Chapter 21 electrochemistry - 21 21.1 21.2 21.3 21.4 21.5 21.6 21.7 21.8 21.9 Chapter Oxidation is a loss of electron(s and an increase in oxidation

Chapter 21 electrochemistry - 21 21.1 21.2 21.3 21.4 21.5...

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21 Chapter Electrochemistry: Chemical Change and Electrical Work 21.1 Oxidation is a loss of electron( s ) and an increase in oxidation number. Reduction is a gain of electron( s ) and a decrease in oxidation number. 21.2 An electrochemical process involves an electron flow. At least one substance must lose electron( s ) and one substance must gain electron( s ) to produce the flow. This electron transfer is a redox process. 21.3 No. Oxidation is always accompanied by reduction. Electrons cannot be created or destroyed, only transferred. 21.4 O 2 - is too strong a base to exist in H 2 O. The reaction O 2 - + H 2 O B 2OH - occurs. Only species actually existing in solution can be used to balance an equation. 21.5 Multiply each half-reaction by the appropriate integer to make e - lost equal to e - gained. 21.6 Add an equal number of OH - ions to both sides to neutralize H + ions and produce H 2 O. 21.7 No. Add spectator ions to the balanced ionic equation to obtain the balanced molecular equation. 21.8 A voltaic or galvanic cell has a G sys < 0. An electrolytic cell has a G sys 0, meaning an increase in free energy. 21.9 a) True. b) True. c) True. d) False. In a voltaic cell, the system does work on the surroundings. e) True. f) False. The electrolyte in a cell provides a solution of mobile ions to maintain charge neutrality. 21.10 16H + ( aq ) + 2MnO 4 - ( aq ) + 10Cl - ( aq ) B 2Mn 2 + ( aq ) + 5Cl 2 ( g ) + 8H 2 O( l ) a) Cl - b) MnO 4 - c) MnO 4 - d) Cl - e) From Cl - to MnO 4 - f) 8H 2 SO 4 ( aq ) + 2KMnO 4 ( aq ) + 10KCl( aq ) B 2MnSO 4 ( aq ) + 6K 2 SO 4 ( aq ) + 5Cl 2 ( g ) + 8H 2 O( l ) 21.11 2 CrO 2 - ( aq ) + 2 H 2 O( l ) + 6 ClO - ( aq ) B 2 CrO 4 2 - ( aq ) + 3 Cl 2 ( g ) + 4 OH - ( aq ) a) CrO 2 - b) ClO - c) ClO - d) CrO 2 - e) from CrO 2 - to ClO - f) 2 NaCrO 2 ( aq ) + 6 NaClO( aq ) + 2 H 2 O( l ) B 2 Na 2 CrO 4 ( aq ) + 3 Cl 2 ( g ) + 4 NaOH( aq ) 21.12 a) ClO 3 - ( aq ) + 6I - ( aq ) + 6H + ( aq ) B Cl - ( aq ) + 3I 2 ( s ) + 3H 2 O( l ) oxidizing agent: ClO 3 - ; reducing agent: I - b) 2MnO 4 - ( aq ) + 3SO 3 2 - ( aq ) + H 2 O( l ) B 2MnO 2 ( s ) + 3SO 4 2 - ( aq ) + 2OH - ( aq ) oxidizing agent: MnO 4 - ; reducing agent: SO 3 2 - c) 2MnO 4 - ( aq ) + 5H 2 O 2 ( aq ) + 6H + ( aq ) B 2Mn 2 + ( aq ) + 5O 2 ( g ) + 8H 2 O( l ) oxidizing agent: MnO 4 - ; reducing agent: H 2 O 2 21.13 a) 3O 2 ( g ) + 4NO( g ) + 2H 2 O( l ) B 4NO 3 - ( aq ) + 4H + ( aq ) oxidizing agent: O 2 ; reducing agent: NO
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b) 2CrO 4 2 - ( aq ) + 8H 2 O( l ) + 3Cu( s ) B 2Cr(OH) 3 ( s ) + 3Cu(OH) 2 ( s ) + 4OH - ( aq ) oxidizing agent: CrO 4 2 - : reducing agent: Cu c) AsO 4 3 - ( aq ) + NO 2 - ( aq ) + H 2 O( l ) B AsO 2 - ( aq ) + NO 3 - ( aq ) + 2OH - ( aq ) oxidizing agent: AsO 4 3 - ; reducing agent: NO 2 - . 21.14 a) Cr 2 O 7 2 - ( aq ) + 3Zn( s ) + 14H + ( aq ) B 2Cr 3 + ( aq ) + 3Zn 2 + ( aq ) + 7H 2 O( l ) oxidizing agent: Cr 2 O 7 2 - ; reducing agent: Zn b) 3Fe(OH) 2 ( s ) + MnO 4 - ( aq ) + 2H 2 O( l ) B MnO 2 ( s ) + 3Fe(OH) 3 ( s ) + OH - ( aq ) oxidizing agent: MnO 4 - ; reducing agent: Fe(OH) 2 c) 5Zn( s ) + 2NO 3 - ( aq ) + 12H + ( aq ) B 5Zn 2 + ( aq ) + N 2 ( g ) + 6H 2 O( l ) oxidizing agent: NO 3 - ; reducing agent: Zn 21.15 a) 3BH 4 - ( aq ) + 4ClO 3 - ( aq ) B 3H 2 BO 3 - ( aq ) + 4Cl - ( aq ) + 3H 2 O( l ) oxidizing agent: ClO 3 - ; reducing agent: BH 4 - b) 2CrO 4 2 - ( aq ) + 3N 2 O( g ) + 10H + ( aq ) B 2Cr 3 + ( aq ) + 6NO( g ) + 5H 2 O( l ) oxidizing agent: CrO 4 2 - ; reducing agent: N 2 O c) 3Br 2 ( l ) + 6OH - ( aq ) B BrO 3 - ( aq ) + 5Br - ( aq ) + 3H 2 O( l ) oxidizing agent: Br 2 ; reducing agent: Br 2 21.16 a) 1[4 Sb( s ) + 6 H 2 O( l ) B Sb 4 O 6 ( s ) + 12 H + ( aq ) + 12 e - ] 4[3 e - + NO 3 - ( aq ) + 4 H + ( aq ) B NO( g ) + 2H 2 O( l ) 4 4 Sb( s ) + 2 6H O ( l ) + 4 NO 3 - ( aq ) + 16 + H ( ) aq + 12 e - 2 B Sb 4 O 6 ( s ) + 4 NO( g ) + 8 H 2 O( l ) + 12H + ( aq ) + 12 e - 4 Sb( s ) + 4 NO 3 - ( aq ) + 4 H + ( aq ) B Sb 4 O 6 ( s ) + 4 NO( g ) + 2 H 2 O( l )
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