Lecture 223/19/07. Displacement reactions Some metals react with acids to produce salts and H 2 gas Balance the following displacement reaction: Zn (s)

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Presentation transcript:

Lecture 223/19/07

Displacement reactions Some metals react with acids to produce salts and H 2 gas Balance the following displacement reaction: Zn (s) + HBr (aq)  ZnBr 2 (aq) + H 2 (g)

voltaic or galvanic cell electrolytic cell Electrochemical cells

Requires Electrodes Salt bridge External circuit

Anode: Cathode: Net reaction: Electrochemical cell notation:

Electromotive force (emf) Cell potential Cell voltage

All other potentials determined from the SHE Zn (s)  Zn 2+ (aq, 1 M) + 2e - E° ox = ? 2 H 3 O + (aq, 1 M) + 2e -  H 2 (g, 1 atm) + 2 H 2 O E° red = 0 V__ Zn (s) + 2 H 3 O +  Zn 2+ + H H 2 O E° cell = V

For any reaction: E° ox = - E° red

Standard Reduction Potentials (25° C) E° F 2 (g) + 2e - ↔ 2F Au e - ↔ Au (s)+1.50 Cl 2 (g) + 2e- ↔ 2 Cl O 2 (g) + 4 H + + 4e - ↔ 2 H 2 O+1.23 Hg e - ↔ Hg (l)+0.85 Ag + + e - ↔ Ag (s)+0.80 Fe 3+ + e - ↔ Fe Cu e - ↔ Cu (s)+0.34 Sn e - ↔ Sn H e - ↔ H 2 (g) 0.00 Pb e - ↔ Pb (s)-0.13 Sn e - ↔ Sn (s)-0.14 Ni e - ↔ Ni (s)-0.26 Zn e - ↔ Zn (s)-0.76 Cr e - ↔ Cr (s)-0.91 Mg e - ↔ Mg (s)-2.37 Na + + e - ↔ Na (s)-2.71 Ca e - ↔ Ca (s)-2.87 Li + + e - ↔ Li (s)- 3.04

Examples: What are the reactions for: F 2 and Cl - F 2 and Cl 2 F - and Cl 2 F - and Cl - Need to consider 2 questions: 1)Are both reduction and oxidation reactions possible? 2)Does the reduction reaction have a higher reduction potential than the oxidation reaction?

E° F 2 (g) + 2e - ↔ 2F Au e - ↔ Au (s)+1.50 O 2 (g) + 4 H + + 4e - ↔ 2 H 2 O+1.23 Br 2 (l) + 2e - ↔ 2Br Ag + + e - ↔ Ag (s)+0.80 Fe 3+ + e - ↔ Fe I 2 + 2e - ↔ 2 I O 2 (g) + 2 H 2 O + 4e - ↔ 4 OH Cu e - ↔ Cu (s) H + + 2e - ↔ H 2 (g) 0.00 Pb e - ↔ Pb (s)-0.13 Ni e - ↔ Ni (s)-0.26 Fe e - ↔ Fe (s)-0.45 Ag 2 S + 2e - ↔ 2 Ag (s) + S Zn e - ↔ Zn (s)-0.76 Al e - ↔ Al (s)-1.66

Four metals A, B, C, and D exhibit the following properties Only A and C react with 1.0 M HCl to give H 2 (g) When C is added to solutions of the ions of the other metals, metallic B, D, and A are formed Metal D reduces B n+ to give metallic B and D n+. Based on the information above, arrange the 4 metals in order of increasing ability to act as reducing agents.