NCERT Class 11 Solutions Hydrogen

Scroll down to download pdf file

NCERT Class 11 Solutions Hydrogen - NCERT Solutions prepared for CBSE students by the best teachers in Delhi.

Class XI Chapter 9 – Hydrogen Chemistry

Question 9.1: Justify the position of hydrogen in the periodic table on the basis of its electronic configuration.

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

Question 9.2: 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.

Question 9.3: Why does hydrogen occur in a diatomic form rather than in a monoatomic form under normal conditions?

Answer :The ionization enthalpy of hydrogen atom is very high (1312 kJ mol–1). Hence, it is very hard to remove its only electron. As a result, its tendency to exist in the monoatomic form is rather low. Instead, hydrogen forms a covalent bond with another hydrogen atom and exists as a diatomic (H2) molecule.

Question 9.4: How can the production of dihydrogen, obtained from ‘coal gasification’, be increased?

Answer :Dihydrogen is produced by coal gasification method as:

The yield of dihydrogen (obtained from coal gasification) can be increased by reacting carbon monoxide (formed during the reaction) with steam in the presence of iron chromate as a catalyst.

This reaction is called the water-gas shift reaction. Carbon dioxide is removed by scrubbing it with a solution of sodium arsenite.

Question 9.5: Describe the bulk preparation of dihydrogen by electrolytic method. What is the role of an electrolyte in this process?

Answer :Dihydrogen is prepared by the electrolysis of acidified or alkaline water using platinum electrodes. Generally, 15 – 20% of an acid (H2SO4) or a base (NaOH) is used. Reduction of water occurs at the cathode as: At the anode, oxidation of OH– ions takes place as: Net reaction can be represented as:

Electrical conductivity of pure water is very low owing to the absence of ions in it. Therefore, electrolysis of pure water also takes place at a low rate. If an electrolyte such as an acid or a base is added to the process, the rate of electrolysis increases. The addition of the electrolyte makes the ions available in the process for the conduction of electricity and for electrolysis to take place.

Question 9.7: Discuss the consequences of high enthalpy of H–H bond in terms of chemical reactivity of dihydrogen.

Answer :The ionization enthalpy of H–H bond is very high (1312 kJ mol–1). This indicates that hydrogen has a low tendency to form H+ ions. Its ionization enthalpy value is comparable to that of halogens. Hence, it forms diatomic molecules (H2), hydrides with elements, and a large number of covalent bonds. Since ionization enthalpy is very high, hydrogen does not possess metallic characteristics (lustre, ductility, etc.) like metals.

Question 9.8: What do you understand by (i) electron-deficient, (ii) electron-precise, and (iii) electronrich compounds of hydrogen? Provide justification with suitable examples.

Answer :Molecular hydrides are classified on the basis of the presence of the total number of electrons and bonds in their Lewis structures as:

1. Electron-deficient hydrides

2. Electron-precise hydrides

3. Electron-rich hydrides

An electron-deficient hydride has very few electrons, less than that required for representing its conventional Lewis structure e.g. diborane (B2H6). In B2H6, there are six bonds in all, out of which only four bonds are regular two centered-two electron bonds. The remaining two bonds are three centered-two electron bonds i.e., two electrons are shared by three atoms. Hence, its conventional Lewis structure cannot be drawn.


Students should free download the NCERT solutions and get better marks in exams. Studiestoday.com panel of teachers recommend students to practice questions in NCERT books and download NCERT solutions.

Tags: 


Click on the text For more study material for Chemistry please click here - Chemistry

Latest NCERT & CBSE News

Read the latest news and announcements from NCERT and CBSE below. Important updates relating to your studies which will help you to keep yourself updated with latest happenings in school level education. Keep yourself updated with all latest news and also read articles from teachers which will help you to improve your studies, increase motivation level and promote faster learning

CBSE Board Practical Exam 2020

CBSE Board Practical Exam 2020: Important changes in date sheet, internal/external examiners and more Are you doing preparations for class 10 and 12 CBSE board exams? If yes, then you have to see what major changes CBSE has brought in the CBSE date sheet for class 10...

Study in India Short-term curriculum

Short-term curriculum for foreign students under 'Study in India': Yoga Global Planning In order to encourage international students to learn yoga, the Human Resource Development Ministry has decided to introduce training courses under the Modi’s government aspiring ‘...

Tips to find an excellent home tutor for your child

Most parents dream of making their children good at school, college and building a successful career. So, what exactly should your parents do when they find out their child is failing behind? Many depressed parents solve this problem by hiring a tutor. Most of the...

CBSE Registration 2019-2020

CBSE Registration 2019-2020: Check latest rules for students' registration in class IX and XI The Central Board of Secondary Education (CBSE) has changed the registration rules for class 9 to streamline the processes related to examinations in a time-efficient manner...

CBSE Class 10 Board Exam 2020

CBSE Class 10 Board Exam 2020: Problems Students May Face In Choosing Subject The Central Board of Secondary Education (CBSE) class 10 board examination will start from February 2020. The Central Board of Secondary Education (CBSE) has started the process of filling...

Do you think getting a tutor to help your child is a good idea

Yes, getting a tutor is a good idea to help your child. There are many reasons why parents choose tutors for their children. Some parents feel unable to help their children with homework and some don’t have enough time for this. Some think that their children are more...

Studies Today