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<title>DP Chemistry: Environmental impact - heavy metals</title>
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<meta name="description" content="Your students will need will to take some care when using solubility products.Consider the following values (at 298 K) which are obtained from the table given in Section 32 of the data book[1].An obvious question might be; Which one of the above salts has the lowest solubility in water at 298 K?Looking at the values for solubility products the answer might appear to be cadmium(II) hydroxide as its Ksp value is considerably...">
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<meta itemprop="description" content="Your students will need will to take some care when using solubility products.Consider the following values (at 298 K) which are obtained from the table given in Section 32 of the data book[1].An obvious question might be; Which one of the above salts has the lowest solubility in water at 298 K?Looking at the values for solubility products the answer might appear to be cadmium(II) hydroxide as its Ksp value is considerably...">
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<meta name="twitter:description" content="Your students will need will to take some care when using solubility products.Consider the following values (at 298 K) which are obtained from the table given in Section 32 of the data book[1].An obvious question might be; Which one of the above salts has the lowest solubility in water at 298 K?Looking at the values for solubility products the answer might appear to be cadmium(II) hydroxide as its Ksp value is considerably...">
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href="../19504/introduction-to-materials-science--1.html">Introduction to materials science </a></li><li><a href="../19519/metals-and-icp-spectroscopy-1.html">Metals and ICP spectroscopy</a></li><li><a href="../19541/catalysts--1.html">Catalysts </a></li><li><a href="../19580/liquid-crystals-1.html">Liquid crystals</a></li><li><a href="../19665/polymers--1.html">Polymers </a></li><li><a href="../19672/nanotechnology-1.html">Nanotechnology</a></li><li><a href="../19843/environmental-impact-plastics-1.html">Environmental impact - plastics</a></li><li><a href="../19858/superconducting-metals-x-ray-crystallography--1.html">Superconducting metals & X-ray crystallography </a></li><li><a href="../19666/condensation-polymers-1.html">Condensation polymers</a></li><li class="selected"><a href="environmental-impact-heavy-metals-1.html">Environmental impact - heavy metals</a></li></ul></li><li><a href="../19284/option-b--1.html" class="father">Option B </a><ul class="level-2"><li><a href="../19290/introduction-to-biochemistry--1.html">Introduction to biochemistry </a></li><li><a href="../19287/proteins-enzymes--1.html">Proteins & enzymes </a></li><li><a href="../19291/lipids-1.html">Lipids</a></li><li><a href="../19299/carbohydrates--1.html">Carbohydrates </a></li><li><a href="../19305/vitamins--1.html">Vitamins </a></li><li><a href="../19313/biochemistry-the-environment--1.html">Biochemistry & the environment </a></li><li><a href="../19336/proteins-enzymes-ahl--1.html">Proteins & enzymes (AHL) </a></li><li><a href="../19347/nucleic-acids--1.html">Nucleic acids </a></li><li><a href="../19361/biological-pigments--1.html">Biological pigments </a></li><li><a href="../19366/stereochemistry-in-biomolecules-1.html">Stereochemistry in biomolecules</a></li></ul></li><li><a href="../19390/option-c--1.html" class="father">Option C </a><ul class="level-2"><li><a href="../19391/energy-sources-1.html">Energy sources</a></li><li><a href="../19407/fossil-fuels-1.html">Fossil fuels</a></li><li><a href="../19411/nuclear-fusion-nuclear-fission-reactions-1.html">Nuclear fusion & nuclear fission reactions</a></li><li><a href="../19429/solar-energy-1.html">Solar energy</a></li><li><a href="../19437/environmental-impact-global-warming-1.html">Environmental impact - global warming</a></li><li><a href="../19453/electrochemistry-rechargeable-batteries-fuel-cells-1.html">Electrochemistry, rechargeable batteries & fuel cells</a></li><li><a href="../19458/nuclear-fusion-fission-hl--1.html">Nuclear fusion & fission (HL) </a></li><li><a href="../19470/photovoltaic-cells-and-dsscs-1.html">Photovoltaic cells and DSSCs</a></li></ul></li><li><a href="../19078/option-d-1.html" class="father">Option D</a><ul class="level-2"><li><a href="../19079/pharmaceutical-products-drug-action--1.html">Pharmaceutical products & drug action </a></li><li><a href="../19158/aspirin-penicillin--1.html">Aspirin & penicillin </a></li><li><a href="../19174/opiates-1.html">Opiates</a></li><li><a href="../19184/ph-regulation-of-the-stomach-1.html">pH regulation of the stomach</a></li><li><a href="../19194/antiviral-medications--1.html">Antiviral medications </a></li><li><a href="../19211/environmental-impact-of-some-medications-1.html">Environmental impact of some medications</a></li><li><a href="../19254/taxol-a-chiral-auxiliary-case-study-1.html">Taxol - a chiral auxiliary case study</a></li><li><a href="../19258/nuclear-medicine--1.html">Nuclear medicine </a></li><li><a href="../19273/drug-detection-analysis--1.html">Drug detection & analysis </a></li></ul></li></ul></li><li><a href="../16592/practical-scheme-of-work-ia--1.html">Practical scheme of work & IA </a><ul class="level-1"><li><a href="../16682/internal-assessment-1.html" class="father">Internal Assessment</a><ul class="level-2"><li><a href="../18892/scaffolding-the-investigation-1.html">'Scaffolding' the investigation</a></li><li><a href="../18896/timing-organisation--1.html">Timing & organisation </a></li><li><a href="../18905/choosing-the-research-question-1.html">Choosing the research question</a></li><li><a href="../18946/personal-engagement-1.html">Personal engagement</a></li><li><a href="../18950/exploration-1.html">Exploration</a></li><li><a href="../18957/analysis-1.html">Analysis</a></li><li><a href="../18965/evaluation-1.html">Evaluation</a></li><li><a href="../18966/communication-1.html">Communication</a></li><li><a href="../19882/internal-standardization-of-the-ia-1.html">Internal standardization of the IA</a></li><li><a href="../19901/submitting-the-samples-for-moderation-2.html">Submitting the samples for moderation</a></li><li><a href="../33754/ten-suggestions-for-ias-using-secondary-data-1.html">Ten suggestions for IAs using secondary data</a></li><li><a href="../37544/gaining-full-marks-for-a-databased-ia--1.html">Gaining full marks for a databased IA </a></li><li><a href="../19506/ia-example-marking-exercise--1.html">IA example & marking exercise </a></li><li><a href="../23929/genuine-examples-of-moderated-ia-reports-1.html">Genuine examples of moderated IA reports</a></li><li><a href="../25234/examples-of-teacher-marked-ia-reports--1.html">Examples of teacher-marked IA reports </a></li><li><a href="../37542/history-of-internal-assessment-1.html">History of Internal Assessment</a></li></ul></li><li><a href="../16598/mandatory-laboratory-components-1.html" class="father">Mandatory laboratory components</a><ul class="level-2"><li><a href="../16613/formula-of-magnesium-oxide--1.html">Formula of magnesium oxide </a></li><li><a href="../16612/determining-the-mr-of-an-unknown-gas-1.html">Determining the <i>M</i><sub>r</sub> of an unknown gas</a></li><li><a href="../16615/acid-base-titrations--1.html">Acid-base titrations </a></li><li><a href="../16616/a-green-acid-base-practical-1.html">A green acid-base practical</a></li><li><a href="../16617/analysis-of-aspirin-tablets-1.html">Analysis of aspirin tablets</a></li><li><a href="../16618/caco3-in-egg-shells-1.html">CaCO<sub>3</sub> in egg shells</a></li><li><a href="../16644/enthalpy-changes-1.html">Enthalpy changes</a></li><li><a href="../16631/reaction-rates-1.html">Reaction rates</a></li><li><a href="../16635/rate-dependent-factors-1.html">Rate-dependent factors</a></li><li><a href="../16636/determining-ea-for-a-reaction-1.html">Determining <i>E</i><sub>a</sub> for a reaction</a></li><li><a href="../16637/iodination-of-propanone-1.html">Iodination of propanone</a></li><li><a href="../18144/titrations-with-a-ph-meter-1.html">Titrations with a pH meter</a></li><li><a href="../18355/redox-titration-with-kmno4--1.html">Redox titration with KMnO<sub>4</sub> </a></li><li><a href="../16640/voltaic-cells-1.html">Voltaic cells</a></li><li><a href="../16659/3-d-molecular-modelling--1.html">3-D molecular modelling </a></li></ul></li><li><a href="../17168/other-good-practicals-1.html" class="father">Other good practicals</a><ul class="level-2"><li><a href="../17196/common-chemical-reactions-1.html">Common chemical reactions</a></li><li><a href="../227/elements-oxides-of-the-third-period--1.html">Elements & oxides of the third period </a></li><li><a href="../17239/the-halogens-1.html">The halogens</a></li><li><a href="../17162/boiling-points-of-mixtures-1.html">Boiling points of mixtures</a></li><li><a href="../17170/polarity-of-molecules-1.html">Polarity of molecules</a></li><li><a href="../18083/le-chateliers-principle--1.html">Le Chatelier's principle </a></li><li><a href="../19582/determining-kc-for-an-esterification-reaction-1.html">Determining <i>K</i><sub>c</sub> for an esterification reaction</a></li><li><a href="../18164/redox-reactions-of-vanadium--1.html">Redox reactions of vanadium </a></li><li><a href="../18351/chlorine-in-swimming-pools--1.html">Chlorine in swimming pools </a></li><li><a href="../18178/analysis-of-cuii-ions-in-solution--1.html">Analysis of Cu(II) ions in solution </a></li><li><a href="../18179/percentage-of-copper-in-brass-1.html">Percentage of copper in brass</a></li><li><a href="../18356/electrolytic-cells--1.html">Electrolytic cells </a></li><li><a href="../18598/reactions-of-organic-compounds-1.html">Reactions of organic compounds</a></li><li><a href="../18752/hydrolysis-of-halogenoalkanes-1.html">Hydrolysis of halogenoalkanes</a></li><li><a href="../18784/preparation-of-13-dinitrobenzene--1.html">Preparation of 1,3-dinitrobenzene </a></li><li><a href="../19022/determination-of-an-organic-structure-1.html">Determination of an organic structure</a></li><li><a href="../19887/preparation-of-nylon-66-1.html">Preparation of nylon 6,6</a></li><li><a href="../19343/determination-of-vitamin-c-content--1.html">Determination of vitamin C content </a></li><li><a href="../19342/hydrolysis-of-starch--1.html">Hydrolysis of starch </a></li><li><a href="../19159/preparation-purification-of-aspirin--1.html">Preparation & purification of aspirin </a></li></ul></li><li><a href="../18851/ict-in-practical-work-1.html" class="father">ICT in practical work</a><ul class="level-2"><li><a href="../18852/data-logging--1.html">Data logging </a></li><li><a href="../18853/software-for-graph-plotting--1.html">Software for graph plotting </a></li><li><a href="../18854/spreadsheets-for-data-processing--1.html">Spreadsheets for data processing </a></li><li><a href="../18855/databases-1.html">Databases</a></li><li><a href="../18856/computer-modelling-simulations--1.html">Computer modelling & simulations </a></li></ul></li><li><a href="../16594/group-4-project-1.html" class="father">Group 4 Project</a><ul class="level-2"><li><a href="../16595/practicalities-1.html">Practicalities</a></li><li><a href="../16596/reflective-statement--2.html">Reflective statement </a></li></ul></li><li><a href="../16666/a-new-laboratory-1.html">A new laboratory?</a></li></ul></li><li><a href="../16284/exams-1.html">Exams</a><ul class="level-1"><li><a href="../16286/essential-facts-1.html" class="father">Essential Facts</a><ul class="level-2"><li><a href="../16287/objectives-command-terms-1.html">Objectives & command terms</a></li><li><a href="../16288/grade-descriptors-1.html">Grade descriptors</a></li><li><a href="../16289/grade-boundaries-1.html">Grade boundaries</a></li></ul></li><li><a href="../16302/paper-1-multiple-choice-1.html" class="father">Paper 1 (Multiple Choice)</a><ul class="level-2"><li><a href="../16303/advice-to-students-paper-1-1.html">Advice to students (Paper 1)</a></li><li><a href="../31515/practice-paper-1-exams-1.html">Practice Paper 1 exams</a></li></ul></li><li><a href="../16305/paper-2-1.html" class="father">Paper 2</a><ul class="level-2"><li><a href="../16306/advice-to-students-paper-2-1.html">Advice to students (Paper 2)</a></li><li><a href="../16307/areas-of-difficulty-1.html">Areas of difficulty</a></li></ul></li><li><a href="../16313/paper-3--1.html" class="father">Paper 3 </a><ul class="level-2"><li><a 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href="../16323/retaking-the-exam-1.html">Retaking the exam</a></li></ul></li><li><a href="../16325/faqs-1.html">FAQs</a></li></ul></li><li><a href="../3147/ib-core-1.html">IB Core</a><ul class="level-1"><li><a href="../3149/learner-profile-1.html">Learner Profile</a></li><li><a href="../21735/extended-essays--1.html" class="father">Extended Essays </a><ul class="level-2"><li><a href="../21736/overview--1.html">Overview </a></li><li><a href="../21780/responsibilities-1.html">Responsibilities</a></li><li><a href="../21790/resources-1.html">Resources</a></li><li><a href="../21800/research-1.html">Research</a></li><li><a href="../21804/writing-the-essay-1.html">Writing the essay</a></li><li><a href="../21810/assessment-1.html">Assessment</a></li><li><a href="../22434/summary-of-advice--1.html">Summary of advice </a></li><li><a href="../25272/faqs--1.html">FAQs </a></li></ul></li><li><a href="../307/theory-of-knowledge-tok-1.html" class="father">Theory of Knowledge (TOK)</a><ul class="level-2"><li><a href="../41171/the-12-tok-concepts-1.html">The 12 TOK concepts</a></li><li><a href="../3507/why-tok-chemistry-1.html">Why TOK & Chemistry?</a></li><li><a href="../3505/a-modern-paradigm-1.html">A modern paradigm</a></li></ul></li></ul></li><li><a href="../17783/fast-track-to-tests-questions-1.html">Fast track to tests & questions</a><ul class="level-1"><li><a href="../17784/sl-multiple-choice-tests-on-individual-topics-1.html">SL Multiple choice tests on individual topics</a></li><li><a href="../24351/sl-multiple-choice-quizzes-on-sub-topics-1.html">SL Multiple choice 'quizzes' on sub-topics</a></li><li><a href="../31519/sl-practice-paper-1-exams-1.html">SL Practice Paper 1 exams</a></li><li><a href="../17786/sl-questions-on-each-sub-topic-1.html">SL Questions on each sub-topic</a></li><li><a href="../20431/sl-paper-3-section-a-questions-1.html">SL Paper 3 Section A questions</a></li><li><a href="../17792/sl-questions-on-the-options-1.html">SL Questions on the options</a></li><li><a href="../24897/sl-quizzes-on-option-sub-topics--1.html">SL Quizzes on option sub-topics </a></li><li><a href="../17785/hl-multiple-choice-tests-on-individual-topics-1.html">HL Multiple choice tests on individual topics</a></li><li><a href="../24352/hl-multiple-choice-quizzes-on-sub-topics-1.html">HL Multiple choice 'quizzes' on sub-topics</a></li><li><a href="../31520/hl-practice-paper-1-exams--1.html">HL Practice Paper 1 exams </a></li><li><a href="../17787/hl-questions-on-each-sub-topic--1.html">HL Questions on each sub-topic </a></li><li><a href="../20428/hl-paper-3-section-a-questions-1.html">HL Paper 3 Section A questions</a></li><li><a href="../17793/hl-questions-on-the-options-1.html">HL Questions on the options</a></li><li><a href="../24973/hl-quizzes-on-option-sub-topics-1.html">HL Quizzes on option sub-topics</a></li><li><a href="../41573/printable-versions-of-written-tasks--1.html">Printable versions of written tasks </a></li></ul></li><li><a 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biomolecules">Stereochemistry in biomolecules</a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../25034/mc-test-stereochemistry-in-biomolecules--1.html" title="MC test: Stereochemistry in biomolecules ">MC test: Stereochemistry in biomolecules </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../19373/stereochemistry-in-biomolecules-questions-1.html" title="Stereochemistry in biomolecules questions">Stereochemistry in biomolecules questions</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../24871/stereochemistry-in-biomolecules-answers--1.html" title="Stereochemistry in biomolecules answers ">Stereochemistry in biomolecules answers </a></li></ul></ul><li class=" parent" style="padding-left: 0px"><i class="expander fa fa-caret-right "></i><a href="../19390/option-c--1.html" title="Option C ">Option C </a></li><ul 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href="../25188/mc-test-nuclear-fusion-nuclear-fission-reactions-1.html" title="MC test: Nuclear fusion & nuclear fission reactions">MC test: Nuclear fusion & nuclear fission reactions</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../19421/nuclear-fusion-nuclear-fission-questions-1.html" title="Nuclear fusion & nuclear fission questions">Nuclear fusion & nuclear fission questions</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../25180/nuclear-fusion-nuclear-fission-answers-1.html" title="Nuclear fusion & nuclear fission answers">Nuclear fusion & nuclear fission answers</a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../19429/solar-energy-1.html" title="Solar energy">Solar energy</a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a 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global warming</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../19450/environmental-impact-global-warming-questions--1.html" title="Environmental impact - global warming questions ">Environmental impact - global warming questions </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../25190/environmental-impact-global-warming-answers-1.html" title="Environmental impact - global warming answers">Environmental impact - global warming answers</a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../19453/electrochemistry-rechargeable-batteries-fuel-cells-1.html" title="Electrochemistry, rechargeable batteries & fuel cells">Electrochemistry, rechargeable batteries & fuel cells</a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a 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title="Nuclear fusion & fission (HL) ">Nuclear fusion & fission (HL) </a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../25269/mc-test-nuclear-fusion-nuclear-fission-hl-1.html" title="MC test: Nuclear fusion & nuclear fission (HL)">MC test: Nuclear fusion & nuclear fission (HL)</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../19468/nuclear-fusion-fission-reactions-hl-questions--1.html" title="Nuclear fusion & fission reactions (HL) questions ">Nuclear fusion & fission reactions (HL) questions </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../25205/nuclear-fusion-fission-reactions-hl-answers-1.html" title="Nuclear fusion & fission reactions (HL) answers">Nuclear fusion & fission reactions (HL) answers</a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../19470/photovoltaic-cells-and-dsscs-1.html" title="Photovoltaic cells and DSSCs">Photovoltaic cells and DSSCs</a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../25302/mc-test-photovoltaic-cells-dsscs-1.html" title="MC test: Photovoltaic cells & DSSCs">MC test: Photovoltaic cells & DSSCs</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../19471/photovoltaic-cells-and-dsscs-questions--1.html" title="Photovoltaic cells and DSSCs questions ">Photovoltaic cells and DSSCs questions </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../25206/photovoltaic-cells-and-dsscs-answers-1.html" title="Photovoltaic cells and DSSCs answers">Photovoltaic cells and DSSCs answers</a></li></ul></ul><li class=" parent" style="padding-left: 0px"><i class="expander fa fa-caret-right "></i><a href="../19078/option-d-1.html" title="Option D">Option D</a></li><ul class="level-1 "><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../19079/pharmaceutical-products-drug-action--1.html" title="Pharmaceutical products & drug action ">Pharmaceutical products & drug action </a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../25440/mc-test-pharmaceutical-products-drug-action-1.html" title="MC test: Pharmaceutical products & drug action">MC test: Pharmaceutical products & drug action</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../19154/pharmaceutical-products-drug-action-questions--1.html" title="Pharmaceutical products & drug action questions ">Pharmaceutical products & drug action questions </a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../25270/pharmaceutical-products-drug-action-answers--1.html" title="Pharmaceutical products & drug action answers ">Pharmaceutical products & drug action answers </a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../19158/aspirin-penicillin--1.html" title="Aspirin & penicillin ">Aspirin & penicillin </a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../25684/mc-test-aspirin-penicillin-1.html" title="MC test: Aspirin & penicillin">MC test: Aspirin & penicillin</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../19171/aspirin-penicillin-questions-1.html" title="Aspirin & penicillin questions">Aspirin & penicillin questions</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../25313/aspirin-penicillin-answers--1.html" title="Aspirin & penicillin answers ">Aspirin & penicillin answers </a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../19174/opiates-1.html" title="Opiates">Opiates</a></li><ul class="level-2 "><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../25494/mc-test-opiates-1.html" title="MC test: Opiates">MC test: Opiates</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../19176/opiates-questions-1.html" title="Opiates questions">Opiates questions</a></li><li class="" style="padding-left: 28px"><i class="expander fa fa-caret-right "></i><a href="../25356/opiates-answers--1.html" title="Opiates answers ">Opiates answers </a></li></ul><li class=" parent" style="padding-left: 14px"><i class="expander fa fa-caret-right "></i><a href="../19184/ph-regulation-of-the-stomach-1.html" title="pH regulation of the stomach">pH regulation of the stomach</a></li><ul class="level-2 "><li 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</div><section id="main-content"><div id="toc-1672969665" class="toc"><a href="#" class="toc-switcher" title="Show table of contents"><small><i class="fa fa-reorder"></i> Table of contents <span class="pull-right"><i class="fa fa-chevron-down"></i></span></small></a></div><h1><img class="ico" src="../../../img/icons/higher-1.png"><strong> A.10 </strong>Environmental impact - heavy metals <strong>(3 hours)</strong></h1><hr class="hidden"><div class="pinkBg"><div><h2><strong>Pause for thought</strong></h2><p>Your students will need will to take some care when using solubility products.</p><p>Consider the following values (at 298 K) which are obtained from the table given in Section 32 of the data book<sup data-footnote-id="9zt1g"><a class="scroll-to" data-target="footnote-1" id="footnote-marker-1-1" rel="footnote">[1]</a></sup>.</p><hr class="hidden"><p style="text-align: center;"><img alt="" class="noborder" src="../../../ib/chemistry/images/2014-Options/Option-A/Ksp-values.jpg" style="width: 320px; height: 145px;"></p><hr class="hidden"><p>An obvious question might be; Which one of the above salts has the lowest solubility in water at 298 K?</p><p>Looking at the values for solubility products the answer might appear to be cadmium(II) hydroxide as its <em>K</em><sub>sp</sub> value is considerably lower than the <em>K</em><sub>sp</sub> values for the other two salts. In the 2001-2007 programme (last exams November 2008) students were expected to know that equilibrium constants had units and they could be asked to deduce them for particular reactions. Since then the IB has correctly stated that equilibrium constants have no units but this can lead to a little confusion when faced with a table of values such as the one given above. To compare the values meaningfully, students need to consider what equilibrium system each <em>K</em><sub>sp</sub> value is referring to.</p><p>Consider the first value of 1.0 x 10<sup>−12</sup> for cadmium carbonate. This refers to:</p><p>CdCO<sub>3</sub>(s) ⇌ Cd<sup>2</sup><sup>+</sup>(aq) + CO<sub>3</sub><sup>2−</sup>(aq)</p><p>and <em>K</em><sub>sp</sub> = [Cd<sup>2</sup><sup>+</sup>(aq)] x [ CO<sub>3</sub><sup>2−</sup>(aq)]</p><p>For a saturated solution of cadmium(II) carbonate at 298 K, [Cd<sup>2</sup><sup>+</sup>(aq)] = [ CO<sub>3</sub><sup>2−</sup>(aq)] = (1.0 x 10<sup>−12</sup>)<sup>½</sup> = 1.0 x 10<sup>−6</sup> mol dm<sup>−3</sup></p><p>so the solubility of cadmium(II) carbonate at 298 K is 1.0 x 10<sup>−6</sup> mol dm<sup>−3</sup>.</p><p>For cadmium(II) hydroxide, <em>K</em><sub>sp</sub> at 298 K is 7.2 x 10<sup>−15</sup>. The equilibrium system this value refers to is:</p><p>Cd(OH)<sub>2</sub>(s) ⇌ Cd<sup>2</sup><sup>+</sup>(aq) + 2OH<sup>−</sup>(aq)</p><p>and <em>K</em><sub>sp</sub> = [Cd<sup>2</sup><sup>+</sup>(aq)] x [OH<sup>−</sup>(aq)]<sup>2</sup></p><p>For a saturated solution of cadmium(II) hydroxide [OH<sup>−</sup>(aq)] = 2 x [Cd<sup>2</sup><sup>+</sup>(aq)]</p><p>so <em>K</em><sub>sp</sub> = 4 x [Cd<sup>2</sup><sup>+</sup>(aq)]<sup>3</sup>, which means [Cd<sup>2</sup><sup>+</sup>(aq)] = (7.2 x 10<sup>−15</sup> ÷ 4)<sup>⅓</sup> = (1.8 x 10<sup>−15</sup>)<sup>⅓</sup> = 1.2 x 10<sup>−5</sup> mol dm<sup>−3</sup></p><p>The solubility of cadmium(II) hydroxide in water at 298 K is therefore 1.2 x 10<sup>−5</sup> mol dm<sup>-3</sup> which means that it is more soluble in water than cadmium(II) carbonate at 298 K.</p><p>However the <em>K</em><sub>sp</sub> value for lead(II) carbonate at 298 K is 7.40 x 10<sup>−14</sup>. By carrying out a similar calculation to the ones above it can be seen that the solubility of lead(II) carbonate in water at 298 K is 2.7 x 10<sup>−7</sup> mol dm<sup>−3</sup>. Thus lead(II) carbonate is the least soluble of the three salts.</p><p>Although it would not affect the order for these three salts, note too that if solubilities are expressed in g dm<sup>−3</sup> rather than mol dm<sup>−3</sup><sup> </sup> then this may also affect the order if the molar solubilities are close in value.</p><hr class="hidden"></div></div><hr class="hidden"><div class="box"><div><h2><strong>Nature of Science</strong></h2><p>Although scientific research often proceeds with perceived benefits in mind, there is a responsibility to also consider the risks and implications.</p><hr class="hidden"></div></div><hr class="hidden"><div class="box"><table align="left" border="0" cellpadding="10" cellspacing="0"><tbody><tr><td style="width: 50%;" valign="top"><div class="yellowBg"><div><h2 id="anchor-3"><strong><strong>Learning outcomes</strong></strong></h2><p>After studying this topic students should be able to:</p><p><strong><strong>Understand:</strong></strong></p><ul><li>The normal oxidation/reduction balance in cells can be disturbed by toxic doses of transition metals through various mechanisms.</li><li>Methods of removing heavy metals include precipitation, adsorption, and chelation.</li><li>Due to the chelate effect polydentate ligands tend to give more stable complexes than monodentate<br>ligands. This can be explained by considering entropy changes.</li></ul><hr class="hidden"><p><strong>Apply their knowledge to:</strong></p><ul><li>Explain the use of chelating substances to remove heavy metals.</li><li>Deduce the number of coordinate bonds a ligand can form with a central metal ion.</li><li>Solve problems involving <em>K</em><sub>sp</sub> as an application of removing metals in solution.</li><li>Compare and contrast the Fenton and Haber–Weiss reaction mechanisms.</li></ul></div></div></td><td style="width: 50%;" valign="top"><h4><b><span style="font-weight: normal; "></span></b></h4><div class="yellowBg"><div><h4><b><span style="font-weight: normal; "><strong>Clarification notes</strong></span></b></h4><p>Consider ethane−1,2−diamine to act as a bidentate ligand and EDTA<sup>4</sup><sup>-</sup> to act as a hexadentate ligand.</p><hr class="hidden"><p>In biological processes the Haber–Weiss reaction naturally generates free radicals. Transition metals can catalyse the reaction. In the Fenton reaction the mechanism for generating reactive hydroxyl radicals involves the iron catalyst.</p><hr class="hidden"><p><em>K</em><sub>sp</sub> values are given in Section 32 of the data booklet.</p><hr class="hidden"><h4 id="anchor-5">International-mindedness</h4>Consider the responsibilities that scientists have for the global impact of their work.</div></div></td></tr></tbody></table></div><hr class="hidden"><div class="box"><table align="left" border="0" cellpadding="10" cellspacing="0"><tbody><tr><td style="width: 50%;" valign="top"><h2><b><span style="font-weight: normal; "><strong>Teaching tips</strong></span></b></h2><p>This is quite a difficult topic to teach but does provide plenty of opportunities for some interesting examination questions. Essentially you need to cover precipitation and chelation as two different ways of removing heavy metals from the environment and also mention adsorption.</p><p>For precipitation you will need to cover the application of the equilibrium law to sparingly soluble (i.e. ‘insoluble’) salts. For binary salts the solubility product is equal to the product of the concentrations of the two ions at equilibrium but care needs to be taken with salts such as lead(II) hydroxide), Pb(OH)<sub>2</sub>, which form more ions in solutions (see “Pause for thought’ above). It is also worth mentioning how the common ion effect can increase the precipitation of metal ions by increasing the concentration of the anion in the saturated solution. Although it does not appear on the syllabus it might also be worth explaining how sometimes the common ion effect can lead to increased solubility due to complex ion formation. For example, zinc hydroxide redissolves in excess hydroxide ions to form [Zn(OH)<sub>4</sub>]<sup>2−</sup>(aq).</p><p>Students already know how monodentate ligands use a non-bonding pair of electrons to form a coordinate bond to a transition metal ion. Explain that polydentate ligands contain more than one non-bonding pair of electrons so can have coordination numbers greater than 1. Use EDTA and ethane-1,2-diamine as examples and explain that as one ion of EDTA<sup>4−</sup> reacts with one ion of [Ni(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup>, for example, the products are one ion of [Ni(EDTA)]<sup>2−</sup> and six molecules of water so the entropy change is positive. This means that Δ<em>G</em> is more negative (since Δ<em>G</em><em> </em>= Δ<em>H</em><em> –</em> <em>T</em>Δ<em>S</em><em>)</em> and the chelated complex will be stable as Δ<em>G</em> = −<em>RT</em>ln<em>K</em> .</p><p>The Haber-Weiss reaction and the more specific Fenton reaction, which uses iron complexes to catalyse the formation of hydroxyl radicals, OH<strong><sup></sup></strong><sup><strong>.</strong></sup> from hydrogen peroxide and the superoxide free radical ion, O<sub>2</sub><sup>−<strong></strong></sup><sup><strong>.</strong></sup>, need to be mentioned. The hydroxyl radical produced is very reactive and is <a href="http://www.lenntech.com/fenton-reaction.htm">used in various industrial processes</a>.</p><p>Adsorption can include the use of activated charcoal or clay etc. to remove heavy metal ions from polluted water.</p><hr class="hidden"></td><td style="width: 50%;" valign="top"><h4><b><span style="font-weight: normal;"><strong>Study guide</strong></span></b></h4><p><img alt="" src="../../../ib/chemistry/images/2014%20Basic%20information/New%20cover.jpg" style="width: 67px; height: 96px;"></p><p style="margin: 0px 0px 1em; padding: 0px; color: rgb(0, 0, 0); font-size: 1em;"></p><hr class="hidden"><p style="margin: 0px 0px 1em; padding: 0px; color: rgb(0, 0, 0); font-size: 1em;"><b><span style="font-weight: normal;">Pages 121 & 122 </span></b></p><hr class="hidden"><h2>Questions</h2><p>For ten 'quiz' questions (for quick testing of knowledge and understanding with the answers explained) see <a href="../27097/mc-test-environmental-impact-heavy-metals-1.html" title="Options » Option A » Environmental impact - heavy metals » MC test: Environmental impact - heavy metals">MC test: Environmental impact - heavy metals</a>.</p><p>For short-answer questions see <a href="../19926/environmental-impact-heavy-metals-questions--1.html" title="Options » Option A » Environmental impact - heavy metals » Environmental impact - heavy metals questions ">Environmental impact - heavy metals questions </a>together with the worked answers on a separate page <a href="../26060/environmental-impact-heavy-metals-answers-1.html" title="Options » Option A » Environmental impact - heavy metals » Environmental impact - heavy metals answers">Environmental impact - heavy metals answers</a>.</p><hr class="hidden"><h4><span style=""><b><span style="font-weight: normal;"><strong>Vocabulary list</strong></span></b></span></h4><p><span style=""><span style="font-weight: normal;">chelate/chelation</span><br>sequestration<br><span style="font-weight: normal;">coordination number<br>polydentate ligand</span></span><br>ethane−1,2−diamine<br>ethylenediaminetetraacetic acid, EDTA<br>solubility product, <em>K</em><sub>sp</sub></p></td></tr></tbody></table></div><hr class="hidden"><div class="greenBg"><div><h2 id="header-12">Teaching slides</h2><p>Teachers may wish to share these slides with students for learning or for reviewing key concepts.</p><div id="myCarousel-13" class="carousel slide" data-id="722"><!-- Carousel items --><div class="carousel-inner"><div class="active item"><a class="fancy" href="../../../tib-galleries/3-722/a101.png" rel="gallery-722" title=""><img alt="" src="files/tib-galleries/3-722/a101.png"></a><div class="carousel-caption"><p>Environmental impact - heavy metals: </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-722/a102.png" rel="gallery-722" title=""><img alt="" src="files/tib-galleries/3-722/a102.png"></a><div class="carousel-caption"><p>Environmental impact - heavy metals: </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-722/a103.png" rel="gallery-722" title=""><img alt="" src="files/tib-galleries/3-722/a103.png"></a><div class="carousel-caption"><p>Environmental impact - heavy metals: </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-722/a104.png" rel="gallery-722" title=""><img alt="" src="files/tib-galleries/3-722/a104.png"></a><div class="carousel-caption"><p>Environmental impact - heavy metals: </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-722/a105.png" rel="gallery-722" title=""><img alt="" src="files/tib-galleries/3-722/a105.png"></a><div class="carousel-caption"><p>Environmental impact - heavy metals: </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-722/a106.png" rel="gallery-722" title=""><img alt="" src="files/tib-galleries/3-722/a106.png"></a><div class="carousel-caption"><p>Environmental impact - heavy metals: </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-722/a107.png" rel="gallery-722" title=""><img alt="" src="files/tib-galleries/3-722/a107.png"></a><div class="carousel-caption"><p>Environmental impact - heavy metals: </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-722/a108.png" rel="gallery-722" title=""><img alt="" src="files/tib-galleries/3-722/a108.png"></a><div class="carousel-caption"><p>Environmental impact - heavy metals: </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-722/a109.png" rel="gallery-722" title=""><img alt="" src="files/tib-galleries/3-722/a109.png"></a><div class="carousel-caption"><p>Environmental impact - heavy metals: </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-722/a1010.png" rel="gallery-722" title=""><img alt="" src="files/tib-galleries/3-722/a1010.png"></a><div class="carousel-caption"><p>Environmental impact - heavy metals: </p></div></div><div class="item"><a class="fancy" href="../../../tib-galleries/3-722/a1011.png" rel="gallery-722" title=""><img alt="" src="files/tib-galleries/3-722/a1011.png"></a><div class="carousel-caption"><p>Environmental impact - heavy metals: </p></div></div></div><!-- Carousel nav --><a class="carousel-control left" href="#myCarousel-13" data-slide="prev">‹</a><a class="carousel-control right" href="#myCarousel-13" data-slide="next">›</a><div class="tib-indicators"><img class="" title="Click to view" style="margin: 10px 4px; width: 48px; height: 48px;" alt="" src="files/tib-galleries/3-722/a101-thumb128.jpg"><img class="" title="Click to view" style="margin: 5px 4px; width: 48px; height: 48px;" alt="" src="files/tib-galleries/3-722/a102-thumb128.jpg"><img class="" title="Click to view" style="margin: 5px 4px; width: 48px; height: 48px;" alt="" src="files/tib-galleries/3-722/a103-thumb128.jpg"><img class="" title="Click to view" style="margin: 5px 4px; width: 48px; height: 48px;" alt="" src="files/tib-galleries/3-722/a104-thumb128.jpg"><img class="" title="Click to view" style="margin: 5px 4px; width: 48px; height: 48px;" alt="" src="files/tib-galleries/3-722/a105-thumb128.jpg"><img class="" title="Click to view" style="margin: 5px 4px; width: 48px; height: 48px;" alt="" src="files/tib-galleries/3-722/a106-thumb128.jpg"><img class="" title="Click to view" style="margin: 5px 4px; width: 48px; height: 48px;" alt="" src="files/tib-galleries/3-722/a107-thumb128.jpg"><img class="" title="Click to view" style="margin: 5px 4px; width: 48px; height: 48px;" alt="" src="files/tib-galleries/3-722/a108-thumb128.jpg"><img class="" title="Click to view" style="margin: 5px 4px; width: 48px; height: 48px;" alt="" src="files/tib-galleries/3-722/a109-thumb128.jpg"><img class="" title="Click to view" style="margin: 5px 4px; width: 48px; height: 48px;" alt="" src="files/tib-galleries/3-722/a1010-thumb128.jpg"><img class="" title="Click to view" style="margin: 5px 4px; width: 48px; height: 48px;" alt="" src="files/tib-galleries/3-722/a1011-thumb128.jpg"></div></div><p> </p></div></div><hr class="hidden"><div class="pinkBg"><h2>Other resources</h2><p><strong>1. </strong>A very simple explanation of <em>K</em><sub>sp</sub> using lead(II) iodide as an example by chemistNATE.</p><p style="text-align: center;"><iframe allowfullscreen="" frameborder="0" height="280" src="//www.youtube.com/embed/FsU8Ss6jiKs?rel=0" width="360"></iframe></p><p style="text-align: center;"><a href="http://youtu.be/FsU8Ss6jiKs" target="_blank" title="Videos"><img class="ico" src="../../../img/icons/video-1.png"><span class="anchor" id="video-1" name="video-1"> </span> Solubility product</a></p><hr class="hidden"><p style="text-align: center;"></p><p><strong>2.</strong> An animation of the common ion effect using silver iodide as an example.</p><p style="text-align: center;"><iframe allowfullscreen="" frameborder="0" height="280" src="//www.youtube.com/embed/pskvC5ROCdc?rel=0" width="360"></iframe></p><p style="text-align: center;"><a href="http://youtu.be/pskvC5ROCdc" target="_blank" title="Videos"><img class="ico" src="../../../img/icons/video-1.png"><span class="anchor" id="video-2" name="video-2"> </span> Common ion effect</a></p><hr class="hidden"><p style="text-align: center;"></p><p><strong>3. </strong>A student demonstrates her Science Fair project on Fenton's reagent.</p><p style="text-align: center;"><iframe allowfullscreen="" frameborder="0" height="280" src="//www.youtube.com/embed/iKHuaCR6aF0?rel=0" width="360"></iframe></p><p style="text-align: center;"><a href="http://youtu.be/iKHuaCR6aF0" target="_blank" title="Videos"><img class="ico" src="../../../img/icons/video-1.png"><span class="anchor" id="video-3" name="video-3"> </span> Demonstration of Fenton's reagent.</a></p><hr class="hidden"></div><section class="footnotes"><header><h2>Footnotes</h2></header><ol><li data-footnote-id="9zt1g" id="footnote-1"><a class="scroll-to" data-target="footnote-marker-1-1">^</a> <cite>Note that some of the <em>K</em>sp values in the data booklet are given to two significant figures and some are given to three significant figures.</cite></li></ol></section></section></article><section id="media-extras"><div class="page-actions no-print navbar inline hidden-desktop"><div class="navbar-inner"><ul class="nav"><li><a class="presentation" href="#" onclick="return false;"><i class="fa fa-desktop"></i></a></li><li><a class="print-section-blog" href="#" onclick="return false;"><i class="fa fa-print"></i></a></li><li><a class="page-bookmarker" data-ticket="IB Docs (2) Team" data-pid="19916" href="#" onclick="return false;"><i class="fa fa-star"></i></a></li><li><a class="personal-notes" href="#" onclick="return false;"><i class="fa fa-file-text"></i></a></li><li><a class="" data-toggle="modal" 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