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A study resource for understanding oxidation and reduction reactions, focusing on the concept of oxidation numbers and how to write half reactions. It includes examples and exercises for practicing these concepts.
What you will learn
Typology: Lecture notes
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The activity series of common metals
Calculating oxidation numbers
Activity series of elements
elements
Lithium Li ®
Li
e-
Potassium K ®
e-
Barium Ba ®
Ba
2+
Calcium Ca ®
Ca
2+
Sodium Na ®
Na
e-
Magnesium Mg ®
Mg
2+
Aluminum Al ®
Al
2+
Manganese Mn ®
Mn
2+
Zinc Zn ®
Zn
2+
Chromium Cr ®
Cr
2+
Iron Fe ®
Fe
2+
Cobalt Co ®
Co
2+
Nickel Ni ®
Ni
2+
Tin Sn ®
Sn
2+
Lead Pb ®
Pb
2+
2e-
Copper Cu ®
Cu
2+
Mercury 2Hg ®
Hg
2
2+
Silver Ag ®
Ag
e-
Mercury Hg ®
Hg
2+
Platinum Pt ®
Pt
2+
Gold Au ®
Au
3+
Notice, also, that the transition elements from groups 8B to 1B are near the bottom of the list. The alkali
and alkaline earth metals are at the top. They are most easily oxidized.
in the series. Cu metal can be oxidized by Ag+ to give silver metal and copper ions.
hydroxide: Li, K, Ba, Ca, Na.
Li, K, Ba, Ca, Na.
Zn, Cr, Fe, Cd, Co, Ni, Sn, Pb.
Zn, Cr, Fe, Cd.
or O 2
2 -
Transition Metals IIIB-IIB (3-12). If the B designation is used the values may range from +2 to
the group number. If the other designation is used, the values may range from +2 to the group
number for columns 3-8 and to the group number minus 10 for groups 11 and 12 (treat columns 9
and 10 as if they were 7 and 6 respectively). Exceptions: Hg 2
2+
(Hg = +1) and Au
3+
(Au = +3).
When an element may have a positive or negative oxidation number, it will normally be negative
if it is to the upper right, on the Periodic Table, with respect to the other elements in the compound
or ion.
When it is negative, under these circumstances, it will probably have the most negative of the
possible values noted in the rules above. Note that in Special Rules 4-8 the range of possible values
is always eight. With these elements, the
more probable oxidation states may be determined by counting from highest to lowest by twos.
Worksheet #1 Writing half reactions
—
)reduction is gain (of e
—
a) Oxidation
b) Reduction
c) Oxidizing agent
d) Reducing agent
reduction. Use the Activity Series Chart.
a) Al
b) Ba
2+
c) Br 2
d) Ca
e) Ga
3+
f) H 2
g) H
Worksheet #2 Finding oxidation numbers
a) NH 3
_____ b) H 2
4
c) ZnSO 3
_____ d) Al(OH) 3
e) Na _____ f) Cl 2
g) AgNO 3
_____ h) ClO 4
i) SO 2
_____ j) K 2
Cr 2
4
k) Ca(ClO 3
2
_____ l) K 2
Cr 2
7
m) HPO 3
2 -
_____ n) HClO _____
o) MnO 2
_____ p) KClO 3
q) PbO 2
_____ r) PbSO 4
s) K 2
4
_____ t) NH 4
u) Na 2
2
_____ v) FeO _____
w) Fe 2
3
_____ x) SiO 4
4 -
y) NaIO 3
_____ z) ClO 3
aa) NO 3
_____ bb) Cr(OH) 4
cc) CaH 2
_____ dd) Pt(H 2
5
2+
ee) Fe(H 2
6
3+
_____ ff) CH 3
a) CO _____ b) C _____
c) CO 2
_____ d) CO 3
2 -
e) C 2
6
_____ f) CH 3
substance oxidized and the substance reduced.
a) Cu
2+
(aq)
→ Cu (s)
2+
(aq)
Substance oxidized _____ Substance reduced _____
Oxidizing agent _____ Reducing agent _____
b) Cl 2 (g)
→ 2 Na
(aq)
(aq)
Substance oxidized _____ Substance reduced ____
Oxidizing agent _____ Reducing agent _____
Substance oxidized _______ Oxidizing agent ________
Cr 2
7
2 —
+ClO 2
—
→Cr
3+
+ClO 4
—
Substance reduced ________ Oxidizing agent ________
3
2
2
4
2 —
2
Substance oxidized __________ Reducing agent __________
As 2
3
3
2
3
AsO 4
Substance reduced __________ Reducing agent __________
2
Cl
Fe Na
Redox Half Reactions and Reactions WS #
Define each
(g)
Oxidation - loss of electrons
(g)
Reduction - gain of electrons
(g)
Oxidizing agent - causes oxidation by undergoing reduction
(g)
Reducing agent - causes reduction by undergoing oxidation
Write half reactions for each of the following atoms or ions. Label each as oxidation or reduction.
3
+ 3e
-
oxidation
2+
+ 2e
—
® Ba reduction
2+
+ 2e
-
oxidation
3+
+ 3e ® Ga reduction
2
+
+ 2e
-
oxidation
+
+ 2e ® H 2
reduction
Balance each spontaneous redox equation. Identify the entities reduced and oxidized. State the
reducing agent and the oxidizing agent.
2+
i. 2Al + 3Zn
2+
→ 2Al
3+
+ 3Zn
ii. oxidized reduced
iii. reducing agent oxidizing agent
2
2 -
i. 2F 2
2 -
-
2
ii. reduced oxidized
iii. oxidizing agent reducing agent
2
& Ca
i. 2Ca + O 2
→ 2Ca
2+
2 -
ii. oxidized reduced
iii. reducing agent oxidizing agent
3+
& Li
aa) NO 3
5 bb) Cr(OH) 4
cc) CaH 2
- 1 dd) Pt(H 2
5
2+
ee) Fe(H 2
6
3+
+3 ff) CH 3
(g)
What is the oxidation number of carbon in each of the following substances?
a) CO 2 b) C 0
c) CO 2
4 d) CO 3
2 -
e) C 2
6
- 3 f) CH 3
(g)
For each of the following reactions, identify: the oxidizing agent, the reducing agent, the
substance oxidized and the substance reduced.
a) Cu
2+
(aq)
--------> Cu (s)
2+
(aq)
Substance oxidized Zn Substance reduced Cu
2+
Oxidizing agent Cu
2+
Reducing agent
Zn
b) Cl 2 (g)
--------> 2 Na+ (aq)
(aq)
Substance oxidized Na Substance reduced Cl 2
Oxidizing agent Cl 2
Reducing agent
Na
WS # 3 Spontaneous and Non-spontaneous Redox Reactions
Describe each reaction as spontaneous or non-spontaneous.
Fe
-----> Fe
Au nonspontaneous (two oxidizing
agents)
------> Fe
Pb
spontaneous
2
nonspontaneous (see exp 9)
—
+Cl 2
® 2 Cl
—
2
spontaneous(see exp 9)
Fe
------> Fe
Pb nonspontaneous
Can you keep 1 M HCl in an iron container. If the answer is no, write a balanced equation for the
reaction that would occur. No, iron is above hydrogen in the activity series. The metal will
react with acid
Fe + 2H
+
--------> Fe
2+
2
Can you keep 1 M HCl in an Ag container. If the answer is no, write a balanced equation for the
reaction that would occur.
Yes. There is no reaction. Silver is below hydrogen in the activity series
Can you keep 1 M HNO 3
in an Au container. If the answer is no, write a balanced equation for the
reaction that would occur. (Remember, HNO 3
consists of two ions H
and NO 3
Yes. There is no reaction.
Circle each formula that is able to lose an elecron
2
Cl
-
Fe Na
Determine the oxidation number for the element underlined.
PbSO 4
6 ClO 3
3
2 -
3 Na 2
2
CaH 2
- 1 Al 2
4
3
NaIO 3
4
12
Al
3+
2+
Substance oxidized Zn Oxidizing agent Al
3+
Cr 2
7
2 -
Cr
3+
Substance reduced Cr 2
7
2 -
Oxidizing agent Cr 2
7
2 -
State the Oxidation Number of each of the elements that is underlined.
a) NH 3
- 3 b) H 2
4
c) ZnCO 3
4 d) Al(OH) 3
e) Na 0 f) Cl 2
