Redox reactions involves both oxidation as well as reduction. If we cut an apple. it turns reddish brown after some time because Fe2+ present in apple gets converted into Fe3+ by loss of electrons. Oxidation is a process in which loss of electrons takes place. Oxidation is carried out with the help of oxidising agent which can give O2 or remove hydrogen or can gain electrons. Non-metals are good oxidising agents, KMnO4, K2Cr207 are also good oxidising agent in acidic medium. Combustion is oxidation reaction. Reduction involve gain of electrons. Reducing agent can add H2 or remove O2 or can lose electrons. Metals are good reducing agents. Reducing agents are used in extraction of metals. (a) Fe203(s) + 3CO(g) — 2Fe(s) + 3CO2(g) Name the oxidising and reducing agent in the above reaction. (b) H2S(g) + Cl2(g) + 2HCI(g) + S(g) Name the substances which are getting oxidising and reduced . (c) Mg(s) + 2H+(aq) —Mg2+ (aq) + H2(g) Why is Mg acting as reducing agent and H-+ions are oxidising agent. (d) Cr203 + 2A] — Al203 + 2Cr What are types of above reaction?
Answers
Concept:
Redox reactions - Oxidation and reduction occurring simultaneously.
Given: The four given reactions are as follows -
(a) Fe203(s) + 3CO(g) —> 2Fe(s) + 3CO2(g)
(b) H2S(g) + Cl2(g) —> 2HCI(g) + S(g)
(c) Mg(s) + 2H+(aq) —> Mg2+ (aq) + H2(g)
(d) Cr203 + 2Al —> Al203 + 2Cr
Answer:
(a) Fe203(s) + 3CO(g) —> 2Fe(s) + 3CO2(g)
Oxidising agent = Fe2O3(s)
Reducing agent = CO(g)
(b) H2S(g) + Cl2(g) —> 2HCI(g) + S(g)
Oxidised substance = H2S(g)
Reduced substance = Cl2(g)
(c) Mg(s) + 2H+(aq) —> Mg2+ (aq) + H2(g)
Mg is acting as reducing agent because it reduces H+ ions (to form H2 molecule) and get oxidised itself.
H+ ions are acting as oxidising agents because they oxidise Mg to form Mg2+ and get reduced themselves.
(d) Cr203 + 2Al —> Al203 + 2Cr
The above reaction is a redox reaction as both oxidation and reduction reactions are occurring simultaneously. Cr2O3 is getting reduced while Al is getting oxidised.
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