NIOS Class 12 Chemistry Chapter 19 p-block Elements and their Compounds – I

NIOS Class 12 Chemistry Chapter 19 p-block Elements and their Compounds – I 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 19 p-block Elements and their Compounds – I 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 19 p-block Elements and their Compounds – I

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p-block Elements and their Compounds – I

Chapter: 19

Module – VI: Chemistry of Elements

INTEXT QUESTIONS 19.1

1. Write the formula of the following:

(i) Boric acid.

(ii) Borax.

Ans: (i) B(OH)₃

(ii) Na₂B₄O₇.10H₂O

2. Write one reaction for the preparation of diborane.

Ans: 4BCl₃ + 3LiAlH₄ → 2B₂H₆ + 3AlCl₃ + 3LiCl.

3. What is the general formula of alums?

Ans: NM(SO₄)₂ .12H₂O

Where N = monovalent large cation like K⁺ or NH⁴⁺ and M = trivalent cation like Al³⁺, Fe³⁺, Cr³⁺

4. Write the formula of anhydrous solid aluminium trichloride and its structure.

Ans: Al₂Cl₆.

5. Mention one use each of:

(i) borax.

(ii) boric acid.

(iii) boron trifluoride.

Ans: (i) as a flux, for glazing pottery and tiles : in the manufacture of optical and borosilicate glasses.

(ii) as an antiseptic, as a food preservative, for making enamels.

(iii) as a catalyst in Friedel-Crafts reaction.

6. Why aluminium become non-reactive after reacting with HNO₃.

Ans: Monoprotonic.

7. Orthoboric acid is monoprotonic or triprotonic.

Ans: Due to the formation of oxide layer

INTEXT QUESTIONS 19.2

1. Write two properties of diamond which are not exhibited by graphite.

Ans: Hardness and conducting nature. Diamond : hard, non conducting; graphite: soft, conducting.

2. What is the state of hybridization of carbon in (i) diamond (ii) graphite?

Ans: sp³ in diamond and sp² in graphite.

3. What is the nature of bond in carborundum?

Ans: Covalent

4. Write the state of hybridization of carbon in CCl₄.

Ans: sp₃

5. Which one is affected by water and why; CCl₄ or SiCl₄?

Ans: SiCl₄, as silicon can accept electron pair in its d-orbitals from water molecule.

6. Which is an acidic oxide, CO or CO₂?

Ans: CO₂

7. What happens when SiO₂ is attacked by F₂?

Ans:. SiO₂ + 2F₂ → SiF₄ + O₂

INTEXT QUESTIONS 19.3

1. Does ‘NH₄OH’ exist as a molecule?

Ans: No. Nitrogen cannot increase its covalency beyond 4.

2. What is the bond angle in NH³ molecule?

Ans: 107⁰

3. What is the state of hybridization of N in NH₃?

Ans: sp³

4. Draw the structure of pyrophosphoric acid.

Ans: 

5. What happen when PCl3 is treated with water?

Ans: PCl₃ + 3H₂O ⎯→ H₃PO₃ + 3HCl

TERMINAL EXERCISE

1. Why is boric acid not a protonic acid?

Ans: Boric acid (H₃BO₃) is not a protonic acid because it doesn’t release H⁺ ions directly. Instead, it accepts OH⁻ ions from water, forming B(OH)₄⁻ and releasing H⁺ indirectly through water’s reaction.

B(OH)₃ + 2H₂O → B(OH)₄⁻ + H₃O⁺

This behavior classifies boric acid as a Lewis acid rather than a traditional protonic acid (Bronsted-Lowry acid).