Chemistry - Electrochemistry - Quick Guides | Chemistry

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Study GuideChemistry–Electrochemistry1. Electrochemical Cells1.1What Is an Electrochemical Cell?Anelectrochemical cell(also called avoltaic cell) is a device that uses achemical reaction toproduce electricity.Because reactions happen more easily in liquids than in solids or gases, most electrochemical cellsuse aliquid solution.This liquid is called anelectrolyte.1.2Electrolytes and ConductivityAnelectrolyteis a solution that containsionsand canconduct electricity.•Pure distilled waterconducts electricity very poorly.•When substances dissolve and form ions, conductivity increases.Types of Electrolytes•Strong electrolytes: Substances (like many acids, bases, and salts) that ionize almostcompletely in water.•Weak electrolytes: Substances that ionize only slightly.The more ions present, the better the solution conducts electricity.1.3Structure of a Simple Electrochemical CellA simple electrochemical cell can be made usingtwo test tubes connected by a third tube, shapedlike an “H”.•The connecting tube allowsions to move, which is necessary to complete the circuit.•Each test tube contains adifferent solution and metal electrode.

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Study GuideWhat Goes in Each Side?•Left test tube:oZinc metal stripoZinc sulfate solution (ZnSO₄)•Right test tube:oCopper metal stripoCopper(II) sulfate solution (CuSO₄)The two metal strips are connected to avoltmeterusing wires.Figure 1.AVoltaiccell.1.4How Electricity Is ProducedWhen the circuit is complete:•The voltmeter shows about1.10 volts.•Electrons move through the wirefrom zinc to copper.•This movement of electrons is what we callelectric current.1.5Oxidation at the Zinc Electrode (Anode)At thezinc electrode, zinc atomslose electrons. This process is calledoxidation.Oxidation Reaction:

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Study Guide•Zinc metal becomes zinc ions.•Electrons are released into the wire.The electrode where oxidation occurs is called theanode.•The anode attractsnegative ions, calledanions.•In this cell, theanode is positive.1.6Reduction at the Copper Electrode (Cathode)At thecopper electrode, copper ionsgain electrons. This process is calledreduction.Reduction Reaction:•Copper ions turn into solid copper metal.•Copper metal builds up on the electrode.The electrode where reduction occurs is called thecathode.•In this cell, thecathode is negative.1.7Why the Charges Make Sense•Electrons movefrom anode to cathode.•Since electrons are negative:oTheanode becomes positiveoThecathode becomes negativeThis is specific tovoltaic (electrochemical) cells.1.8Overall Reaction of the CellWhen we add the oxidation and reduction reactions together, we get theoverall redox reaction:Zn(s) + Cu²⁺(aq) → Cu(s) + Zn²⁺(aq)This reaction explains howchemical energy is converted into electrical energyin a zinc–copperelectrochemical cell.

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Study GuideSummary•OIL RIGhelps remember redox:oOxidation Is Loss(of electrons)oReduction Is Gain(of electrons)2. Quiz: Electrochemical Cells1. QuestionAnother name for a spontaneous electrochemical cell isAnswer Choices•salt bridge•volt meter•voltaic cellCorrect Answervoltaic cellWhy This Is CorrectA spontaneous electrochemical cell generates electrical energy from a chemical reaction on its own.Such cells are calledvoltaic cells(or galvanic cells).A salt bridge is only a component of the cell, and a voltmeter is a measuring device.2. QuestionA voltaic cell uses a chemical reaction to produce

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Study GuideAnswer Choices•pressure•change in temperature•electricityCorrect AnswerelectricityWhy This Is CorrectIn a voltaic cell, chemical energy from a redox reaction is converted directly into electrical energy,which flows through an external circuit.3. QuestionThe ions in a solution which conduct electricity are known asAnswer Choices•colloids•electrolytes•electrodesCorrect AnswerelectrolytesWhy This Is CorrectElectrolytes dissociate into ions in solution, allowing the solution to conduct electricity.Colloids do not fully ionize, and electrodes are solid conductors, not ions in solution.4. QuestionReduction occurs at the

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Study GuideAnswer Choices•anion•cathode•salt bridgeCorrect AnswercathodeWhy This Is CorrectReduction (gain of electrons) always occurs at thecathodein electrochemical cells.This is summarized by the mnemonic“RED CAT”(Reduction at Cathode).5. QuestionIn a voltaic cell, oxidation occurs at the __________ and is the __________ electrode.Answer Choices•cathode, positive•anode, positive•anode, negativeCorrect Answeranode, negativeWhy This Is CorrectOxidation (loss of electrons) occurs at theanode.In a voltaic cell, the anode isnegativebecause it supplies electrons to the circuit.6. QuestionThe positive electrode in a voltaic cell is known as a(n)

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Study GuideAnswer Choices•anode•cathode•antinodeCorrect AnswercathodeWhy This Is CorrectIn a voltaic cell, electrons flow toward the cathode, making it thepositive electrode.An antinode is unrelated to electrochemistry.7. QuestionCompounds that have a high degree of ionization in solution are known asAnswer Choices•weak electrolytes•nonconductors•strong electrolytesCorrect Answerstrong electrolytesWhy This Is CorrectStrong electrolytes ionize almost completely in solution, producing many ions that conduct electricityefficiently.

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Study GuideUse the following balanced ionic equation to answer questions 8–10:Equation8. QuestionWhich species is oxidized?Answer Choices•MnO₄⁻•Fe•Mn²⁺Correct AnswerFeWhy This Is CorrectIron (Fe) changes fromFe (0)toFe²⁺, meaning it loses electrons.Loss of electrons is oxidation.9. QuestionWhich species is the oxidizing agent?Answer Choices•MnO₄⁻•Fe•Mn²⁺

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Study GuideCorrect AnswerMnO₄⁻Why This Is CorrectThe oxidizing agent is the substance thatgets reduced.MnO₄⁻is reduced to Mn²⁺, so it causes oxidation of iron.10. QuestionHow many electrons are transferred in the balanced redox reaction?Answer Choices•2•5•10Correct Answer10Why This Is CorrectEach Fe atom loses2 electrons, and there are5 Fe atomsinvolved:5 × 2 =10 electrons transferred.3. Electrode Potential3.1What Is Electrode Potential?Electrode potential is a measure of how strongly an electrode can gain or lose electrons.It is measured involts (V).In an electrochemical cell, electricity is produced because chemical reactions occur attwoelectrodes. The total voltage of the cell depends on the substances used at these electrodes.

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Study Guide3.2Electromotive Force (EMF)The voltage produced by a cell is calledEMF (electromotive force).EMF is simply another name forelectrical potential.For any electrochemical cell:EMF of the cell = EMF of oxidation + EMF of reductionThis means we add the voltage from the oxidation reaction and the voltage from the reductionreaction to find the total cell voltage.3.3The Standard Hydrogen Electrode (SHE)To compare different electrodes, scientists needed a reference point.They chose thestandard hydrogen electrode (SHE).Conditions for the standard hydrogen electrode:•Hydrogen gas at1 atmosphere•A platinum electrode•A solution with1 M H⁺ions•Temperature of25°CThe standard hydrogen electrode isassigned a potential of 0.00 V.All other electrode potentials are measuredrelative to this value.

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