Hydrogen Class 11 Notes CBSE Chemistry Chapter 9 (Free PDF Download)

Section – A (1 Mark Questions)

1. Which isotope of hydrogen

(i) does not contain neutron?

(ii) is radioactive?

Ans. (i) Protium

(ii) Tritium

2. Name the isotopes of hydrogen.  

Ans. Hydrogen has three isotopes:

Protium, $^1_1\text{H}$

deuterium, $^2_1\text{H}$

tritium, $^3_1\text{H}$

3. Give the laboratory method of preparation of hydrogen.  

Ans. Hydrogen is usually prepared by the reaction of granulated zinc with dilute hydrochloric acid

$\text{Zn}+2\text{H}^+\rightarrow\text{Zn}^{2+}+\text{H}_2.$

4. Give the commercial method of preparation of dihydrogen.  

Ans. Electrolysis of acidified water using platinum electrodes give hydrogen.

$2\text{H}_2\text{O}(\text{l})\xrightarrow[\text{Trace of acid/base}(\text{H}^+/\text{OH}^-)]{\text{Electrolysis}}2\text{H}_2(\text{g})+\text{O}_2(\text{g})$

5. Why is dihydrogen gas not preferred in balloons?  

Ans. Dihydrogen is the lightest gas and should have been used in balloons. But it is not preferred due to its highly combustible nature.

6. How is ammonia prepared using dihydrogen?  

Ans. With dinitrogen it forms ammonia.

$3\text{H}_2(\text{g})+\text{N}_2(\text{g})\xrightarrow[\text{Fe}]{\text{673K,200atm}}\text{2NH}_3(\text{g})$

$\Delta\text{H}^{\text{O}}=-92.6\text{kJ}/\text{mol}$

This is the method for the manufacture of ammonia by the Haber process.

7. Give an example of each of an ionic hydride and a covalent hydride. 

Ans. Ionic hydride: LiH, NaH. 

Covalent hydride : CH4, NH3 and H2O.

8. What happens when water is added to calcium hydride?  

Ans. Calcium hydroxide is formed $\underset{(\text{calcium hydride})}{\text{CaH}_2}+2\text{H}_2\text{O}\rightarrow\underset{\text{calcium hydroxide}}{\text{CaOH}_2}+2\text{H}_2$

9. What is Calgon?  

Ans. Sodium hexametaphosphate (Na6P6O18) is commercially called Calgon.

10. How is heavy water obtained from ordinary water?

Ans. Heavy water is obtained from ordinary water by repeated electrolysis in the presence of 3% NaOH.

Section – B (2 Marks Questions)

11. Define hard water. What makes water hard? Does hard water give lather with soap ?  

Ans. Water which does not produce lather with soap solution readily is called hard water. E.g. Hand pump water, river water, sea water etc. Presence of calcium and magnesium salts in the form of hydrogen carbonate, chloride and sulphate in water makes water hard. It does not give lather with soap.

12. Why is ice less dense then water and what kind of attractive forces must be overcome to melt ice?  

Ans. The structure of ice is an open structure having a number of vacant spaces. Therefore, the density of ice is less than water. When ice melts the hydrogen bonds are broken and the water molecules go in between the vacant spaces. As a result, the structure of liquid water is less open than structure of ice. Thus, ice is less dense than water.

13. Why is water an excellent solvent for ionic or polar substances?  

Ans. Water is a polar solvent with a high dielectric constant. Due to high dielectric constant of water the force of attraction between cation and added substance gets weakened. Thus water molecules are able to remove ions from the lattice site using ion dipole forces easily.

14. What do you understand by : 

(i)water – gas shift reaction

(ii) syn-gas?  

Ans. (i)The production of dihydrogen can be increased by reacting carbon monoxide of syn gas mixtures with steam in the presence of iron chromate as catalyst.

$\text{CO}(\text{g})+\text{H}_2\text{O}(\text{g})\xrightarrow[\text{Catalyst}]{673\text{K}}\text{CO}_2(\text{g})+\text{H}_2\text{(g)}$

This is called water gas – shift reaction.Carbon dioxide is removed by scrubbing with sodium arsenite solution.

(ii) The mixture of CO and H2 is called water gas.As this mixture of CO and H2 is used for the synthesis of methanol and a number of hydrocarbons it is also called synthesis gas or ‘syngas’

15. Write two uses of interstitial hydrides.  

Ans. Two important uses of  interstitial hydrides are :

(i) For storing H2 gas

(ii) As catalysts for hydrogenation reactions.

16. What happens when sodium hydride reacts with water?

Ans. Saline hydride (sodium hydride) react violently with water producing dihydrogen gas

NaH(s) + H2O(aq) → NaOH(aq) + H2(g)

17. Show with reaction the amphoteric nature of water.  

Ans. Water acts as an acid with NH3 and base with H2S

$\text{H}_2\text{O}(\text{l})+\text{NH}_3(\text{aq})\rightleftharpoons\text{OH}^-(\text{aq})+\text{NH}^+_4(\text{aq})$

$\text{H}_2\text{O}(\text{l})+\text{H}_2\text{S}(\text{aq})\rightleftharpoons\text{H}_3\text{O}^+(\text{aq})+\text{HS}^-(\text{aq})$

18. Distinguish between:

Temporary hardness & permanent hardness of the water.

Ans.

19. Give the main characteristics of isotopes.  

Ans. Since, the isotopes have the same electronic configuration, they have almost the same chemical properties. The only difference is in their rates of reactions, mainly due to their different enthalpy of bond dissociation. However, in physical property these isotopes differ considerably due to their large mass differences.

20. Classify the following as covalent, ionic polymer or interstitial hydrides:

(i) BeH2

(ii) CaH2

(iii) GeH4

(iv) TiH2

Ans.

PDF Summary - Class 11 Chemistry Hydrogen Notes (Chapter 6)

About Hydrogen Revision Notes

Firstly, we can say that hydrogen is the lightest atom, which has only one electron. Further, the loss of this electron results in an elementary particle, which is the proton. Furthermore, this is a unique characteristic property of hydrogen. Moreover, hydrogen has three isotopes, which are called deuterium, protium, and tritium. Among all these three isotopes, only the tritium is radioactive. On the other side, it resembles both halogens and alkali metals. Most noteworthy is that it has occupied a separate position in the periodic table because of its unique properties. Also, it cannot be found in the earth’s atmosphere, in its free state.

On the industrial scale, the dihydrogen is prepared by the water-gas shift reaction from the petrochemicals. Furthermore, the dissociation enthalpy of the H-H bond of dihydrogen is the highest for a single bond between the two atoms of any element. Moreover, this property is used in a hydrogen torch, which can be ideal for welding. Besides, the reducing reaction of dihydrogen leads to the formation of methanol, hydrogen halides, ammonia, water, and more. In addition, the heavy water is the other important compound that is formed by the electrolytic enrichment of normal water.

Sub-topics Covered Under Hydrogen

Let us look at some of the sub-topics that fall under the Hydrogen chapter.

• Hydrogen Position in the Periodic Table - This topic highlights hydrogen and its respective position in the periodic table.

• Hydrides - This topic describes the hydrides and their various types.

• Dihydrogen - This topic teaches about the dihydrogen in detail.

• Preparation and Properties of Dihydrogen - This topic tells the overview of the preparation of dihydrogen and its properties as well.

• Water - This topic tells about water and its physical, chemical properties, along with its structure.

• Heavy Water and Hydrogen Economy - This topic covers heavy water, its uses, whether it is safe to consume, and the hydrogen economy.

• Hydrogen Peroxide - This particular topic defines hydrogen peroxide, its preparation method, its structure, and its uses.

Importance of Class 11 Chemistry Hydrogen

Hydrogen is also an important topic in Chemistry. It matches to the realtime applications and uses in our daily lives. By studying this topic, students can get a good score in their final examinations and know about its real uses and applications and how to use it when necessary for realtime. The revision notes provided here at Vedantu help the students get a clear understanding of the topic and help them answer the questions given in the exams.

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Position of Hydrogen in the Periodic Table

Let us get to know the details of hydrogen about its position in the periodic table.

• It is the lightest element which is having the atomic number 1.

• It is also used as a Dihydrogen.

• It resembles both halogens and alkali metals, and therefore, its respective position is anomalous.

• In the modern periodic table, it is separately located.

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Increase Attention Span

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