NCERT Class 11 Part 2 - Chemistry

J.V. Narlikar

Chapter 9

Hydrogen - all with Video Answers

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Chapter Questions

Problem 1

Justify the position of hydrogen in the periodic table on the basis of its electronic configuration.

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Problem 2

Write the names of isotopes of hydrogen. What is the mass ratio of these isotopes?

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Problem 3

Why does hydrogen occur in a diatomic form rather than in a monoatomic form under normal conditions?

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Problem 4

How can the production of dihydrogen, obtained from 'coal gasification', be increased?

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Problem 5

Describe the bulk preparation of dihydrogen by electrolytic method. What is the role of an electrolyte in this process?

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Problem 6

Complete the following reactions:
(i) $\mathrm{H}_{2}(\mathrm{~g})+\mathrm{M}_{\mathrm{m}} \mathrm{O}_{0}(\mathrm{~s}) \stackrel{\Delta}{\longrightarrow}$
(ii) $\quad \mathrm{CO}(\mathrm{g})+\mathrm{H}_{2}(\mathrm{~g}) \longrightarrow \underset{\text { catalyst }}{\Delta}{\longrightarrow}$
(iii) $\quad \mathrm{C}_{3} \mathrm{H}_{\mathrm{g}}(\mathrm{g})+3 \mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \frac{\Delta}{\text { catalyst }}{\longrightarrow}$
(iv) $\mathrm{Zn}(\mathrm{s})+\mathrm{NaOH}(\mathrm{aq}) \stackrel{\text { heat }}{\longrightarrow}$

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Problem 7

Discuss the consequences of high enthalpy of $\mathrm{H}-\mathrm{H}$ bond in terms of chemical reactivity of dihydrogen.

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Problem 8

What do you understand by (i) electron-deficient. (ii) electron-precise, and (iii) electron-rich compounds of hydrogen? Provide justification with suitable examples.

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Problem 9

What characteristics do you expect from an electron-deficient hydride with respect to its structure and chemical reactions?

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Problem 10

Do you expect the carbon hydrides of the type $\left(\mathrm{C}_{\mathrm{n}} \mathrm{H}_{2 n+2}\right)$ to act as 'Lewis' acid or base? Justify your answer.

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Problem 11

What do you understand by the term "non-stoichiometric hydrides"? Do you expect this type of the hydrides to be formed by alkali metals? Justify your answer.

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Problem 12

How do you expect the metallic hydrides to be useful for hydrogen storage? Explain.

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Problem 13

How does the atomic hydrogen or oxy-hydrogen torch function for cutting and welding purposes ? Explain.

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Problem 14

Among $\mathrm{NH}_{3}, \mathrm{H}_{2} \mathrm{O}$ and $\mathrm{HF}$, which would you expect to have highest magnitude of hydrogen bonding and why?

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Problem 15

Saline hydrides are known to react with water violently producing fire. Can $\mathrm{CO}_{2}$, a well known fire extinguisher, be used in this case? Explain.

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Problem 16

Arrange the following
(i) $\mathrm{CaH}_{2}, \mathrm{BeH}_{2}$ and $\mathrm{TIH}_{2}$ in order of increasing electrical conductance.
(ii) LiH. NaH and CsH in order of increasing ionic character.
(iii) $\mathrm{H}-\mathrm{H}, \mathrm{D}-\mathrm{D}$ and $\mathrm{F}-\mathrm{F}$ in order of increasing bond dissociation enthalpy.
(iv) NaH, $\mathrm{MgH}_{2}$ and $\mathrm{H}_{2} \mathrm{O}$ in order of increasing reducing property.

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Problem 17

Compare the structures of $\mathrm{H}_{2} \mathrm{O}$ and $\mathrm{H}_{2} \mathrm{O}_{2}$.

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Problem 18

What do you understand by the term 'auto-protolysis' of water? What is its significance?

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Problem 19

Consider the reactlon of water with $\mathrm{F}_{2}$ and suggest, in terms of oxidation and reduction, which species are oxidised/reduced.

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Problem 20

Complete the following chemical reactions.
(i) $\mathrm{PbS}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq}) \rightarrow$
(ii) $\mathrm{MnO}_{4}^{-}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq}) \rightarrow$
(iii) $\mathrm{CaO}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \rightarrow$
(v) $\mathrm{AlCl}_{3}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(1) \rightarrow$
(vi) $\mathrm{Ca}_{3} \mathrm{~N}_{2}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{O}(1) \rightarrow$

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Problem 21

Describe the structure of the common form of ice.

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Problem 22

What causes the temporary and permanent hardness of water?

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Problem 23

Discuss the principle and method of softening of hard water by synthetic ionexchange resins.

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Problem 24

Write chemical reactions to show the amphoteric nature of water.

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Problem 25

Write chemical reactions to justify that hydrogen peroxide can function as an oxidising as well as reducing agent.

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Problem 26

What is meant by 'demineralised' water and how can it be obtained ?

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Problem 27

Is demineralised or distilled water useful for drinking purposes? If not, how can it be made useful?

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Problem 28

Describe the usefulness of water in biosphere and biological systems.

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Problem 29

What properties of water make it useful as a solvent? What types of compound can it (i) dissolve, and (ii) hydrolyse?

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Problem 30

Knowing the properties of $\mathrm{H}_{2} \mathrm{O}$ and $\mathrm{D}_{2} \mathrm{O}$, do you think that $\mathrm{D}_{2} \mathrm{O}$ can be used for drinking purposes?

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Problem 31

What is the difference between the terms 'hydrolysis' and 'hydration'?

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Problem 32

How can saline hydrides remove traces of water from organic compounds?

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Problem 33

What do you expect the nature of hydrides is, if formed by elements of atomic numbers $15,19,23$ and 44 with dihydrogen? Compare their behaviour towards water.

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Problem 34

Do you expect dillerent products in soluuon when aluminium(III) chloride and potassium chloride treated separately with (i) normal water (ii) acidified water. and (iii) alkaline water? Write equations wherever necessary.

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Problem 35

How does $\mathrm{H}_{2} \mathrm{O}_{2}$ behave as a bleaching agent?

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Problem 36

What do you understand by the terms:
(i) hydrogen cconomy (ii) hydrogenation (iii) 'syngas' (iv) water-gas shift reaction
(v) fuel-cell?

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