Chemistry

The p-Block Elements.

Question:

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, reaction doesn't proceed. Explain the reason.

Answer:

Al being amphoteric dissolves both in acids and alkalies evolving H2 gas which bums with a pop sound.

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The p-Block Elements.

Q 1.

Describe two similarities and two dissimilarities between B and Al.

Q 2.

A certain salt X, gives the following results.
(i) Its aqueous solution is alkaline to litmus.
(ii) It swells up to a glassy material Y on strong heating.
(iii) When cone.H2SO4is added to a hot solution of X, white crystal of an acid Z separates out.

Q 3.

Why is boron used in nuclear reactions?

Q 4.

What is the basic building unit of all silicates?

Q 5.

Explain the difference in properties of diamond and graphite on the basis of their structures.

Q 6.

What is the state of hybridisation of carbon in
(a) CO32- (b) diamond (c) graphite?

Q 7.

Give reason why boron and aluminium tend to form covalent compounds.

Q 8.

Why do boron halides form addition compounds with NH3?

Q 9.

What happens when NaBH4 reacts with iodine?

Q 10.

Give reasons for the following:
(a) CCl4 is immiscible in water, whereas SiCl4 is easily hydrolysed.
(b) Carbon has a strong tendency for catenation compared to silicon.

Q 11.

Assertion (A): Silicones are water repelling in nature.
Reason (R): Silicones are organosilicon polymers, which have (-R2SiO-) as repeating unit.
(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) Both A and R are not correct. ‘
(d) A is not correct but R is correct.

Q 12.

Suggest a reason as to why CO is poisonous.

Q 13.

An aqueous solution of borax is
(a) neutral (b) amphoteric (c) basic (d) acidic

Q 14.

What happens when
(a) Borax is heated strongly
(b) Boric acid is added to water
(c) Aluminium is treated with dilute NaOH
(d) BF3 is reacted with ammonia?

Q 15.

How is excessive content of C02 responsible for global warming?

Q 16.

What are Fullerenes ? How are they prepared ?

Q 17.

Give reasons:
(a) Why do Boron halides form addition compound with NH3?
(b) The tendency for catenation decreases down the group in Group 14.
(c) PbO2 is a stronger oxidising agent than SnO2.

Q 18.

How is boron obtained from borax? Give chemical equations with reaction conditions.

Q 19.

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

Column I Column II
(i) Diborane (a) Used as a flux for soldering metals
(ii) Gallium                                         ‘ (b) Crystalline form of silica
(iii) Borax (c) Banana bonds
(iv) Aluminosilicate (d) Low melting, high boiling, useful for measuring high temperatures
(v) Quartz (e) Used as catalyst in petrochemical industries

 

Q 20.

Consider the compounds, BCl3 and CCl4. How will they’behave with water justify?

Q 21.

Describe the shapes of BF3 and BH4. Assign the hybridisation of boron in these species.

Q 22.

The reason for small radius of Ga compared to Al is_________ .
(a) poor screening effect of d and f orbitals
(b) increase in nuclear charge
(c) presence of higher orbitals
(d) higher atomic number

Q 23.

Which of the following statements are correct?
(a) Fullerenes have dangling bonds.
(b) Fullerenes are cage-like molecules.
(c) Graphite is thermodynamically most stable allotrope of carbon.
(d) Graphite is slippery and hard and therefore used as a dry lubricant in

Q 24.

If the starting material for the manufacture of silicons is RSiCl3 write the structure of the product formed.

Q 25.

The linear shape of C02 is due to  ______ .
(a) sp3 hybridisation of carbon
(b) sp hybridisation of carbon
(c) pπ-pπ bonding between carbon and oxygen
(d) sp2 hybridisation of carbon

Q 26.

Me3SiCl is used during polymerisation of organo silicones because
(a) the chain length of organo silicone polymers can be controlled by adding Me3
(b) Me3SiCl blocks the end terminal of silicone polymer.
(c) Me3SiCl improves the quality and yield of the polymer. –
(d) Me3SiCl acts as a catalyst during polymerization.

Q 27.

Explain why the following compounds behave as Lewis acids?
(i) BC13
(ii) AICI3

Q 28.

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.
(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) Both A and R are not correct.
(d) A is not correct but R is correct.

Q 29.

Aluminium trifluoride is insoluble in anhydrous HF but dissolves on addition of NaF. Aluminium trifluoride precipitates out of the resulting solution when gaseous BF3 is bubbled through. Give reason.

Q 30.

Silicon has a strong tendency to form polymers like silicones. The chain length of silicone polymer can be controlled by adding f (a) MeSiCl3 (b) Me2SiCl2 (c) Me3SiCl (d) Me4Si

Q 31.

Draw the structure of BC13.NH3 and AlCl3 (dimer).

Q 32.

Which oxide of carbon is regarded as anhydride of carbonic acid?

Q 33.

Give reason.
(i) C and Si are always tetravalent but Ge, Sn, Pb show divalency.
(ii) Gallium has higher ionization enthalpy than Al. Explain.

Q 34.

Explain the following:
(i) C02 is a gas whereas Si02 is a solid.
(b) Silicon forms SiF62- ion whereas corresponding fluoro compound of carbon is not known.

Q 35.

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

Q 36.

Discuss the pattern of variation in the oxidation states of
(i) B to Tl (ii) C to Pb.

Q 37.

What are electron deficient compounds? Are BCl3 and SiCl4 electron deficient species? Explain.

Q 38.

In some of the reactions thallium resembles aluminium, whereas in others it resembles with group 1 metals. Support this statement by giving some evidences.

Q 39.

Write the state of hybridisation of’B’ in BF3.

Q 40.

Suggest reason why the B-F bond lengths in BF3 (130 pm) and BF (143 pm) differ.

Q 41.

What is dry ice? Why is it so called?

Q 42.

Give the chemical reactions as an evidence for each of the following observations.
(i) Tin (II) is a reducing agent whereas lead (II) is not.
(ii) Gallium (I) undergoes disproportionation reaction.

Q 43.

(a) Why do Boron halides form addition compound with NH3?
(b) Assign appropriate reason for each of the following observations:-
(i) Anhydrous AlCl3 is used as a catalyst in many organic reactions.
(ii) No form of elemental silicon is comparable to graphite.

Q 44.

The geometry of a complex species can be understood from the knowledge of type of hybridisation of orbitals of central atom. The hybridisation of orbitals of central atom in [B(OH)4]- and the geometry of the complex are respectively
(a) sp3, tetrahedral
(b) sp3, square planar                                                    
(c) sp3d2, octahedral                                                            
(d) dsp2, square planar

Q 45.

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

Q 46.

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

Column I Column II
(i) Boron in [B(OH)4]" (a) sp2
(ii) Aluminium in [A1(H20)6]3+ (b) sp3
(iii) Boron in B2H6 (c) sp3d2
(iv) Carbon in Buckminsterfullerene  
(v) Silicon in SiO44-  
(vi) Germanium in [GeCl6]2-  

 

Q 47.

Is boric acid a protonic acid? Explain.

Q 48.

(a) What is general formula of silicons?
(b) How are linear silicons obtained?

Q 49.

Explain what happens when boric acid is heated.

Q 50.

Explain the following reactions.
(a) Silicon is heated with methyl chloride at high temperature in the presence of copper.
(b) Silicon dioxide is treated with hydrogen fluoride.
(c) CO is heated with ZnO.
(d) Hydrated alumina is treated with aqueous NaOH solution.