Chemistry

The d-Block and f-Block Elements

Question:

Write down the number of 3d electrons in each of the following ions:Ti2+, V2+, Cr3+, Mn2+, Fe2+, Fe2+, Co2+, Ni2+ and Cu2+. Indicate how would you expect the five 3d orbitals to be occupied for these hydrated ions (octahedral).

Answer:

ncert-solutions-for-class-12-chemistry-the-d-and-f-block-elements-10

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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.

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

Q 9.

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 10.

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

Q 11.

(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 12.

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 13.

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 14.

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

Q 15.

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

Q 16.

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

Q 17.

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

Q 18.

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

Q 19.

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

Q 20.

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

Q 21.

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

Q 22.

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

Q 23.

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 24.

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

Q 25.

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

Q 26.

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

Q 27.

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

Q 28.

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 29.

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

Q 30.

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

Q 31.

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

Q 32.

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 33.

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 34.

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

Q 35.

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

Q 36.

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

Q 37.

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

Q 38.

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 39.

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 40.

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

Q 41.

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

Q 42.

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

Q 43.

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 44.

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 45.

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.

Q 46.

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

Q 47.

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

Q 48.

Com pare 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

Q 49.

When KMnO4 solution is added to oxalic acid solution, the decolourisation is slow in the beginning but becomes instantaneous after some time because
(a) CO2 is formed as the product (b) Reaction is exothermic
(c) Mn04 catalyses the reaction (d) Mn2+ acts as autocatalyst

Q 50.

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