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<title>DP Chemistry: Using electrode potentials</title>
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<meta name="description" content="I think the main problem with questions involving oxidation and reduction and standard electrode potentials is that teachers often teach cell convention – and many teach it wrongly. This can be seen when examiners mark scripts as students often use the phrases ‘left hand side’ or ‘right hand side’ and have no clue about what they are referring to. Equations like Etotal = ELHS – ERHL are often used in completely...">
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<meta itemprop="description" content="I think the main problem with questions involving oxidation and reduction and standard electrode potentials is that teachers often teach cell convention – and many teach it wrongly. This can be seen when examiners mark scripts as students often use the phrases ‘left hand side’ or ‘right hand side’ and have no clue about what they are referring to. Equations like Etotal = ELHS – ERHL are often used in completely...">
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<meta name="twitter:description" content="I think the main problem with questions involving oxidation and reduction and standard electrode potentials is that teachers often teach cell convention – and many teach it wrongly. This can be seen when examiners mark scripts as students often use the phrases ‘left hand side’ or ‘right hand side’ and have no clue about what they are referring to. Equations like Etotal = ELHS – ERHL are often used in completely...">
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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 class="selected"><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 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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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</div><section id="main-content"><div class="blueBg"><h1>The problem and background knowledge</h1><p>I think the main problem with questions involving oxidation and reduction and standard electrode potentials is that teachers often teach <a href="https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Analytical_Chemistry)/Electrochemistry/Voltaic_Cells/Electrochemical_Cell_Conventions">cell convention</a> – and many teach it wrongly. This can be seen when examiners mark scripts as students often use the phrases ‘left hand side’ or ‘right hand side’ and have no clue about what they are referring to. Equations like <em>E</em><sub><em>t</em>otal</sub> = <em>E<sub>LHS</sub></em> – <em>E<sub>RHL</sub></em> are often used in completely the wrong way. A cell will produce the same amount of electricity whichever way round the two half-cells are physically connected so it really does not matter which is on ‘the right’ or ‘the left’. The use of ‘anode’ and cathode’ can also be confusing as the anode is the positive electrode in an electrolysis cell and yet is the negative electrode in a voltaic (or electrochemical) cell.</p><p>Cell convention is not specifically on the IB syllabus<sup>1</sup> and to my mind adds a totally unnecessary complication to what is a very simple problem. I also prefer to use positive and negative electrode and do not refer to anode or cathode although the syllabus does use anode and cathode so students will need to know these words. It is probably best if they learn that oxidation always occurs at the anode. Students really only need to understand and learn three basic facts about half-equations and electrochemical cells.</p><hr class="hidden"><p><strong>1.</strong> The half-equation represents an equilibrium reaction and can go either way. The <em>E</em><sup>⦵</sup><sup> </sup>value is not an enthalpy term and does not change value if the equation is written the other way round.</p><hr class="hidden"><p><strong>2.</strong> The standard electrode potential is a measure of the potential difference obtained when a standard half-cell (1.00 mol dm<sup>-3</sup> concentration, 298 K and 1 atmosphere pressure) is connected to a standard hydrogen half-cell (using a standard hydrogen electrode). By convention (and stress that it is only a convention) if the value for <em>E<sup>⦵</sup></em> is <strong>negative</strong> electrons flow <strong>from</strong> the half-cell <strong>to</strong> the standard hydrogen electrode and if the value is positive the electrons flow from the hydrogen half-cell to the other half-cell.</p><hr class="hidden"><p><strong>3.</strong> When half-cells are connected (either using a salt bridge or when they react when brought together) the electrons flow <strong>from</strong> the more negative half-cell <strong>to</strong> the more positive half-cell.</p><hr class="hidden"><p>Armed with this knowledge, students should be able to answer correctly any IB questions on <span data-scayt-word="redox" data-wsc-lang="en_US">redox</span> chemistry that involves standard electrode potentials.</p><hr class="hidden"><h4>Footnote</h4><p><sup>1</sup> In fact in sub-topic 9.2 under 'guidance it states "For voltaic cells, a cell diagram convention should be covered." However this would appear to be for giving a shorthand version of a diagram of a cell such as Zn(s)/Zn<sup>2</sup><sup>+</sup>(aq) || Cu<sup>2</sup><sup>+</sup>(aq)/Cu(s) rather than as a way of calculating the total EMF produced by the <span data-scayt-word="redox" data-wsc-lang="en_US">redox</span> reaction between zinc metal and copper(II) ions.</p><hr class="hidden"></div><hr class="hidden"><div class="greenBg"><h1>Examples</h1><p>Let’s look at a simple example first. What will be <span data-scayt-word="oxidised" data-wsc-lang="en_US">oxidised</span> and what will be reduced when a Mn(s)/Mn<sup>2</sup><sup>+</sup>(aq) half-cell with <em>E<sup>⦵</sup></em> = – 1.18 V is connected to a Ni(s)/Ni<sup>2</sup><sup>+</sup>(aq) half-cell with <em>E<sup>⦵</sup><sup> </sup></em>= – 0.26 V and what will be the total EMF of the cell?</p><p>To answer this simply get the students to write down the two half-equations. It really does not matter which they write first and which way round they write them, although probably they should use the cell convention. For example:</p><p>Mn(s) ⇌ Mn<sup>2</sup><sup>+</sup>(aq) + 2e− <em>E<sup>⦵</sup><sup> </sup></em>= – 1.18 V</p><p>Ni(s) ⇌ Ni<sup>2</sup><sup>+</sup>(aq) + 2e<sup>−</sup> <em>E<sup>⦵</sup></em> = – 0.26 V</p><p>Since the manganese half-cell is the more negative the electrons will flow from this half-cell to the nickel half-cell. That is the manganese half-cell is giving up electrons and the nickel half-cell is receiving electrons so the actual reactions occurring are:</p><p>Mn(s) → Mn<sup>2</sup><sup>+</sup>(aq) + 2e­<sup>−</sup><sup> </sup><em>E<sup>⦵</sup><sup> </sup></em> = – 1.18 V</p><p>Ni<sup>2</sup><sup>+</sup>(aq) + 2e<sup>−</sup> → Ni(s) <em>E<sup>⦵</sup><sup> </sup></em>= – 0.26 V</p><p>So the overall reaction will be<br><br>Mn(s) + Ni<sup>2</sup><sup>+</sup>(aq) → Mn<sup>2</sup><sup>+</sup>(aq) + Ni(s)</p><p>That is, the manganese metal is <span data-scayt-word="oxidised" data-wsc-lang="en_US">oxidised</span> and the nickel(II) ions are reduced. The total EMF is the <strong>quantitative</strong> <strong>difference</strong> between the two values and will always be positive for the spontaneous reaction. In this case it will equal the difference between – 1.18 V and – 0.26 V which is 0.92 V.</p><hr class="hidden"><p>Exactly the same principle can be applied when any two half-cells are joined together, either, as in cell, using a salt bridge or in a test-tube type reaction.</p><p>For example, can potassium dichromate(VI) <span data-scayt-word="oxidise" data-wsc-lang="en_US">oxidise</span> hydrochloric acid to chlorine?</p><p>To answer this get the students to write the two half-equations. Dichromate(VI) is in equilibrium with chromium(III) ions in its half-cell and chloride ions are in equilibrium with chlorine in the second half-cell.</p><p>Cr<sub>2</sub>O<sub>7</sub><sup>2</sup><sup>−</sup> + 14H<sup>+</sup>(aq) + 6e<sup>−</sup> ⇌ 2Cr<sup>3</sup><sup>+</sup>(aq) + 7H<sub>2</sub>O <em>E<sup>⦵</sup><sup> </sup></em>= + 1.36 V</p><p>2Cl<sup>−</sup>(aq) ⇌ Cl<sub>2</sub> + 2e<sup>−</sup> <em>E<sup>⦵</sup><sup> </sup></em>= + 1.36 V</p><p>Not only do both have positive <em>E<sup>⦵</sup><sup> </sup></em> values but they also have exactly the same value. This means that no electrons will flow from one cell to the other so no reaction will occur.</p><p>In other data books, including the previous IB data booklet, the value for the dichromate/chromium(III) half-cell is + 1.33 V. If this value is used then electrons will flow from the chromium half-cell (less positive) to the chlorine half-cell (more positive) so the spontaneous half-equations will be:</p><p>2Cr<sup>3</sup><sup>+</sup>(aq) + 7H<sub>2</sub>O → Cr<sub>2</sub>O<sub>7</sub><sup>2</sup><sup>−</sup>(aq) + 14H<sup>+</sup>(aq) + 6e<sup>−</sup> <em>E<sup>⦵</sup><sup> </sup></em> = + 1.33 V</p><p>Cl<sub>2</sub>(aq) + 2e<sup>−</sup> → 2Cl<sup>−</sup>(aq) <em>E<sup>⦵</sup><sup> </sup></em> = + 1.36 V</p><p>By multiplying the second equation by three to balance the number of electrons we can get the overall spontaneous equation. Stress to students when you do this that, unlike enthalpy change values, the standard electrode value is not multiplied and remains unchanged. The overall equation is thus:</p><p>2Cr<sup>3</sup><sup>+</sup>(aq) + 3Cl<sub>2</sub>(aq) + 7H<sub>2</sub>O → Cr<sub>2</sub>O<sub>7</sub><sup>2</sup><sup>−</sup>(aq) + 14H<sup>+</sup>(aq) + 6Cl<sup>−</sup>(aq) <em>E<sup>⦵</sup><sup> </sup></em><sub>total</sub> = 0.03 V</p><p>This means that chlorine can <span data-scayt-word="oxidise" data-wsc-lang="en_US">oxidise</span> chromium(III) ions and that dichromate cannot spontaneously <span data-scayt-word="oxidise" data-wsc-lang="en_US">oxidise</span> chloride ions. The total EMF for the spontaneous reaction will be 0.03 V . This answer is interesting as it is only true that dichromate cannot spontaneously <span data-scayt-word="oxidise" data-wsc-lang="en_US">oxidise</span> chloride ions <strong>under standard conditions</strong>. If the conditions (e.g. concentrations) are altered then the <em>E<sup>⦵</sup><sup> </sup></em>values are so close that they may switch under different conditions with the chlorine half-cell becoming the more negative. For this reason hydrochloric acid is not used to acidify potassium dichromate(VI) when the dichromate is being used as an oxidizing agent in analytical chemistry.</p><hr class="hidden">Try a couple more and then click on the 'eye' to reveal the answer.<hr class="hidden"><strong>1.</strong> What will be the total EMF and what will be oxidized and what will be reduced when a Cu(s)/Cu<sup>2</sup><sup>+</sup>(aq) half-cell is connected to a Pb(s)/Pb<sup>2</sup><sup>+</sup>(aq) half-cell using a salt bridge and in which direction will the electrons flow in the external circuit?<hr class="hidden"><section class="tib-hiddenbox"><p>Lead, Pb, will be oxidized and copper(II) ions will be reduced. The EMF will be 0.47 V (using the values from Section 24 in the IB data booklet). Electrons will flow from the lead half-cell to the copper half-cell.</p></section><hr class="hidden"><p><strong>2.</strong> Will hydrogen peroxide act as an <span data-scayt-word="oxidising" data-wsc-lang="en_US">oxidising</span> agent or a reducing agent when it reacts with an acidified solution of potassium permanganate?</p><p>The two relevant hydrogen peroxide half-equations are</p><p>O<sub>2</sub>(aq) + 2H<sup>+</sup>(aq) + 2e<sup>−</sup><sup> </sup>⇌ H<sub>2</sub>O<sub>2</sub>(aq) <em>E<sup>⦵</sup><sup> </sup></em> = + 0.68 V</p><p>and</p><p>H<sub>2</sub>O<sub>2</sub>(aq) + 2H<sup>+</sup>(aq) + 2e<sup>−</sup><sup> </sup>⇌ 2H<sub>2</sub>O(aq) <em>E<sup>⦵</sup><sup> </sup></em> = +1.78 V</p><hr class="hidden"><section class="tib-hiddenbox"><p>The permanganate/manganese(II) half-cell has the more positive standard electrode potential (+ 1.51 V compared to + 0.68 V) so permanganate ions will be the oxidizing agent and hydrogen peroxide the reducing agent. If students do this reaction they will see bubbles of oxygen being evolved. (You could also deduce that hydrogen peroxide can spontaneously oxidise manganese(II) ions with a total EMF of 0.27 V although this was not asked for.)</p></section><hr class="hidden"></div></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="16310" 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" href="#modal-feedback" onclick="return false;"><i class="fa fa-envelope-o"></i></a></li><li class="dropdown"><a class="dropdown-toggle" data-toggle="dropdown" data-target="#" href="#"><i class="fa fa-share-alt"></i></a><ul class="dropdown-menu" role="menu"><li><a class="" target="_blank" title="Share on Twitter" href="https://twitter.com/share?text=%22Using+electrode+potentials%22+-+via+%40InThinker+%23chemistry%0A&url=https%3A%2F%2Fwww.thinkib.net%2Fchemistry%2Fpage%2F16310%2Fusing-electrode-potentials"><i class="fa fa-twitter-square"></i><span>Twitter</span></a></li><li><a class="" target="_blank" title="Share on Facebook" href="https://www.facebook.com/sharer.php?u=https%3A%2F%2Fwww.thinkib.net%2Fchemistry%2Fpage%2F16310%2Fusing-electrode-potentials&t=Using+electrode+potentials"><i class="fa fa-facebook-square"></i><span>Facebook</span></a></li><li><a class="" href="http://www.linkedin.com/shareArticle?mini=true&url=https%3A%2F%2Fwww.thinkib.net%2Fchemistry%2Fpage%2F16310%2Fusing-electrode-potentials"><i class="fa fa-linkedin-square"></i><span>LinkedIn</span></a></li><li><a class="" href="https://plus.google.com/share?url=https%3A%2F%2Fwww.thinkib.net%2Fchemistry%2Fpage%2F16310%2Fusing-electrode-potentials"><i class="fa fa-google-plus-square"></i><span>Google +</span></a></li><li><a class="" href="mailto:?subject=Using electrode potentials&body=I think the main problem with questions involving oxidation and reduction and standard electrode potentials is that teachers often teach cell convention – and many teach it wrongly. 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function loadComments(){$.get("pages/comment.php",{action:"get-list",ticket:"IB Docs (2) Team",site_with_comments:"1",general_id:"3",sitename:"chemistry",section_id:"16310"},(function(t){"1"==t.success?($("#comments").html(t.html),"undefined"!=typeof CKEDITOR&&initCommentsEditor()):alert("Error (lc1): please contact support")}),"json")}$(document).ready((function(){loadComments()}));let commentEditor={};function initCommentsEditor(){const t=document.querySelector("#comment-content");t&&CKEDITOR.BasicEditor.create(t,{toolbar:{viewportTopOffset:50,items:["bold","italic","link","subscript","superscript"]},link:{decorators:{addLinkNoFollow:{mode:"automatic",callback:function(t){if(null!=t)return["http://","http://www","https://","https://www","ftp:"].some((o=>t.startsWith(o)))},attributes:{target:"_blank",class:"ck-link",rel:"nofollow"}}}}}).then((function(t){commentEditor=t,commentEditor.execute("heading",{value:"paragraph"})})).catch((function(t){console.error(t)}))}function 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