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Unformatted text preview: e ducing age nt. In the example above, zinc metal is the reducing agent; it loses two electrons (is
oxidized) and becomes Zn2+ ion. The reactant that gains electrons (is reduced) causes an oxidation and is called
an oxidizing age nt. Cu2+ ion gains two electrons (is reduced) to form copper metal.
In order to have a
complete, balanced redox system, there must be at least one reduction and one oxidation; one cannot occur
without the other and they will occur simultaneously. For a balanced system, the number of electrons lost in the
oxidation reaction must be equal to the number of electrons gained in the reduction step. This is the key to
balancing equations for redox reactions. To keep track of electrons, it is convenient to write the oxidation and
reduction reactions as half-re actions . The half- reactions for equation 1
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
are shown below. In this example, zinc loses two electrons and copper(II) accepts both.
Zn → Zn2+ + 2 e− (oxidation half- reaction, reducing agent)
Cu2+ + 2 e− → Cu (reduction half reaction, oxidizing agent)
In a (slightly) more complicated example, copper metal transfers electrons to silver ions, which have an
oxidation state of +1. The half- reactions and the balanced net equation are shown below. Since the number of
electrons lost must equal the number of electrons gained, two silver ions each accept one electron from a single
copper atom, which loses two electrons.
Cu → Cu2+ + 2 e− (oxidation half- reaction)
Ag+ + 1 e− → Ag (reduction half- reaction)
2 Ag+ + Cu → 2 Ag + Cu2+ (net reaction)
In this example, copper donates electrons (is oxidized). This indicates that silver ion has a vacant orbital at
lower energy than that in which two of copper's electrons reside.
In redox reactions, the oxidized and
reduced forms of each reactant are called a re dox couple . Redox couples are written "ox/red". The oxidized
form of the couple is shown on the left, the reduced form on the right with a slash in between. For example,
Cu2+/Cu and Zn2+/Zn. Part A: Relative Reactivities
In Part A of this experiment, you will rank the relative strengths of oxidizing and reducing agents by observing
if reactions occur or not. A visible change will accompany each reaction....
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