March 27, 2009

March 27, 2009 - zn – E Fe =-0.76 – 0.77 =-1.53V • If...

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March 27, 2009
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A + B + → A + + B Or A | A + # B + |B For both B product metal A reactant metal E reaction = E B o - E A o
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Reference electrode 2H + + 2e H 2 E = 0 Pt|H 2 (g)|H + To measure reduction potentials, place on right side
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Standard Potential for Zn 2+ + 2e → Zn Pt|H 2 |H + # Zn 2+ |Zn E = E Zn - E H2 = -0.76V on Zn 2+ electrode =- 0.76V – 0 Electrons right to left , cations left to right Zn metal disappears, H 2 is formed
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Pt|H 2 |H + # Cu 2+ |Cu Cu electrode 0.34 • E = E Cu – E H2 = +.34 – 0 = 0.34V Reaction left to right so H 2 + Cu 2+ 2 H + + Cu Spontaneous • H 2 oxidized Cu 2+ reduced
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Zn + Cu 2+ Zn 2+ + Cu E = E Cu – E Zn = 0.34 – (-0.76) + 1.1V Reaction spontaneous as written Further down table more likely to be reduced oxidizing agent
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Non metals See from table “electrode” metal ion with higher charge it will receive electron(s) Fe 3+ + 1e → Fe 2+ 0.77 Fe 2+ (lower charge) is like metal Fe 2+
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Fe 3+ + e → Fe 2+ + e E = 0.77 Zn 2+ + 2e Zn E = -0.76 Fe 2+ + Zn 2+ Fe 3+ + Zn (unbalanced) • E = E
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Unformatted text preview: zn – E Fe = -0.76 – (+0.77) = -1.53V • If know Zn position – just take “Fe” from table and insert • Electrode of second kind • Ag + ion can be very poisonous • For biological systems • Cl 2 also poisonous but Cl-is not • Ag|AgCl electrode really Cl-electrode • +V • electrode 1 Ag + Cl-|Ag • AgCl insoluble on surface • Ag + moves to Ag electrode, receives e and becomes Ag leaving a Cl-behind • Cl-moves off surface into solution • Ag never leaves the electrode • Other electrode • Ag | Ag + Cl-• e separates from Ag metal to move in wire and creates Ag + ion near surface • Cl- ion moves to electrode AgCl precipitate on surface • Net effect for a spontaneous reaction • Electrodes move left to right in wire • Cl- ions move right to left in solution • Left to right rule is reversed for negative ions • Only Cl-enters or leaves solution...
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This note was uploaded on 02/26/2012 for the course CHEM 108 taught by Professor Dr.brennan during the Spring '09 term at Binghamton.

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March 27, 2009 - zn – E Fe =-0.76 – 0.77 =-1.53V • If...

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