Oxidation-Reduction Reactions Chemistry Worksheet Page 3
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41209
6.1 An Introduction to Oxidation-Reduction Reactions
Formation of NaCl
−
e
+
−
→
→
+
−
−
e
Sodium chloride
Sodium
Chlorine
Sodium
Chloride
+
+
→
atoms
molecule
ions
ions
Ionic bonds
Oxidation of zinc
−
2e
2−
2+
→
→
2+
2−
−
2e
Zi nc o x i de
Zinc
Oxygen
Zinc
Oxide
→
+
+
ions
ions
atoms
molecule
Figure 6.1
O
2
bjeCtive
Oxidation and the Formation of Binary Ionic Compounds
The concept of reduction has undergone a similar evolution. At high temperature,
zinc oxide, ZnO, reacts with carbon, C, to form molten zinc and carbon monoxide
gas.
∆
ZnO(s) + C(s) →
Zn(l ) + CO( g )
Bonds between zinc atoms and oxygen atoms are lost in this reaction, so chemists
say the zinc has been reduced. Like the term oxidation, the term reduction has been
expanded to include similar reactions, even when oxygen is not a participant. The zinc
ions in zinc oxide have a +2 charge, and the atoms in metallic zinc are uncharged. Thus,
in the conversion of zinc oxide to metallic zinc, each zinc ion must gain two electrons.
According to the modern definition, any chemical change in which an element gains
electrons is called a reduction. (Yes, reduction means a gain of electrons.) Because this
O I L
can be confusing, some people use a memory aid to remember what oxidation and
reduction mean in terms of the electron transfer. One device is the phrase oil rig which
stands for oxidation is loss (of electrons) and reduction is gain (of electrons).
R I G
When an electric current passes through molten sodium chloride, the sodium ions,
+
‒
Na
, are converted to uncharged sodium atoms, and the chloride ions, Cl
, are converted
to uncharged chlorine molecules, Cl
. Because sodium ions gain one electron each, we
2
say they are reduced. Chloride ions lose one electron each, so they are oxidized.
Electric current
2Na(l ) + Cl
2NaCl(l )
( g)
2
‒
→ Cl
+ 2e
‒
oxidation:
2Cl
2
+
+ 2e
‒
→ 2Na
reduction:
2Na
Electrons are rarely found unattached to atoms. Thus, for one element or compound
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