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Electrochemistry - Redox reaction.

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INTRODUCTION One reactant is oxidized and another reactant is reduced, this chemical reaction is called Redox reaction. Redox reactions involve in generation of electricity in electrochemical cells. [1] Two different solid metals in solution of their ions made up of electrochemical cell, which are connected by a salt bridge or a wire. Each metal is an electrode, which will either be oxidized or reduced in a half-cell. [2] The pairs of species, e.g. Zn2+(a.q)/Zn(s) and Cu2+(a.q)/Cu(s), etc. are known as redox couple. The relative oxidizing or reducing strengths of redox couples are expressed in terms of their standard electrode potentials, EO, which have the units of Volts.[3] A general cell diagram for an electrochemical cell is shown below: fig 1 [2] The standard potential of the cell, EO=EOR-EOL where EOR =the EO of the right-hand-side electrode and EOL= the EO of the left-hand-side electrode.[4] Aim of the experiment was to understand how electricity worked to form a simple circuit. This experiment had three sub-experiments. First was to build a simple circuit. Second was to make an electrochemical cell. ...read more.


Fe2+(a.q) + 2e- Reduction: Ni2+(a.q) + 2e- Ni (s) Reduction: Ni2+(a.q) + 2e- Ni(s) Redox reaction: Redox reaction: Zn(s)+ Ni2+(a.q) Zn2+(a.q)+ Ni (s) Ni(s)+ Fe2+(a.q) Ni2+(a.q)+ Fe (s) 5 FeSO4 & CuSO4 V = 0.6V Oxidation: Fe(s) Fe2+(a.q) + 2e- Reduction: Cu2+(a.q) + 2e- Cu (s) Redox reaction: Fe (s)+ Cu2+(a.q) Fe2+(a.q)+ Cu (s) EXPERIMENT III. Zn & Cu: Fe & Zn: V = 0.839 V V = 0.337 V Ni & Zn: Ni & Fe: V = 0.757 V V = 0.513 V DISCUSS EXPERIMENT II A negative EO means that a redox couple is a stronger reducing agent than the H+(a.q)/H2(g) couple. A positive EO means that a redox couple is a weaker reducing agent than the H+(a.q)/H2(g) couple. [5] 1 ZnSO4 & CuSO4 The Table of Standard Electrode Potentials, which was attached as Appendix A, suggested that Zn is better reducing agent than Cu and Cu2+ ions were better oxygenating agent than Zn2+. Oxidation = Lose e- According to fig.1 (page 1, introduction), Zn side was the anode of the cell and Cu side was the cathode of the cell. ...read more.


EXPERIMENT III The lemon battery experiment was the same rule as the experiment II. Only half lemon was used in this experiment. Electrodes Zn and Cu were placed into the lemon. Zn was oxidized and ions were coming off. Chemical equation was Zn(s) Zn2+(a.q) + 2e-. The Zn2+ ions were flow into the lemon and Zn became negatively charged due to electron loss. Cu was reduced by gaining those electrons from Zn via lemon, hence became positively charged. Chemical equation was Cu2+(a.q) + 2e- Cu(s) Then the ions from negatively charged Zn to positively charged Cu generated electricity and Voltmeter could detect voltage. Voltmeter could detect voltages among electrodes Fe and Zn, Ni and Zn, and Ni and Fe, but the voltages were different due to the different abilities of reduction and oxidation. Reference [1] Lewis R and Evans W(2006) Chemistry. Page100. 3rd Edition. Palgrave Macmillan. New York [2] Handout from Electrochemistry practical sheet. 29th Apr 2008 [3] Lewis R and Evans W(2006) Chemistry. Page107. 3rd Edition. Palgrave Macmillan. New York [4] Lewis R and Evans W(2006) Chemistry. Page109. 3rd Edition. Palgrave Macmillan. New York [5] Lewis R and Evans W(2006) Chemistry. Page110. 3rd Edition. Palgrave Macmillan. New York ?? ?? ?? ?? 1 ...read more.

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