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# NCERT solutions Chemistry Class 12 Part 1 chapter 7 The p-block Elements

#### Chapters

NCERT Solutions for Chemistry Class 12 Part 2

## Chapter 7 - The p-block Elements

#### Pages 169 - 205

Why are pentahalides more covalent than trihalides?

Q 1 | Page 169

Why is BiH3 the strongest reducing agent amongst all the hydrides of Group 15 elements?

Q 2 | Page 169

Account for the following:

N2 is less reactive at room temperature.

Q 3 | Page 170

Mention the conditions required to maximise the yield of ammonia.

Q 4 | Page 172

How does ammonia react with a solution of Cu2+?

Q 5 | Page 172

What is the covalence of nitrogen in N2O5?

Q 6 | Page 173

Bond angle in PH_(4)^(+) is higher than that in PH3. Why?

Q 7 | Page 177

What happens when white phosphorus is heated with concentrated NaOH solution in an inert atmosphere of CO2?

Q 8 | Page 177

What happens when PCl5 is heated?

Q 9 | Page 177

Write a balanced equation for the hydrolytic reaction of PCl5 in heavy water.

Q 10 | Page 177

What is the basicity of H3PO4 ?

Q 11 | Page 180

What happens when

H3PO3 is heated ?

Write the reactions involved.

Q 12 | Page 180

List the important sources of sulphur.

Q 13 | Page 183

Write the order of thermal stability of the hydrides of Group 16 elements.

Q 14 | Page 183

Why is H2O a liquid and H2S a gas?

Q 15 | Page 183

Which of the following does not react with oxygen directly?

Zn, Ti, Pt, Fe

Q 16 | Page 185

Complete the following reactions: C2H4 + O2 →

Q 17.1 | Page 185

Complete the following reactions:  4Al + 3O2 →

Q 17.2 | Page 185

Why does O3 act as a powerful oxidising agent?

Q 18 | Page 187

How is O3 estimated quantitatively?

Q 19 | Page 187

What happens when sulphur dioxide is passed through an aqueous solution of Fe(III) salt?

Q 20 | Page 189

Comment on the nature of two S−O bonds formed in SO2 molecule. Are the two S−O bonds in this molecule equal?

Q 21 | Page 189

How is the presence of SO2 detected?

Q 22 | Page 189

Mention three areas in which H2SO4 plays an important role.

Q 23 | Page 191

Write the conditions to maximize the yield of H2SO4 by contact process.

Q 24 | Page 191

Why is K_(a_2) "<<" K_(a_1) for H_2SO_4 in water?

Q 25 | Page 191

Give two examples to show the anomalous behaviour of fluorine.

Q 27 | Page 196

Sea is the greatest source of some halogens. Comment.

Q 28 | Page 196

Give the reason for bleaching action of Cl2.

Q 29 | Page 198

Name two poisonous gases which can be prepared from chlorine gas.

Q 30 | Page 198

Why is ICl more reactive than I2?

Q 31 | Page 202

Account for the following:

Helium is used in diving apparatus.

Q 32 | Page 205

Balance the following equation: XeF6 + H2O → XeO2F2 + HF

Q 33 | Page 205

Why has it been difficult to study the chemistry of radon?

Q 34 | Page 205

#### Pages 207 - 208

Discuss the general characteristics of Group 15 elements with reference to their electronic configuration, oxidation state, atomic size, ionisation enthalpy and electronegativity.

Q 1 | Page 207

Why does the reactivity of nitrogen differ from phosphorus?

Q 2 | Page 207

Discuss the trends in chemical reactivity of group 15 elements.

Q 3 | Page 207

Why does NH3 form hydrogen bond but PH3 does not?

Q 4 | Page 207

How is nitrogen prepared in the laboratory? Write the chemical equations of the reactions involved.

Q 5 | Page 207

How is ammonia manufactured industrially?

Q 6 | Page 207

Illustrate how copper metal can give different products on reaction with HNO3.

Q 7 | Page 207

Give the resonating structures of NO2 and N2O5.

Q 8 | Page 207

The HNH angle value is higher than HPH, HAsH and HSbH angles. Why? [Hint: Can be explained on the basis of sp3 hybridisation in NH3 and only s−p bonding between hydrogen and other elements of the group].

Q 9 | Page 207

Why does R3P=O exist but R3N=O does not (R = alkyl group)?

Q 10 | Page 207

Explain why NH3 is basic while BiH3 is only feebly basic.

Q 11 | Page 207

Nitrogen exists as diatomic molecule and phosphorus as P4. Why?

Q 12 | Page 207

Write main differences between the properties of white phosphorus and red phosphorus.

Q 13 | Page 207

Why does nitrogen show catenation properties less than phosphorus?

Q 14 | Page 207

Give the disproportionation reaction of H3PO3

Q 15 | Page 207

Can PCl5 act as an oxidising as well as a reducing agent? Justify.

Q 16 | Page 207

Justify the placement of O, S, Se, Te and Po in the same group of the periodic table in terms of electronic configuration, oxidation state and hydride formation.

Q 17 | Page 207

Why is dioxygen a gas but sulphur a solid?

Q 18 | Page 207

Knowing the electron gain enthalpy values for O → O and O → O2− as −141 and 702 kJ mol−1 respectively, how can you account for the formation of a large number of oxides having O2− species and not O? (Hint: Consider lattice energy factor in the formation of compounds).

Q 19 | Page 207

Which aerosols deplete ozone?

Q 20 | Page 207

Describe the manufacture of H2SO4 by contact process?

Q 21 | Page 207

How is SO2 an air pollutant?

Q 22 | Page 207

Why are halogens strong oxidising agents?

Q 23 | Page 207

Account for the following :

Fluorine forms only one oxoacid HOF

Q 24 | Page 207

Explain why inspite of nearly the same electronegativity, oxygen forms hydrogen bonding while chlorine does not.

Q 25 | Page 207

Write two uses of ClO2.

Q 26 | Page 207

Why are halogens coloured?

Q 27 | Page 207

Write the reactions of F2 and Cl2 with water.

Q 28 | Page 207

How can you prepare Cl2 from HCl and HCl from Cl2? Write reactions only.

Q 29 | Page 207

What inspired N. Bartlett for carrying out reaction between Xe and PtF6?

Q 30 | Page 207

What are the oxidation states of phosphorus in H3PO3

Q 31.1 | Page 207

What are the oxidation states of phosphorus in the following:

PCl

Q 31.2 | Page 207

What are the oxidation states of phosphorus in the following:

Ca3P2

Q 31.3 | Page 207

What are the oxidation states of phosphorus in the following:

Na3PO4

Q 31.4 | Page 207

What are the oxidation states of phosphorus in the following:

POF3

Q 31.5 | Page 207

Write balanced equations for NaCl is heated with sulphuric acid in the presence of MnO2

Q 32.1 | Page 208

Write balanced equations for Chlorine gas is passed into a solution of NaI in water.

Q 32.2 | Page 208

How are xenon fluorides XeF2, XeF4 and XeF6 obtained?

Q 33 | Page 208

With what neutral molecule is ClO isoelectronic? Is that molecule a Lewis base?

Q 34 | Page 208

How are XeO3 and XeOF4 prepared?

Q 35 | Page 208

Arrange the following in the order of property indicated for each set:

F2, Cl2, Br2, I2 - increasing bond dissociation enthalpy.

Q 36.1 | Page 208

Arrange the following in the order of property indicated for each set:

HF, HCl, HBr, HI - increasing acid strength.

Q 36.2 | Page 208

Which one of the following does not exist?

(i) XeOF4

(ii) NeF2

(iii) XeF2

(iv) XeF6

Q 37 | Page 208

Give the formula and describe the structure of a noble gas species which is isostructural with

ICI_4^(-)

Q 38.1 | Page 208

Give the formula and describe the structure of a noble gas species which is isostructural with:

IBr_2^(-)

Q 38.2 | Page 208

Give the formula and describe the structure of a noble gas species which is isostructural with:

BrO_3^(-)

Q 38.3 | Page 208

Why do noble gases have comparatively large atomic sizes?

Q 39 | Page 208

List the uses of Neon and argon gases.

Q 40 | Page 208

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