Oxidation And Reduction Reactions MCQ Quiz in मल्याळम - Objective Question with Answer for Oxidation And Reduction Reactions - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Option 3 is correct.

Key Points

• Electrons are lost in an oxidation reaction. 
• Oxidation simply means a gain of oxygen and an oxidizing agent is a substance that oxidizes something.
• The reduction is the gain of electrons. A reducing agent reduces something in a reaction.
• As when one molecule gets reduced, another molecule gets oxidized. Most of the time, Oxidation and Reduction take place simultaneously and such a reaction is called a redox reaction.
• Redox reaction example- In a reaction between hydrogen and fluorine, hydrogen is oxidized and fluorine is reduced.

Option 4 is correct.

Key Points

• Electrons are lost in an oxidation reaction. 
• Oxidation simply means a gain of oxygen and an oxidizing agent is a substance that oxidizes something.
• The reduction is the gain of electrons. A reducing agent reduces something in a reaction.
• As when one molecule gets reduced, another molecule gets oxidized. Most of the time, Oxidation and Reduction take place simultaneously and such a reaction is called a redox reaction.
• Redox reaction example- In a reaction between hydrogen and fluorine, hydrogen is oxidized and fluorine is reduced.

The correct answer is  Rust and iron have the same composition.

Key Points

• A reddish-brown deposit called rust, forms over a piece of iron when it is exposed to moist air for some time. Rust is hydrated iron (III) oxide (Fe2O3.xH2O).
• When iron metal is exposed to air for a long time, it oxidises and forms a reddish-brown colour iron oxide on its surface.
• The iron rusting formula is 4Fe + 3O2 + 6H2O → 4Fe(OH)3.

Additional Information

• The slow conversion of iron into its hydrated oxide, in the presence of moisture and air is called rusting, whereas the hydrated oxide of iron is called rust.
• When some grease or oil is applied to the surface of an iron object, then air and moisture cannot come in contact with it and hence rusting is prevented.
• The most common method of preventing the rusting of iron (or corrosion of iron) is to coat its surface with paint.
• Galvanization is the process of coating a metal with a zinc layer for protection. It is a widely used technique for protecting iron from rusting.

Concept:

Standard electrode potential - It is the potential difference that arises between the electrode and electrolyte in an electrochemical cell under standard conditions of 298K temperature and 1 atm pressure and for 1M concentration of ions in solution.

It is denoted by E^o.

\(E^o_{cell} = E^o_{oxidation} + E^o_{reduction} \)

The oxidation potential of an electrode is negative of its reduction potential.

→ The lower the value of standard electrode potential more will be the reducing power of the electrode and hence are good reducing agents.

Explanation:

→ Metals having the least value of standard electrode potential show more reducing power.

From the given table-

E^o value are in order - Xn+/X (-2.93 < Yn+/Y (-1.66) < Zn+/Z (+0.8)  < Wn+/W (+1.81) 

Therefore, their reducing power is in the order of - 

Xn+/X (-2.93 > Yn+/Y (-1.66) > Zn+/Z (+0.8)  > Wn+/W (+1.81).

 Conclusion:

Therefore, the correct decreasing order of their reducing power is X > Y > Z > W.

Concept:

Disproportionation reaction - A type of redox reaction in which the same element or species is oxidised and reduced simultaneously to give two different products is called disproportionation reaction.

• These are also called dismutation reaction.
• An element undergoing disproportionation reaction must show minimum 3 different oxidation state.
• The element should be less stable in a particular oxidation state.

Explanation:

(i)

• This is only a redox reaction.
• In this reaction Cl gets reduced to Cl^- and I gets oxidized to I₂.

(ii)

• This is a disproportionation reaction.
• In this reaction Cl is simultaneously reduced and oxidised to Cl^- and ClO^- respectively.

(iii) 

• This is only a redox reaction.
• In this reaction, H(+1) gets reduced to H(0) and Mg(0) gets oxidized to Mg(+2).

(iv)

• This is the decomposition reaction of hydrogen peroxide also a disproportionation reaction.
• Here oxygen shows disproportionation.
• In peroxide 'O' is in -1 oxidation state, gets oxidised into 0 oxidation state in 'O₂' and reduced to -2 oxidation state in H₂O.

Conclusion:

Therefore only (ii) and (iv) are the disproportionation reaction.

Correct answer: 1) 

Concept:

• The titrations involving redox reaction are called redox titrations. 
• A reaction, which involves simultaneous oxidation and reduction, is called a redox reaction.
• A titration is a technique where a solution of known concentration is used to determine the concentration of an unknown solution.
• Typically, the titrant (the know solution) is added from a burette to a known quantity of the analyte (the unknown solution) until the reaction is complete.
• Knowing the volume of titrant added allows the determination of the concentration of the unknown.
• Often, an indicator is used to usually signal the end of the reaction, the endpoint.
• Oxalic acid acts as a reducing agent, it can be titrated against potassium permanganate in the acidic medium.

Explanation:

• Oxalic acid can be oxidized to carbon dioxide by a suitable oxidizing agent like aqueous potassium permanganate.
• KMnO4 is an oxidizing agent which works in an acidic medium more strongly than an alkaline medium.
• So, for quantitative analysis potassium permanganate is generally used in an acidic medium only. 
• The reaction will be faster in aqueous HCl because chlorine ion present HCl get oxidised into chlorine gas by KMnO₄.
• So, the amount of KMnO₄ will be more as it oxidises both oxalic acid and chlorine ion when HCl is present.

Conclusion:

Thus, the reaction will be faster with aq.HCl

Concept:

Anode - 

• Anode is a positive electrode.
• Normally oxidation occurs at the anode in an electrochemical reaction i.e. it will lose electrons.
• Thus, anode act as a stronger reducing agent than hydrogen when connected to standard hydrogen electrode.
• Therefore, EΘ value for anode will be less than zero or negative because it is having negative electrode potential.
• For example, Al/Al3+  EΘ = –1.66 will act as anode due to having -ve electrode potential.

Explanation:

→ The electrode which has more negative standard reduction potential as compare to standard hydrogen electrode. As they are stronger reducing agent than H₂ gas.

Therefore, 

• Al/Al3+  EΘ = –1.66
• Fe/Fe2+  EΘ = – 0.44

will act as anode as they both have negative reduction potential i.e. EΘ< 0.

→ The electrode which has more positive standard reduction potential as compared to standard hydrogen electrode.

Therefore, 

• Cu/Cu2+  EΘ = + 0.34
• F2 (g)/2F– (aq)  EΘ = + 2.87

will act as cathode as they both have positive reduction potential i.e. EΘ> 0.

Conclusion:

Hence, 

• Al/Al3+  EΘ = –1.66
• Fe/Fe2+  EΘ = – 0.44

will act as anodes, when connected to Standard Hydrogen Electrodes.

\therefore, the correct answers are option 1 and option 2.

Concept:

Oxidant and reductant-

• Oxidant and reductant are also called oxidizing agent and reducing agents respectively.
• The species that oxidized other reactant species and itself reduced in a redox reaction is acting as an oxidizing agent or oxidant.
• The species that reduced other reactant species and itself oxidized in a redox reaction is acting as a reducing agent or reductant.
• The oxidant accepts electrons from other reactant species.
• The reductant loses its electron to other reactant species.

Explanation:

The given reaction is -

Zn + 2HCl → ZnCl2 + H2

→ The species that reduced other reactant species and itself oxidized in a redox reaction is acting as a reducing agent or reductant.

Thus,

• Zinc is undergoing oxidation.
• The oxidation no. of Zn is changed from 0 to +2.
• Therefore, it acts as a reductant here.

∴ Statement 4 "Zinc is acting as a reductant" is correct and statement 1 "Zinc is acting as an oxidant" is incorrect.

→ The species that oxidized other reactant species and itself reduced in a redox reaction is acting as an oxidizing agent or oxidant.

Thus,

• Hydrogen is undergoing reduction.
• Hydrogen oxidation no. is changed from +1 to 0.
• Therefore, it acts as an oxidant here.

∴ Statement 3 "Hydrogen ion is acting as an oxidant" is correct.

→  The species whose oxidation no. remain same is neither undergoing oxidation nor reduction and therefore can neither act as oxidant nor as reductant.

Thus, 

• Chlorine is neither oxidized nor reduced during the decomposition reaction.
• As the oxidation number of Cl remains the same during the reaction i.e. -1.

∴ Statement 2 "Chlorine is acting as a reductant" is incorrect.

Conclusion:

Therefore, the correct statement (s) in relation to the reaction, Zn + 2HCl → ZnCl2 + H2 is statement 3 and statement 4.

Hence the correct answer is option 3, and option 4.

Concept:

Decomposition reaction -

• A chemical reaction in which a reactant is decomposed into two or more products is called a decomposition reaction.
• The reaction is represented by the general notation as -  AB → A + B
• The opposite of decomposition reactions are the combination reactions.

Explanation:

The given decomposition reaction is -

2KClO3 → 2KCl + 3O2.

→ The species whose oxidation no. is increased or which loses electrons during the reaction is undergoing oxidation.

Thus,

• Oxygen is undergoing oxidation.
• Oxygen oxidation no. is changed from -2 to 0.

∴ Statement 3 "Oxygen is reduced" is incorrect.

→ The species whose oxidation no. is decreased or which accepts electrons during the reaction is undergoing reduction.

Thus,

• Chlorine is undergoing reduction.
• Cl oxidation no. is changed from +5 to -1.

∴ Statement 2 "Chlorine is undergoing oxidation" is incorrect.

→  The species whose oxidation no. remain same is neither undergoing oxidation nor reduction.

Thus, 

• Potassium is neither oxidised nor reduced during the decomposition reaction.
• As the oxidation number of K remains the same during the reaction i.e. 1.

∴ Statement 1 "Potassium is undergoing oxidation" is incorrect.

→ Statement 4 "None of the species are undergoing oxidation or reduction" is also incorrect as  Cl and O are undergoing oxidation and reduction.

Conclusion:

Therefore, all the given statements are incorrect.

Hence the correct answer is option 1, 2, 3, 4.

Correct answer: 4)

Concept:​

Oxidizing agents and reducing agents in terms of electrode potential:

• In terms of electrode potential, the higher the positive value of EΘ, the stronger the oxidizing agent.
• Species which is stronger oxidizing agents have a great tendency to get reduced.
• Species having lower positive values of electrode potential are stronger reducing agents.
• The strongest reducing agent means it has a greater tendency to get oxidized. 

Explanation:

• The value of reduction potential determines the tendency of the specie to get reduced.
• The more positive the value of E⁰, the greater is the tendency of the species to get reduced, and the stronger the oxidizing agent. 

              EΘ values : Br2 /Br– = + 1.90; Ag+ /Ag(s) = + 0.80

             Cu2+/Cu(s) = + 0.34; I2 (s)/I– = + 0.54

• From the EΘ values, it is clear that copper(lowest electrode potential: + 0.34) has a strong tendency to reduce bromine(Highest electrode potential:+ 1.90).
• For the given species, the correct order of getting reduced is as follows:  Br₂> Ag⁺> I₂> Cu²⁺.
• Therefore, Cu has the least tendency to get reduced and will itself gets oxidize and reduce other species such as Br₂, Ag^+, and I₂.

Conclusion:

Therefore, among the given species and their electrode potential, Cu has a strong tendency to reduce Br2.

Additional Information