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Q4.11(iv):
Explain giving reasons: (iv) Transition metals and their many compounds act as good catalyst.
Solution :
Core Theoretical Foundation
The catalytic activity of transition metals and their compounds is primarily attributed to their variable oxidation states and the availability of partially filled d-orbitals [Per the Electronic Configuration Principle ($n-1)d^{1-10}ns^{1-2}$].
Step 1: Mechanism of Surface Adsorption
Transition metals provide a large surface area with high free valencies. When reactants are introduced, they adsorb onto the metal surface via chemical bonds (chemisorption). This adsorption serves two purposes:
- Concentration Effect: Increases the local concentration of reactants on the surface [Per the Collision Theory].
- Bond Weakening: Facilitates the breaking of existing bonds in the reactant molecules by transferring electron density from the metal d-orbitals to the antibonding orbitals of the reactants.
Step 2: Variable Oxidation States & Complex Formation
Transition metals can easily transition between multiple oxidation states (e.g., $Fe^{2+}/Fe^{3+}$, $V^{4+}/V^{5+}$). This allows them to form unstable intermediate compounds with reactants, which subsequently decompose to provide the final products, regenerating the catalyst.
The general mechanism for a reaction involving a catalyst ($C$) and reactants ($R_1, R_2$) is:
1. Formation of Intermediate: $R_1 + C \rightarrow [R_1-C]$
2. Reaction with second reactant: $[R_1-C] + R_2 \rightarrow Product + C$
[By the Intermediate Complex Formation Theory]
Visual Representation: Catalytic Surface Interaction
Step 3: Comparative Analysis of Catalytic Efficiency
| Catalyst | Reaction | Primary Mechanism |
|---|---|---|
| $V_2O_5$ | Contact Process ($SO_2 \rightarrow SO_3$) | Variable oxidation states of Vanadium |
| $Fe$ | Haber's Process ($N_2 + H_2 \rightarrow NH_3$) | Adsorption of gases on metal surface |
| $Ni$ | Hydrogenation of oils | Surface adsorption & bond activation |
Final Solution: Transition metals act as excellent catalysts because their ability to exhibit variable oxidation states allows for the formation of intermediate compounds with lower activation energy, and their unfilled d-orbitals provide active sites for reactant adsorption and subsequent bond weakening, significantly increasing the reaction rate.
More Questions from Class 12 Chemistry The d- and f-Block Elements Exercises
- Q4.1 (i): Write down the electronic configuration of: (i) Cr^{3+}
- Q4.1 (ii): Write down the electronic configuration of: (ii) Pm^{3+}
- Q4.1 (iii): Write down the electronic configuration of: (iii) Cu^{+}
- Q4.1 (iv): Write down the electronic configuration of: (iv) Ce^{4+}
- Q4.1 (v): Write down the electronic configuration of: (v) Co^{2+}
- Q4.1 (vi): Write down the electronic configuration of: (vi) Lu^{2+}
- Q4.1 (vii): Write down the electronic configuration of: (vii) Mn^{2+}
- Q4.1 (viii): Write down the electronic configuration of: (viii) Th^{4+}
- Q4.1(i): Write down the electronic configuration of: (i) \(Cr^{3+}\)
- Q4.1(ii): Write down the electronic configuration of: (ii) \(Pm^{3+}\)
- Q4.1(iii): Write down the electronic configuration of: (iii) \(Cu^{+}\)
- Q4.1(iv): Write down the electronic configuration of: (iv) \(Ce^{4+}\)
- Q4.1(v): Write down the electronic configuration of: (v) \(Co^{2+}\)
- Q4.1(vi): Write down the electronic configuration of: (vi) \(Lu^{2+}\)
- Q4.1(vii): Write down the electronic configuration of: (vii) \(Mn^{2+}\)
- Q4.1(viii): Write down the electronic configuration of: (viii) \(Th^{4+}\)
- Q4.10: What are the different oxidation states exhibited by the lanthanoids?
- Q4.10: What are the different oxidation states exhibited by the lanthanoids?
- Q4.11 (i): Explain giving reasons: (i) Transition metals and many of their compounds show paramagnetic behaviour.
- Q4.11 (ii): Explain giving reasons: (ii) The enthalpies of atomisation of the transition metals are high.
- Q4.11 (iii): Explain giving reasons: (iii) The transition metals generally form coloured compounds.
- Q4.11 (iv): Explain giving reasons: (iv) Transition metals and their many compounds act as good catalyst.
- Q4.11(i): Explain giving reasons: (i) Transition metals and many of their compounds show paramagnetic behaviour.
- Q4.11(ii): Explain giving reasons: (ii) The enthalpies of atomisation of the transition metals are high.
- Q4.11(iii): Explain giving reasons: (iii) The transition metals generally form coloured compounds.
- Q4.12: What are interstitial compounds? Why are such compounds well known for transition metals?
- Q4.12: What are interstitial compounds? Why are such compounds well known for transition metals?
- Q4.13: How is the variability in oxidation states of transition metals different from that of the non transition metals? Illustrate with examples.
- Q4.13: How is the variability in oxidation states of transition metals different from that of the non transition metals? Illustrate with examples.
- Q4.14: Describe the preparation of potassium dichromate from iron chromite ore. What is the effect of increasing pH on a solution of potassium dichromate?
- Q4.14: Describe the preparation of potassium dichromate from iron chromite ore. What is the effect of increasing pH on a solution of potassium dichromate?
- Q4.15 (i): Describe the oxidising action of potassium dichromate and write the ionic equations for its reaction with: (i) iodide
- Q4.15 (ii): Describe the oxidising action of potassium dichromate and write the ionic equations for its reaction with: (ii) iron(II) solution and
- Q4.15 (iii): Describe the oxidising action of potassium dichromate and write the ionic equations for its reaction with: (iii) H_{2}S
- Q4.15(i): Describe the oxidising action of potassium dichromate and write the ionic equations for its reaction with: (i) iodide
- Q4.15(ii): Describe the oxidising action of potassium dichromate and write the ionic equations for its reaction with: (ii) iron(II) solution
- Q4.15(iii): Describe the oxidising action of potassium dichromate and write the ionic equations for its reaction with: (iii) \(H_{2}S\)
- Q4.16: Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with (i) iron(II) ions (ii) \(SO_{2}\) and (iii) oxalic acid? Write the ionic equations for the reactions.
- Q4.16: Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with (i) iron(II) ions (ii) SO_{2} and (iii) oxalic acid? Write the ionic equations for the reactions.
- Q4.17: For M^{2+}/M and M^{3+}/M^{2+} systems the E^{o} values for some metals are as follows: Use this data to comment upon: (i) the stability of Fe^{3+} in acid solution as compared to that of Cr^{3+} or Mn^{3+} and (ii) the ease with which iron can be oxidised as compared to a similar process for either chromium or manganese metal.
- Q4.17(i): For \(M^{2+}/M\) and \(M^{3+}/M^{2+}\) systems the \(E^{o}\) values for some metals are as follows: (i) the stability of \(Fe^{3+}\) in acid solution as compared to that of \(Cr^{3+}\) or \(Mn^{3+}\)
- Q4.17(ii): For \(M^{2+}/M\) and \(M^{3+}/M^{2+}\) systems the \(E^{o}\) values for some metals are as follows: Use this data to comment upon: (ii) the ease with which iron can be oxidised as compared to a similar process for either chromium or manganese metal.
- Q4.18: Predict which of the following will be coloured in aqueous solution? \(Ti^{3+}\), \(V^{3+}\), \(Cu^{+}\), \(Sc^{3+}\), \(Mn^{2+}\), \(Fe^{3+}\) and \(Co^{2+}\). Give reasons for each.
- Q4.18: Predict which of the following will be coloured in aqueous solution? Ti^{3+}, V^{3+}, Cu^{+}, Sc^{3+}, Mn^{2+}, Fe^{3+} and Co^{2+}. Give reasons for each.
- Q4.19: Compare the stability of +2 oxidation state for the elements of the first transition series.
- Q4.19: Compare the stability of +2 oxidation state for the elements of the first transition series.
- Q4.2: Why are \(Mn^{2+}\) compounds more stable than \(Fe^{2+}\) towards oxidation to their +3 state?
- Q4.2: Why are Mn^{2+} compounds more stable than Fe^{2+} towards oxidation to their +3 state?
- Q4.20 (i): Compare the chemistry of actinoids with that of the lanthanoids with special reference to: (i) electronic configuration
- Q4.20 (ii): Compare the chemistry of actinoids with that of the lanthanoids with special reference to: (ii) atomic and ionic sizes and
- Q4.20 (iii): Compare the chemistry of actinoids with that of the lanthanoids with special reference to: (iii) oxidation state
- Q4.20 (iv): Compare the chemistry of actinoids with that of the lanthanoids with special reference to: (iv) chemical reactivity.
- Q4.20(i): Compare the chemistry of actinoids with that of the lanthanoids with special reference to: (i) electronic configuration
- Q4.20(ii): Compare the chemistry of actinoids with that of the lanthanoids with special reference to: (ii) atomic and ionic sizes
- Q4.20(iii): Compare the chemistry of actinoids with that of the lanthanoids with special reference to: (iii) oxidation state
- Q4.20(iv): Compare the chemistry of actinoids with that of the lanthanoids with special reference to: (iv) chemical reactivity.
- Q4.21 (i): How would you account for the following: (i) Of the d^{4} species, Cr^{2+} is strongly reducing while manganese(III) is strongly oxidising.
- Q4.21 (ii): How would you account for the following: (ii) Cobalt(II) is stable in aqueous solution but in the presence of complexing reagents it is easily oxidised.
- Q4.21 (iii): How would you account for the following: (iii) The d^{1} configuration is very unstable in ions.
- Q4.21(i): How would you account for the following: (i) Of the \(d^{4}\) species, \(Cr^{2+}\) is strongly reducing while manganese(III) is strongly oxidising.
- Q4.21(ii): How would you account for the following: (ii) Cobalt(II) is stable in aqueous solution but in the presence of complexing reagents it is easily oxidised.
- Q4.21(iii): How would you account for the following: (iii) The \(d^{1}\) configuration is very unstable in ions.
- Q4.22: What is meant by ‘disproportionation’? Give two examples of disproportionation reaction in aqueous solution.
- Q4.22: What is meant by ‘disproportionation’? Give two examples of disproportionation reaction in aqueous solution.
- Q4.23: Which metal in the first series of transition metals exhibits +1 oxidation state most frequently and why?
- Q4.23: Which metal in the first series of transition metals exhibits +1 oxidation state most frequently and why?
- Q4.24: Calculate the number of unpaired electrons in the following gaseous ions: \(Mn^{3+}\), \(Cr^{3+}\), \(V^{3+}\) and \(Ti^{3+}\). Which one of these is the most stable in aqueous solution?
- Q4.24: Calculate the number of unpaired electrons in the following gaseous ions: Mn^{3+}, Cr^{3+}, V^{3+} and Ti^{3+}. Which one of these is the most stable in aqueous solution?
- Q4.25 (i): Give examples and suggest reasons for the following features of the transition metal chemistry: (i) The lowest oxide of transition metal is basic, the highest is amphoteric/acidic.
- Q4.25 (ii): Give examples and suggest reasons for the following features of the transition metal chemistry: (ii) A transition metal exhibits highest oxidation state in oxides and fluorides.
- Q4.25 (iii): Give examples and suggest reasons for the following features of the transition metal chemistry: (iii) The highest oxidation state is exhibited in oxoanions of a metal.
- Q4.25(i): Give examples and suggest reasons for the following features of the transition metal chemistry: (i) The lowest oxide of transition metal is basic, the highest is amphoteric/acidic.
- Q4.25(ii): Give examples and suggest reasons for the following features of the transition metal chemistry: (ii) A transition metal exhibits highest oxidation state in oxides and fluorides.
- Q4.25(iii): Give examples and suggest reasons for the following features of the transition metal chemistry: (iii) The highest oxidation state is exhibited in oxoanions of a metal.
- Q4.26 (i): Indicate the steps in the preparation of: (i) K_{2}Cr_{2}O_{7} from chromite ore.
- Q4.26 (ii): Indicate the steps in the preparation of: (ii) KMnO_{4} from pyrolusite ore.
- Q4.26(i): Indicate the steps in the preparation of: (i) \(K_{2}Cr_{2}O_{7}\) from chromite ore.
- Q4.26(ii): Indicate the steps in the preparation of: (ii) \(KMnO_{4}\) from pyrolusite ore.
- Q4.27: What are alloys? Name an important alloy which contains some of the lanthanoid metals. Mention its uses.
- Q4.27: What are alloys? Name an important alloy which contains some of the lanthanoid metals. Mention its uses.
- Q4.28: What are inner transition elements? Decide which of the following atomic numbers are the atomic numbers of the inner transition elements : 29, 59, 74, 95, 102, 104.
- Q4.28: What are inner transition elements? Decide which of the following atomic numbers are the atomic numbers of the inner transition elements : 29, 59, 74, 95, 102, 104.
- Q4.29: The chemistry of the actinoid elements is not so smooth as that of the lanthanoids. Justify this statement by giving some examples from the oxidation state of these elements.
- Q4.29: The chemistry of the actinoid elements is not so smooth as that of the lanthanoids. Justify this statement by giving some examples from the oxidation state of these elements.
- Q4.3: Explain briefly how +2 state becomes more and more stable in the first half of the first row transition elements with increasing atomic number?
- Q4.3: Explain briefly how +2 state becomes more and more stable in the first half of the first row transition elements with increasing atomic number?
- Q4.30: Which is the last element in the series of the actinoids? Write the electronic configuration of this element. Comment on the possible oxidation state of this element.
- Q4.30: Which is the last element in the series of the actinoids? Write the electronic configuration of this element. Comment on the possible oxidation state of this element.
- Q4.31: Use Hund’s rule to derive the electronic configuration of \(Ce^{3+}\) ion, and calculate its magnetic moment on the basis of ‘spin-only’ formula.
- Q4.31: Use Hund’s rule to derive the electronic configuration of Ce^{3+} ion, and calculate its magnetic moment on the basis of ‘spin-only’ formula.
- Q4.32: Name the members of the lanthanoid series which exhibit +4 oxidation states and those which exhibit +2 oxidation states. Try to correlate this type of behaviour with the electronic configurations of these elements.
- Q4.32: Name the members of the lanthanoid series which exhibit +4 oxidation states and those which exhibit +2 oxidation states. Try to correlate this type of behaviour with the electronic configurations of these elements.
- Q4.33 (i): Compare the chemistry of the actinoids with that of lanthanoids with reference to: (i) electronic configuration
- Q4.33 (ii): Compare the chemistry of the actinoids with that of lanthanoids with reference to: (ii) oxidation states and
- Q4.33 (iii): Compare the chemistry of the actinoids with that of lanthanoids with reference to: (iii) chemical reactivity.
- Q4.33(i): Compare the chemistry of the actinoids with that of lanthanoids with reference to: (i) electronic configuration
- Q4.33(ii): Compare the chemistry of the actinoids with that of lanthanoids with reference to: (ii) oxidation states
- Q4.33(iii): Compare the chemistry of the actinoids with that of lanthanoids with reference to: (iii) chemical reactivity.
- Q4.34: Write the electronic configurations of the elements with the atomic numbers 61, 91, 101, and 109.
- Q4.34: Write the electronic configurations of the elements with the atomic numbers 61, 91, 101, and 109.
- Q4.35 (i): Compare the general characteristics of the first series of the transition metals with those of the second and third series metals in the respective vertical columns. Give special emphasis on the following points: (i) electronic configurations
- Q4.35 (ii): Compare the general characteristics of the first series of the transition metals with those of the second and third series metals in the respective vertical columns. Give special emphasis on the following points: (ii) oxidation states
- Q4.35 (iii): Compare the general characteristics of the first series of the transition metals with those of the second and third series metals in the respective vertical columns. Give special emphasis on the following points: (iii) ionisation enthalpies
- Q4.35 (iv): Compare the general characteristics of the first series of the transition metals with those of the second and third series metals in the respective vertical columns. Give special emphasis on the following points: (iv) atomic sizes.
- Q4.35(i): Compare the general characteristics of the first series of the transition metals with those of the second and third series metals in the respective vertical columns. Give special emphasis on the following points: (i) electronic configurations
- Q4.35(ii): Compare the general characteristics of the first series of the transition metals with those of the second and third series metals in the respective vertical columns. Give special emphasis on the following points: (ii) oxidation states
- Q4.35(iii): Compare the general characteristics of the first series of the transition metals with those of the second and third series metals in the respective vertical columns. Give special emphasis on the following points: (iii) ionisation enthalpies
- Q4.35(iv): Compare the general characteristics of the first series of the transition metals with those of the second and third series metals in the respective vertical columns. Give special emphasis on the following points: (iv) atomic sizes.
- Q4.36: Write down the number of 3d electrons in each of the following ions: \(Ti^{2+}\), \(V^{2+}\), \(Cr^{3+}\), \(Mn^{2+}\), \(Fe^{2+}\), \(Fe^{3+}\), \(Co^{2+}\), \(Ni^{2+}\) and \(Cu^{2+}\). Indicate how would you expect the five 3d orbitals to be occupied for these hydrated ions (octahedral).
- Q4.36: Write down the number of 3d electrons in each of the following ions: Ti^{2+}, V^{2+}, Cr^{3+}, Mn^{2+}, Fe^{2+}, Fe^{3+}, Co^{2+}, Ni^{2+} and Cu^{2+}. Indicate how would you expect the five 3d orbitals to be occupied for these hydrated ions (octahedral).
- Q4.37: Comment on the statement that elements of the first transition series possess many properties different from those of heavier transition elements.
- Q4.37: Comment on the statement that elements of the first transition series possess many properties different from those of heavier transition elements.
- Q4.38: What can be inferred from the magnetic moment values of the following complex species ?
- Q4.38: What can be inferred from the magnetic moment values of the following complex species ?
- Q4.4: To what extent do the electronic configurations decide the stability of oxidation states in the first series of the transition elements? Illustrate your answer with examples.
- Q4.4: To what extent do the electronic configurations decide the stability of oxidation states in the first series of the transition elements? Illustrate your answer with examples.
- Q4.5: What may be the stable oxidation state of the transition element with the following d electron configurations in the ground state of their atoms : \(3d^{3}\), \(3d^{5}\), \(3d^{8}\) and \(3d^{4}\)?
- Q4.5: What may be the stable oxidation state of the transition element with the following d electron configurations in the ground state of their atoms : 3d^{3}, 3d^{5}, 3d^{8} and 3d^{4}?
- Q4.6: Name the oxometal anions of the first series of the transition metals in which the metal exhibits the oxidation state equal to its group number.
- Q4.6: Name the oxometal anions of the first series of the transition metals in which the metal exhibits the oxidation state equal to its group number.
- Q4.7: What is lanthanoid contraction? What are the consequences of lanthanoid contraction?
- Q4.7: What is lanthanoid contraction? What are the consequences of lanthanoid contraction?
- Q4.8: What are the characteristics of the transition elements and why are they called transition elements? Which of the d-block elements may not be regarded as the transition elements?
- Q4.8: What are the characteristics of the transition elements and why are they called transition elements? Which of the d-block elements may not be regarded as the transition elements?
- Q4.9: In what way is the electronic configuration of the transition elements different from that of the non transition elements?
- Q4.9: In what way is the electronic configuration of the transition elements different from that of the non transition elements?
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