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OXIDIZING AND REDUCING AGENTS
- Oxidizing agent: This is a substance which adds oxygen or removes hydrogen form a substance or a substance which accepts electron, i.e. electron acceptor. Consider the following reactions.
- Oxidation in terms of addition of oxygen: oxidizing agent will add oxygen to a substance e.g.
C(s) +2ZnO(s) → CO2(g) + 2Zn (s)
ZnO is the oxidising agent because it added oxygen to (i.e. oxidise) carbon to form CO2
- Oxidation in terms of removal of hydrogen: oxidizing agent will add oxygen to a substance e.g
2H2S (g) + O2 (g) → 2H2O (l) + 2S(s) or
H2S (g) + Cl2 (g) → 2HCl (g) + S(s)
Oxygen and chlorine are the oxidizing agents because they removed hydrogen from H2S to form sulphur
- Oxidation in terms of loss of electrons: oxidizing agent will gain electrons e.g
2FeCl2(s) + Cl2 (g) → 2FeCl3(s)
Fe2+ → Fe3+ + 2e–
Cl2 + 2e– → 2Cl–
The oxidizing agent is chlorine (Cl2) because it gained electrons lost by Fe2+
Other means of identifying an oxidising agent is the substance.
- Which is reduced
- Whose oxidation number has decreased
- Reducing agent: This is a substance which adds hydrogen to another substance or removes oxygen from that substance or this substance which donates election, i.e. an electron donor.
Consider the following reactions
- Adds hydrogen e.g hydrogen sulphide reduces chloride to hydrogen chloride in
H2S(g) + Cl2(g) → 2HCl (g) + 2S(s)
- Removes oxygen e.g. Carbon in
C(s) + ZnO(s) → CO2(g) + 2Zn(s)
- Has its oxidation number increases e.g. in
Zn(s) + CuSO4 (aq) → ZnSO4 (a q) + Cu(s)
Zinc is the reducing agent because its oxidation number increased from zero in zinc to +2 in zinc tetraoxosulphate (vi) that is, it was oxidized.
The Table below give some common reducing agent and oxidizing agents.
OXIDIZING AGENTS
Oxygen | O2 |
Hydrogen peroxide | H2O2 |
Chlorine (and other halogen) | Cl2 |
Acidified potassium tetraoxomanganate (viii) | KMnO4 |
Acidified potassium heptaoxchromate (vi) | K2Cr2O7 |
Hot concentrated tetraoxsulphate (vi) acid | H2SO4 |
Concentrated trioxonitrate(v) acid | HNO3 |
Silver salt (and metals low in the series e.g cu) | Ag+ |
REDUCING AGENTS
Hydrogen | H2 |
Carbon | C |
Potassium | KI |
Hydrogen sulphide | H2S |
Sulphur(iv) oxide | SO2 |
Iron(II) salt | SO2 |
Sodium (and other reactive metals) | Na |
Ammonia | NH3 |
Generally, metals that are highly electro positive e.g. Na, K and Mg lose electrons easily and so are good reducing agents (they release their electrons to another thus reducing it). Non-metals that are highly electro negative e.g. O, Cl and F are good oxidizing agents (they easily accept electrons from another thus oxidizing it).
TEST FOR OXIDIZING AGENTS
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