TOPIC : d- and f – BLOCK ELEMENTS

2010

Q1. Explain the folowing

(i) The highest oxidation state of a metal is exhibited in its oxide or fluoride.

(ii) The atomic radii of the metals of the third (5d) series of transition elements

are virtually the same as those of the corresponding member of the second (4d) series.

(iii) Zinc is not regarded as a transition element.

Q2. Explain

(i) Generally there is an increase in density of elements from Ti (Z = 22) to Cu

(Z = 29) in the first series of transition elements.

(ii) Transition elements and their compounds are generally found to be good

catalysts in chemical reactions.

(iii) The E^ovalue for Mn³⁺/Mn²⁺ couple is much more positive than that for Cr³⁺/

Cr²⁺ couple or Fe³⁺/ Fe²⁺ couple.

2009

Q1. (a) Complete the following chemical reacton equation:

(i) MnO^-₄(aq) + C₂O₄^2-(aq) + H⁺(aq) ®

(ii) Cr₂O₇^2-(aq) + Fe⁺²(aq) ®

(b) Explain the following observations about the transition/ inner transition

elements:

(i) There is in general an increase in density of element from Ti (Z=22) to Cu

(Z=29).

(ii) There occurs much more frequent metal – metal bonding in compounds of

heavy transition elements (3^rd series).

(iii) The members in the actinoid series exhibit a larger number of oxidation

states than the corresponding members in the lanthanoid series.

Q2. (a) Complete the following equations:-

(i) MnO₄^- + S₂O₃^2- + H₂O ®

(ii) Cr₂O₇^2- + H₂S + H⁺ ®

(b) Explain the following:-

(i) The gradual decrease in size (actinoid contraction) from element to element

is greater among the actinoids than that among the (lanthanoid

contraction).

(ii) The greatest number of oxidation states are exhibited by the members in

the middle of a transition series.

(iii) With the same d – orbitals configuration (d⁴) Cr⁺² ion is a reducing agent

but Mn⁺³ ion is an oxidising agent.

Q3. Explain the following:-

(i) Transition elements are known to form many interstitial compounds.

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

(iii) Actinoids exhibit a greater range of oxidation states than lanthanoids.

(iv) Transition metals exhibit variable oxidation states.

(v) Transition metals from compounds which are usually coloured.

Q4. Complete the following:-

(i) MnO₂(s) + KOH(aq) + O₂ ®

(ii) Cr₂O₇^2-(aq) + I^-(aq) + H⁺(aq) ®

Q5. Explain the following:-

(i) In general the atomic radii of transition elements decrease with atomic

number in a given series.

(ii) E_M²⁺_/M for Cu is positive (0.34 V). It is only metal in the first series of transition

elements showing this type of behaviour.

(iii) E^o value for Mn⁺³/Mn⁺² couple is much more positive than Cr⁺³/ Cr⁺² or Fe⁺³/

Fe⁺² couple.

(iv) Cu⁺ ion is unstable in aqueous solutions.

(v) Although C_O⁺² ion appears to be stable, it is easily oxidised to C_O⁺³ in

presence of strong ligand.

(vi) E_Mn⁺²_/Mn value for Mn is much more than expected from the trend for the

other elements in the series.

Q6. What is meant by the term lanthanoid contraction? What is it due to and what

consequences does it have on the chemistry of elements following lanthanoids in

the periodic table?

Q7. (a) Describe the preparation of K_­2Cr₂O₇ from chromite ore

(b) Give reason:

(i) Sc(Z = 21) salts are white

(ii) Mn(II) ion shows maximum paramagnetic s amongst the bivalent ions of

first transition series.

Q8. (a) Name an important alloy which contains some of the lanthanoid metals.

Mention its two uses.

(b) Describe the following characteristics of first series of transition and their

trend in series (Sc to Zn)

(i) Atomic radii

(ii)Oxidation states

(iii) Ionisation enthalpies

2008

Q1. (a) What may be the possible oxidation states of the transition metals with the

following d electronic configuration if the ground state of their atoms:

3d³4s², 3d⁵ 4s² & 3d⁶4s². Indicate relative stability of oxidation states in each

case.

(b) Write steps involved in the preparation of

(i) Na₂CrO₄ from chromite ore

(ii) K₂MnO₄ from pyrolusite ore

Q2. Write complete chemical equation for:

(i) Oxidation of Fe⁺² by Cr₂O₇^2- in acid medium.

(ii) Oxidation of S₂O₃^2- by MnO₄^- in neutral aqueous medium.

Q3. (a) Describe commercial preparation of KMnO₄ from pyrolusite ore.

(b) Write ionic equation to represent the reaction of acidified solution of KMnO₄

with oxalic acid.

Q4. Account for the following:-

(i) There are irregularities in the electronic configuration of actinoids.

(ii) The second and third members in each group of the transition elements have

very similar atomic radii.

(iii) The colour of K₂Cr₂O­­₇ solution changes with the change of pH of the solution.

2007

Q1. Account for the following:-

(i) Cd²⁺ salts are white.

(ii) The transition metals and their compounds are found to be good catalysts in

many processes.

2006

Q1. Why is +2 oxidation state of Mn quite stable, while the same is not true for iron?

Q2. Write formula of a compound where the transition metal is in +7 oxidation state.

Q3. Give reasons:-

(i) An aqueous solution of K₂Cr₂O₇ is yellow but changes its colour on decreasing

the pH of the solution.

(ii) Interstitial compounds are well known for transition elements.

Q4. How is the variability in oxidation states of the transition elements different from

that of the non – transition elements? Illustrate with examples.

Q5. (a) Of the lanthanoids only cerium (z=58) is known to exhibit quite stable + 4

oxidation state in solutions. 

(b) Explain How do transition elements form interstitial compunds? State an industrial

advantage of such occurrence.

2005

Q1. The outer electronic configurations of two members of the lanthanoid series are as

follows:

4f¹4d¹6s² and 4f⁷5d⁰ 6s²

What are their atomic numbers? Predict the oxidtion state exhibited by these

elements in their compounds.

Q2. Compare the chemistry of actinoids with that of the lanthanoids in reference to

(i) atomic and ionic sizes

(ii) Oxidation states

Q3. Draw the structure of Cr₂O₇^2- ion.