NCERT Solutions for Class 11 Chemistry Chemistry Part-2 Chapter 9

Hydrogen Class 11

Chapter 9 Hydrogen Exercise Solutions

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Exercise : Solutions of Questions on Page Number : 288

Q1 :  

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


Answer :

Hydrogen is the first element of the periodic table. Its electronic configuration is [1s1]. Due to the presence of only one electron in its 1s shell, hydrogen exhibits a dual behaviour, i.e., it resembles both alkali metals and halogens.

Resemblance with alkali metals:

1. Like alkali metals, hydrogen contains one valence electron in its valency shell.

H : 1s1

Li : [He] 2s1

Hence, it can lose one electron to form a unipositive ion.

2. Like alkali metals, hydrogen combines with electronegative elements to form oxides, halides, and sulphides.

Resemblance with halogens:

1. Both hydrogen and halogens require one electron to complete their octets.

H : 1s1

F : 1s2 2s2 2p5

Cl : 1s2 2s2 2p6 3s2 3p5

Hence, hydrogen can gain one electron to form a uninegative ion.

2. Like halogens, it forms a diatomic molecule and several covalent compounds.

Though hydrogen shows some similarity with both alkali metals and halogens, it differs from them on some grounds. Unlike alkali metals, hydrogen does not possess metallic characteristics. On the other hand, it possesses a high ionization enthalpy. Also, it is less reactive than halogens.

Owing to these reasons, hydrogen cannot be placed with alkali metals (group I) or with halogens (group VII). In addition, it was also established that H+ ions cannot exist freely as they are extremely small. H+ ions are always associated with other atoms or molecules. Hence, hydrogen is best placed separately in the periodic table.

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Q2 :  

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


Answer :

Hydrogen has three isotopes. They are:

1. Protium, ,

2. Deuterium, or D, and

3. Tritium, or T

The mass ratio of protium, deuterium and tritium  is 1:2:3.

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Q3 :  

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


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Q4 :  

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


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Q5 :  

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


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Q6 :  

Complete the following reactions:

(i)

(ii)

(iii)

(iv)


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Q7 :  

Discuss the consequences of high enthalpy of H-H bond in terms of chemical reactivity of dihydrogen.


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Q8 :  

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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Q9 :  

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


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Q10 :  

Do you expect the carbon hydrides of the type (CnH2n+ 2) to act as 'Lewis' acid or base? Justify your answer.


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Q11 :  

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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Q12 :  

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


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Q13 :  

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


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Q14 :  

Among NH3, H2O and HF, which would you expect to have highest magnitude of hydrogen bonding and why?


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Q15 :  

Saline hydrides are known to react with water violently producing fire. Can CO2, a well known fire extinguisher, be used in this case? Explain.


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Q16 :  

Arrange the following

(i) CaH2, BeH2and TiH2in order of increasing electrical conductance.

(ii) LiH, NaH and CsH in order of increasing ionic character.

(iii) H-H, D-D and F-F in order of increasing bond dissociation enthalpy.

(iv) NaH, MgH2and H2O in order of increasing reducing property.


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Q17 :  

Compare the structures of H2O and H2O2.


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Q18 :  

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


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Q19 :  

Consider the reaction of water with F2 and suggest, in terms of oxidation and reduction, which species are oxidized/reduced.


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Q20 :  

Complete the following chemical reactions.

(i)

(ii)

(iii)

(iv)

(v)

Classify the above into (a) hydrolysis, (b) redox and (c) hydration reactions.


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Q21 :  

Describe the structure of the common form of ice.


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Q22 :  

What causes the temporary and permanent hardness of water?


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Q23 :  

Discuss the principle and method of softening of hard water by synthetic ion-exchange resins.


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Q24 :  

Write chemical reactions to show the amphoteric nature of water.


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Q25 :  

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


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Q26 :  

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


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Q27 :  

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


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Q28 :  

Describe the usefulness of water in biosphere and biological systems.


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Q29 :  

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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Q30 :  

Knowing the properties of H2O and D2O, do you think that D2O can be used for drinking purposes?


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Q31 :  

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


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Q32 :  

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


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Q33 :  

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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Q34 :  

Do you expect different products in solution 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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Q35 :  

How does H2O2 behave as a bleaching agent?


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Q36 :  

What do you understand by the terms:

(i) hydrogen economy (ii) hydrogenation (iii) 'syngas' (iv) water-gas shift reaction (v) fuel-cell ?


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<< Previous Chapter 8 : Redox Reactions Next Chapter 10 : The s-Block Elements >>

Chemistry Part-2 - Chemistry : CBSE NCERT Exercise Solutions for Class 11th for Hydrogen 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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