Consider Fe^2+ at standard conditions. a Will the reaction below occur? 2Fe^3+(aq) + 2I^-(aq) → 2Fe^2+(aq) + I2(s)

Question

Consider [latex]Fe^{2+}[/latex] at standard conditions.

a Will the reaction below occur?
[latex]2Fe^{3+}(aq) + 2I^-(aq) \longrightarrow 2Fe^{2+}(aq) + I_2(s)[/latex]

ANALYSIS

Information given: equation for the reaction [latex](2Fe^{3+}(aq) + 2I^-(aq) \longrightarrow 2Fe^{2+}(aq) + I_2(s))[/latex]
Information implied: Table 17.1 (standard reduction potentials)
Asked for: Will the reaction occur?

STRATEGY

1. Assign oxidation numbers.
2. Write oxidation and reduction half-reactions. Include [latex]E^{\circ}_{ox}[/latex] and [latex]E^{\circ}_{red}[/latex].
3. Find E°. The reaction will occur if E° > 0.

b Can Fe(s) be oxidized to [latex]Fe^{2+}[/latex] by treatment with hydrochloric acid?

ANALYSIS

Information given: oxidation half-reaction [latex](Fe(s) \longrightarrow Fe^{2+}(aq) + 2e^-)[/latex]
Information implied: Table 17.1 (standard reduction potentials)
Asked for: Will HCl oxidize Fe?

STRATEGY

1. HCl(aq) is made up of two ions, [latex]H^+[/latex] and [latex]Cl^-[/latex]. Since an oxidizing agent is needed (to oxidize Fe to [latex]Fe^{2+}[/latex]), find either [latex]H^+[/latex] or [latex]Cl^-[/latex] (or both) in the left column of Table 17.1.
2. Write the possible half-reactions.
3. Write the redox reaction and find E°.

c What redox reactions occur when the following species are mixed in acidic solution: [latex]Cl^-, Fe^{2+}, Cr^{2+}, I_2[/latex]?

ANALYSIS

Information given: ions in acidic solution [latex](Cl^-, Fe^{2+}, Cr^{2+}, I^-)[/latex]
Information implied: Table 17.1
Asked for: Will a redox reaction occur when the ions are mixed?

STRATEGY

1. Check the left column of Table 17.1 to determine which of the ions are oxidizing agents (i.e., they are reduced). Write the reduction half-reactions of the oxidizing agents.
2. Check the right column of Table 17.1 to determine which of the ions are reducing agents (i.e., they are oxidized). Write the reduction half-reactions of the reducing agents.
3. Write all possible combinations of oxidation and reduction half-reactions. The combination(s) that give positive E° values are possible.
4. Write the redox equation(s) for the reaction(s) that occur.

Accepted Answer

a

1. oxidation numbers Fe: +3 → +2 reduction I: -1 → 0 oxidation

2. half-reactions [latex]2Fe^{3+}(aq) + 2e^- \longrightarrow 2Fe^{2+}(aq)[/latex] [latex]E^{\circ}_{red}[/latex]= +0.769 V
[latex]2I^-(aq) \longrightarrow I_2(s) + 2e^-[/latex] [latex]E^{\circ}_{ox}[/latex] = -0.534 V

3. E° E° = 0.769 V + (-0.534 V) = +0.235 V
E° > 0, the reaction will occur at standard conditions.

b

1. Oxidizing agent Only [latex]H^+[/latex] appears in the left column.

2. Half-reactions [latex]2H^+(aq) + 2e^- \longrightarrow H_2(g)[/latex] [latex]E^{\circ}_{red}[/latex] = 0.000 V
[latex]Fe(s) \longrightarrow Fe^{2+}(aq) + 2e^-[/latex] [latex]E^{\circ}_{ox}[/latex] = 0.409 V

3. Redox reaction [latex]Fe(s) + 2H^+(aq) \longrightarrow Fe^{2+}(aq) + H_2(g)[/latex] E° = 0.409 V
E° > 0, HCl will oxidize Fe at standard conditions (Figure 17.8).

c

1. Oxidizing agents [latex]Fe^{2+}(aq) + 2e^- \longrightarrow Fe(s)[/latex] [latex]E^{\circ}_{red}[/latex] = -0.409 V
[latex]I_2(s) + 2e^- \longrightarrow 2I^-(aq)[/latex] [latex]E^{\circ}_{red}[/latex] = +0.534 V

2. Reducing agents [latex]2Cl^-(aq) \longrightarrow Cl_2(g) + 2e^-[/latex] [latex]E^{\circ}_{ox}[/latex] = -1.360 V
[latex]Cr^{2+}(aq) \longrightarrow Cr^{3+}(aq) + e^-[/latex] [latex]E^{\circ}_{ox}[/latex]= +0.408 V
[latex]Fe^{2+}(aq) \longrightarrow Fe^{3+}(aq) + e^-[/latex] [latex]E^{\circ}_{ox}[/latex]= -0.769 V

3. Possible combinations [latex] Fe^{2+} + Cl^-[/latex]: E° <0 [latex]I_2 + Cl^-:[/latex] E° < 0
[latex]Fe^{2+} + Cr^{2+}:[/latex] E° < 0 [latex]I_2 + Cr^{2+}:[/latex] E° > 0 ✓
[latex]Fe^{2+} + Fe^{2+}:[/latex] E° < 0 [latex]I_2 + Fe^{2+}[/latex]: E° < 0

4. Redox reaction [latex]I_2(s) + 2Cr^{2+}(aq) \longrightarrow 2I^-(aq) + 2Cr^{3+}(aq)[/latex] E° = 0.942 V

Table 17.1 Standard Potentials in Water Solution at 25°C
Acidic Solution, $[H^+]$ = 1 M
${E^{\circ}}_{red}$ (V)
	$Li^+(aq) + e^-$	$\longrightarrow Li(s)\blacktriangleleft ⓘ$	-3.04
	$K^+(aq) + e^-$	$\longrightarrow K(s)$	-2.936
	$Ba^{2+}(aq) + 2e^{-}$	$\longrightarrow Ba(s)$	-2.906
	$Ca^{2+}(aq) + 2e^-$	$\longrightarrow Ca(s)$	-2.869
	$Na^+(aq) + e^-$	$\longrightarrow Na(s)$	-2.714
	$Mg^{2+}(aq) + 2e^-$	$\longrightarrow Mg(s)$	-2.357
	$Al^{3+}(aq) + 3e^-$	$\longrightarrow Al(s)$	-1.68
	$Mn^{2+}(aq) + 2e^-$	$\longrightarrow Mn(s)$	-1.182
	$Zn^{2+}(aq) + 2e^-$	$\longrightarrow Zn(s)$	-0.762
	$Cr^{3+}(aq) + 3e^-$	$\longrightarrow Cr(s)$	-0.744
	$Fe^{2+}(aq) + 2e^-$	$\longrightarrow Fe(s)$	-0.409
	$Cr^{3+}(aq) + e^-$	$\longrightarrow Cr^{2+}(aq)$	-0.408
	$Cd^{2+}(aq) + 2e^-$	$\longrightarrow Cd(s)$	-0.402
	$PbSO_4(s) + 2e^-$	$\longrightarrow Pb(s) + {SO_4}^{2-}(aq)$	-0.356
	$Tl^+(aq) + e^-$	$\longrightarrow Tl(s)$	-0.336
	$Co^{2+}(aq) + 2e^-$	$\longrightarrow Co(s)$	-0.282
	$Ni^{2+}(aq) + 2e^-$	$\longrightarrow Ni(s)$	-0.236
	$AgI(s) + e^-$	$\longrightarrow Ag(s) + I^-(aq)$	-0.152
	$Sn^{2+}(aq) + 2e^-$	$\longrightarrow Sn(s)$	-0.141
	$Pb^{2+}(aq) + 2e^-$	$\longrightarrow Pb(s)$	-0.127
	$2H^+(aq) + 2e^-$	$\longrightarrow H_2(g)$	0
	$AgBr(s) + e^-$	$\longrightarrow Ag(s) + Br^-(aq)$	0.073
	$S(s) + 2H^+(aq) + 2e^-$	$\longrightarrow H_2S(aq)$	0.144
	$Sn^{4+}(aq) + 2e^-$	$\longrightarrow Sn^{2+}(aq)$	0.154
	${SO_4}^{2-}(aq) + 4H^+(aq) + 2e^-$	$\longrightarrow SO_2(g)+ 2H_2O$	0.155
	$Cu^{2+}(aq) + e^-$	$\longrightarrow Cu^+(aq)$	0.161
	$Cu^{2+}(aq) + 2e^-$	$\longrightarrow Cu(s)$	0.339
	$Cu^+(aq) + e^-$	$\longrightarrow Cu(s)$	0.518
	$I_2(s) + 2e^-$	$\longrightarrow 2I^-(aq)$	0.534
	$Fe^{3+}(aq) + e^-$	$\longrightarrow Fe^{2+}(aq)$	0.769
	${Hg_2}^{2+}(aq) + 2e^-$	$\longrightarrow 2Hg(l)$	0.796
	$Ag^+(aq) + e^-$	$\longrightarrow Ag(s)$	0.799
	$2Hg^{2+}(aq) + 2e^-$	$\longrightarrow {Hg_{2}}^{2+}(aq)$	0.908
	${NO_3}^-(aq) + 4H^+(aq) + 3e^-$	$\longrightarrow NO(g) + 2H_2O$	0.964
	${AuCl_4}^-(aq) + 3e^-$	$\longrightarrow Au(s) + 4Cl^-(aq)$	1.001
	$Br_2(l) + 2e^-$	$\longrightarrow 2Br^-(aq)$	1.077
	$O_2(g) + 4H^+(aq) + 4e^-$	$\longrightarrow 2H_2O$	1.229
	$MnO_2(s) + 4H^+(aq) + 2e^-$	$\longrightarrow Mn^{2+}(aq) + 2H_2O$	1.229
	${Cr_2O_7}^{2-}(aq) + 14H^+(aq) + 6e^-$	$\longrightarrow 2Cr^{3+}(aq) + 7H_2O$	1.33
	$Cl_2(g) + 2e^-$	$\longrightarrow 2Cl^-(aq)$	1.36
	${ClO_3}^{-}(aq) + 6H^+(aq) + 5e^-$	$\longrightarrow \frac{1}{2} Cl_2(g) + 3H_2O$	1.458
	$Au^{3+}(aq) + 3e^-$	$\longrightarrow Au(s)$	1.498
	${MnO_4}^{-}(aq) + 8H^+(aq) + 5e^-$	$\longrightarrow Mn^{2+}(aq) + 4H_2O$	1.512
	$PbO_2(s) + {SO_4}^{2-}(aq) + 4H^+(aq) + 2e^-$	$\longrightarrow PbSO_4(s) + 2H_2O$	1.687
	$H_2O_2(aq) + 2H^+(aq) + 2e^-$	$\longrightarrow 2H_2O$	1.763
	$Co^{3+}(aq) + e^-$	$\longrightarrow Co^{2+}(aq)$	1.953
	$F_2(g) + 2e^- \blacktriangleleft ⓘ$	$\longrightarrow 2F^-(aq)$	2.889
Basic Solution, $[OH^-]$ = 1 M
${E^{\circ}}_{red}$ (V)
$Fe(OH)_2(s) + 2e^-$		$\longrightarrow Fe(s) + 2OH^-(aq)$	-0.891
$2H_2O + 2e^-$		$\longrightarrow H_2(g) + 2OH^-(aq)$	-0.828
$Fe(OH)_3(s) + e^-$		$\longrightarrow Fe(OH)_2(s) + OH^-(aq)$	-0.547
$S(s) + 2e^-$		$\longrightarrow S^{2-}(aq)$	-0.445
${NO_3}^{-}(aq) + 2H_2O + 3e^-$		$\longrightarrow NO(g) + 4OH^-(aq)$	-0.14
${NO_3}^-(aq) + H_2O + 2e^-$		$\longrightarrow {NO_2}^-(aq) + 2OH^-(aq)$	0.004
	${ClO_4}^-(aq) + H_2O + 2e^-$	$\longrightarrow {ClO_3}^-(aq) + 2OH^-(aq)$	0.398
$O_2(g) + 2H_2O + 4e^-$		$\longrightarrow 4OH^-(aq)$	0.401
${ClO_3}^-(aq) + 3H_2O + 6e^-$		$\longrightarrow Cl^-(aq) + 6OH^-(aq)$	0.614
$ClO^-(aq) + H_2O + 2e^-$		$\longrightarrow Cl^-(aq) + 2OH^-(aq)$	0.89

Question 17.6: Consider Fe^2+ at standard conditions. a Will the reaction b...

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