NCERT Solutions for Class 11 Chemistry Chemistry Part-2 Chapter 11

The p-Block Elements Class 11

Chapter 11 The p-Block Elements Exercise Solutions

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Exercise : Solutions of Questions on Page Number : 323

Q1 :  

Discuss the pattern of variation in the oxidation states of

(i) B to Tl and (ii) C to Pb.


Answer :

(i) B to Tl

The electric configuration of group 13 elements is ns2 np1. Therefore, the most common oxidation state exhibited by them should be +3. However, it is only boron and aluminium which practically show the +3 oxidation state. The remaining elements, i.e., Ga, In, Tl, show both the +1 and +3 oxidation states. On moving down the group, the +1 state becomes more stable. For example, Tl (+1) is more stable than Tl (+3). This is because of the inert pair effect. The two electrons present in the s-shell are strongly attracted by the nucleus and do not participate in bonding. This inert pair effect becomes more and more prominent on moving down the group. Hence, Ga (+1) is unstable, In (+1) is fairly stable, and Tl (+1) is very stable.

Group 13 element

Oxidation state

B

+3

Al

+3

Ga, In, Tl

+1, +3

The stability of the +3 oxidation state decreases on moving down the group.

(ii) C to Pb

The electronic configuration of group 14 elements is ns2 np2. Therefore, the most common oxidation state exhibited by them should be +4. However, the +2 oxidation state becomes more and more common on moving down the group. C and Si mostly show the +4 state. On moving down the group, the higher oxidation state becomes less stable. This is because of the inert pair effect. Thus, although Ge, Sn, and Pb show both the +2 and + 4 states, the stability of the lower oxidation state increases and that of the higher oxidation state decreases on moving down the group.

Group 14 element

Oxidation state

C

+4

Si

+4

Ge, Sn, Pb

+2, +4

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Q2 :  

How can you explain higher stability of BCl3 as compared to TlCl3?


Answer :

Boron and thallium belong to group 13 of the periodic table. In this group, the +1 oxidation state becomes more stable on moving down the group. BCl3is more stable than TlCl3because the +3 oxidation state of B is more stable than the +3 oxidation state of Tl. In Tl, the +3 state is highly oxidising and it reverts back to the more stable +1 state.

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Q3 :  

Why does boron trifluoride behave as a Lewis acid?


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Q4 :  

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


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Q5 :  

Is boric acid a protic acid? Explain.


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Q6 :  

Explain what happens when boric acid is heated.


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Q7 :  

Describe the shapes of BF3and BH4-. Assign the hybridisation of boron in these species.


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Q8 :  

Write reactions to justify amphoteric nature of aluminium.


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Q9 :  

What are electron deficient compounds? Are BCl3and SiCl4electron deficient species? Explain.


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Q10 :  

Write the resonance structures of and.


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Q11 :  

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


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Q12 :  

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


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Q13 :  

Rationalise the given statements and give chemical reactions:

Ӣ Lead(II) chloride reacts with Cl2to give PbCl4.

Ӣ Lead(IV) chloride is highly unstable towards heat.

Ӣ Lead is known not to form an iodide, PbI4.


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Q14 :  

Suggest reasons why the B–F bond lengths in BF3(130 pm) and (143 pm) differ.


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Q15 :  

If B-Cl bond has a dipole moment, explain why BCl3molecule has zero dipole moment.


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Q16 :  

Aluminium trifluoride is insoluble in anhydrous HF but dissolves on addition of NaF. Aluminium trifluoride precipitates out of the resulting solution when gaseous BF3is bubbled through. Give reasons.


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Q17 :  

Suggest a reason as to why CO is poisonous.


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Q18 :  

How is excessive content of CO2 responsible for global warming?


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Q19 :  

Explain structures of diborane and boric acid.


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Q20 :  

What happens when

(a) Borax is heated strongly,

(b) Boric acid is added to water,

(c) Aluminium is treated with dilute NaOH,

(d) BF3is reacted with ammonia?


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Q21 :  

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.


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Q22 :  

Give reasons:

(i) Conc. HNO3can be transported in aluminium container.

(ii) A mixture of dilute NaOH and aluminium pieces is used to open drain.

(iii) Graphite is used as lubricant.

(iv) Diamond is used as an abrasive.

(v) Aluminium alloys are used to make aircraft body.

(vi) Aluminium utensils should not be kept in water overnight.

(vii) Aluminium wire is used to make transmission cables.


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Q23 :  

Explain why is there a phenomenal decrease in ionisation enthalpy from carbon to silicon?


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Q24 :  

How would you explain the lower atomic radius of Ga as compared to Al?


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Q25 :  

What are allotropes? Sketch the structure of two allotropes of carbon namely diamond and graphite. What is the impact of structure on physical properties of two allotropes?


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Q26 :  

(a) Classify following oxides as neutral, acidic, basic or amphoteric:

CO, B2O3, SiO2, CO2, Al2O3, PbO2, Tl2O3

(b) Write suitable chemical equations to show their nature.


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Q27 :  

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


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Q28 :  

When metal X is treated with sodium hydroxide, a white precipitate (A) is obtained, which is soluble in excess of NaOH to give soluble complex (B). Compound (A) is soluble in dilute HCl to form compound (C). The compound (A) when heated strongly gives (D), which is used to extract metal. Identify (X), (A), (B), (C) and (D). Write suitable equations to support their identities.


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Q29 :  

What do you understand by (a) inert pair effect (b) allotropy and(c) catenation?


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Q30 :  

A certain salt X, gives the following results.

(i) Its aqueous solution is alkaline to litmus.

(ii) It swells up to a glassy material Yon strong heating.

(iii) When conc. H2SO4is added to a hot solution of X, white crystal of an acid Zseparates out.

Write equations for all the above reactions and identify X, Y and Z.


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Q31 :  

Write balanced equations for:

(i) BF3 + LiH →

(ii) B2H6 + H2O →

(iii) NaH + B2H6 →

(iv) H3BO3

(v) Al + NaOH →

(vi) B2H6 + NH3 →


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Q32 :  

Give one method for industrial preparation and one for laboratory preparation of CO and CO2 each.


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Q33 :  

An aqueous solution of borax is

(a) neutral (b) amphoteric

(c) basic (d) acidic


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Q34 :  

Boric acid is polymeric due to

(a) its acidic nature (b) the presence of hydrogen bonds

(c) its monobasic nature (d) its geometry


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Q35 :  

The type of hybridisation of boron in diborane is

(a) sp (b) sp2(c) sp3 (d) dsp2


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Q36 :  

Thermodynamically the most stable form of carbon is

(a) diamond (b) graphite

(c) fullerenes (d) coal


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Q37 :  

Elements of group 14

(a) exhibit oxidation state of +4 only

(b) exhibit oxidation state of +2 and +4

(c) form M2-and M4+ion

(d) form M2+and M4+ions


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Q38 :  

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


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<< Previous Chapter 10 : The s-Block Elements Next Chapter 12 : Organic Chemistry : Some Basic Principles and Techniques >>

Chemistry Part-2 - Chemistry : CBSE NCERT Exercise Solutions for Class 11th for The p-Block Elements will be available online in PDF book form soon. The solutions are absolutely Free. Soon you will be able to download the solutions.

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