Solution of Chapter 11. The p -block Elements (Chemistry - Exemplar Book)

The element which exists in liquid state for a wide range of temperature and can be used for measuring high temperature is

Which of the following is a Lewis acid?

The geometry of a complex species can be understood from the knowledge of the type of hybridisation of orbitals of central atom. The hybridisation of orbitals of central atom in [Be(OH)₄]^- and the geometry of the complex are respectively

Which of the following oxides is acidic in nature?

The exhibition of the highest co-ordination number depends on the availability of vacant orbitals in the central atom. Which of the following elements is not likely to act as central atom in MF₆^3-?

Boric acid is an acid because its molecule

Catenation i.e., linking of similar atoms depends on size and electronic configuration of atoms. The tendency of catenation in Group 14 elements follows the order:

Silicon has a strong tendency to form polymers like silicones. The chain length of silicone polymer can be controlled by adding

Ionisation enthalpy (∆_i H₁ kJ mol^-1) for the elements of Group 13 follows the order.

In the structure of diborane

A compound X, of boron reacts with NH₃ on heating to give another compound Y which is called inorganic benzene. The compound X can be prepared by treating BF₃ with Lithium aluminium hydride. The compounds X and Y are represented by the formulas.

Quartz is extensively used as a piezoelectric material, it contains ___________.

The most commonly used reducing agent is

Dry ice is

Cement, the important building material is a mixture of oxides of several elements. Besides calcium, iron and sulphur, oxides of elements of which of the group (s) are present in the mixture?

The reason for small radius of Ga compared to Al is _______.

The linear shape of CO₂ is due to _________.

Me₃ SiCl is used during polymerisation of organo silicones because

Which of the following statements are correct?

Which of the following statements are correct. Answer on the basis of Fig.11.1.

Identify the correct resonance structures of carbon dioxide from the ones given below :

Draw the structures of BCl₃.NH₃ and AlCl₃ (dimer).

Explain the nature of boric acid as a Lewis acid in water.

Draw the structure of boric acid showing hydrogen bonding. Which species is present in water? What is the hybridisation of boron in this species?

Explain why the following compounds behave as Lewis acids?

(i) BCl₃

(ii) AlCl₃

Give reasons for the following:

(i) CCl₄ is immiscible in water, whereas SiCl₄ is easily hydrolyzed.

(ii) Carbon has a strong tendency for catenation compared to silicon.

Explain the following :

(i) CO₂ is a gas whereas SiO₂ is solid.

(ii) Silicon forms SiF₆^2- ion whereas the corresponding fluoro compound of carbon is not known.

The +1 oxidation state in group 13 and +2 oxidation state in group 14 becomes more and more stable with increasing atomic number. Explain.

Carbon and silicon both belong to the group 14, but inspite of the stoichiometric similarity, the dioxides, (i.e., carbon dioxide and silicon dioxide), differ in their structures. Comment.

If a trivalent atom replaces a few silicon atoms in three dimensional network of silicon dioxide, what would be the type of charge on overall structure?

When BCl₃ is treated with water, it hydrolyses and forms [B[OH]₄]^- only whereas AlCl₃ in acidified aqueous solution forms [Al (H₂O)₆]³⁺ ion. Explain what is the hybridisation of boron and aluminium in these species?

Aluminium dissolves in mineral acids and aqueous alkalies and thus shows amphoteric character. A piece of aluminium foil is treated with dilute hydrochloric acid or dilute sodium hydroxide solution in a test tube and on bringing a burning matchstick near the mouth of the test tube, a pop sound indicates the evolution of hydrogen gas. The same activity when performed with concentrated nitric acid, the reaction doesn’t proceed. Explain the reason.

Explain the following :

(i) Gallium has higher ionisation enthalpy than aluminium.

(ii) Boron does not exist as B3+ ion.

(iii) Aluminium forms [AlF₆]^3- ion but boron does not form [BF₆]^3- ion.

(iv) PbX₂ is more stable than PbX₄.

(v) Pb⁴⁺ acts as an oxidising agent but Sn²⁺ acts as a reducing agent.

(vi) Electron gain enthalpy of chlorine is more negative as compared to fluorine.

(vii) Tl (NO₃)₃ acts as an oxidising agent.

(viii) Carbon shows catenation property but lead does not.

(ix) BF₃ does not hydrolyse.

(x) Why does the element silicon, not form a graphite like structure whereas carbon does.

Identify the compounds A, X and Z in the following reactions :

(i) A + 2HCL + 5H₂O → 2NaCI + X

X → HBO₂ → Z

Complete the following chemical equations :

Z + 3 LiAiH₄ → X + 3 Lif + 3AIF₃

3X + 3O₂ → B₂ O₃ + 3H₂O

Match the species given in Column I with the properties mentioned in Column II.

Match the species given in Column I with properties given in Column II.

Match the species given in Column I with the hybridisation given in Column II.

Note: In the following questions a statement of Assertion (A) followed by a statementof Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): If aluminium atoms replace a few silicon atoms in three-dimensional network of silicon dioxide, the overall structure acquires a negative charge.

Reason (R): Aluminium is trivalent while silicon is tetravalent.

Note: In the following questions a statement of Assertion (A) followed by a statementof Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): Silicones are water repelling in nature.

Reason (R): Silicones are organosilicon polymers, which have (–R₂SiO–) as repeating unit.

Describe the general trends in the following properties of the elements in Groups 13 and 14.

(i) Atomic size

(ii) Ionisation enthalpy

(iii) Metallic character

(iv) Oxidation states

(v) Nature of halides

Account for the following observations:

(i) AlCl₃ is a Lewis acid

(ii) Though fluorine is more electronegative than chlorine yet BF₃ is a weaker Lewis acid than BCl₃

(iii) PbO₂ is a stronger oxidising agent than SnO₂

(iv) The +1 oxidation state of thallium is more stable than its +3 state.

When an aqueous solution of borax is acidified with hydrochloric acid, a white crystalline solid is formed which is soapy to touch. Is this solid acidic or basic in nature? Explain.

Three pairs of compounds are given below. Identify that compound in each of the pairs which have group 13 element in more stable oxidation state. Give a reason for your choice. State the nature of bonding also.

(i) TlCl₃, TlCl

(ii) AlCl₃ ,AlCl

(iii) InCl₃ ,InCl

BCl₃ exists as monomer whereas AlCl₃ is dimerised through halogen bridging. Give reason. Explain the structure of the dimer of AlCl₃ also.

Boron fluoride exists as BF₃ but boron hydride doesn’t exist as BH₃. Give reason. In which form does it exist? Explain its structure

(i) What are silicones? State the uses of silicones.

(ii) What are boranes? Give the chemical equation for the preparation of diborane.

A compound (A) of boron reacts with NMe3 to give an adduct (B) which on hydrolysis gives a compound (C) and hydrogen gas. Compound (C) is an acid. Identify the compounds A, B and C. Give the reactions involved.

A nonmetallic element of group 13, used in making bulletproof vests is extremely hard solid of black colour. It can exist in many allotropic forms and has an unusually high melting point. Its trifluoride acts as Lewis acid towards ammonia. The element exhibits maximum covalency of four. Identify the element and write the reaction of its trifluoride with ammonia. Explain why does the trifluoride act as a Lewis acid.

A tetravalent element forms monoxide and dioxide with oxygen. When air is passed over the heated element (1273 K), producer gas is obtained. Monoxide of the element is a powerful reducing agent and reduces ferric oxide to iron. Identify the element and write formulas of its monoxide and dioxide. Write chemical equations for the formation of producer gas and reduction of the ferric oxide with the monoxide.