Electroch emical ce What is an Electrochemical Cell

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Electroch emical ce What is an Electrochemical • Cell? lls: Measure the relati ve

Electroch emical ce What is an Electrochemical • Cell? lls: Measure the relati ve reducing ability of different • 2 different metals • Lets yo species • Dipped in salt solutions of their own ions u predict the direction • Connected by a wire (external circuit) of sponta neous change. • Salt bridge • High-resistance volt meter • E. g. , Zinc/copper electrochemical cell

Do Now - Zinc/copper electrochemical cell 1. Write half equations for the reactions 2.

Do Now - Zinc/copper electrochemical cell 1. Write half equations for the reactions 2. Which is an oxidation reaction and which is reduction? 3. What has happened to the SO 42 - ions? 4. Name the reducing agent. 5. Name the oxidising agent. 6. What is the overall equation? Half equations: Zn(s) → Zn 2+(aq) + 2 e. Cu 2+ (aq) + 2 e- → Cu(s) • Oxidation Reduction

A simple zinc half-cell Zn 2+(aq) + 2 e– ↔ Zn(s)

A simple zinc half-cell Zn 2+(aq) + 2 e– ↔ Zn(s)

In this electrochemical cell, e- flow in the external circuit from left to right,

In this electrochemical cell, e- flow in the external circuit from left to right, giving a pd of +1. 103 V The zinc electrode loses e- so the position of Eqm lies to the left. Zn 2+(aq) +2 e- ↔ Zn The copper electrode gains e- so the position of Eqm lies to the right. Cu 2+(aq) +2 e- ↔ Cu

- electrode anode oxidation At this electrode the metal loses electrons and so is

- electrode anode oxidation At this electrode the metal loses electrons and so is oxidised to metal ions. + electrode cathode reduction electron flow REDCAT At this electrode the metal ions gain electrons and so is reduced to metal atoms. Zn These electrons make the electrode negative. Zn 2+ + 2 eoxidation Cu As electrons are used up, this makes the electrode positive. Cu 2+ + 2 e- Cu reduction

Representing Cells • Simple way to represent cells. . . • Standard cell notation

Representing Cells • Simple way to represent cells. . . • Standard cell notation or cell diagram for zinc/copper cell. • OIL R O RIG O R Zn(s) I Zn 2+(aq) II Cu 2+(aq) ICu(s) • Single vertical line: Separates 2 phases (s, and aq) • Double vertical line: Salt bridge. • 2 (aq) solutions are next to the salt bridge • 2 single lines at each end • If a half-cell contains a mixture of aq ions, a comma is used to separate them • Fe(s) I Fe 2+(aq), Fe 3+(aq)

OIL RO UNLESS TOLD IN THE QUESTION … Reduction on the RIGHT Lowest on

OIL RO UNLESS TOLD IN THE QUESTION … Reduction on the RIGHT Lowest on the LEFT RIG OR Ni(s) | Ni 2+(aq) || Sn 4+(aq), Sn 2+(aq) | Pt(s) K(s) | K+(aq) || Mg 2+(aq) | Mg(s)

Example Magnesium and Copper Mg: E°= -2. 37 V Cu: E° = +0. 34

Example Magnesium and Copper Mg: E°= -2. 37 V Cu: E° = +0. 34 V Which one will carry out oxidation? Which one will carry out reduction? What is the overall emf of the cell? (Clue: E° cell = E°right - E°left)

Calculating emf (Eθcell) Eθcell = EθR - EθL Eθcell = EθReduced - Eθoxidised Zn

Calculating emf (Eθcell) Eθcell = EθR - EθL Eθcell = EθReduced - Eθoxidised Zn 2+ + 2 e- ↔ Zn E° = -0. 76 Cu 2+ + 2 e- ↔ Cu E° = +0. 34 UNLESS TOLD IN THE QUESTION … Reduction on the RIGHT Lowest on the LEFT (the most + goes in forward direction) Zn + Cu 2+ → Zn 2+ + Cu Eθ cell = Eθ R - Eθ L = +0. 34 – (-0. 76) = +1. 10 V + answers tells us that the reaction IS feasible

Task • Electrochemistry Workbook Task 7 Q 1 -7

Task • Electrochemistry Workbook Task 7 Q 1 -7

ELECTRODE POTENTIALS – Q 1 Emf = E°right - E°left - 2. 71 =

ELECTRODE POTENTIALS – Q 1 Emf = E°right - E°left - 2. 71 = E°right - 0 E°right = - 2. 71 V

ELECTRODE POTENTIALS – Q 2 Emf = E°right - E°left Emf = - 0.

ELECTRODE POTENTIALS – Q 2 Emf = E°right - E°left Emf = - 0. 44 - 0. 22 Emf = - 0. 66 V

ELECTRODE POTENTIALS – Q 3 Emf = E°right - Evleft Emf = - 0.

ELECTRODE POTENTIALS – Q 3 Emf = E°right - Evleft Emf = - 0. 13 - (-0. 76) Emf = + 0. 63 V

ELECTRODE POTENTIALS – Q 4 Emf = E°right - E°left a) Emf = +

ELECTRODE POTENTIALS – Q 4 Emf = E°right - E°left a) Emf = + 0. 15 - (-0. 25) = +0. 40 V b) Emf = + 0. 80 - 0. 54 = +0. 26 V c) Emf = + 1. 07 - 1. 36 = - 0. 29 V

ELECTRODE POTENTIALS – Q 5 Emf = E°right - E°left +1. 02 = +1.

ELECTRODE POTENTIALS – Q 5 Emf = E°right - E°left +1. 02 = +1. 36 - E°left = + 1. 36 - 1. 02 = +0. 34 V

ELECTRODE POTENTIALS – Q 6 Emf = E°right - E°left a) E°right = +2.

ELECTRODE POTENTIALS – Q 6 Emf = E°right - E°left a) E°right = +2. 00 - 2. 38 = - 0. 38 V Ti 3+(aq) + e- ↔ Ti 2+(aq) b) E°left = -2. 38 - 0. 54 = - 2. 92 V K+(aq) + e- ↔ K(aq) c) E°right = - 3. 19 + 0. 27 = - 2. 92 V Ti 3+(aq) + e- ↔ Ti 2+(aq)

ELECTRODE POTENTIALS – Q 7 a) Cr(s) | Cr 2+(aq) || Zn 2+(aq) |

ELECTRODE POTENTIALS – Q 7 a) Cr(s) | Cr 2+(aq) || Zn 2+(aq) | Zn(s) Emf = -0. 76 - (-0. 91) = +0. 15 V b) Cu(s) |Cu 2+(aq)|| Fe 3+(aq), Fe 2+(aq)| Pt(s) Emf = +0. 77 - 0. 34 = +0. 43 V c) Pt(s) | Cl-(aq)| Cl 2(g) || Mn. O 4 -(aq), H+(aq), Mn 2+(aq)| Pt(s) Emf = +1. 51 – 1. 36 = +0. 15 V

Standard Electrode Potential Cell Diagrams • Standard hydrogen electrode is always written on the

Standard Electrode Potential Cell Diagrams • Standard hydrogen electrode is always written on the left-hand side. • Pt(s) I ½ H 2 (g) I H+ (aq) II Zn 2+(aq) I Zn(s) • Pt(s) I ½ H 2 (g) I H+ (aq) II Cu 2+(aq) I Cu(s)

Quick Check 1. a. Explain the functions in an electrochemical cell of a salt

Quick Check 1. a. Explain the functions in an electrochemical cell of a salt bridge and a high-resistance voltmeter. b. Describe the electrochemical cell represented by: Pt(s) I Fe 2+(aq), Fe 3+(aq) II Ag+(aq) I Ag(s) Complete Questions on page 91 of textbook.

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