Here's the solution to question 3:
a) Define
- i) Oxidation in terms of oxygen: Oxidation is the gain of oxygen by a substance.
- ii) Reduction in term of Hydrogen: Reduction is the gain of hydrogen by a substance.
b) Identify
- i) The reducing agent in equation I: In 2Cu(s)+O2(g)→2CuO(s), Copper (Cu) gains oxygen, so it is oxidized. The substance that is oxidized is the reducing agent.
- The reducing agent is Cu.
- ii) The oxidizing agent in equation II: In CuO+H2(g)→Cu+H2O(l), Copper oxide (CuO) loses oxygen, so it is reduced. The substance that is reduced is the oxidizing agent.
- The oxidizing agent is CuO.
c) Determine the oxidation state of
- i) Copper in Cu: Copper in its elemental form has an oxidation state of 0.
- The oxidation state is 0.
- ii) Oxygen in H2O: In water, hydrogen has an oxidation state of +1. Since there are two hydrogen atoms and the molecule is neutral, the oxygen atom must balance the charge.
2(+1)+x=0
2+x=0
x=−2
- The oxidation state is −2.
d) State whether each of these reactions involves oxidation or reduction or both.
- i) Al3++3e−→Al: Aluminum ion gains electrons to become neutral aluminum. The gain of electrons is reduction.
- This reaction involves reduction.
- ii) 2O2−→O2+4e−: Oxide ions lose electrons to form oxygen gas. The loss of electrons is oxidation.
- This reaction involves oxidation.
- iii) 2H2+O2→2H2O: Hydrogen goes from an oxidation state of 0 to +1 (oxidation), and oxygen goes from an oxidation state of 0 to -2 (reduction). Since both processes occur, it is a redox reaction.
- This reaction involves both.
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