palm oil Glycerol Fatty acids Figure 5.24 Components of palm oil Palm oil is made up of saturated fatty acids such as palmitic acid and stearic acid, as well as unsaturated fatty acids such as oleic acid and linoleic acid. Composition of Palm Oil and Other Vegetable Oils The composition of palm oil and other vegetable oils is shown in Table 5.3. To prepare a review about a visit to a palm oil processing factory or to the Malaysian Palm Oil Board (MPOB) Instructions 1. Pay a visit to a palm oil processing factory or to the Malaysian Palm Oil Board (MPOB). 2. Gather and record information on the sequence of the industrial extraction process of palm oil in your notebook. 3. Based on the information gathered, review the industrial extraction process of palm oil. To study the differences in composition such as glycerol and fatty acid in palm oil and other vegetable oils Instructions 1. Carry out this activity in groups. 2. Conduct online searches through the Internet to gather information on the differences in composition such as the glycerol and fatty acid content in palm oil and other vegetable oils. 3. Discuss the information gathered. 4. Present your findings using a graphic organiser. 21 Century Skills st • TPS, ISS, ICS • Inquiry-based activity 21 Century Skills st ICS 163 Chapter 5 Carbon Compounds 5.5.3 5.5.4 5.5.5
Table 5.3 Comparing and contrasting the composition of palm oil with other vegetable oils Weight percentage of fatty acids (%) Oil or fat Ratio of unsaturated fats/ saturated fats Capric acid Lauric acid Myristic acid Stearic acid Oleic acid Linoleic acid Alpha linoleic acid Palmitic acid Mono unsaturated Poly unsaturated Saturated Coconut oil Corn oil Olive oil Palm oil Peanut oil Sesame oil 0.1 6 47 18 6.7 - 4.6 1.0 - - - - Palm kernel oil Soya bean oil 0.2 4 1 48 16 4.0 - 6.6 - - 1 1 7 - - - - - 5.7 - - - - - - - - - 9 11 13 45 8 11 9 11 3 2 3 4 3 2 4 4 6 28 71 40 15 48 41 24 2 58 10 10 2 32 45 54 Source: MPOB, UCCS, NCBI and Oil Palm Knowledge Base 164 5.5.5
The Chemical Properties of Palm Oil The chemical properties of palm oil are explained in the following aspects: (a) Oxidation Oxidation of palm oil occurs when its oil molecules combine with oxygen in the air or from other reactants. The oxidation of palm oil produces free radicals and compounds which are harmful to human health. (b) Hydrolysis Hydrolysis occurs in palm oil when palm oil molecules react with water. In the hydrolysis process, the reaction between palm oil and water produces glycerol and fatty acids. (c) Esterification Esterification of palm oil occurs when its fatty acid molecules react with alcohol to produce ester (methyl ester), that is palm oil biodiesel. Emulsification Process of Palm Oil The emulsification of palm oil is a process where palm oil is broken into smaller droplets. This increases the total surface area of the palm oil. How does the increase in total surface area of palm oil influence the rate of digestion of palm oil? The emulsification of palm oil by bile juice is shown in the video on the right. Nutritional Content of Palm Oil The nutritional content of palm oil are as follows: (a) Fats Palm oil is a balanced oil with the same amount of saturated fats and unsaturated fats (Table 5.3). (b) Vitamins Palm oil is a rich source of vitamin E and vitamin A. Video Emulsification process of oil such as palm oil http://buku-teks. com/sc5165a My Malaysia Scientists from the Malaysian Palm Oil Board have conducted various research on the nutritional content of palm oil. http://buku-teks.com/sc5165b 165 Chapter 5 Carbon Compounds 5.5.6 5.5.7 5.5.8
Activity 5.12 (c) Antioxidants Palm oil contains antioxidants such as carotene and vitamin E which slow down or stop the oxidation process. (d) Substances in palm oil which constitute less than 1% Among the substances contained in palm oil include sterol, phosphatides, triterpene and aliphatic alcohols. These substances add nutritional value, stability and facilitate the filtration of oil. Use of Palm Oil in Healthcare and Food Besides a balanced content of saturated fats and unsaturated fats, palm oil contains many nutrients suitable for use in various types of food such as cooking oil, vegetable oil, margarine and chocolate. Palm oil is also used to make non-food substances (Photograph 5.7). Photograph 5.7 Examples of palm oil-based products To study the use of palm oil-based products as well as their effects on human health Instructions 1. Carry out this activity in groups. 2. Conduct online searches through the Internet to gather information on the uses of palm oilbased products in: (a) medicine (b) plastic surgery (c) cosmetics (d) prosthetics 3. Discuss the information gathered. Give reasons why the use of palm oil-based products and their effects on human health need to be justified. 4. Present your findings using a graphic organiser or multimedia presentation. 21 Century Skills st • ICS • Discussion 166 5.5.8 5.5.9
Experiment 5.1 Soap Production Soap is a fatty acid salt normally produced through the reaction between palm oil and concentrated alkali (concentrated sodium hydroxide or concentrated potassium hydroxide) as in the following word equation: Oil + Alkali Fatty acid salt (soap) + Glycerol Aim: To produce soap through saponification Problem statement: How is soap produced? Materials: Palm oil, 5 mol dm–3 concentrated sodium hydroxide solution, distilled water, sodium chloride, filter paper, red litmus paper and blue litmus paper Apparatus: Beaker, measuring cylinder, glass rod, Bunsen burner, tripod stand, wire gauze, filter funnel, retort stand, spatula, test tube and conical flask Procedure: xxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxx 50 cm3 of 5 mol dm–3 sodium hydroxide solution 10 cm3 of palm oil Heat Heat Distilled water Sodium chloride Soap Filtrate (a) (b) (c) (d) (e) (f) Filter paper Figure 5.25 Process of soap production 1. Measure and pour 10 cm3 of palm oil into a clean beaker using a measuring cylinder. 2. Measure and pour 50 cm3 of 5 mol dm–3 concentrated sodium hydroxide solution into the beaker (Figure 5.25(a)). Observe and record the changes of the mixture in the beaker. 3. Stir and boil the mixture in the beaker for 5 minutes (Figure 5.25(b)). Observe and record the changes to the mixture in the beaker after heating. A soap business can be carried out from home. The substances used are natural substances, natural fruit extracts and fragrances from approved aromatic resources for making organic soap. Entrepreneurship 167 Chapter 5 Carbon Compounds 5.5.10
4. Stop heating the mixture. Measure and pour 50 cm3 of distilled water as well as three spatula full of sodium chloride into the solution in the beaker (Figure 5.25(c)). Observe and record changes to the mixture in the beaker. 5. Stir and boil the mixture in the beaker again for 5 minutes (Figure 5.25(d)). 6. Filter the mixture in the beaker (Figure 5.25(e)). 7. Rinse the residue with distilled water and dry it. 8. Add a little water to the dried residue in a test tube and shake it. Observe and record the changes when the residue is mixed with water and shaken, and when you touch it with your fingers (Figure 5.25 (f)). 9. Test the mixture of the residue and water with red and blue litmus papers. Observe and record the change in colour, if any, to the red and blue litmus papers. Observations: Record your observations for procedures 2, 3, 4, 8 and 9. Conclusion: What is the conclusion for this experiment? Molecular Components of Soap and Cleansing Action of Soap Molecular Components of Soap Soap molecules are made up of two parts (Figure 5.26), namely: (a) the ‘head’ or ‘hydrophilic’ part which can dissolve in water and is made up of an ionic group. (b) the ‘tail’ or ‘hydrophobic’ part which cannot dissolve in water but can dissolve in oil or grease. This part is made up of a hydrocarbon chain. Hydrophilic part (can dissolve in water) Hydrophobic part (can dissolve in grease or oil) Head Tail Figure 5.26 Molecular structure of soap Why is soap able to dissolve in water as well as in oil or grease? 168 5.5.10 5.5.11
Cleansing Action of Soap The cleansing action of soap is as follows: (a) when soap dissolves in water, the surface tension of the water is reduced. Therefore, the surface of cloth becomes completely wet with soap water. (b) the hydrophobic part of the soap molecules will dissolve and attach to the greasy dirt on the cloth surface while the hydrophilic part will dissolve in water (Figures 5.27(a) and (b)). (c) scrubbing and brushing the cloth will dislodge the greasy dirt from the cloth surface to form greasy droplets that are surrounded by soap molecules and suspended in soapy water (Figure 5.27(c)). (d) soap bubbles produced by soapy water trap greasy droplets in the soapy water. When the soapy water and bubbles are removed during rinsing, the greasy dirt will also be removed as well. In this way, soap removes greasy dirt and cleans the cloth. Figure 5.27 Cleansing action of soap Water Greasy droplets surrounded by soap molecules Soap (a) (b) (c) Greasy dirt Water Water Surface of cloth Surface of cloth Surface of cloth Sustainable Management and its Importance in the Palm Oil Industry The scope of sustainable management and its importance in the palm oil industry include: (a) Land use Replanting is carried out to optimise land use. (b) Wastewater Palm oil mill effluent (POME) (Photograph 5.8) produced from sterilisation processes are made into organic fertilisers and biogas energy substances. 169 Chapter 5 Carbon Compounds 5.5.11 5.5.12
(c) Air quality The quality of air improves when carbon dioxide is absorbed and oxygen is released by oil palm trees during photosynthesis. (d) Oil palm waste Sustainable management of oil palm industry normally practises zero waste concept by converting oil palm waste into various types of useful products (Figure 5.28). Figure 5.28 Applications of the zero waste concept in the oil palm industry Photograph 5.8 POME from palm oil mill Types of biomass (Oil palm waste) Fronds made into fertilisers Tree trunks as wood replacement Empty fruit bunches turned into compost Shells are burnt to boil water Pulp fibre is made into carpets and textile POME turned into biogas and fertilisers 170 5.5.12
Activity 5.13 21 Century Skills st • ICS, ISS, TPS • Debate Formative Practice 5.5 To conduct a debate or forum on the efficient management of the palm oil industry to counter the negative perceptions of Western countries on local palm oil Instructions 1. Carry out this activity in groups. 2. Gather information from the Internet, print media and other electronic media on the negative perceptions of Western countries on local palm oil. Example of negative perception The oil palm industry has been linked to worldwide deforestation. This happens when forests are burnt to provide agricultural land for planting oil palm trees. 3. Discuss and generate ideas on sustainable management to counter the negative perceptions of Western countries on local palm oil. The scope of discussion should include: (a) land use (b) wastewater (c) air quality (d) oil palm waste 4. Conduct a debate or forum to discuss this topic. 1. Name the oil extracted from the following parts of the oil palm fruit: (a) pulp (b) kernel 2. Why are the oil palm fruits steamed before oil is extracted? 3. What are the reactants that react with palm oil in the following processes? (a) Hydrolysis (b) Esterification 4. Name two antioxidants found in palm oil. 171 Chapter 5 Carbon Compounds 5.5.12
Summary Summary S fermentation Physical properties of alcohol: • colour • odour • physical condition at room temperature • volatility • boiling point Chemical properties of alcohol: • combustion • esterification Saturated fats Unsaturated fats Saturated hydrocarbons Unsaturated hydrocarbons Alkane Alkene Glucose or starch Uses of alcohol: • fuel • medicine • cosmetics • industry Excessive alcohol consumption Alcohol addiction Alcohol Fats Hydrocarbon compounds Organic carbon compounds Inorganic carbon compounds Products: • soap • medicine • plastic surgery • cosmetics • prosthetics Chemical properties: • oxidation • hydrolysis • esterification Its importance Carbon cycle Contents: • unsaturated fats • saturated fats • vitamins • antioxidants Palm oil Pulp Oil palm fruit Palm kernel oil Kernel Carbon Compounds 172
5.1 Introduction to Carbon Compounds Identify carbon compounds in nature. Explain the importance of carbon cycle. 5.2 Hydrocarbons Describe hydrocarbon compounds and explain how carbon compounds are obtained from natural sources. Name members of the homologous series of alkanes and alkenes from carbon 1 to carbon 6. Communicate about alternative energy sources and renewable energy in daily life. 5.3 Alcohol Describe the preparation of alcohol. Identify the physical properties and chemical properties of alcohol. Communicate about the uses of alcohol in daily life. Communicate about the effects of excessive alcohol consumption. 5.4 Fats State the content of fats and its sources. Compare and contrast between saturated and unsaturated fats. Explain with examples, the effects of eating food containing excess fat on health. 5.5 Palm Oil Describe the structure of oil palm fruit. Identify the quantity of oil from pulp and kernel. Explain in order the process of palm oil extraction in industry. Describe components of palm oil. Compare and contrast the composition of palm oil with other vegetable oils. State the chemical properties of palm oil. Explain the emulsification process of palm oil. List the nutritional content of palm oil. Justify the use of palm oil in healthcare and food. Carry out an experiment to produce soap through saponification. Communicate about the cleansing action of soap. Generate ideas on sustainable management and their importance in the palm oil industry. After studying this chapter, you are able to: Self-Reflection Self-Reflection 173 Chapter 5 Carbon Compounds
Answer the following questions: 1. Figure 1 shows an experiment to study the preparation of a type of carbon compound. Conical flask Sugar solution + yeast Test tube Limewater Figure 1 (a) Name the process in Figure 1. (b) What type of carbon compound is prepared? (c) State your observation of the limewater. (d) State the inference for your answer in 1(c). 2. Figure 2 shows a cross section of an artery blocked by substance P which causes the lumen of the artery to become narrow and disrupts or blocks blood flow. Substance P Lumen Figure 2 (a) Name the condition. (b) Name substance P. (c) What class of food causes blocked arteries? (d) Suggest two ways to avoid blocked arteries. Summative Practice 5 Summative Practice 5 Quiz http://bukuteks.com/ sc5174 174
Enrichment Practice 3. Figure 3 shows a cross section of an oil palm fruit. X: Y: Z: Figure 3 (a) Name the parts labelled X, Y and Z. (b) Name the type of oil extracted from parts X and Y. (c) Complete the flow chart for the extraction process of palm oil. (i) (ii) Purification Extraction (iii) Threshing (d) Give three reasons why palm oil is suitable as cooking oil. 4. Assume that you are tasked to build a new palm oil mill which operates based on zero waste concept. Figure 4 Build a graphic organiser to show how zero waste concept is applied in the oil palm industry such as the conversion of oil palm waste into oil palm biomass. 175 Chapter 5 Carbon Compounds
ELECTROCHEMISTRY Let’s study L t&MFDUSPMZUJDDFMM t$IFNJDBMDFMM State three uses of electrolysis. Name the process used in the treatment of wastewater by applying electrolysis. Give one example of a fruit and one example of a plant part which can be used to build a chemical cell that produces electrical energy. 6 CHAPTER 176
r &MFDUSPDIFNJDBMDFMM r &MFDUSPMZUJDDFMM r $IFNJDBMDFMM r &MFDUSPMZTJT r "OPEF r $BUIPEF r "OJPO r $BUJPO r &MFDUSPEF r &MFDUSPMZUF r /POFMFDUSPMZUF r *POJDDPNQPVOE r &MFDUSPDIFNJDBMTFSJFT r 5ZQFPGFMFDUSPEF r .FUBMFYUSBDUJPO r 1VSJàDBUJPOPGNFUBM r &MFDUSPQMBUJOH r &MFDUSPDPBHVMBUJPO Science Bulletin Science Bulletin Success stories in the field of electric automobiles such as electric cars are closely related to the technological development and advancement of battery. The properties of superior car batteries include, their ability to produce and store a lot of energy, rapid rate of charging, durable, light and can be safely used at high or low temperatures without exploding. What are the advantages of the battery fitted to electric cars? Charging the electric car battery Lithium-ion batteries in an electric car Keywords 177
Electrochemistry is a study in chemistry of the relationship between electrical and chemical phenomena like those occurring in two types of electrochemical cells as follows: (a) Electrolytic cell In an electrolytic cell, electric current flows through an electrolyte to produce a chemical reaction. Electrical energy is converted to chemical energy through electrolysis. (b) Chemical cell (voltaic cell or galvanic cell) In a chemical cell, chemical changes that occur in the cell produce an electric current. Chemical energy is converted to electrical energy in the cell. Electrolysis In Form 2, you studied about electrolysis that is used to determine the composition of elements in water molecules using an electrolytic cell (Figure 6.1). Electrolysis is the decomposition of a compound in the molten or aqueous state into its constituent elements when electric current flows through it. What are the decomposed compound and constituent elements produced in the electrolysis process (Figure 6.1)? An electrolytic cell is made up of: • an electrical source such as battery • an anode which is the electrode connected to the positive terminal of an electrical source • a cathode which is the electrode connected to the negative terminal of an electrical source • an electrolyte which contains positive ions (cations) and negative ions (anions) (Figure 6.2) 6.1 Electrolytic Cell Figure 6.2 Electrolytic cell Anion Anode (+) Cathode (–) Rheostat Cation Electrolyte Battery + + + + + A _ _ _ _ ee- + – Test tube Carbon electrodes Switch + – Distilled water + dilute hydrochloric acid Figure 6.1 Electrolytic cell 178 6.1.1
Activity 6.1 To draw and label the structures of an electrolytic cell Instructions 1. Carry out this activity individually. 2. Draw and label the electrolytic cell in Figure 6.1. The parts that need to be labelled include: (a) anode (b) cathode (c) electrolyte 3. Present the drawing of the labelled electrolytic cell to the class. 21 Century Skills st • TPS Electrical Source The function of the electrical source in an electrolytic cell is to produce electric current to carry out electrolysis. Electrolysis cannot take place if there is no electric current flowing through the electrolyte. Electrode Electrode is the electric conductor that is connected to the battery and enables electric current to enter or leave the electrolyte during electrolysis. The electrode connected to the positive terminal of the electrical source is known as the anode while the electrode connected to the negative terminal of the electrical source is known as the cathode. Electrolyte Substances in the molten or aqueous state which allow electric current to flow through them and undergo chemical changes are known as electrolytes. Substances which do not allow electric current to flow through them in the molten or aqueous state are known as non-electrolytes. Table 6.1 Examples of electrolyte and non-electrolyte Examples of electrolyte Examples of non-electrolyte • Molten lead(II) bromide, PbBr2 • Molten sodium chloride, NaCl • Sodium hydroxide solution, NaOH • Copper(II) sulphate solution, CuSO4 • Naphthalene, C10H8 • Acetamide, CH3CONH2 • Glucose solution, C6H12O6 • Ethanol, C2H5OH Electrolytes are ionic compounds in the molten or aqueous state which consist of positive ions, cations and negative ions, anions. For example, sodium chloride is an electrolyte which is an ionic compound made up of sodium ions, Na+ (positively charged ions) and chloride ions, Cl– (negatively charged ions). NaCl Na+ + Cl– 179 Chapter 6 Electrochemistry 6.1.1
Experiment 6.1 Electrolysis Process During the electrolysis process, • positively charged ions (cations) move to the cathode (negative electrode) • negatively charged ions (anions) move to the anode (positive electrode) For example, during the electrolysis of molten lead(II) bromide, PbBr2, positively charged lead(II) ions, Pb2+, move to the negatively charged cathode while negatively charged bromide ions, Br– , move to the positively charged anode (Figure 6.3). Electrolytes in the solid state cannot conduct electricity because there are no free-moving ions to conduct the electricity. Figure 6.3 Movement of ions towards electrodes during the electrolysis of molten lead(II) bromide, PbBr2 Battery Cathode Heat Positively charged anode Negatively charged cathode Anode Molten lead(II) bromide, PbBr2 Lead(II) ion, Pb2+ Bromide ion, Br– Pb2+ Pb2+ Pb2+ Br– Br– Br– Br– Br– Br– + – Aim: To study the electrolysis of ionic compounds in solid, molten and aqueous states Problem statement: Can ionic compounds in solid, molten and aqueous states be electrolysed? Hypotheses: 1. Ionic compounds in molten and aqueous states can be electrolysed. 2. Ionic compounds in solid state cannot be electrolysed. Variables: (a) manipulated : State of ionic compound, namely solid, molten or aqueous (b) responding : Condition of light bulb (c) constant : Type of electrode Materials: Solid lead(II) bromide, PbBr2 and 0.1 mol dm–3 copper(II) sulphate solution, CuSO4 Apparatus: Battery, carbon electrodes, connecting wires with crocodile clips, crucible, tripod stand, pipe clay triangle, Bunsen burner, switch, beaker, light bulb, electrolytic cell, spatula and test tubes 180 6.1.1 6.1.2
Procedure: A Electrolysis of ionic compound in solid and molten states Teacher’s demonstration (carried out in a fume chamber) 1. Put solid lead(II) bromide powder, PbBr2, into a dry crucible until it is half-full. 2. Place the crucible on a pipe clay triangle atop a tripod stand (Figure 6.4). 3. Complete the circuit by connecting the carbon electrodes, switch, battery and light bulb with connecting wires and crocodile clips. 4. Turn on the switch. Observe and record the changes that happen to the light bulb. 5. Heat the solid lead(II) bromide, PbBr2, until it melts (Figure 6.5). 6. Repeat steps 3 and 4. B Electrolysis of ionic compound in aqueous state 1. Prepare the apparatus set-up with an electrolytic cell half-filled with 0.1 mol dm–3 copper(II) sulphate solution, CuSO4 , and two test tubes filled completely with 0.1 mol dm–3 copper(II) sulphate solution, CuSO4 (Figure 6.6). Figure 6.6 2. Turn on the switch for 5 minutes. Observe and record the changes that happen to the light bulb. Battery Light bulb Carbon electrodes Solid lead(II) bromide, PbBr2 Crucible Crocodile clip Switch Pipe clay triangle + – Battery Light bulb Carbon electrodes Molten lead(II) bromide, PbBr2 Crucible Crocodile clip Switch Heat + – Pipe clay triangle Figure 6.4 Electrolysis of solid lead(II) bromide, PbBr2 Figure 6.5 Electrolysis of molten lead(II) bromide, PbBr2 CAUTION! Bromine gas is poisonous. Do not inhale the bromine gas. 0.1 mol dm–3 copper(II) sulphate solution, CuSO4 Battery Light bulb Carbon electrodes Test tube + – Crocodile clip Switch + – 181 Chapter 6 Electrochemistry 6.1.2
Observation: Material Condition of light bulb Inference Solid lead(II) bromide, PbBr2 Molten lead(II) bromide, PbBr2 0.1 mol dm–3 copper(II) sulphate solution, CuSO4 Conclusion: Are the hypotheses accepted? What is the conclusion for this experiment? Questions: 1. Why should the electrolysis of molten lead(II) bromide, PbBr2, be carried out in a fume chamber? 2. What is the purpose of connecting a light bulb to the electrolytic cell? 3. Why does electrolysis not occur in ionic compounds that are in the solid state? Factors Affecting the Products in Electrolysis Three factors which affect the selection of ions to be discharged at the electrodes in the electrolysis of aqueous solutions are: • position of ions in the electrochemical series • concentration of electrolyte • types of electrode Science When a positive ion is discharged, the ion will receive one or more electrons, become neutral, and form an atom or a molecule. When a negative ion is discharged, the ion will donate one or more electrons, become neutral, and form an atom or a molecule. 182 6.1.2 6.1.3
Position of Ions in the Electrochemical Series In the electrochemical series, metals are arranged according to the tendency of their atom to donate electron(s). The higher the position of a metal in the electrochemical series, the easier it is for the metal to donate electron(s). Figure 6.7 shows the arrangement of ions in the electrochemical series according to their tendency to be discharged. Figure 6.7 Arrangement of ions in the electrochemical series according to their tendency to be discharged Ions at the bottom of the electrochemical series have higher tendencies to be discharged. Ease of discharge increases Potassium ion, K+ Sodium ion, Na+ Calcium ion, Ca2+ Magnesium ion, Mg2+ Aluminium ion, Al3+ Zinc ion, Zn2+ Iron(II) ion, Fe2+ Tin ion, Sn2+ Lead(II) ion, Pb2+ Hydrogen ion, H+ Copper(II) ion, Cu2+ Silver ion, Ag+ Cation Fluoride ion, F – Sulphate ion, SO4 2– Nitrate ion, NO3 – Chloride ion, Cl – Bromide ion, Br – Iodide ion, I – Hydroxide ion, OH– Anion Example 1 Electrolysis of sodium sulphate solution (a) Ions present in a sodium sulphate solution during electrolysis are sodium ions, sulphate ions, hydrogen ions and hydroxide ions (b) Cathode (negative electrode) (i) Attracts positive ions, namely sodium ions and hydrogen ions (ii) Hydrogen ions are selected to be discharged because the hydrogen ion is less electropositive compared to the sodium ion (iii) Hydrogen gas is produced at the cathode (c) Anode (positive electrode) (i) Attracts negative ions, namely sulphate ions and hydroxide ions (ii) Hydroxide ions are selected to be discharged because the hydroxide ion is less electronegative compared to the sulphate ion (iii) Oxygen gas is produced at the anode 183 Chapter 6 Electrochemistry 6.1.3
Experiment 6.2 Example 2 Electrolysis of copper(II) sulphate solution (a) Ions present in a copper(II) sulphate solution during electrolysis are copper(II) ions, sulphate ions, hydrogen ions and hydroxide ions. (b) Cathode (negative electrode) (i) Attracts positive ions, namely copper(II) ions and hydrogen ions (ii) Copper(II) ions are selected to be discharged because the copper(II) ion is less electropositive compared to the hydrogen ion (iii) Copper is deposited at the cathode (c) Anode (positive electrode) (i) Attracts negative ions, namely sulphate ions and hydroxide ions (ii) Hydroxide ions are selected to be discharged because the hydroxide ion is less electronegative compared to the sulphate ion (iii) Oxygen gas is produced at the anode Aim: To study the effect of the position of ions in the electrochemical series on the tendency of the ion to be discharged at the electrode Problem statement: How does the position of ions in the electrochemical series affect the tendency of the ion to be discharged at the electrode? Hypothesis: The lower the position of an ion in the electrochemical series, the easier it is for the ion to be discharged. Variables: (a) manipulated : Position of ion in the electrochemical series (b) responding : Product at electrode (c) constant : Concentration of electrolyte and type of electrode Materials: 0.5 mol dm–3 magnesium nitrate solution, Mg(NO3)2, 0.5 mol dm–3 sodium sulphate solution, Na2SO4 and wooden splinter Apparatus: Battery, carbon electrodes, connecting wires with crocodile clips, electrolytic cell, ammeter, test tubes and switch Figure 6.8 Arrangement of ions in the electrochemical series according to their tendency to be discharged Cation Anion K+ F– Na+ SO4 2– NO3 – Cl – Br – OH– I – Ca2+ Mg2+ Al3+ Zn2+ Fe2+ Sn2+ Pb2+ H+ Cu2+ Ag+ Ease of discharge increases 184 6.1.3
Procedure: 1. Prepare the apparatus set-up with an electrolytic cell half-filled with 0.5 mol dm–3 magnesium nitrate solution, Mg(NO3)2. 2. Fill completely two test tubes with 0.5 mol dm–3 magnesium nitrate solution, Mg(NO3)2, and invert both test tubes in the electrolytic cell (Figure 6.9). 3. Turn on the switch. Observe and record the changes that occur at the anode and cathode. 4. Turn off the switch when the test tube is almost full with gas released from the electrode. 5. Test the gas released using a glowing wooden splinter and a burning wooden splinter. 6. Observe and record the results. 7. Repeat steps 1 to 6 by replacing magnesium nitrate solution, Mg(NO3)2, with sodium sulphate solution, Na2SO4. Observation: Electrolyte Test for gas released at anode cathode Magnesium nitrate solution, Mg(NO3)2 Glowing wooden splinter test: Burning wooden splinter test: Glowing wooden splinter test: Burning wooden splinter test: Sodium sulphate solution, Na2SO4 Glowing wooden splinter test: Burning wooden splinter test: Glowing wooden splinter test: Burning wooden splinter test: Conclusion: Is the hypothesis accepted? What is the conclusion for this experiment? Battery Ammeter Carbon electrodes Test tube Magnesium nitrate solution, Mg(NO3)2 Crocodile clip Switch A + + – – Figure 6.9 Science Glowing wooden splinter test (test for oxygen gas) • Insert a glowing wooden splinter into the test tube containing the gas. • If the glowing wooden splinter ignites, the gas in the test tube is oxygen. Glowing wooden splinter Burning wooden splinter Burning wooden splinter test (test for hydrogen gas) • Bring a burning wooden splinter close to the mouth of the test tube containing the gas. • If the gas explodes with a ‘pop’ sound, the gas in the test tube is hydrogen. 185 Chapter 6 Electrochemistry 6.1.3
Questions: 1. Name the ions in the following solutions: (a) magnesium nitrate solution, Mg(NO3)2 (b) sodium sulphate solution, Na2SO4 2. Based on your observations in Experiment 6.2, name the gas produced at the anode and cathode for each electrolyte in the table below. Electrolyte Product formed at anode cathode Magnesium nitrate solution, Mg(NO3)2 Sodium sulphate solution, Na2SO4 3. Name the ion selected to be discharged at the anode and cathode for each electrolyte in the table below. Electrolyte Ion selected to be discharged at anode cathode Magnesium nitrate solution, Mg(NO3)2 Sodium sulphate solution, Na2SO4 Concentration of Electrolyte The concentration of ions in an electrolyte also affects the selection of ion to be discharged. Negative ions which are more concentrated in an electrolyte are more likely to be discharged at the anode. However, the selection of positive ions to be discharged at the cathode is still influenced by the position of the positive ions in the electrochemical series. Electrolysis of concentrated sodium chloride solution and dilute sodium chloride solution (a) Ions present in a concentrated or dilute sodium chloride solution during electrolysis are sodium ions, chloride ions, hydrogen ions and hydroxide ions. (b) Cathode (negative electrode) (i) Attracts positive ions, namely sodium ions and hydrogen ions (ii) Hydrogen ions are selected to be discharged because the hydrogen ion is less electropositive compared to the sodium ion (iii) Hydrogen gas is produced at the cathode (c) Anode (positive electrode) (i) Attracts negative ions, namely chloride ions and hydroxide ions (ii) The negative ion discharged at the anode is influenced by the concentration of the negative ion in the electrolyte as follows: Example 186 6.1.3
Experiment 6.3 Aim: To study the effect of concentration of ions in electrolytes on the selection of ion to be discharged at the anode Problem statement: How does the concentration of hydrochloric acid, HCl, influence the selection of ion to be discharged at the anode? Hypothesis: Ions of a higher concentration will be selected to be discharged at the anode Variables: (a) manipulated : Concentration of ion in electrolyte (b) responding : Product at anode (c) constant : Type of electrode Materials: 1.0 mol dm–3 hydrochloric acid, HCl, 0.0001 mol dm–3 hydrochloric acid, HCl and wooden splinter Apparatus: Battery, carbon electrodes, connecting wires with crocodile clips, electrolytic cell, ammeter, test tubes, litmus paper and switch Procedure: 1. Prepare the apparatus set-up with an electrolytic cell half-filled with 1.0 mol dm–3 hydrochloric acid, HCl. 2. Fill completely two test tubes with 1.0 mol dm–3 hydrochloric acid, HCl, and invert both test tubes in the electrolytic cell (Figure 6.10). 3. Turn on the switch. Observe and record the changes which occur at the anode. 4. Turn off the switch when the test tube is almost filled with gas released from the anode. • the concentration of chloride ion is higher than the concentration of hydroxide ion in a concentrated sodium chloride solution such as 1.0 mol dm–3 sodium chloride solution, therefore the chloride ion will be selected to be discharged even though the position of the chloride ion is higher than the hydroxide ion in the electrochemical series. Chlorine gas is produced at the anode. • the concentration of chloride ion is lower than the concentration of hydroxide ion in a dilute sodium chloride solution such as 0.0001 mol dm–3 sodium chloride solution, therefore the hydroxide ion will be selected to be discharged because it is less electronegative compared to the chloride ion. Oxygen gas is produced at the anode. CAUTION! Chlorine gas is poisonous. Carbon electrodes Battery Ammeter Test tube Hydrochloric acid, HCl Crocodile clip Switch A + + – – Figure 6.10 187 Chapter 6 Electrochemistry 6.1.3
5. Test any gas released using a glowing wooden splinter, and moist blue and red litmus papers. 6. Observe and record the results of the gas tests. 7. Repeat steps 1 to 6 by replacing 1.0 mol dm–3 hydrochloric acid, HCl, with 0.0001 mol dm–3 hydrochloric acid, HCl. Science Moist blue litmus paper test • Place a piece of moist blue litmus paper close to the mouth of the test tube containing the gas. • If the moist blue litmus paper turns red, the gas in the test tube is acidic. • If the colour of the moist blue litmus paper bleaches, the gas in the test tube is halogen gas. • If the moist blue litmus paper does not change colour, the gas in the test tube is alkaline or neutral. Moist red litmus paper Moist blue litmus paper Moist red litmus paper test • Place a piece of moist red litmus paper close to the mouth of the test tube containing the gas. • If the moist red litmus paper turns blue, the gas in the test tube is alkaline. • If the moist red litmus paper does not change colour, the gas in the test tube is acidic or neutral. Observation: Electrolyte Test for gas produced at the anode 1.0 mol dm–3 hydrochloric acid, HCl Glowing wooden splinter test: Moist blue litmus paper test: Moist red litmus paper test: 0.0001 mol dm–3 hydrochloric acid, HCl Glowing wooden splinter test: Moist blue litmus paper test: Moist red litmus paper test: Conclusion: Is the hypothesis accepted? What is the conclusion for this experiment? Questions: 1. What is the difference in the concentration of chloride ion, Cl– , between 1.0 mol dm–3 hydrochloric acid, HCl and 0.0001 mol dm–3 hydrochloric acid, HCl? 2. Based on your observations in Experiment 6.3, name the product formed at the anode of each of the following electrolytes: (a) 1.0 mol dm–3 hydrochloric acid, HCl (b) 0.0001 mol dm–3 hydrochloric acid, HCl 3. Name the ion selected to be discharged at the anode of each of the following electrolytes: (a) 1.0 mol dm–3 hydrochloric acid, HCl (b) 0.0001 mol dm–3 hydrochloric acid, HCl 188 6.1.3
Types of Electrode The type of electrode used also affects the selection of ion to be discharged as follows: (a) If the metal used as the anode is the same as the metal ion in the electrolyte, then • at the anode, the metal atoms will ionise to form positive ions that dissolve into the electrolyte • at the cathode, the metal ions will discharge to form atoms of the metal which are then deposited at the cathode • the concentration of metal ions in the electrolyte does not change because the rate of metal atoms ionised to form metal ions at the anode is the same as the rate of metal ions discharged to form metal atoms which are then deposited at the cathode (b) If the type of substance used as the anode is not the same as the type of metal ion in the electrolyte, then • the atoms of the anode do not dissolve in the electrolyte. Negative ions in the electrolyte are discharged at the anode • at the cathode, the less electropositive ion will be selected to be discharged Electrolysis of silver nitrate solution using: • Silver electrode (a) Ions present in a silver nitrate solution during electrolysis are silver ions, nitrate ions, hydrogen ions and hydroxide ions. (b) Cathode (negative electrode) (i) Attracts positive ions, namely silver ions and hydrogen ions (ii) Silver ions are selected to be discharged because the silver ion is less electropositive compared to the hydrogen ion (iii) Silver is deposited at the cathode (c) Anode (positive electrode) (i) Forms silver ions when silver atoms at the anode ionise. Nitrate ions and hydroxide ions are not discharged (ii) The silver electrode dissolves in the electrolyte (d) The concentration of silver ions in the electrolyte does not change because the rate of silver atoms ionised to form silver ions at the anode is the same as the rate of silver ions discharged to form silver atoms which are deposited at the cathode. • Carbon electrode (a) Ions present in a silver nitrate solution during electrolysis are silver ions, nitrate ions, hydrogen ions and hydroxide ions. Example 189 Chapter 6 Electrochemistry 6.1.3