NIOS Class 12 Chemistry Chapter 21 d-Block and f- Block Elements

NIOS Class 12 Chemistry Chapter 21 d-Block and f- Block Elements Solutions English Medium As Per New Syllabus to each chapter is provided in the list so that you can easily browse throughout different chapters NIOS Class 12 Chemistry Chapter 21 d-Block and f- Block Elements Notes in English and select need one. NIOS Class 12 Chemistry Solutions English Medium Download PDF. NIOS Study Material of Class 12 Chemistry Notes Paper Code: 313.

NIOS Class 12 Chemistry Chapter 21 d-Block and f- Block Elements

Also, you can read the NIOS book online in these sections Solutions by Expert Teachers as per National Institute of Open Schooling (NIOS) Book guidelines. These solutions are part of NIOS All Subject Solutions. Here we have given NIOS Class 12 Chemistry Notes, NIOS Senior Secondary Course Chemistry Solutions in English for All Chapter, You can practice these here.

d-Block and f- Block Elements

Chapter: 21

INTEXT QUESTIONS 21.1

1. What are transition elements?

Ans: Transition elements are defined as “Elements whose atoms have partially filled d-orbitals either in the atomic or in ionic state ( common oxidation state ).

2. How many elements comprise the first transition series? Give names of all these elements.

Ans: 10 elements constitute the first transition series. These are Sc, Ti, V, Cr, Mn,Fe, Co, Ni, Cu and Zn.

3. Whereas copper is a transition element, zinc is not included amongst transition elements. Explain.

Ans: Since zinc does not have partially filled d-orbitals either in atomic or in ionic state.

4. Although Cu⁺, Ag⁺ and Au⁺ have d¹⁰ configuration but Cu, Ag and Au are transition elements, why?

Ans: Because there are partially filled d-orbitals in Cu²⁺, Ag²⁺ and Au³⁺.

INTEXT QUESTIONS 21.2

1. Write the general electronic configuration of transition elements.

Ans: General electronic configuration of transition elements is: (n–1)d¹⁻¹⁰ ns¹ ᵒʳ ²

2. Write down the electronic configuration of the following elements in ground state: Sc, Cr, Cu and Zn.

Ans: Sc = [Ar]3d¹4s², Cr = [Ar]3d⁵4s¹, Zn = [Ar]3d¹⁰4s², Cu = [Ar] 3d¹⁰ 4s¹.

3. Write down the electronic configuration of the following ions: Cr³⁺, Ti⁴⁺, Ni³⁺ and Cu²⁺.

Ans: Cr³⁺ = [Ar]3d³, Ti⁴⁺ = [Ar]3d⁰, Ni³⁺ = [Ar]3d⁷and Cu²⁺ = [Ar]3d⁹.

4. Why the electronic configuration of Mn²⁺ is 3d⁵ and not 3d² 4s²?

Ans: Because less amount of energy is required to remove an electron from 4s instead of 3d orbital. It is due to the fact that after Sc, 3d, becomes lower in energy than 4s.

INTEXT QUESTIONS 21.3

1. Why do transition elements show higher melting and boiling points?

Ans: Due to strong interatomic bonding.

2. Why do the radii of transition elements decrease along a period?

Ans: Due to increase in effective nuclear charge.

3. Why do transition elements show higher density as compared to s-block elements?

Ans: Due to small size. Size does not increase in the same proportion as the atomic mass.

INTEXT QUESTIONS 21.4

1. Why do transition elements act as good catalysts?

Ans: Due to variable oxidation states.

2. Name some of the common catalysts you have studied.

Ans: V₂O₅ (contact process for H₂SO₄) and iron (Haber’s process)

3. Which of the following compounds are expected to be diamagnetic: CrCl₃, ScCl3₃, CuSO₄, CoCl₂, TiCl₄ and ZnCl₂?

Ans: ScCl₃(3d⁰), TiCl₄(3d⁰) and ZnCl₂(3d¹⁰).

4. Which of the following do you expect to be colored and why, Cr+ and Cu+?

Ans: Cr+ because it has partially filled d-orbital i.e. 3d⁵.

5. Name any two alloys of transition elements.

Ans: Nichrome and brass.

6. Calculate in B.M., magnetic moments expected for the following ions: V⁴⁺, Ni³⁺, V⁴⁺, Ni³⁺, Cr³⁺ and Ti⁴⁺.

Ans: V⁴+3d¹ √n(n+2) = √n(1+2) = √3 = 1.73 B.M., Ni³⁺3d⁷ n = 3, √3(3 + 2) = 15 = 3.87 B.M.

INTEXT QUESTIONS 21.5

1. Name the starting materials used in preparation of soluble chromate and dichromates.

Ans: Chromite ore, Na₂CO₃ and O₂.

2. Write down the formula of chromite ore.

Ans: FeO.Cr₂O₃.

3. How is sodium dichromate converted into potassium dichromate?

Ans: Na₂Cr₂O₇ + 2KCl → K₂Cr₂O₇ + 2NaCl.

4. What happens when potassium dichromate is heated with an alkali metal chloride and concentrated sulphuric acid?

Ans:  K₂Cr₂O₇ + 4NaCl = 6H₂SO₄ → 2KHSO₄ + 4NaHSO₄ + 2CrO₂Cl₂ + 3H₂O

5. Give the molecular formula of chrome alum. What are its uses?

Ans: KCr(SO₄)₂.12H₂O or K₂SO₄.Cr₂(SO₄)₃.24H₂O, tanning of leather and dyeingfabrics.

6. Why does dichromate act as an oxidizing agent?

Ans: For Cr, +3 is the stable oxidation state but in K₂Cr₂O₇ the oxidation state of Cr is +6.

7. What happens when a base is added to dichromate?

Ans: Cr₂O₇²⁻+ 2OH⁻ → 2CrO₄²⁻ + H₂O. Dichromate changes to chromate.

8. What is the oxidation state of chromium in (i) K2CrO4 and (ii) K₂Cr₂O₇?

Ans: (i) +6 (ii) +6.

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