Transcript Electrochemistry Lesson 4 Using Oxidation Numbers Using Oxidation Numbers If the oxidation number of the central atom increases going from left to right, its oxidation. +3 Increase.

Electrochemistry
Lesson 4
Using Oxidation
Numbers
Using Oxidation Numbers
If the oxidation number of the central atom increases going
from left to right, its oxidation.
+3
Increase is oxidation
ClO2oxidation
reducing agent
4 electrons lost

+7
ClO4-
Using Oxidation Numbers
If the oxidation number of the central atom decreases going
from left to right, its reduction.
+5
decrease is reduction
NO3reduction
2 electrons gained
oxidizing agent

+3
HNO2
Label the oxidizing agent and the reducing agent.
+7
ReO4-
+
+1
IO-

Reduced
Oxidized
Ox Agent
Red Agent
+5
IO3-
+
0
Re
Label the oxidizing agent and the reducing agent.
+3
+5
+5
+2
3As2O3 + 4NO3- + 7H2O + 4H+  6H3AsO4 + 4NO
oxidized
reduced
red agent
ox agent
Predicting Spontaneous Reactions
Using the
Standard Reduction Chart
Does Au3+ react with Cl-?
If it does write the spontaneous reaction.
The top reaction is written forward- reduction
The bottom reaction is written in reverse- oxidation
2 (Au3+ +
3e-

3 (2Cl-  Cl2(g) +
Au(s))
2e-)
2Au3+ + 6Cl-  3Cl2(g) + 2Au(s)
Does Ag+ react with Br-?
nonspontaneous
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+
Does Sn2+ react with Cr?
Check both
3(Sn2+ + 2e2 (Cr(s)

spontaneous
Sn(s))
 Cr3+ + 3e-)
2Cr (s) + 3Sn2+  2Cr3+ + 3Sn(s)
Can you keep HCl in a Cu container? Explain!
nonspontaneous
Can you keep HCl in a Cu container? Explain!
Yes, nonspontaneous.
H+ is a weaker oxidizing agent than Cu2+ and Cu+.
Can you keep HCl in a Zn container? Explain!
Spontaneous- no
H+ is a stronger oxidizing agent than Zn2+
Write the spontaneous reaction.
2H+
Zn(s)

+ 2e
2H+ +
H2(g)
Zn2+ + 2eZn(s)

H2(g) +
Zn2+
Can you keep HNO3 in a Au container? Explain!
Can you keep HNO3 in a Au container? Explain!
Yes, nonspontaneous.
HNO3 is a weaker oxidizing agent than Au3+.
Can you keep HNO3 in a Cu container? Explain!
Take the strongest ox agent- higher
Take the strongest red agent- lower
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
Cu(s)

2NO3- +
Cu2+ + 2e8H+ +
3Cu(s)

x
2
x
3
2NO(g) + 4H2O
+ 3Cu2+