Chapter 5: Chemical reactions Answers

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1 Think about chemical reactions Chapter 5: Chemical reactions Answers What do plastic fruit juice containers, a toilet seat and a $100 note have in common? Why are some plastics harder than others? How does zinc slow down the rusting of iron? They are all made of synthetic polymers derived from crude oil. The harder polymers often have cross-linking between the polymer chains, which gives them extra strength and rigidity. Alternatively, the inclusion of large atoms (such as chlorine) or large groups (e.g. benzene rings) prevents bending of the plastic, so they are more rigid. Thermosetting plastics are hard as well. Zinc is a more active metal than iron, so it corrodes instead and protects the iron. Spectacles that turn into sunglasses how do they do it? Bottled gas, candle wax and petrol all come from one substance. What is it? Cow manure to replace petroleum? How is that possible? In what part of your body do you find catalytic catalase? How do light sticks produce light? Photochromic glasses contain silver chloride crystals in the glass. On exposure to UV rays in sunlight, the silver ions receive an electron from the chloride ion to form atoms of silver that cause the lens to darken. When the light is removed the products are converted back to silver ions and chloride ions by a series of chemical reactions involving copper ions dissolved in the glass. Petroleum or crude oil Cow manure can be placed in a biogas digester where it ferments to generate methane, which is a fuel gas. Liver Chemiluminescence is a process in which chemical energy is converted to light energy. Inside the glow stick are chemicals which are mixed when the inner tubes break when the stick is bent. The energy released is absorbed by a fluorescent dye that makes the tube glow. John Wiley & Sons Australia, Ltd 1

2 Your quest 1. (a) Combustion (b) All are exothermic (c) Oxygen (d) Natural gas; hydrogen ; petrol (e) Water (and carbon dioxide and carbon monoxide and carbon) (f) Water 2. (a) Photosynthesis (b) Glucose (c) Respiration Understanding and inquring 5.1 Form and Function: Plastic Facts 1. Plastic is derived from a Greek word plastikos, meaning able to be moulded. 2. Polymers are along chain molecules made up of smaller molecules called monomers. 3. Carbon 4. Both are polymeric and made up of chains of monomers. Thermoplastic polymers are able to be remoulded by heating and cooling. Thermosetting plastics cannot be remoulded by heating. They are hard and rigid and often char when heated. 5. Thermosetting: bakelite, melamine Thermoplastic: PVC, polythene (polyethene ); 6. Crosslinks are chemical bonds that attach one polymer chain to another and give it extra strength and rigidity. 7. Thermosoftening 8 (a) Polyethene (b) Polyvinyl chloride (c) Polystyrene (d) Polypropene 9. Thermosetting plastics do not melt easily because the large number of crosslinks in them prevent the chains moving apart on heating. Instead, they decompose. John Wiley & Sons Australia, Ltd 2

3 10. (a) and (d) Should be made of a thermoplastic as these can be moulded readily and remain flexible. (b) and (c) Should be made from a thermosetting plastic as they should be made from rigid materials that do not deform. 11. to 13 Individual responses. 14. Individual research. Photo-degradation is the breaking down of the plastic's structure by sunlight. 5.2 A game of balance 1. Word equations do not have the formulae of the chemicals involved. They do not always include the states of the reactants and products. Numbers are not used in word equations, so it is not possible to know the numbers of atoms involved. 2. (s) for solid, (l) for liquid, (g) for gas 3. An aqueous solution is formed when a substance is dissolved in water. It is indicated by the symbol (aq). 5. C 6 H 8 O 7 (aq) + 3NaHCO 3 (aq) C 6 H 5 O 7 Na 3 (aq) + 3CO 2 (g) + 3H 2 O(l) 6. Balancing an equation ensures that it shows both the reactants and products have the same type and number of atoms, which conforms to the Law of Conservation of Mass. 7. ebookplus activity 8. ebookplus activity 5.3 Precipitation reactions 1. A precipitate is an insoluble, or slightly soluble, solid that can form when two aqueous ionic solutions react together. 2 CuSO 4 (s) Cu 2+ (aq) + SO 2 4 (aq) 3 NaNO 3 and KI are soluble in water. 4 CuCO 3, AgI and Mg(OH) 2 are insoluble in water. 5 (a) Na + 2 and SO 4 ; Cu 2+ and Cl (b) Cu 2+ and OH ; Na + 2 and SO 4 (c) Pb 2+ and OH ; Na + and NO 3 (d) K + and CO 2 3 ; Na + and I John Wiley & Sons Australia, Ltd 3

4 6 (a) No precipitate (b) (c) (d) Copper hydroxide Lead hydroxide No precipitate 7. ebookplus activity 8. Soluble Slightly Soluble Insoluble All compounds of Na +, K +, NH 4 +, NO All compounds of Cl, Br and I, except those of Ag +, Hg 2+ PbCl 2, PbBr 2 AgCl, AgBr, AgI, HgCl 2, HgBr 2, HgI 2 All compounds of SO 4 2, except those of Ba 2+, Pb 2+, Ca 2+ Carbonates of Na +, K +, NH 4 +, Phosphates of Na +, K +, NH 4 +, Ag 2 CO 3 ; CaSO 4 BaSO 4, PbSO 4 - All carbonate compounds, except those of Na +, K +, NH All phosphate compounds, except those of Na +, K +, NH 4 + Hydroxides of Na +, K +, NH 4 + Ca(OH) 2 All hydroxide compounds, except those of Na +, K +, NH Health: Chemicals can be a health hazard 1. Dangerous goods are chemicals that could be dangerous to people, property or the environment. 2. The decision is based on the greatest immediate risk that the chemical presents. 3. They have an effect on human health. 4. Dangerous poison, poison, warning and caution are four examples of signal words. John Wiley & Sons Australia, Ltd 4

5 5. An MSDS is a material safety data sheet. It should include information about a chemical including: the date of issue the ingredients information about health hazards and first aid instructions precautions to be taken when using it information about storage and safe handling. 6. An MSDS can be downloaded from the internet. It can also be delivered with the chemical. 7. It is the employer s responsibility. 8. They are dangerous to people. 9. Explosive liquids (Class 1) are not as easily ignited as flammable liquids (Class 3). Flammable liquids can ignite on contact with air at temperatures below 60.5 C. 10. An MSDS provides information about a particular chemical. A risk assessment sheet provides information about an experiment that could involve the use of more than one chemical. 11. Any chemical could be a health hazard if spilled on the skin, breathed in or ingested. Even water could be a hazard because it could be contaminated with another substance. 12. Student investigation John Wiley & Sons Australia, Ltd 5

5.5 A world of reactions 1. 2 All redox reactions involve the transfer of electrons. 3 Oxidation occurs when electrons are lost, or transferred away from an atom or ion.

6 5.5 A world of reactions 1. 2 All redox reactions involve the transfer of electrons. 3 Oxidation occurs when electrons are lost, or transferred away from an atom or ion. 4 Reduction is when electrons are gained, or transferred to an atom or ion. 5 The word redox comes from combining the words reduction and oxidation. 6 (a) The electrons are being transferred from the zinc. (b) The electrons are being transferred to the oxygen. 7 In the combustion reaction between methane and oxygen, the electron transfer is not complete. 8. (a) (i) Cu(s) + ZnSO 4 (aq) Zn(s) + CuSO 4 (aq) (ii) 4Na(S) + O 2 (g) 2Na 2 O(s) (iii) 2CO(g) + O 2 (g) 2CO 2 (g) (iv) H 2 O 2 (ag) H 2 (g) + O 2 (g) (b) (i) Displacement (ii) Dry corrosion (iii) Combustion (iv) Decomposition John Wiley & Sons Australia, Ltd 6

7 9. The reaction between magnesium and oxygen is: a combustion reaction because light and heat are produced a combination reaction because two elements are combining to form a compound a redox reaction because electrons are being transferred from the magnesium to the oxygen an exothermic reaction because energy is released. 10. ebookplus activity 12. ebookplus activity 5.6 Producing Salts 1. A salt is an ionic compound that results from the reaction between an acid and a base or between a metal and an acid. 2. A salt, carbon dioxide and water 3. (a) 2NaHCO 3 (s) + H 2 SO 4 (aq) Na 2 SO 4 (aq) + 2CO 2 (g) + 2H 2 O(l) (b) KOH(s) + HCI(aq) KCI(aq) + H 2 O(l) (c) CuO(s) + H 2 SO 4 (aq) CuSO 4 (aq) + H 2 O(l) 4. (a) Magnesium chloride (b) Potassium acetate (c) Sodium sulfate John Wiley & Sons Australia, Ltd 7

5.7 Fuelling our Life Style 1. 2. Fossil fuels are formed when plants and marine organisms are buried under sediment before they decay.

8 5.7 Fuelling our Life Style Fossil fuels are formed when plants and marine organisms are buried under sediment before they decay. Over millions of years, the increasing temperatures and pressures convert some of these materials into coal or oil. 3. Combustion 4. Methane + oxygen carbon dioxide + water 5. A molecule composed only of carbon and hydrogen atoms 6. Boiling point 7. Petroleum gases fuel gases for heating Gasoline petrol, plastic manufacture Naphtha cracked to produce petrol, fertilisers, plastics Kerosene aviation fuel, home heating Diesel truck fuel, domestic oil heating Residue tar for roads, paraffin waxes, lubrication 8. Biomass mainly plant based materials (e.g. cellulose) that can be used to produce fuels. Biogas a gaseous hydrocarbon fuel produced from biomass. 9. Biomass digesters produce biogas (mainly methane) when animal waste and general biomass undergoes decomposition as it rots. 10. Methane and carbon dioxide John Wiley & Sons Australia, Ltd 8

9 11. Biomass is produced mainly by the process of photosynthesis. Solar energy (sunlight) is absorbed by plants and used to manufacture carbon compounds such as carbohydrates, such as glucose, starch and cellulose. These compounds have chemical bonds which store this energy. If biomass is converted to fossil fuels, the chemical energy is stored inside the fossil until it is dug up and used. 12. Diesel oil 13. Fermentation is an oxidation-reduction reaction 14. Student activity 15. Student and group activity 16. Student research 5.8 The need for speed 1. A catalyst is a chemical that helps speed up a reaction, but is not changed by the reaction. Examples include platinum, rhodium and aluminium oxide in the catalytic converters of cars; platinum in contact cleaning solution; enzymes such as amylase and catalase in the human body. 2. Catalysts are important to industry because they help maximise the production of chemicals in a given time, thus saving time and money. 3. Enzymes are large protein molecules that act as biological catalysts in the cells of living organisms. 4. Catalytic surfaces are honeycombed so that their surface area is increased. This maximises the conversion of harmful gases into harmless ones. 5. Amylase is added to bread to aid the breakdown of its starch content by the digestive system. 6. The waste from leaded petrol contaminate the surface of the catalytic converter, inhibiting its ability to convert harmful gases. 7. Student research 8. Student research 5.9 A cool light 1. Chemiluminescence refers to the process in which the chemical energy released in a chemical change is partly converted to light energy. Bioluminescence involves the production of light energy from chemical reactions occurring inside a living thing such as a firefly. Fluorescent molecules in the body of the organism emit the light. John Wiley & Sons Australia, Ltd 9

10 2. 3. Student investigation 4. Student investigation 5.10 Target maps and single bubble maps 1. Neutralisation or acid-base reactions 2. (a) Words in inner circle: broken bonds, reactants, products, energy absorbed (b) Words in inner circle: hydrocarbons, rust, burning, oxygen, broken bonds, reactants, products (c) Words in inner circle: rust, burning, water, oxygen, broken bonds, reactants, products 3. Student activity 4. Individual responses. The following is an example for precipitation John Wiley & Sons Australia, Ltd 10

11 5. Individual response 6. The following are three groups from which the bubble maps can be created. Salts: sodium chloride, magnesium chloride, sodium acetate, copper nitrate, sodium sulfate Fuels: biogas, coal, hydrocarbons, methane, propane, ethanol Catalysts: enzymes, zeolites, amylase, platinum, vanadium oxide Looking back 1. C 2. Synthetic polymers that are able to be moulded. 3. Polymers are made by joining monomers together with covalent chemical bonds. In some polymers, there is only one type of monomer that forms the chain. In others, there are two different monomers that alternate along the chain. 4. Thermoplastic Thermosetting Properties Soften when heated Bonding and structure Less hard and rigid Individual polymer chains Chains slide past each other when polymer is heated due to weak forces between chains Examples Plastic drink bottles Spectacle lenses Does not soften when heated Hard and rigid Polymer chains are connected by chemical bonds (called crosslinking) Crosslinks prevent movement of chains when heated Toilet seats Door knobs John Wiley & Sons Australia, Ltd 11

12 5. (e) The liver contains catalase enzyme which increases the rate of the decomposition of hydrogen peroxide into oxygen gas. John Wiley & Sons Australia, Ltd 12

13 6. 7. (a) An aqueous solution consists of a substance dissolved in water. (b) It is an endothermic reaction. The reduction in temperature occurs because the reaction absorbs energy from the surroundings (i.e. the surrounding water). (c) It is used to break the bonds between atoms in the reactants. 8. (a) Precipitation (b) The formation of a substance that does not dissolve in water 9 C 10. D 11. (a) Dangerous goods are chemicals that could be dangerous to people, property or the environment. Hazardous substances are chemicals that have an effect on human health. (b) Both groups of chemicals are dangerous to people. 12. An MSDS is a material safety data sheet. It is used to inform people about the dangers of substances, the precautions that should be taken when using or storing them and first aid instructions in the event of an accident with the substance. 13. (a) 4Al(s) 3O2(g) 2Al2O3(s) (b) K(s) O2(g) KO2(s) (c) C(s) O2(g) CO2(g) (d) CuCO3(s) CuO(s) CO2(g) (e) 4Fe(s) S8(s) 4FeS2(s) (f) CuSO4(aq) Zn(s) Cu(s) ZnSO4(aq) (g) CuSO4(aq) 2NaOH(aq) Cu(OH)2(s) Na2SO4(aq) (h) Mg(OH)2(s) 2HCl(aq) MgCl2(aq) 2H2O(l) John Wiley & Sons Australia, Ltd 13

14. (a) Combination (b) Combination (c) Combination and combustion (d) Decomposition (e) Combination (f) Displacement (g) Precipitation (h) Neutralisation 15. (a), (b), (c), (e) and (f) 16.

14 14. (a) Combination (b) Combination (c) Combination and combustion (d) Decomposition (e) Combination (f) Displacement (g) Precipitation (h) Neutralisation 15. (a), (b), (c), (e) and (f) 16. (a) (b) The hydrogen ions in solution gain electrons and leave the solution as hydrogen and the metal atoms ionise and enter the solution as metal ions. Chemists say that the metals have displaced (or replaced) the hydrogen ions from the solution. (c) Hydrogen 17. (a) Magnesium chloride (b) Copper sulfate (c) Sodium acetate (d) Sodium nitrate 18. Boiling point 19. Methane is CH 4 and octane is C 8 H Diesel fraction 21. Methane, ethane, propane, butane 22. Rotting waste liquid (sludge)residue + biogas 23. Glucose ethanol + carbon dioxide John Wiley & Sons Australia, Ltd 14

15 24. (a) A substance that makes a reaction go faster, but is reformed at the end. (b) Because it reacts but reforms; therefore, there is no change in the amount of the catalyst. Effectively there is no overall change in the catalyst. (c) Enzymes 25. (a) Responses may vary as there are many reactions. Possible answers include darkening of photographic film by light (silver bromide is converted to metallic silver), destruction of ozone by UV light in the stratosphere. (b) Chemiluminescence is the production of light by a chemical reaction. (c) In bioluminescence, the chemical reactions inside some living things generate energy, some of which is used to activate fluorescent molecules that emit light. John Wiley & Sons Australia, Ltd 15

10.3 Types of Chemical Reactions

10.3 Types of Chemical Reactions Chemical equations follow certain patterns Combination (synthesis ) The number of possible chemical is very large. However, there are a limited number of structural patterns