Chemistry

The d-Block and f-Block Elements

Question:

E of Cu is +0.34 V while that of Zn is -0.76 V. Explain.

Answer:

High ionisation enthalpy to change Cu(s) to Cu2+ is not balanced by hydration enthalpy. Therefore, it exhibits a positive E ° value. However, Zn exhibits a lower value of ionization enthalpy because a stable 3d10 configuration is attained after losing two electrons. The hydration energy for Zn2+ is comparable to that ofCu2+. Therefore, E ° for Zn is negative.

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The d-Block and f-Block Elements

Q 1.

Although fluorine is more electronegative than oxygen, but the ability of oxygen to stabilize higher oxidation states exceeds that of fluorine. Why?

Q 2.

Mention the type of compounds formed when small atoms like H, C and N get trapped inside the crystal lattice of transition metals. Also give physical and chemical characteristics of these compounds.

Q 3.

Metallic radii of some transition elements are given below. Which of these elements will have highest density?
ncert-exemplar-problems-class-12-chemistry-d-f-block-elements-2

Q 4.

Which of the following will not act as oxidizing agents?
(a) CrO3  (b) MoO3(c) WO3   (d) CrO42-

Q 5.

How would you account for the following:
(i) Of the d4 species, Cr2+ is strongly reducing while manganese (III) is strongly oxidizing.
(ii) Cobalt (II) is stable in aqueous solution but in the presence of complexing reagents it is easily oxidised.
(iii) The d1  configuration is very unstable in ions.

Q 6.

Compare the chemistry of actinoids with that of lanthanoids with reference to:
(i) Electronic configuration
(ii) Oxidation states
(iii) Chemical reactivity

Q 7.

Transition elements show high melting points. Why?

Q 8.

Reactivity of transition elements decreases almost regularly from Sc to Cu. Explain.

Q 9.

(a) Answer the following questions:
(i) Which element of the first transition series has highest second ionization enthalpy?
(ii) Which element of the first transition series has highest third ionization enthalpy?
(iii) Which element of the first transition series has lowest enthalpy of atomization?
(b) Identify the metal and justify your answer:
(i) Carbonyl M(CO)5 (ii) MO3F

Q 10.

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

Q 11.

What may be the stable oxidation state of the transition element with the following delectron configurations in the ground state of their atoms: 3d3,3d5, 3d8 and 3d4?

Q 12.

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

Q 13.

Which of the following reactions are disproportionation reactions?
ncert-exemplar-problems-class-12-chemistry-d-f-block-elements-4

Q 14.

Which of the following ions show higher spin only magnetic moment value?
(a) Ti3+ (b) Mn2+ (c) Fe2+ (d)  Co3+

Q 15.

Transition elements form binary compounds with halogens. Which of the following elements will form MF3 type compounds?
(a) Cr (b) Co (c) Cu (d) Ni

Q 16.

When Cu2+ ion is treated with KI, a white precipitate is formed. Explain the reaction with the help of chemical equation.

Q 17.

A solution of KMnO4 on reduction yields either a colourless solution or a brown precipitate or a green solution depending on pH of the solution. What different stages of the reduction do these represent and how are they carried out?

Q 18.

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

Q 19.

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

Q 20.

Explain briefly how+2 state becomes more and more stable in the first half of the first row transition elements with increasing atomic number?

Q 21.

In what way is the electronic configuration of the transition elements different from that of the non transition elements?

Q 22.

Describe the preparation of potassium dichromate from iron chromite ore. What is the effect of increasing pH on a solution of potassium dichromate?

Q 23.

Predict which of the following will be coloured in aqueous solution? Ti3+, V3+,Cu+, Sc3+, Mn2+, Fe3+ and Co2+ Give reasons for each.

Q 24.

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

Q 25.

Name the members of the lanthanoid series which exhibit+4oxidatk>nstatesandthosewhichexhibit +2 oxidation states. Try to correlate this type of behaviour with the electronic configurations of these elements.

Q 26.

KMnO4 acts as an oxidizing agent in acidic medium. The number of moles of KMn04 that will be needed to react with one mole of sulphide ions in acidic solution is
ncert-exemplar-problems-class-12-chemistry-d-f-block-elements-8

Q 27.

General electronic configuration of actinoids is (n – 2)f1-14  (n – 1 )d0-2  ns2. Which of the following actinoids have one electron in 6d orbital?
(a) U (Atomic no. 92) (b) Np (Atomic no. 93)
(c) Pu (Atomic no. 94) (d) Am (Atomic no. 95)

Q 28.

Why does copper not replace hydrogen from acids?

Q 29.

Why first ionization enthalpy of Cr is lower than that of Zn?

Q 30.

Out of Cu2Cl2  and CuCl2, which is more stable and why?

Q 31.

The second and third rows of tfansition elements resemble each other much more than they resemble the first row. Explain why?

Q 32.

Assertion (A): The highest oxidation state of osmium is +8.
Reason (R): Osmium is a 5d-block element.

Q 33.

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

Q 34.

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?

Q 35.

Predict which of the following will be coloured in aqueous solution? Ti3+, V3+,Cu+, Sc3+, Mn2+, Fe3+ and Co2+ Give reasons for each.

Q 36.

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

Q 37.

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.

Q 38.

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

Q 39.

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.

Q 40.

Gadolinium belongs to 4f series. Its atomic number is 64. Which of the following is the correct electronic configuration of gadolinium?
ncert-exemplar-problems-class-12-chemistry-d-f-block-elements-10

Q 41.

Transition elements show magnetic moment due to spin and orbital motion of electrons. Which of the following metallic ions have almost same spin only magnetic moment?
(a) Co2+ (b) Cr2+ (c) Mn2+ (d)  Cr3+

Q 42.

In the form of dichromate, Cr (VI) is a strong oxidizing agent in acidic medium but Mo (VI) in MoO3 and W (VI) in WO3 are not because
(a) Cr (VI) is more stable than Mo(VI) and W(VI)
(b) Mo(VI) and W(VI) are more stable than Cr(VI)
(c) higher oxidation states of heavier members of group-6 of transition series are more stable
(d) lower oxidation states of heavier members of group-6 of transition series are more stable

Q 43.

Although +3 is the characteristic oxidation state for lanthanoids but cerium
also shows +4 oxidation state because  
(a) it has variable ionization enthalpy
(b) it has a tendency to attain noble gas configuration
(c) it has a tendency to attain f ° configuration
(d) it resembles  Pb4+

Q 44.

Why E ° value for Mn, Ni and Zn are more negative than expected?

Q 45.

Although Zr belongs to 4d and Hf belongs to 5d transition series but it is quite difficult to separate them. Why?

Q 46.

Although +3 oxidation states is the characteristic oxidation state of lanthanoids but cerium shows +4 oxidation state also. Why?

Q 47.

While filling up of electrons in the atomic orbitals, the 4s orbital is filled before the 3d-orbital but reverse happens during the ionization of the atom. Explain why?

Q 48.

Assertion (A): Separation of Zr and Hf is difficult.
Reason (R): Because Zr and Hf lie in the same group of the periodic table.

Q 49.

When a chromite ore (A) is fused with sodium carbonate in free excess of air and the product is dissolved in water, a yellow solution of compound (B) is obtained. After treatment of this yellow solution with sulphuric acid, compound (C) can be crystallized from the solution. When compound (C) is treated with KCl, orange crystals of compound (D) crystallise out. Identify A to D and also explain the reactions.

Q 50.

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