d and f-block Elements - Some Important Questions

A. Multiple Choice Questions:

 

1.     KMnO₄ is coloured due to -

a.     charge transfer from ligand to metal

b.     unpaired electron in d orbital of  Mn

c.     charge transfer from metal to ligand

d.     d-d transition

 

2.     Which of the following is a diamagnetic ion (atomic no of Sc ,V,  Mn  and  Cu are 21,23,25 and 29 respectively )                                           

a.     V2+

b.     Sc3+

c.     Cu2+

d.     Mn2+

 

3.     Which of the following lanthanoids show +2 oxidation state besides the characteristic oxidation state +3 of lanthanoids?

a.       Ce

b.      Eu

c.       Lu

d.      Ho

 

4.     The magnetic moment is associated with its spin angular momentum and orbital angular momentum. Spin only magnetic moment value of Mn²⁺ ion is

a.       5.87 B.M.

b.      5.92 B.M.

c.       3.47 B.M 

d.      4.57 B.M

 

5.     How does the increase in the pH affect the K2Cr2O7 solution?      

a.     It cause the K2Cr2O7 solution to release CrO3 gas

b.     It causes the coagulation of K2Cr2O7 solution

c.     It causes the K2Cr2O7 solution to change its color from orange to yellow

d.     It doesn’t bring about any change in the K2Cr2O7 solution

 

6.     Which of the following elements can stabilize the higher oxidation states like +6, +7 and +8 of transition metals to the greatest extent?    

a.      Nitrogen  

b.      Fluorine

c.       Chlorine  

d.      Oxygen

 

7.     Given below are two statements labelled as Assertion (A) and Reason (R)

            Assertion (A): [Ti(H₂O)₆]³⁺ is coloured while [Sc(H₂O)₆]³⁺ is colourless .

            Reason (R): d-d transition is not possible in [Sc(H₂O)₆]³⁺ .

            Select the most appropriate answer from the options given below: 

a.       Both A and R are true and R is the correct explanation of A 

b.      Both A and R are true but R is not the correct explanation of A.

c.       A is true but R is false. 

d.      A is false but R is true.

 

Answer:

1.     a

2.     b

3.     b

4.     b

5.     c

6.     d

7.     a

 

B. Fill in the blanks:

1. The d-block elements are also called __________ because they are located in the transition block of the periodic table.
2. The maximum oxidation state of manganese in its compounds is __________.
3. The lanthanide series starts with the element __________ and ends with __________.
4. The electronic configuration of Cr (Chromium) is __________.
5. The element with atomic number 30 is __________, and it is a member of the __________ block.
6. In the case of transition metals, the energy of the __________ subshell is very close to the __________ subshell, which leads to their variable oxidation states.
7. The actinide series starts with the element __________ and ends with __________.
8. Copper (Cu) exhibits an oxidation state of __________ in CuCl₂ and __________ in Cu₂O.
9. The transition elements typically form __________ compounds, which are often colored due to the presence of unpaired electrons in the d-orbitals.
10. The element __________ is used in making surgical instruments due to its corrosion resistance and is a member of the platinum group metals.

Answers:

1.     Transition elements

2.     +7

3.     La (Lanthanum), Lu (Lutetium)

4.   [Ar] 3d⁵ 4s¹.

5.   Zinc, d-block

6.      4s, 3d

7.      Ac (Actinium) and ends with Lr (Lawrencium).

8.   +2,+1

9.    Coloured

10.  Platinum

C. True/False Questions:

1. The d-block elements have incompletely filled d-orbitals in at least one of their oxidation states. (True/False)
2. All transition metals form colored compounds because of the excitation of electrons in the d-orbitals. (True/False)
3. Lanthanides and actinides are collectively known as inner transition elements. (True/False)
4. The transition elements do not form complex ions due to their large size. (True/False)
5. Zinc is a transition metal because it has a partially filled d-subshell. (True/False)
6. The element with atomic number 79, gold (Au), belongs to the d-block elements. (True/False)
7. The f-block elements are also known as rare earth metals. (True/False)
8. The presence of unpaired d-electrons is responsible for the magnetic properties of many transition metals. (True/False)
9. Actinides are all radioactive in nature. (True/False)
10. The d-block elements show a regular increase in atomic radius across the period. (True/False)

Answer:

1.     True

2.     True (Note: Not all transition metals form colored compounds, but the majority do because of the d-d transitions. Some, like zinc, do not have any unpaired electrons and thus don't form colored compounds.)

3.     True

4.     False (Transition metals are known for forming complex ions due to their ability to coordinate     with ligands.)

5.   False  (Zinc has a completely filled d-subshell in its ground state, so it is not considered a transition metal.)

6.     True

7.     True (Note: The term "rare earth" is typically used for the lanthanides, but it is sometimes applied to the f-block elements as a whole.)

8.     True

9.    True (All actinides are radioactive, with the exception of some isotopes of actinium and thorium, but these are still considered radioactive by modern standards.)

10. False (The atomic radius of transition metals generally decreases from left to right due to the increasing nuclear charge, although the trend may vary slightly.)

D. Some Important questions with answer

 1.     Which of the following ions will have a magnetic moment value of 1.73 BM. Sc³⁺, Ti³⁺, Ti²⁺,   Cu²⁺, Zn²⁺

Ans: Both Ti³⁺ and Cu²⁺ have 1 unpaired electron, so the magnetic moment for both will be 1.73 BM. 

 

2.     In order to protect iron from corrosion, which one will you prefer as a sacrificial electrode, Ni or Zn? Why? (Given standard electrode potentials of Ni, Fe and Zn are -0.25 V, -0.44 V and -0.76 V respectively.)

Ans: Zn, it has a more negative electrode potential so will corrode itself in place of iron.

 

3.     The second ionization enthalpies of chromium and manganese are 1592 and 1509 kJ/mol respectively. Explain the lower value of Mn. 

Ans: Mn⁺ has 3d ⁵4s¹ configuration and configuration of Cr⁺ is 3d⁵ , therefore, ionisation   enthalpy of Mn⁺ is lower than Cr⁺

 

4.     Give two similarities in the properties of Sc and Zn. 

Ans: Sc and Zn both form colourless compound and are diamagnetic.

 

5.     What is actinoid contraction? What causes actinoid contraction? 

Ans: The decrease in the atomic and ionic radii with increase in atomic number of actinoids due to poor shielding effect of 5f electrons.

 

6.     What is the oxidation state of chromium in chromate ion and dichromate ion?

Ans:  In both chromate and dichromate ion the oxidation state of Cr  is +6.

 

7.     Write the ionic equation for reaction of KI with acidified KMnO₄.

Ans: 10I^- + 2MnO₄ ^- + 16H⁺ →  2Mn²⁺ + 8H₂O + 5I₂

 

8.     Why enthalpy of atomisation of transition metals are quite high.

Ans: This is because transition metals have strong metallic bonds as they have large number of unpaired electrons.

 

9.     There is a close similarity in physical and chemical properties of the 4d and 5d series of the transition elements, Explain.

Ans: This is because 5d and 4d-series elements have virtually the same atomic and ionic radii due to lanthanoid contraction.

 

10.  Why the members in the actinoid series exhibit larger number of oxidation states than the corresponding members in the lanthanoid series.

Ans: due to the fact that the 5f, 6d and 7s levels are of comparable energies.

 

11.  𝐶𝑢²⁺ is stable in aqueous solution inspite of having 3𝑑 configuration. Why?

Ans: The high energy to transform Cu(s) to Cu(aq) is balanced by its hydration enthalpy.

 

12.  The E° values of Mn and Zn is more negative. Give reason.

Ans: The stability of the half-filled d sub-shell in Mn and the completely filled Zn configuration in Zn are related to their more negative E° V values

 

13.  The transition metals are generally paramagnetic in nature why?

Ans: due to incomplete d orbitals and presence of unpaired electron.

 

14.  Scandium is a transition element but Zinc is not. Why?

Ans: Because of fully filled d orbitals in zinc.

 

15.  Give reasons:

a.     The compounds of Zn²⁺ are colorless.

Ans: It has fully-filled d¹⁰ configuration, so no d-d transition is possible.

b.     Among the first transition series, chromium is the hardest metal.

       Ans: It has six unpaired electrons, so it forms extensive metallic/covalent bonds

c.     Scandium doesn’t show variable oxidation states.

       Ans: It achieves stable noble gas configuration after losing three electrons.

d.     Transition elements form interstitial compounds.

   Ans: They have reasonably large void where a small-sized element like hydrogen, boron or carbon can be trapped.                         

e.     Zinc, cadmium and mercury are not considered as transitions elements.

Ans: They don’t have unpaired electrons in their (n−1)d orbital in their elemental form or in their common oxidation states.        

f.      What is lanthanide contraction? Mention its cause and any two consequences.

Ans: Lanthanide contraction is the steady decrease in the atomic and ionic sizes of lanthanide elements.

     Its major cause is the inability of inner 4f electrons to screen the outer 6s electrons.

       Its consequences include comparable atomic sizes of 4d and 5d series elements and regular decrease in basic strength from La(OH)3 to Lu(OH)3.

g.     Cerium, in its +4 oxidation state, is oxidizing in nature. Why?

Ans: It is because Ce⁴⁺ gains one electron to convert to more stable Ce³⁺.

h.     Write the balanced ionic equation for the oxidation of iodide in the presence of alkaline potassium permanganate.

       Ans: 2MnO₄⁻ + H₂O + I⁻ → 2MnO₂ + 2OH⁻ + IO₃⁻