Electrochemistry

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Electrochemistry Lesson 4 Using Oxidation
Numbers
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Using Oxidation Numbers   If the oxidation number
of the central atom increases going from left to
right, its oxidation. ClO2- ? ClO4-
Increase is oxidation
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oxidation
reducing agent
4 electrons lost
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Using Oxidation Numbers   If the oxidation number
of the central atom decreases going from left to
right, its reduction. NO3- ?
HNO2
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decrease is reduction
reduction
2 electrons gained
oxidizing agent
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Label the oxidizing agent and the reducing
agent.   7 1 5
0 ReO4- IO- ? IO3- Re Reduced
Oxidized Ox Agent Red Agent
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Label the oxidizing agent and the reducing
agent.   3 5 5
2 3As2O3 4NO3- 7H2O 4H ?
6H3AsO4 4NO oxidized reduced red
agent ox agent
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Predicting Spontaneous Reactions Using
the Standard Reduction Chart Does Au3 react
with Cl-? If it does write the spontaneous
reaction.
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The top reaction is written forward- reduction
The bottom reaction is written in reverse-
oxidation
(Au3 3e- ? Au(s))
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(2Cl- ? Cl2(g) 2e-)
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2Au3 6Cl- ? 3Cl2(g) 2Au(s)
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Does Ag react with Br-?
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nonspontaneous
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Some ions are on both sides of the table and are
oxidizing or reducing agents. For
example   Fe ? Fe2 ? Fe3   Sn ? Sn2 ? Sn4   
Cu ? Cu ? Cu2
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Does Sn2 react with Cr?
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Check both
spontaneous
(Sn2 2e- ? Sn(s))
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(Cr(s) ? Cr3 3e-)
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2Cr (s) 3Sn2 ? 2Cr3 3Sn(s)
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Can you keep HCl in a Cu container? Explain!
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nonspontaneous
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Can you keep HCl in a Cu container?
Explain! Yes, nonspontaneous. H is a weaker
oxidizing agent than Cu2 and Cu.
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Can you keep HCl in a Zn container? Explain!
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Spontaneous- no
H is a stronger oxidizing agent than Zn2
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Write the spontaneous reaction. 2H 2e-
? H2(g) Zn(s) ? Zn2
2e- 2H Zn(s) ? H2(g)
Zn2
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Can you keep HNO3 in a Au container? Explain!
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(No Transcript)
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Can you keep HNO3 in a Au container?
Explain! Yes, nonspontaneous. HNO3 is a
weaker oxidizing agent than Au3.
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Can you keep HNO3 in a Cu container? Explain!
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Take the strongest ox agent- higher
Take the strongest red agent- lower
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Can you keep HNO3 in a Cu container? No,
spontaneous. HNO3 is a stronger oxidizing agent
than Cu2. Write the spontaneous
reaction. NO3- 4H 3e- ? NO(g)
2H2O x 2 Cu(s) ? Cu2 2e- x 3 2NO3-
8H 3Cu(s) ? 2NO(g) 4H2O
3Cu2