5 Cells

 

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1.11 Electrode Potentials Page 6 - 7

Oxford Textbook Pages : 310 - 312

CGP Revision Guide Pages : 80

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Show Specification Ref : 3.1.11.2

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Question 1 / 5

AQA Jan 2011 Paper 5 Q5 do not write outside the box a lithium ion cells are used to power cameras and mobile phones a simplified representation of a cell is shown below li li li coo licoo pt the reagents in the cell are absorbed onto powdered graphite that acts as a support medium the support medium allows the ions to react in the absence of a solvent such as water the half equation for the reaction at the positive electrode can be represented as follows li coo e li coo a i identify the element that undergoes a change in oxidation state at the positive electrode and deduce these oxidation states of the element element oxidation state oxidation state marks a ii write a half equation for the reaction at the negative electrode during operation of the lithium ion cell mark a iii suggest two properties of platinum that make it suitable for use as an external electrical contact in the cell property property marks a iv suggest one reason why water is not used as a solvent in this cell mark wmp jan chem do not write outside the box b the half equations for two electrodes used to make an electrochemical cell are shown below clo so aq h aq e cl aq h o i e v aq h aq e so aq h o i e v b i write the conventional representation for the cell using platinum contacts marks b ii write an overall equation for the cell reaction and identify the oxidising and reducing agents overall equation oxidising agent reducing agent marks turn over for the next question turn over wmp jan chem
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Question 2 / 5

AQA Jun 2011 Paper 5 Q5 do not write outside the box redox reactions occur in the discharge of all electrochemical cells some of these cells are of commercial value the table below shows some redox half equations and standard electrode potentials half equation zn aq e zn s ag o s h aq e o g h aq e f g e ag s h o i h o i f aq e v a in terms of electrons state what happens to a reducing agent in a redox reaction mark b use the table above to identify the strongest reducing agent from the species in the table explain how you deduced your answer strongest reducing agent explanation marks c use data from the table to explain why fluorine reacts with water write an equation for the reaction that occurs explanation equation marks wmp jun chem do not write outside the box d an electrochemical cell can be constructed using a zinc electrode and an electrode in which silver is in contact with silver oxide this cell can be used to power electronic devices d i give the conventional representation for this cell marks d ii calculate the e m f of the cell mark d iii suggest one reason why the cell cannot be electrically recharged mark e the electrode half equations in a lead acid cell are shown in the table below half equation pbo s h aq hso aq e pbso s h o i pbso s h aq e pb s hso aq e v to be calculated e i the pbo pbso electrode is the positive terminal of the cell and the e m f of the cell is v use this information to calculate the missing electrode potential for the half equation shown in the table mark e ii a lead acid cell can be recharged write an equation for the overall reaction that occurs when the cell is being recharged marks question continues on the next page turn over wmp jun chem do not write outside the box f the diagrams below show how the e m f of each of two cells changes with time when each cell is used to provide an electric current lead acid cell cell x e m f v e m f v time hours time hours f i give one reason why the e m f of the lead acid cell changes after several hours mark f ii identify the type of cell that behaves like cell x mark f iii explain why the voltage remains constant in cell x marks extra space wmp jun chem
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Question 3 / 5

AQA Jun 2012 Paper 5 Q5 do not write outside the box the table shows some electrode half equations and the associated standard electrode potentials equation number electrode half equation cd oh s e cd s oh aq zn aq e zn s nio oh s h o i e ni oh s oh aq mno s h o l e mno oh s oh aq o g h aq e h o i e v a in terms of electrons state the meaning of the term oxidising agent mark b deduce the identity of the weakest oxidising agent in the table explain how e values can be used to make this deduction weakest oxidising agent explanation marks c the diagram shows a non rechargeable cell that can be used to power electronic devices the relevant half equations for this cell are equations and in the table above cover carbon rod mno paste porous separator zinc zncl paste wmp jun chem do not write outside the box c i calculate the e m f of this cell mark c ii write an equation for the overall reaction that occurs when the cell discharges mark c iii deduce one essential property of the non reactive porous separator labelled in the diagram mark c iv suggest the function of the carbon rod in the cell mark c v the zinc electrode acts as a container for the cell and is protected from external damage suggest why a cell often leaks after being used for a long time mark question continues on the next page turn over wmp jun chem do not write outside the box d a rechargeable nickel cadmium cell is an alternative to the cell shown in part c the relevant half equations for this cell are equations and in the table on page d i deduce the oxidation state of the nickel in this cell after recharging is complete write an equation for the overall reaction that occurs when the cell is recharged oxidation state equation marks d ii state one environmental advantage of this rechargeable cell compared with the non rechargeable cell described in part c mark e an ethanol oxygen fuel cell may be an alternative to a hydrogen oxygen fuel cell when the cell operates all of the carbon atoms in the ethanol molecules are converted into carbon dioxide e i deduce the equation for the overall reaction that occurs in the ethanol oxygen fuel cell mark e ii deduce a half equation for the reaction at the ethanol electrode in this half equation ethanol reacts with water to form carbon dioxide and hydrogen ions mark e iii the e m f of an ethanol oxygen fuel cell is v use data from the table on page to calculate a value for the electrode potential of the ethanol electrode mark wmp jun chem e iv suggest why ethanol can be considered to be a carbon neutral fuel do not write outside the box marks turn over for the next question turn over wmp jun chem
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Question 4 / 5

AQA Jun 2013 Paper 5 Q5 do not write outside the box an electrochemical cell is shown in the diagram in this cell the amount of copper in the electrodes is much greater than the amount of copper ions in the copper sulfate solutions copper copper mol dm cuso aq mol dm cuso aq a explain how the salt bridge d provides an electrical connection between the two electrodes mark b suggest why potassium chloride would not be a suitable salt for the salt bridge in this cell mark c in the external circuit of this cell the electrons flow through the ammeter from right to left suggest why the electrons move in this direction marks wmp jun chem do not write outside the box d explain why the current in the external circuit of this cell falls to zero after the cell has operated for some time mark e the simplified electrode reactions in a rechargeable lithium cell are electrode a electrode b li mno e li e electrode b is the negative electrode limno e v li e i the e m f of this cell is v use this information to calculate a value for the electrode potential of electrode b mark e ii write an equation for the overall reaction that occurs when this lithium cell is being recharged marks e iii suggest why the recharging of a lithium cell may lead to release of carbon dioxide into the atmosphere mark turn over wmp jun chem
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Question 5 / 5

AQA Jun 2014 Paper 5 Q5 table shows some standard electrode potential data do not write outside the box table e v zno s h o i e zn s oh aq fe aq e fe s o g h o i e oh aq hocl aq h aq e cl g h o i a give the conventional representation of the cell that is used to measure the standard electrode potential of iron as shown in table marks b with reference to electrons give the meaning of the term reducing agent mark c identify the weakest reducing agent from the species in table explain how you deduced your answer marks species explanation wmp jun chem do not write outside the box d when hocl acts as an oxidising agent one of the atoms in the molecule is reduced d i place a tick next to the atom that is reduced mark atom that is reduced tick cl d ii explain your answer to question d i in terms of the change in the oxidation state of this atom mark e using the information given in table deduce an equation for the redox reaction that would occur when hydroxide ions are added to hocl marks question continues on the next page turn over wmp jun chem do not write outside the box f table is repeated to help you answer this question table e v zno s h o i e zn s oh aq fe aq e fe s o g h o i e oh aq hocl aq h aq e cl g h o i the half equations from table that involve zinc and oxygen are simplified versions of those that occur in hearing aid cells a simplified diagram of a hearing aid cell is shown in figure figure air hole aqueous alkaline paste a stainless steel lid porous partition acting as salt bridge zinc powder in alkaline paste insulator b stainless steel can f i use data from table to calculate the e m f of this cell mark answer wmp jun chem do not write outside the box f ii use half equations from table to construct an overall equation for the cell reaction mark f iii identify which of a or b in figure is the positive electrode give a reason for your answer marks positive electrode reason f iv suggest one reason other than cost why this type of cell is not recharged mark turn over for the next question turn over wmp jun chem
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