Preview Understanding basic chemistry through problem solving the learners approach by Kim Seng Chan Jeanne Tan (2017) Preview Understanding basic chemistry through problem solving the learners approach by Kim Seng Chan Jeanne Tan (2017) Preview Understanding basic chemistry through problem solving the learners approach by Kim Seng Chan Jeanne Tan (2017) Preview Understanding basic chemistry through problem solving the learners approach by Kim Seng Chan Jeanne Tan (2017) Preview Understanding basic chemistry through problem solving the learners approach by Kim Seng Chan Jeanne Tan (2017)
Revised Edition UNDERSTANDING BASIC CHEMISTRY THROUGH PROBLEM SOLVING THE LEARNER’S APPROACH 10441sc_9789813209770_tp.indd 3/2/17 3:54 PM b2530 International Strategic Relations and China’s National Security: World at the Crossroads This page intentionally left blank b2530_FM.indd 01-Sep-16 11:03:06 AM Revised Edition UNDERSTANDING BASIC CHEMISTRY THROUGH PROBLEM SOLVING THE LEARNER’S APPROACH KIM SENG CHAN JEANNE TAN WS Education NEW JERSEY • LONDON 10441sc_9789813209770_tp.indd • SINGAPORE • BEIJING • SHANGHAI • HONG KONG • TAIPEI • CHENNAI • TOKYO 3/2/17 3:54 PM Published by WS Education, an imprint of World Scientific Publishing Co Pte Ltd Toh Tuck Link, Singapore 596224 USA office: 27 Warren Street, Suite 401-402, Hackensack, NJ 07601 UK office: 57 Shelton Street, Covent Garden, London WC2H 9HE Library of Congress Cataloging-in-Publication Data Names: Chan, Kim Seng | Tan, Jeanne Title: Understanding basic chemistry through problem solving / by Kim Seng Chan (Victoria Junior College, Singapore), Jeanne Tan Description: Revised edition | Hackensack, NJ : World Scientific, 2017 | "Written for students taking either the University of Cambridge O-level examinations or the GCSE examinations" Preface | Includes index Identifiers: LCCN 2016059284 | ISBN 9789813209770 (softcover : alk paper) Subjects: LCSH: Chemistry Great Britain Textbooks | Chemistry Textbooks | Chemistry Great Britain Examinations, questions, etc. Study guides | Chemistry Examinations, questions, etc. Study guides Classification: LCC QD31.3 C374 2017 | DDC 540 dc23 LC record available at https://lccn.loc.gov/2016059284 British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Copyright © 2017 by World Scientific Publishing Co Pte Ltd All rights reserved This book, or parts thereof, may not be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording or any information storage and retrieval system now known or to be invented, without written permission from the publisher For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA In this case permission to photocopy is not required from the publisher Typeset by Stallion Press Email: enquiries@stallionpress.com Printed in Singapore Devi - Understanding Basic Chemistry.indd 03-02-17 4:37:23 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving PREFACE When a major examination approaches, students would start going around in search for guidebooks that can help them to consolidate the important concepts that are necessary to meet the requirements of these assessments in the shortest amount of time Unfortunately, most guidebooks are of the expository and non-refutational type, presenting facts rather than explaining them In addition, the links between concepts are often not made explicit and presupposes that learners would be able to make the necessary integration with the multitude of concepts that they have come across in their few years of chemical education, forgetting that some of them may lack the prior knowledge and metacognitive skills to it meaningfully Hence, learners would at most be able to reproduce the information that is structured and organized by the guidebook writer, but not able to construct a meaningful conceptual mental model for oneself As a result, they would not be able to fluidly apply what they should know across different contextual questions that appear when sitting for that major examination This revised edition is a continuation of our previous few books — Understanding Advanced Physical Inorganic Chemistry, Understanding Advanced Organic and Analytical Chemistry, Understanding Advanced Chemistry Through Problem Solving, and Understanding Basic Chemistry, retaining the main refutational characteristics of the previous books by strategically planting think-aloud questions to promote conceptual understanding, knowledge construction, reinforcement of important concepts, and discourse opportunities It is hoped that these essential questions would make learners be more aware of the possible conflict between their prior knowledge, which may be counterintuitive or misleading, with those presented in the text, and hence in the process, make the necessary v b2779_FM.indd 2/3/2017 4:32:30 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving vi Understanding Basic Chemistry Through Problem Solving c onceptual changes In essence, we are trying to effect metaconceptual awareness — awareness of the theoretical nature of one’s thinking — while learners are trying to master the essential chemistry concepts and be more familiar with their applications in problem solving We hope that by pointing out the differences between possible misconceptions and the actual chemistry content, we can promote such metaconceptual awareness and thus assist the learner to construct a meaningful conceptual model of understanding to meet the necessary assessment criteria We want our learners to not only know what they know, but at the same time, have a sense of how they know what they know and how their new learnings are interrelated within the discipline This would enable them to better appreciate and easily apply what they have learned in any novel question that they come across in major examinations Lastly, the content of this book would be both informative and challenging to the practices of teachers This book would certainly illuminate the instruction of all chemistry teachers who strongly believe in teaching chemistry in a meaningful and integrative approach, from the learners’ perspective The integrated questions that are used as problemsolving tools would definitely prove useful to students in helping them revise fundamental concepts learned from previous chapters, and also grasp the importance and relevancy in the application to their current learning Collectively, this book offers a vision of understanding and applying chemistry meaningfully and fundamentally from the learners’ approach and to fellow chemistry teachers, we hope that it would help you develop a greater insight into what makes you tick, explain, enthuse, and develop in the course of your teaching b2779_FM.indd 2/3/2017 4:32:30 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving ACKNOWLEDGEMENTS We would like to express our sincere thanks to the staff at World Scientific Publishing Co Pte Ltd for the care and attention which they have given to this book, particularly our editors Lim Sook Cheng and Sandhya Devi, our editorial assistant Chow Meng Wai and Stallion Press Special appreciation goes to Ms Ek Soo Ben (Principal of Victoria Junior College), Mr Cheong Tien Beng, Mrs Foo Chui Hoon, Mrs Toh Chin Ling and Mrs Ting Hsiao Shan for their unwavering support to Kim Seng Chan Special thanks go to all our students who have made our teaching of chemistry fruitful and interesting We have learnt a lot from them just as they have learnt some good chemistry from us Finally, we thank our families for their wholehearted support and understanding throughout the period of writing this book We would like to share with all the passionate learners of chemistry two important quotes from the Analects of Confucius: 學而時習之,不亦悅乎? (Isn’t it a pleasure to learn and practice what is learned time and again?) 學而不思則罔,思而不學則殆 (Learning without thinking leads to confusion, thinking without learning results in wasted effort) Kim Seng Chan BSc (Hons), PhD, PDGE (Sec) MEd, MA (Ed Mgt), MEd (G Ed), MEd (Dev Psy) Jeanne Tan BSc (Hons), PDGE (Sec), MEd (LST) vii b2779_FM.indd 2/3/2017 4:32:30 PM b2530 International Strategic Relations and China’s National Security: World at the Crossroads This page intentionally left blank b2530_FM.indd 01-Sep-16 11:03:06 AM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving CONTENTS v Preface vii Acknowledgements Chapter The Particulate Nature of Matter Chapter Atomic Structure 21 Chapter Chemical Bonding 37 Chapter Mole Concept, Formula, and Stoichiometry 71 Chapter Energy Change and Fuels 83 Chapter Rate of Chemical Reactions 105 Chapter Equilibria, Ammonia, and Sulfur 133 Chapter Acids, Bases, and Salts 167 Chapter Redox Reactions 201 Chapter 10 Electric Cells and the Reactivity Series 225 Chapter 11 Electrolysis 255 Chapter 12 The Periodic Table 285 Chapter 13 Metals and Extraction 323 Chapter 14 Air and the Environment 351 Chapter 15 Organic Chemistry 369 Chapter 16 Experimental Chemistry 419 Index451 ix b2779_FM.indd 2/3/2017 4:32:30 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving 56 Understanding Basic Chemistry Through Problem Solving 2. Sulfur is in Group 16 of the Periodic Table There are four naturally occurring isotopes of sulfur However, not all four isotopes are present in each sample of sulfur (a) Give the number of protons, neutrons, and electrons for isotopes, 34 S and 35S Explanation: Isotope No of protons No of neutrons No of electrons 34 16 34 - 16 = 18 16 35 16 35 - 16 = 19 16 S S (b) A sample of sulfur was found to contain 15% of 34S and 85% of 35S Suggest how could this information be found experimentally and calculate the relative atomic mass of this sample of sulfur Explanation: The isotopic composition can be determined by a method known as mass spectrometry (refer to Understanding Advanced Organic and Analytical Chemistry by K.S Chan and J Tan) The relative atomic mass is a weighted average of the relative isotopic masses of the different isotopes: Ar of sulfur = 15(34) + 85(35) = 34.9 (15 + 85) Did you notice that the relative atomic mass is closer to the relative isotopic mass of the isotope that has a higher proportion in the mixture of isotopes? b2779_Ch-03.indd 56 2/3/2017 4:08:26 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving Chemical Bonding 57 Q Why is the relative isotopic mass equivalent to the sum of the relative mass of the nucleons? A: The bulk mass of an atom comes from the nucleus, which consists of p rotons and neutrons, as the mass of an electron is negligible as compared to the mass of a nucleon (c) The eruption of volcano releases hydrogen sulfide (H2S), a toxic gas Give the dot-and-cross diagram of hydrogen sulfide, showing the valence electrons only Explanation: 3. Aluminum is widely used in the production of aircraft and automobiles, kitchenware, and high-voltage power cables (a) Describe the bonding present in solid aluminum Explain why aluminum is a conductor of electricity Explanation: The aluminum atoms are being held together by metallic bonds The loosely bound valence electrons of each aluminum atom are delocalized A metallic bond is the electrostatic attraction between the positive ions and the delocalized valence electrons As the valence electrons are delocalized, they can serve as charge carriers when an electrical potential difference is applied across a piece of metal This thus gives rise to the electrical conductivity nature of aluminum b2779_Ch-03.indd 57 2/3/2017 4:08:26 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving 58 Understanding Basic Chemistry Through Problem Solving So, when an electrical potential difference is applied across a piece of metal, the delocalized electrons actually move from one end of the metal to the other? Q A: No! Although the valence electrons are delocalized, they are not so mobile that they can actually move from one end of the metal to the other In fact, when a potential difference is applied, the electrons at one end of the metal move out of the metal first, thus creating “holes.” Subsequently, nearby electrons then “hop” into these holes This process repeated itself till the other end of the metal piece That is really how metals conduct electricity In addition, metals are also good thermal conductors due to their low mass and mobile delocalized valence electrons When heat is applied to one end of the metal, the vibrational kinetic energy of the electrons and cations increases Being low in mass, the kinetic energy of the mobile electrons will rapidly be transferred down the solid lattice structure (b) Give one chemical property of aluminum and support your answer with a chemical equation Explanation: Being a metal, aluminum can react with acid to give hydrogen gas: 2Al(s) + 3H2SO4(aq) → Al2(SO4)3(aq) + 3H2(g) b2779_Ch-03.indd 58 2/3/2017 4:08:27 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving Chemical Bonding 59 (c) Aluminum combines readily with both dry fluorine and dry chlorine Anhydrous aluminum chloride is a white solid which sublimes at about 200oC; it reacts with water and dissolves in non-polar solvents Aluminum fluoride melts at 1290°C and it conducts electricity; it is insoluble in non-polar solvents (i) Suggest, using the information above, the name of the bond type present in both aluminum chloride and aluminum fluoride Draw the dot-and-cross diagrams for these two compounds Explanation: The useful guideline to use is, “a metal reacts with a non-metal to give an ionic compound.” Based on the higher melting point of aluminum fluoride than aluminum chloride, aluminum fluoride is more likely to be an ionic compound with ionic bonding between the Al3+ and F - ions In addition, AlF3 is insoluble in non-polar solvent, an indication of its ionic nature In contrast, aluminum chloride is a covalent compound, with covalent bonds between the Al and the three Cl atoms The fact that AlCl3 is soluble in non-polar solvent is a good evidence of its molecular nature Q Why are ionic compounds soluble in water but not in non-polar solvents such as hexane? A: Polar molecules such as water molecules can interact with the ions as shown below: b2779_Ch-03.indd 59 2/3/2017 4:08:28 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving 60 Understanding Basic Chemistry Through Problem Solving The interaction releases energy since such an interaction is actually a type of bond formation and when bonds form, energy is evolved The energy that is released can be channeled to break the ionic bond Non-polar solvent molecules cannot form sufficiently strong interactions with the ions Hence, the ionic compound is insoluble in non-polar solvents as insufficient energy is released from the interaction of the ions and the solvent molecules to compensate for the energy that is needed to overcome the ionic bond The above is the explanation behind the maxim “like dissolves in like.” (ii) Explain why the bonding in aluminum fluoride leads to a high melting temperature, while the bonding in aluminum chloride results in a compound which sublimes Explanation: The higher melting point of aluminum fluoride is due to the stronger ionic bond between the Al3+ and F - ions The lower sublimation temperature of aluminum chloride is due to the weak intermolecular forces between the AlCl3 molecules Q So, the covalent bonds in AlCl3 are still intact when AlCl3 sublimes? A: Absolutely right When you melt or boil simple molecular compounds such as water, AlCl3, etc., you are breaking intermolecular forces and not the intramolecular covalent bonds Q So, does it mean that there is still ionic bonding in a molten ionic compound? A: Yes, of course Similarly, there is still metallic bonding in molten metal b2779_Ch-03.indd 60 2/3/2017 4:08:28 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving Chemical Bonding 61 Q So, the ability of a molten metal to conduct electricity is still due to the sea of delocalized electrons? A: Yes! (d) Aluminum is a preferred choice for high-voltage electric cables relative to copper Suggest a reason for this Explanation: Although copper is a better electrical conductor than aluminum due to the greater number of delocalized electrons as charge carriers, aluminum is lighter than copper This makes aluminum able to provide a better conductivity: weight ratio than copper 4. (a) Draw a dot-and-cross diagram to show the bonding in sodium oxide, Na2O, and sodium chloride, NaCl Explanation: (b) Dichloromethane, CH2Cl2, is a covalent compound with carbon as the central atom and single bonds formed between it and the other atoms Draw a dot-and-cross diagram for the molecule Explanation: b2779_Ch-03.indd 61 2/3/2017 4:08:29 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving 62 Understanding Basic Chemistry Through Problem Solving (c) The following pairs of elements join together to form covalent compounds Work out the formulae of the following compounds: (i) silicon and chlorine; Explanation: Using the octet rule as a guideline, the chemical formula for silicon tetrachloride is SiCl4 (ii) carbon and oxygen; Explanation: Carbon and oxygen can form both CO and CO2, in which all the atoms in both compounds fulfill the octet rule: There is a triple bond in CO in which one of the bonds is a dative covalent bond, where the electrons are donated by the oxygen atom (iii) hydrogen and phosphorous; Explanation: Hydrogen and phosphorous can form PH3 (iv) carbon and chlorine; Explanation: Using the octet rule as a guideline, the chemical formula for carbon tetrachloride is CCl4 b2779_Ch-03.indd 62 2/3/2017 4:08:29 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving Chemical Bonding 63 Q Which compound, CCl4 or SiCl4, would have a higher boiling point? A: Since both CCl4 and SiCl4 are non-polar molecules, the intermolecular forces that hold the particles together are id-id interactions As SiCl4 has more electrons than CCl4, its electron cloud is more polarizable Hence, the id-id interactions between SiCl4 molecules are stronger than those between the CCl4 molecules Thus, SiCl4 would have a higher boiling point than CCl4 (v) carbon and sulfur; and Explanation: Since both sulfur and oxygen belongs to the same group, based on the octet rule, the chemical formula for carbon disulfide is CS2 (vi) nitrogen and fluorine Explanation: Using the octet rule as a guideline, the chemical formula for nitrogen trifluoride is NF3 Q Does NF5 exist? A: No A nitrogen atom cannot have more than eight electrons in its valence shell This is because its valence shell is the n = electronic shell, which can only accommodate a maximum of eight electrons b2779_Ch-03.indd 63 2/3/2017 4:08:29 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving 64 Understanding Basic Chemistry Through Problem Solving 5. (a) When carbon dioxide dissolves in water, it forms carbonic acid, H2CO3, which contains a C=O double bond, two C-O single bonds, and two O-H single bonds Draw a dot-and-cross diagram to represent the structure of H2CO3 Explanation: The dot and cross diagram of H2CO3 is: Q Based on the dot-and-cross diagram, can H2CO3 have hydrogen bonding? A: Yes Since there is an H atom bonded to an O atom and there are lone pair of electrons on the various O atoms, hydrogen bonding can form between the H2CO3 molecules Q Is carbonic acid acidic because the O-H bonds can break to release H3O+ ions? A: Absolutely right The H2CO3 can dissociate as follows: H2CO3(aq) + 2H2O(l) CO32-(aq) + 2H3O+(aq) (b) Iodine can form either covalent or ionic bonds Draw dot-and-cross diagrams to show the bonding in potassium iodide (KI) and iodine (I2) b2779_Ch-03.indd 64 2/3/2017 4:08:29 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving Chemical Bonding 65 Explanation: (c) Explain why potassium iodide has a higher melting point than iodine Explanation: The strong ionic bond in potassium iodide causes it to have a higher melting point than the intermolecular forces of the id-id type between the iodine molecules Do you know? — When we melt or boil simple molecular compounds, we are breaking the intermolecular forces between the molecules and not the intramolecular covalent bonds (d) Explain why iodine and potassium iodide not conduct electricity when in the solid state, but when in the molten and a queous states, only potassium iodide can conduct electricity Explanation: In the solid state, the ions in potassium iodide are rigidly held in the lattice structure Thus, they cannot move when an electrical potential difference is applied But when melted or in the aqueous state, both the cations and anions are mobile Hence, these ions can act as charge carriers As for iodine, the molecules are overall electrically neutral Therefore, the molecules cannot move under the influence of an electrical potential difference b2779_Ch-03.indd 65 2/3/2017 4:08:30 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving 66 Understanding Basic Chemistry Through Problem Solving (e) A boron (B) atom has one fewer electron than a carbon atom, and a nitrogen (N) atom has one more Some B-N compounds are known to be isoelectronic with C-C compounds One form of boron nitride, a colorless electrical insulator, has a planar hexagonal layered structure of alternating boron and nitrogen atoms, similar to graphite (i) Explain the meaning of the term isoelectronic Explanation: When two particles have the same number of electrons, they are termed isoelectronic Q What is the significance of knowing the concept of being isoelectronic? A: If the particles are isoelectronic, where they have the same number of electrons, the inter-electronic repulsion within each of the particles are the same (ii) Suggest the type of bonding which is present within the layers Explanation: Since the structure of boron nitride is similar to that of graphite, the B and N atoms must be held together by B-N covalent bonds (iii) Suggest the type of interaction between the layers Explanation: From the outset, a layer of atoms is none other than a mass of electron cloud Since there is no covalent bond between the layers, what holds the different layers together would be intermolecular forces of the id-id type b2779_Ch-03.indd 66 2/3/2017 4:08:30 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving Chemical Bonding 67 Do you know? — Since the layers are being held together by intermolecular forces of the id-id dipole type, which are not strong in nature, the different layers can slide over each other easily This allows boron nitride to be used as a lubricant, like graphite (iv) Suggest a possible use in which this compound would behave similarly to the corresponding carbon compound Explanation: Boron nitride can replace graphite as a high-temperature lubricant Do you know? — Since the atoms in boron nitride are bonded by strong B-N covalent bonds which will only break at high temperatures, it can be used as a lubricant at high temperatures (v) When heated under high pressure, this form of boron nitride is converted into another form which is an extremely hard solid Suggest the type of structure adopted by this new material Explanation: In this new material, each of the boron and nitrogen would adopt a tetrahedral shape Among the four covalent bonds that an N atom forms with four B atoms, one of the N→B bond is a dative covalent bond The overall structure of this new material is very similar to the structure of diamond b2779_Ch-03.indd 67 2/3/2017 4:08:30 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving 68 Understanding Basic Chemistry Through Problem Solving Q If we have not come across the chemistry of boron nitride before, how would we know how to answer this question? A: In this chapter on Chemical Bonding, you need to know the structures and bonding of some basic substances such as diamond, graphite, sodium chloride, water, silicon dioxide, etc In the very beginning, the question already tells you that b oron nitride is similar to graphite So, you need to use the physical and chemical properties of graphite here Now, since diamond is related to graphite in terms of allotropy, we thus can infer that the planar layered structure of boron nitride can be transformed into the tetrahedral form This is applying what we have learned into a new context Q What is the meaning of allotropy? A: Allotropy refers to the phenomenon in which atoms of the same element are bonded differently together For example, both graphite and diamond consist of carbon atoms But in graphite, each carbon atom is bonded to three other carbon atoms But each carbon atom is bonded to four other carbon atoms in diamond The term allotropy is applicable only to elements but not compounds! (f ) The boiling points and molar masses of some hydrides are tabulated below Substance Boiling point/K Molar mass/g mol–1 CH4 109 16 NH3 240 17 H2O 373 18 (i) Suggest reasons for the difference in boiling points between NH3 and CH4 in terms of the type of molecules involved and the nature of the forces between them b2779_Ch-03.indd 68 2/3/2017 4:08:30 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving Chemical Bonding 69 Explanation: Both NH3 and CH4 exist as simple discrete molecular compounds held together by weak intermolecular forces The intermolecular forces between the non-polar CH4 molecules are of the id-id type This is much weaker than the hydrogen bonds between the NH3 molecules Hence, CH4 has a lower boiling point than NH3 (ii) Why does H2O have a higher boiling point than NH3? Explanation: Both NH3 and H2O exist as simple discrete molecular compounds held together by hydrogen bonds The hydrogen bonds between the H2O mole cules are more extensive than those between NH3 molecules This is because a H2O molecule can form, on average, two hydrogen bonds per molecule, whereas a NH3 molecule can only form one hydrogen bond per molecule Hence, the boiling point of water is higher than that of ammonia Q So, a HF molecule can also form, on average, one hydrogen bond per HF molecule? A: Yes! This thus explains why although the hydrogen bond between two HF molecules is stronger than that between water molecules, water has a higher boiling point than HF because there are more hydrogen bonds being formed per water molecule than per HF molecule b2779_Ch-03.indd 69 2/3/2017 4:08:30 PM b2530 International Strategic Relations and China’s National Security: World at the Crossroads This page intentionally left blank b2530_FM.indd 01-Sep-16 11:03:06 AM ... Understanding Basic Chemistry Through Problem Solving 22 ? ?Understanding Basic Chemistry Through Problem Solving For the valence electrons, other than the attractive force that is exerted by the. .. Cataloging-in-Publication Data Names: Chan, Kim Seng | Tan, Jeanne Title: Understanding basic chemistry through problem solving / by Kim Seng Chan (Victoria Junior College, Singapore), Jeanne Tan Description: Revised... 4:07:40 PM 6x9 b2779 Understanding Basic Chemistry Through Problem Solving 24 ? ?Understanding Basic Chemistry Through Problem Solving At an infinite distance from the nucleus, the energy of a free