NCERT Solutions for Class 12 Chemistry Chemistry Part-1 Chapter 8

The d-and f-Block Elements Class 12

Chapter 8 The d-and f-Block Elements Exercise Solutions

<< Previous Chapter 7 : The p-Block Elements Next Chapter 9 : Coordination Compounds >>

In text : Solutions of Questions on Page Number : 212

Q1 :  

Silver atom has completely filled d orbitals (4d10) in its ground state. How can you say that it is a transition element?


Answer :

Ag has a completely filled 4d orbital (4d10 5s1) in its ground state. Now, silver displays two oxidation states (+1 and +2). In the +1 oxidation state, an electron is removed from the s-orboital. However, in the +2 oxidation state, an electron is removed from the d-orbital. Thus, the d-orbital now becomes incomplete (4d9). Hence, it is a transition element.

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Q2 :  

In the series Sc (Z = 21) to Zn (Z = 30), the enthalpy of atomization of zinc is the lowest, i.e., 126 kJ mol-1. Why?


Answer :

The extent of metallic bonding an element undergoes decides the enthalpy of atomization. The more extensive the metallic bonding of an element, the more will be its enthalpy of atomization. In all transition metals (except Zn, electronic configuration: 3d10 4s2), there are some unpaired electrons that account for their stronger metallic bonding. Due to the absence of these unpaired electrons, the inter-atomic electronic bonding is the weakest in Zn and as a result, it has the least enthalpy of atomization.

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Q3 :  

Which of the 3d series of the transition metals exhibits the largest number of oxidation states and why?


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Q4 :  

The Eθ(M2+/M) value for copper is positive (+0.34V). What is possibly the reason for this? (Hint: consider its high ΔaHθ and low ΔhydHθ)


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Q5 :  

How would you account for the irregular variation of ionization enthalpies (first and second) in the first series of the transition elements?


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Q6 :  

Why is the highest oxidation state of a metal exhibited in its oxide or fluoride only?


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Q7 :  

Which is a stronger reducing agent Cr2+ or Fe2+ and why?


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Q8 :  

Calculate the 'spin only' magnetic moment of M2+(aq) ion (Z = 27).


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Q9 :  

Explain why Cu+ ion is not stable in aqueous solutions?


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Q10 :  

Actinoid contraction is greater from element to element than lanthanoid contraction. Why?


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<< Previous Chapter 7 : The p-Block Elements Next Chapter 9 : Coordination Compounds >>

Exercise : Solutions of Questions on Page Number : 234

Q1 :  

Write down the electronic configuration of:

(i) Cr3++ (iii) Cu+ (v) Co2+ (vii) Mn2+

(ii) Pm3+ (iv) Ce4+ (vi) Lu2+ (viii) Th4+


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Q2 :  

Why are Mn2+compounds more stable than Fe2+ towards oxidation to their +3 state?


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Q3 :  

Explain briefly how +2 state becomes more and more stable in the first half

of the first row transition elements with increasing atomic number?


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Q4 :  

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.


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Q5 :  

What may be the stable oxidation state of the transition element with the

following d electron configurations in the ground state of their atoms : 3d3,

3d5, 3d8and 3d4?


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Q6 :  

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.


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Q7 :  

What is lanthanoid contraction? What are the consequences of lanthanoid

contraction?


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Q8 :  

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?


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Q9 :  

In what way is the electronic configuration of the transition elements different

from that of the non-transition elements?


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Q10 :  

What are the different oxidation states exhibited by the lanthanoids?


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Q11 :  

Explain giving reasons:

(i) Transition metals and many of their compounds show paramagnetic

behaviour.

(ii) The enthalpies of atomisation of the transition metals are high.

(iii) The transition metals generally form coloured compounds.

(iv) Transition metals and their many compounds act as good catalyst.


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Q12 :  

What are interstitial compounds? Why are such compounds well known for

transition metals?


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Q13 :  

How is the variability in oxidation states of transition metals different from

that of the non-transition metals? Illustrate with examples.


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Q14 :  

Describe the preparation of potassium dichromate from iron chromite ore.

What is the effect of increasing pH on a solution of potassium dichromate?


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Q15 :  

Describe the oxidising action of potassium dichromate and write the ionicequations for its reaction with:

(i) iodide (ii) iron(II) solution and (iii) H2S


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Q16 :  

Describe the preparation of potassium permanganate. How does the acidifiedpermanganate solution react with (i) iron(II) ions (ii) SO2and (iii) oxalic acid?

Write the ionic equations for the reactions.


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Q17 :  

For M2+/M and M3+/M2+ systems, the values for some metals are as follows:

Cr2+/Cr -0.9V

Cr3/Cr2+ -0.4 V

Mn2+/Mn -1.2V

Mn3+/Mn2+ +1.5 V

Fe2+/Fe -0.4V

Fe3+/Fe2+ +0.8 V

Use this data to comment upon:

(i) The stability of Fe3+in acid solution as compared to that of Cr3+or Mn3+ and

(ii) The ease with which iron can be oxidised as compared to a similar process for either chromium or manganese metal.


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Q18 :  

Predict which of the following will be coloured in aqueous solution? Ti3+, V3+,

Cu+, Sc3+, Mn2+, Fe3+ and Co2+. Give reasons for each.


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Q19 :  

Compare the stability of +2 oxidation state for the elements of the first transition series.


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Q20 :  

Compare the chemistry of actinoids with that of the lanthanoids with specialreference to:

(i) electronic configuration (iii) oxidation state

(ii) atomic and ionic sizes and (iv) chemical reactivity.


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Q21 :  

How would you account for the following:

(i) Of the d4species, Cr2+is strongly reducing while manganese(III) is strongly oxidising.

(ii) Cobalt(II) is stable in aqueous solution but in the presence of complexing reagents it is easily oxidised.

(iii) The d1configuration is very unstable in ions.


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Q22 :  

What is meant by 'disproportionation'? Give two examples of disproportionation reaction in aqueous solution.


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Q23 :  

Which metal in the first series of transition metals exhibits +1 oxidationstate most frequently and why?


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Q24 :  

Calculate the number of unpaired electrons in the following gaseous ions: Mn3+, Cr3+, V3+ and Ti3+. Which one of these is the most stable in aqueous solution?


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Q25 :  

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.

(ii)A transition metal exhibits highest oxidation state in oxides and fluorides.

(iii) The highest oxidation state is exhibited in oxoanions of a metal.


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Q26 :  

Indicate the steps in the preparation of:

(i) K2Cr2O7 from chromite ore.

(ii) KMnO4 from pyrolusite ore.


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Q27 :  

What are alloys? Name an important alloy which contains some of thelanthanoid metals. Mention its uses.


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Q28 :  

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.


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Q29 :  

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.


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Q30 :  

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.


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Q31 :  

Use Hund's rule to derive the electronic configuration of Ce3+ ion and calculate its magnetic moment on the basis of 'spin-only' formula.


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Q32 :  

Name the members of the lanthanoid series which exhibit +4 oxidation state and those which exhibit +2 oxidation state. Try to correlate this type of behavior with the electronic configurations of these elements.


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Q33 :  

Compare the chemistry of the actinoids with that of lanthanoids with reference to:

(i) electronic configuration

(ii) oxidation states and

(iii) chemical reactivity.


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Q34 :  

Write the electronic configurations of the elements with the atomic numbers 61, 91, 101, and 109.


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Q35 :  

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,

(ii) oxidation states,

(iii) ionisation enthalpies, and

(iv) atomic sizes.


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Q36 :  

Write down the number of 3d electrons in each of the following ions:

Ti2+, V2+, Cr3+, Mn2+, Fe2+, Fe3+, CO2+, Ni2+ and Cu2+.

Indicate how would you expect the five 3d orbitals to be occupied for these hydrated ions (octahedral).


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Q37 :  

Comment on the statement that elements of the first transition series possess many properties different from those of heavier transition elements.


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Q38 :  

What can be inferred from the magnetic moment values of the following complex species?

Example Magnetic Moment (BM)

K4[Mn(CN)6] 2.2

[Fe(H2O)6]2+ 5.3

K2[MnCl4] 5.9


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<< Previous Chapter 7 : The p-Block Elements Next Chapter 9 : Coordination Compounds >>

Chemistry Part-1 - Chemistry : CBSE NCERT Exercise Solutions for Class 12th for The d-and f-Block Elements will be available online in PDF book form soon. The solutions are absolutely Free. Soon you will be able to download the solutions.

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