Additional Questions - Chapter 4 Hydrogen 11th Chemistry Guide Samacheer Kalvi Solutions - SaraNextGen [2024-2025]

Updated By SaraNextGen

On April 24, 2024, 11:35 AM

Additional Questions Solved
I. Choose the correct answer:
Question 1.
Which one of the following element mostly present in the sun and the stars?
(a) Hydrogen
(b) Lithium
(c) Helium
(d) Beryllium
Answer:
(a) Hydrogen
Question 2.
is the most abundant $90 \%$ of all atoms...........
(a) Lithium
(b) Hydrogen
(c) Oxygen
(d) Silicon
Answer:
(A) Hydrogen
Question 3.
At room temperature normal hydrogen consists of
(a) $25 \%$ ortho form $+75 \%$ para form
(b) $50 \%$ ortho form $+50 \%$ para form
(c) $75 \%$ ortho form $+25 \%$ para form
(d) $60 \%$ ortho form $+40 \%$ para form
Answer:
(c) $75 \%$ ortho form $+25 \%$ para form

Question 4.
Which one of the metal is used to convert para hydrogen into ortho hydrogen?
(a) Copper
(b) Aluminium
(c) Sodium
(d) Platinum
Answer:
(d) Platinum
Question 5.
Consider the following statements
(i) In ortho form of hydrogen molecule, the nuclear spins are opposed to each other
(ii) The magnetic moment of para hydrogen is twice that of ortho hydrogen
(iii) By passing an electric discharge, para hydrogen can be converted into ortho hydrogen. Which of the above statement is/are not correct?
(a) (i) only
(b) (iii) only
(c) (i) and (ii)
(d) (ii) and (iii)
Answer:
(c) (i) and (ii)
Question 6.
Which of the following is not used in the conversion of para hydrogen into ortho hydrogen?
(a) by heating more than $800^{\circ} \mathrm{C}$
(b) by passing an electric discharge
(c) by mixing with atomic hydrogen
(d) by mixing with diamagnetic molecules
Answer:
(d) by mixing with diamagnetic molecules
Question 7.
The magnetic moment of para hydrogen is
(a) one
(b) zero
(c) twice
(d) maximum
Answer:
(b) zero

Question 8 .
Which one of the following does not contain neutron?
(a) ordinary hydrogen
(b) Heavy hydrogen
(c) Radioactive hydrogen
(d) Deuterium
Answer:
(a) ordinary hydrogen
Question 9.
The half life period of tritium is
(a) 123.3 year
(b) 12.33 years
(c) 1 year
(d) 1600 years
Answer:
(a) 12.33 years
Question 10 .
Which of the following is used in illumination of wrist watches?
(a) Phosphorous
(b) Radon
(c) Tritium
(d) Deuterium
Answer:
(c) Tritium
Question 11.
Which one of the following is used to study the movements of ground water?
(a) Deuterium
(b) Protium
(c) Tritium
(d) $\mathrm{HD}$
Answer:

(a) Deuterium

Question 12.
By which rays nuclear reactions are induced in upper atmosphere to produce tritium?
(a) $\alpha$-rays
(b) $\beta$-rays
(c) $\gamma$-rays
(d) cosmic rays
Answer:
(d) cosmic rays
Question 13.
Which of the following is produced by bombardment of neutrons with lithium?
(a) Deuterium
(b) Protium
(c) Tritium
(d) Beryllium
Answer:
(c) Tritium

Question 14 .
Consider the following statements
(i) Tritium is a beta emitting radioactive isotope of hydrogen.
(ii) Deuterium is known as heavy hydrogen.
(iii) Deuterium is used in emergency exit signs.
Which of the following statement is/are not correct?
(a) (i) only
(b) (iii) only
(c) (i) and (ii)
(d) (i) (ii) and (iii)
Answer:
(b) (iii) only
Question 15.
Which of the following mixture of gases is called water gas?
(a) $\mathrm{CO}_{2(\mathrm{~g})}+\mathrm{H}_{2(\mathrm{~g})}$
(b) $\mathrm{CO}_{2(\mathrm{~g})}+\mathrm{N}_2(\mathrm{~g})$
(c) $\mathrm{CO}_{(\mathrm{g})}+\mathrm{H}_2(\mathrm{~g})$
(d) $\mathrm{N}_{2(\mathrm{~g})}+\mathrm{H}_2(\mathrm{~g})$
Answer:
(c) $\mathrm{CO}_{(\mathrm{g})}+\mathrm{H}_{2(\mathrm{~g})}$
Question 16.
Consider the following statements.
(i)Hydrogen is a colourless, odourless, tasteless heavy and highly inflammable gas.
(ii) Hydrogen is a good reducing agent.
(ii) Hydrogen can be liquefied under low pressure and high temperature.
Which of the above statements is/are not correct?
(a) (i) only
(b) (ii) only (c)
(c) (i) and (iii)
(d) (ii) and (Hi)
Answer:
(c) (i) and (iii)

Question 17.
The products formed during the cracking long chain hydrocarbon $\mathrm{C}_6 \mathrm{H}_{12}$ are
(a) $\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O}$
(b) $\mathrm{CO}+\mathrm{H}_2$
(c) $\mathrm{C}_6 \mathrm{H}_{10}+\mathrm{H}_2$
(d) $\mathrm{C}_6 \mathrm{H}_6+3 \mathrm{H}_2$
Answer:
(d) $\mathrm{C}_6 \mathrm{H}_6+3 \mathrm{H}_2$
Question 18 .
Which one of the following is manufactured in Haber's process?
(a) $\mathrm{SO}_3$
(b) $\mathrm{NH}_3$
(C) $\mathrm{N}_2$
(d) $\mathrm{H}_2$
Answer:
(b) $\mathrm{NH}_3$

Question 19.
Hydrogen combines with carbon monoxide in the presence of copper catalyst will synthesise
(a) Ethanol
(b) Methane
(c) Methanol
(d) Methanal
Answer:
(c) Methanol
Question 20.
Match the List-I and List-II using the correct code given below the list.
List-I
A. Hydrogenation of unsaturated vegetable oils
B. Calcium hydride
C. Liquid hydrogen
D. Atomic hydrogen
List-II
1. Rocket fuel
2. Welding of metals
3. Desiccant
4. Margarine

Answer:
(a) $\quad \begin{array}{lllll}4 & 3 & 1 & 2\end{array}$
Question 21.
Statement-I: Hydrogen is placed at the top of the group which is in-line with the latest periodic table.
Statement-II: Hydrogen has a tendency to lose its electron to form $\mathrm{H}^{+}$, thus showing electropositive character like alkali metals. On the other hand, hydrogen has a tendency to gain an electron to yield $\mathrm{H}$, thus showing electronegative character like halogens.
(a) Statements-I and II are correct and Statement-II is the correct explanation of statement-I.
(b) Statements-I and II are correct but Statement-II is not the correct explanation of statement-I.
(c) Statement-I is correct but Statement-II is wrong.
(d) Statement-I is wrong but Statement-II is correct.
Answer:
(a) Statements-I and II are correct and Statement-II is the correct explanation of statement-I.
Question 22.
Statement-I: The magnetic moment of para-hydrogen is zero.
Statement-II: The spins of two hydrogen atoms in para $\mathrm{H}_2$ molecule neutralise each other.
(a) Statements-I and II are correct and Statement-II is the correct explanation of statement-I.
(b) Statements-I and II are correct but Statement-II is not the correct explanation of statement-I.
(c) Statement-I is correct but Statement-II is wrong.
(d) Statement-I is wrong but Statement-II is correct.
Answer:
(a) Statements-I and II are correct and Statement-II is the correct explanation of statement-I.
Question 23.
Which of the following process is important in food industry?
(a) Dehydration
(b) Dehalogenation
(c) Hydrogenation
(d) Carboxylation
Answer:
(c) Hydrogenation
Question 24 .
Which of the following is used as desiccants to remove moisture from organic solvents?
(a) Calcium hydride
(b) $\mathrm{LiAlH}_4$
(c) Sodium boro hydride
(d) Sodium hydride
Answer:
(a) Calcium hydride
Question 25.
Which of the following is used for cutting and welding?
(a) Atomic hydrogen and oxy hydrogen torches
(b) Liquid hydrogen
(c) Calcium hydride
(d) Sodium boro hydride
Answer:
(a) Atomic hydrogen and oxy hydrogen torches

Question 26.
Liquid hydrogen is used as
(a) a rocket fuel as well as in space research
(b) fuel cells for generating electrical energy
(c) cutting and welding torch
(d) desiccant to remove moisture from organic solvent
Answer:
(a) a rocket fuel as well as in space research
Question 27.
Which one of the following is a universal solvent?
(a) Alcohol
(b) Ether
(c) $\mathrm{CCl}_4$
(d) Water
Answer:
(d) Water
Question 28.
At the temperature conditions of the earth (300K) the OPR of $\mathrm{H}_2 \mathrm{O}$ is
(a) 2.5
(b) 3
(c) 1
(d) zero
Answer:
(b) 3

Question 29.
Water does not react with
(a) Sodium
(b) Magnesium
(c) Beryllium
(d) Calcium
Answer:
(c) Beryllium
Question 30.
Which of the following does not have any effect with water?
(a) Sodium
(b) Iron
(c) Lead
(d) Mercury
Answer:
(d) Mercury
Question 31.
Which set of the metals do not have any effect on water?
(a) $\mathrm{Ag}, \mathrm{Au}, \mathrm{Pt}$
(b) $\mathrm{Na}, \mathrm{Mg}, \mathrm{Al}$
(c) $\mathrm{Fe}, \mathrm{Ca}, \mathrm{Zn}$
(d) $\mathrm{Fe}, \mathrm{Pb}, \mathrm{Na}$
Answer:
(a) Ag, Au, Pt

Question 32.
Which of the following non-metal reacts with ordinary water?
(a) Carbon
(b) Sulphur
(c) Chlorine
(d) Phosphorous
Answer:
(c) Chlorine
Question 33.
Consider the following statements.
(i) Silver, Gold, Mercury and Platinum do not have any effect on water.
(ii) Carbon, Sulphur and Phosphorous do not react with water.
(iii) Beryllium reacts with water less violently.
Which of the following statements is/are not correct?
(a) (i) only
(b) (ii) and (iii)
(c) (iii) only
(d) (ii) only
Answer:
(c) (iii) only
Question 34.
Which one of the following is used as a bleach?
(a) $\mathrm{Cl}_2$ water
(b) $\mathrm{Br}$, water
(c) Water gas
(d) Liquid hydrogen
Answer:
(a) $\mathrm{Cl}_2$ water
Question 35.
Water is an/a oxide.
(a) neutral
(b) acidic
(c) basic
(d) amphoteric
Answer:
(d) amphoteric

Question 36.
Permanent hardness of water is removed by
(a) boiling
(b) lime
(c) washing soda
(d) chlorine
Answer:
(c) washing soda
Question 37.
Which one of the following is used as water softener?
(a) Zeolites
(b) lime
(c) washing soda
(d) bleaching powder
Answer:
(a) Zeolites
Question 38.
In chelating method of softening of hard water is used.
(a) magnesia
(b) lime
(c) EDTA
(d) washing soda
Answer:
(c) EDTA
Question 39.
Which of the following is used to remove toxic and heavy metals from water?
(a) zeolites
(b) magnesia
(c) Bleaching agent
(d) lime
Answer:
(a) zeolites

Question 40.
Match the List-I and List-Il using the code given below the list. List-I
A. Heavy water
B. Hydrogen peroxide
C. Heavy hydrogen
D. Lithium Aluminium hydride
List-Il
1. Antiseptic
2. Moderator
3. Reducing agent
4. Tracer

Answer:
(b) 213
Question 41.
Consider the following statements.
(i) $\mathrm{H}_2 \mathrm{O}_2$ is a powerful oxidising agent.
(ii) $\mathrm{H}_2 \mathrm{O}_2$ is stored in dark coloured bottles
(iii) $\mathrm{H}_2 \mathrm{O}_2$ is used as moderator in nuclear reactors.
Which of the above statements is/are not correct.
(a) (i) only
(b) (i) and (ii)
(c) (iii) only
(d) (i), (ii) and (iii)
Answer:
(c) (iii) only
Question 42.
Statement-I: Heavy water has been widely used as moderator in nuclear reactors.
Statement-Il: Heavy water can lower the energies of fast moving neutrons.
(a) Statements-I and II are correct and Statement-Il is the correct explanation of statement-I.
(b) Statements-I and II are correct but Statement-IT is not the correct explanation of statement-I;
(c) Statement-I is correct but Statement-Il is wrong.
(d) Statement-I is wrong but Statement-Il is correct.
Answer:
(a) Statements-I and II are correct and Statement-Ills the correct explanation of statement-I.
Question 43.
Which one of the following is prepared in industry by the auto oxidation of 2-alkylanthraquional?
(a) Heavy water
(b) Deuterium
(c) Hydrogen peroxide
(d) Tritium
Answer:
(c) Hydrogen peroxide
Question 44.
Which one of the following is an ionic or saline hydride?
(a) $\mathrm{SiH}_4$
(b) $\mathrm{GeH}_4$
(c) $\mathrm{B}_2 \mathrm{H}_6$

(c) $\mathrm{LiH}$
Answer:
(d) $\mathrm{LiH}$
Question 45 .
Which one of the following is an electron deficient hydride?
(a) $\mathrm{C}_2 \mathrm{H}_6$
(b) $\mathrm{B}_2 \mathrm{H}_6$
(c) $\mathrm{GeH}_4$
(d) $\mathrm{CH}_4$
Answer:
(b) $\mathrm{B}_2 \mathrm{H}_6$
Question 46.
Which of the following pair is an electron rich hydride?
(a) $\mathrm{NH}_3, \mathrm{H}_2 \mathrm{O}$
(b) $\mathrm{CH}_4, \mathrm{C}_2 \mathrm{H}_6$
(c) $\mathrm{B}_2 \mathrm{H}_6, \mathrm{GeH}_4$
(d) $\mathrm{CH}_4, \mathrm{SiH}_4$
Answer:
(a) $\mathrm{NH}_3, \mathrm{H}_2 \mathrm{O}$
Question 47.
Which one of the following is not a covalent hydride?
(a) Ammonia
(b) Methane
(c) Lithium hydride
(d) water
Answer:
(e) Lithium hydride
Question 48.
Metallic hydrides are otherwise called
(a) Salt hydrides
(b) Saline hydrides
(c) molecular hydrides
(d) Interstitial hydrides
Answer:
(d) Interstitial hydrides
Question 49.
Which one of the following is used for hydrogen storage applications?
(a) Saline hydrides

(b) Interstitial hydrides
(c) covalent hydrides
(d) molecular hydrides
Answer:
(b) Interstitial hydrides
Question 50 .
Which one of the following is known as Hydrogen sponge?
(a) Lithium hydride
(b) Diborane
(c) Palladium hydride
(d) Ammonia
Answer:
(c) Palladium hydride
Question 51.
Which of the following is the correct order of stability of bonds?
(a) Hydrogen bond $<$ CovaLent bond $<$ Vanderwaals bond
(b) Vanderwaals bond $<$ Hydrogen bond $<$ Covalent, bond
(c) Vanderwaals bond $>$ Hydrogen bond $>$ Covalent bond
(d) Covalent bond $<$ Hydrogen bond $<$ Vanderwaals bond
Answer:
(b) Vanderwaals bond $<$ Hydrogen bond $<$ Covalent, bond
Question 52 .
Which one of the following does not have intramolecular hydrogen bonding?
(a) water
(b) o-nitrophenol
(c) Salicylaldehyde
(d) Salicylic acid
Answer:
(a) water

Question 53.
Which of the following contains intramolecular hydrogen bonding?
(a) Acetic acid
(b) o-nitrophenol
(c) Hydrogen fluoride
(d) water
Answer:
(b) o-nitrophenol
Question 54.
Consider the following statements.
(i) In ice, each oxygen atom is surrounded by hydrogen atoms tetrahedrally to four water molecules.
(ii) Acetic acid exists as dimer due to intra molecular hydrogen bonding.
(iii) Strong hydrogen bonds lead to an increase in the melting and boiling points.
Which of the above statements is/are not correct?
(a) (ii) only
(b) (i) and (iii)
(c) (i) (ii) and (iii)
(d) (i) only
Answer:
(a) (ii) only

Question 55.
Which one of the following is an example for Clatharate hydrate?
(a) $\mathrm{CuSO}_4 \cdot 5 \mathrm{H}_2 \mathrm{O}$
(b) $\mathrm{Na}_2 \mathrm{CO}_3 \cdot 10 \mathrm{H}_2 \mathrm{O}$
(c) $\mathrm{CH}_4 \cdot 20 \mathrm{H}_2 \mathrm{O}$
(d) $\mathrm{FeSO}_3 \cdot 7 \mathrm{H}_2 \mathrm{O}$
Answer:
(c) $\mathrm{CH}_4 \cdot 20 \mathrm{H}_2 \mathrm{O}$
Question 56.
Which one of the following is not a crystalline hydrate?
(a) $\mathrm{CH}_4 \cdot 20 \mathrm{H}_2 \mathrm{O}$
(b) $\mathrm{Na}_2, \mathrm{CO}_3 \cdot 10 \mathrm{H}_2 \mathrm{O}$
(c) $\mathrm{CuSO}_4 \cdot 5 \mathrm{H}_2 \mathrm{O}$
(d) $\mathrm{FeSO}_4 \cdot 7 \mathrm{H}_2 0$
Answer:
(a) $\mathrm{CH}_4 \cdot 20 \mathrm{H}_2 \mathrm{O}$
Question 57.
Statement-I: Hydrogen can be used as a clean burning fuel.
Statement-II: Hydrogen on combustion give only water as end product and it is free from pollutants.
(a) Statements-I and li are correct and Statement-lI is the correct explanation of statement-I.
(b) Statements-I and II are correct but Statement-Il is not the correct explanation of statement-I.
(e) Statement-I is correct but Statement-Il is wrong.
(d) Statement-I is wrong but Statement-II is correct.
Answer:
(a) Statements-I and II are correct and Statement-Il is the correct explanation of statement-I.
Question 58.
Which isotope of hydrogen is radioactive?
(a) Protium
(b) Deuterium
(c) Tritium
(d) $\mathrm{H}$
Answer:
(c) Tritium
Question 59.
Which type of elements form interstitial hydrides
(a) s-block and p-block

(b) p-block only
(c) d-block and f-block
(d) s-block only
Answer:
(c) d-block and f-block
Question 60 .
Which of the following is named as perhydrol and used as an antiseptic?
(a) $\mathrm{D}_2 \mathrm{O}$
(b) $\mathrm{H}_2 \mathrm{O}_2$
(c) $\mathrm{NaH}$
(d) $\mathrm{B}_2 \mathrm{H}_6$
Answer:
(b) $\mathrm{H}_2 \mathrm{O}_2$
Question 61 .
Which of the following causes temporary hardness of water?
(a) $\mathrm{MgCl}_2$
(b) $\mathrm{Na}_2 \mathrm{SO}_4$
(c) $\mathrm{Mg}\left(\mathrm{HCO}_3\right)_2$
(d) $\mathrm{NaCl}$
Answer:
(c) $\mathrm{Mg}\left(\mathrm{HCO}_3\right)_2$
Question 62 .
Which of the following can oxidise Hydrogen peroxide?
(a) acidified $\mathrm{KMnO}_4$
(b) $\mathrm{Cu}$
(c) dil. $\mathrm{HNO}_4$
(d) $\mathrm{CrO}_2 \mathrm{Cl}_2$
Answer:
(a) acidified $\mathrm{KMnO}_4$
Question 63.
Which type of hydrides are generally non-stoichiometric in nature?
(a) Metallic hydride
(b) Covalent hydrides
(c) Ionic hydride
(d) Saline hydride
Answer:
(a) Metallic hydride

Question 64.
Hydrogen gas is generally prepared by the
(a) reaction of granulated zinc with dilute $\mathrm{H}_2 \mathrm{SO}_4$
(b) reaction of zinc with cone, $\mathrm{H}_2 \mathrm{SO}_4$
(c) reaction of pure zinc with dil. $\mathrm{H}_2 \mathrm{SO}_4$
(d) action of stream on red hot coke
Answer:
(a) reaction of granulated zinc with dilute $\mathrm{H}_2 \mathrm{SO}_4$
Question 65 .
The higher density of water than that of ice is due to
(a) dipole-dipole interaction
(b) dipole-induced dipole interaction
(c) hydrogen bonding
(d) all of these
Answer:
(c) hydrogen bonding
Question 66.
Hydrogen resembles halogens in many respects for which several factors are responsible. Of the following factors which one is most important in this respect?
(a) Its tendency to lose an electron to form a cation.
(b) Its tendency to gain an electron to attain stable electronic configuration.
(c) Its low negative electron gain enthalpy value.
(d) Its small size.
Answer:
(b) Its tendency to gain an electron to attain stable electronic configuration.

Question 67.
Metal hydrides are ionic, covalent or molecular in nature. Among $\mathrm{L} 1 \mathrm{H}, \mathrm{NaH}, \mathrm{KH}, \mathrm{RbH}, \mathrm{CsH}$, the correct order of increasing ionic character is
(a) $\mathrm{LiH}>\mathrm{NaH}>\mathrm{CsH}>\mathrm{KH}>\mathrm{RbH}$
(b) $\mathrm{LiH}<\mathrm{NaH}<\mathrm{KH}<\mathrm{RbHCsH}>\mathrm{NaH}>\mathrm{Kil}>\mathrm{LIH}$
(d) $\mathrm{NaH}>\mathrm{CsH}>\mathrm{RbH}>\mathrm{LiH}>\mathrm{KH}$
Answer:
(b) $\mathrm{LiH}<\mathrm{NaH}<\mathrm{KH}<\mathrm{RbH}<\mathrm{CsH}$
Question 68 .
Statement-I: Permanent hardness of water is removed by treatment with washing soda ........... Statement-II: Washing soda reacts with soluble magnesium and calcium sulphate to form insoluble carbonate.
(a) Statements-I and II are correct and Statement-Il is the correct explanation of statement-I.
(b) Statements-I and II are correct but Statement-Il is not the correct explanation of statement-I.
(c) Statement-I is correct but Statement-II is wrong.
(d) Statement-I is wrong but Statement-II is correct.
Answer:
(a) Statements-I and II are correct and Statement-Ills the correct explanation of statement-I.
Question 69.
Which of the following is a saline hydride?
(a) $\mathrm{HCl}$
(b) $\mathrm{NH}_3$
(c) $\mathrm{NaH}$
(d) $\mathrm{PbH}$
Answer
(e) $\mathrm{NaH}$

Question 70.
Which metal does not liberate $\mathrm{H}_2$ gas from dilute aqueous hydrochloric acid at $298 \mathrm{~K}$ ?
(a) $\mathrm{Mg}$
(b) $\mathrm{Zn}$
(c) $\mathrm{Al}$
(d) $\mathrm{Cu}$
Answer:
(d) $\mathrm{Cu}$
Question 71.
When zeolite is treated with hard water, the sodium ions are exchanged with
(a) $\mathrm{H}^{+}$ions and $\mathrm{Cl}^{-}$ions
(b) $\mathrm{Ca}^{2+}$ ions
(c) $\mathrm{Cl}^{-}$ions
(d) $\mathrm{Ca}^{2+}$ ions and $\mathrm{Mg}^{2+}$ ions
Answer:
(d) $\mathrm{Ca}^{2+}$ ions and $\mathrm{Mg}^{2+}$ ions
Question 72.
The most abundant element in the universe is
(a) Carbon
(b) Nitrogen
(c) Silicon
(d) Hydrogen
Answer:
(d) Hydrogen
Question 73.
Which of the following can effectively remove all types of hardness of water?
(a) Soap
(b) Slaked lime
(c) Washing soda
(d) Zeolite
Answer:
(a) Soap
Question 74.
A commercial sample of $\mathrm{H}_2 \mathrm{O}_2$ is labelled as 100 volume. Its percentage strength is nearly
(a) $10 \%$

(b) $30 \%$
(c) $100 \%$
(d) $90 \%$
Answer:
(b) $30 \%$
Question 75.
Which of the following will not produce di hydrogen gas?
(a) $\mathrm{Cu}+\operatorname{dil}(\mathrm{HCl})$
(b) $\mathrm{CH}_{2(\mathrm{~g})}+\mathrm{H}_2 \mathrm{O}_{(\mathrm{g})}$
(c) $\mathrm{Zn}+$ dil. $\mathrm{HCl}$
(cl) $\mathrm{C}_{(\mathrm{s})}+\mathrm{H}_2 \mathrm{O}_{(\mathrm{g})}$
Answer:
(a) $\mathrm{Cu}+\operatorname{dil}(\mathrm{HCl})$
2-Mark Questions
Question 1.
Draw and define ortho and para hydrogen molecule.
Answer:
Molecular hydrogen have oriho and para form in which the nuclear spins are aligned or opposed, respectively.

Question 2.
What is the nuclear reaction that take place in the sun and other stars?
Answer:
The sun and other stars are composed mainly of $85-95 \%$ hydrogen which generates their energy by nuclear fusion of hydrogen nuclei into helium.
Question 3.
Mention the uses of tritium.
Answer:
- Tritium has replaced radium in application such as emergency exit sign.
- Tritium is used in illumination of wrist watches.
Question 4.
Draw the structures of three isotopes of hydrogen, Hydrogen Deuterium
Answer:

Question 5 .
What is the half life period of tritium? How is it undergoes radioactive disintegration? Answer:
- The half life of tritium $=12.33$ years.
- Tritium is a beta-emitting radioactive isotope of hydrogen. ${ }_1^3 \mathrm{H} \rightarrow{ }_{-1}^0 \mathrm{e}+{ }_2^3 \mathrm{He}$
Question 6.
Why hydrogen gas is used as fuel?
Answer:
Hydrogen burns in air, virtually free from pollution and produces significant amount of energy. This reaction is used in fuel cells to generate electricity.
$
2 \mathrm{H}_{2(\mathrm{~g})}+\mathrm{O}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{H}_2 \mathrm{O}_{(1)}+\text { energy }
$
Question 7.
How ammonia is manufactured from Hydrogen? Give the uses of ammonia. Answer:
- Ammonia is manufactured by Habe?s prôcess in which the largest consumer of hydrogen is used.
$
\mathrm{N}_{2(\mathrm{~g})}+3 \mathrm{H}_{2(\mathrm{~g})} \rightleftharpoons 2 \mathrm{NH}_3(\mathrm{~g})
$
- Ammonia is employed for the manufacture of nitric acid, fertilizers and explosives.
Question 8 . how is methanol synthesized from hydrogen? Give the uses of methanol. Answer:
- Huge quantities of hydrogen are used for the synthesis of methanol from carbon monoxide in presence of copper catalyst.
$
\mathrm{CO}_{(\mathrm{g})}+2 \mathrm{H}_{2(\mathrm{~g})} \rightarrow \mathrm{CH}_3 \mathrm{OH}_{(1)}
$
- Methanol is an industrial solvent and a starting material for the manufacture of formaldehyde used in makihg plastics.
Question 9.
What is hydrogenation? Give one example.
Answer:
Hydrogenation is a reaction in which addition of hydrogen to an alkene /alkyne. Compounds containing multiple bonds.

Question 10.
How is hydrogen used in metallurgy? Prove it with an example.
Answer:
In metallurgy, for the extraction of pure metals from their mineral sources, hydrogen is used to reduce many metal oxides to metals at high temperatures.
$
\mathrm{CuO}_{(\mathrm{s})}+\mathrm{H}_{2(\mathrm{~g})} \rightarrow \mathrm{Cu}_{(\mathrm{s})}+\mathrm{H}_{(2)} \mathrm{O}_{(\mathrm{g})}
$
Question 11.
How alkali metals react with water? Give an equation?
Answer:
The most reactive alkali metals decompose water in the cold with the evolution of hydrogen and leaving an alkali solution.
$
2 \mathrm{Na}_{(\mathrm{s})}+2 \mathrm{H}_2 \mathrm{O}_{(\mathrm{l})} \rightarrow 2 \mathrm{NaOH}_{(\mathrm{aq})}+\mathrm{H}_{2(\mathrm{~g})}
$
Question 12.
What happens when steam is passed over red hot iron?
Answer:
When steam is passed over red hot iron, iron oxide will be formed with the release of hydrogen.
$
3 \mathrm{Fe}_{(\mathrm{s})}+4 \mathrm{H}_2 \mathrm{O}_{(1)} \rightarrow \mathrm{Fe}_3 \mathrm{O}+4 \mathrm{H}_4(\mathrm{~g})
$
Question 13.
Explain the action of chlorine with water.
Answer:
Chlorine reacts with the water to form hydrochloric acid and hypochiorous acid.
$
\mathrm{Cl}_{2(\mathrm{~g})}+\mathrm{H}_2 \mathrm{O}_{(\mathrm{l})} \rightarrow \mathrm{HCl}_{(\mathrm{aq})}+\mathrm{HOCl}_{(\mathrm{aq})}
$
Question 14.
What is temporary hardness of water? How is it removed?
Answer:
Temporary hardness of water is due to the presence of soluble bicarbonates of magnesium and calcium. By heating / boiling, these salts decomposed into insoluble carbonate and hydroxide, respectively. The resulting precipitates can be removed by filtration.
$
\begin{aligned}
& \mathrm{Ca}\left(\mathrm{HCO}_3\right)_{2(\mathrm{aq})} \rightarrow \mathrm{CaCO}_3+\mathrm{s}_2 \mathrm{O}_{(\mathrm{l})}+\mathrm{CO}_2(\mathrm{l}) \\
& \mathrm{Mg}\left(\mathrm{HCO}_3\right)_{2(\mathrm{aq})} \rightarrow \mathrm{Mg}(\mathrm{OH})_{2(\mathrm{~s})}+\mathrm{CO}_2(\mathrm{~g})
\end{aligned}
$
Question 15.
What is permanent hardness of water? How $j t$ will be removed?
Answer:
Permanent hardness of water is due to the presence of soluble salts of magnesium and calcium in the form of chlorides and suiphates in water. It can be removed by adding washing soda which reacts with these metal chlorides and suiphates in hard water to form insoluble carbonates.
Where $\mathrm{M}=\mathrm{Ca}$ or $\mathrm{Mg}$.
Question 16.
How would you prepare Hydrogen peroxide?
Answer:
Hydrogen peroxide can be prepared by adding a metal peroxide to dilute acid.
$
\mathrm{BaO}_{2(\mathrm{~s})}+\mathrm{H}_2 \mathrm{SO}_{4(\mathrm{aq})} \rightarrow \mathrm{BaSO}_{4(\mathrm{~s})}+\mathrm{H}_3 \mathrm{O}_{2(\mathrm{aq})}
$
Question 17.
$\mathrm{H}_2 \mathrm{O}_2$ is always stored in plastic bottles. Why?
Answer:
The aqueous solution of hydrogen peroxide is spontaneously disproportionate to give oxygen. The reaction is slow but it is explosive when it is catalyzed by metal or alkali dissolved from glass. For this reason, its solution are stored in plastic bottles.
$
\mathrm{H}_2 \mathrm{O}_{2(\mathrm{aq})} \rightarrow \mathrm{H}_2 \mathrm{O}_{(1)}+1 / 2 \mathrm{O}_2(\mathrm{~g})
$
Question 18.
Why $\mathrm{H}_2 \mathrm{O}_2$ is used as mild antiseptic?
Answer:
The oxidising property of hydrogen peroxide and harmless nature of its products such as water and oxygen, leads to oxidation of pollutants in water and act as a mild antiseptic.
Question 19.
Why the bond angle in solid phase of $\mathrm{H}_2 \mathrm{O}_2$ is reduced when compared to gas phase of $\mathrm{H}_2 \mathrm{O}_2$ ?
Answer:
Both the gas phase and solid phase, $\mathrm{H}_2 \mathrm{O}_2$ adopt a skew configuration due to the repulsive interaction of the $\mathrm{OH}$ bonds with lone pairs of electrons on each oxygen atoms. Indeed, it is the smallest molecule known to show hindered rotation about a single bond. In the solid phase, the dihedral angle is sensitive and hydrogen bonding decreases from 111.50 in the gas phase to 90.2 in the solid phase.
Question 20.
What is meant by 100 - volume hydrogen peroxide?
Answer:
A $30 \%$ solution is marketed as 100 - volume hydrogen peroxide indicating that at STP, 100 volumes of oxygen are liberated per millimeter of the solution.
Question 21.
Prove that Hydrogen peroxide is a vigorous oxidizing agent and the solution of $\mathrm{H}_2 \mathrm{O}_2$ is slightly acidic.
Answer:
$
\mathrm{H}_2 \mathrm{O}_{2(\mathrm{aq})}+2 \mathrm{H}_2 \mathrm{O}_{(1)} \rightleftharpoons \mathrm{H}_3 \mathrm{O}_{(\mathrm{aq})}^{+}+\mathrm{HO}_2^{+}{ }_{(\mathrm{aq})}
$
$\mathrm{H}_3 \mathrm{O}^{+}$Hydronium ion formation proves that solution of $\mathrm{H}_2 \mathrm{O}_2$ is acidic. Because it donates $\mathrm{H}^{+}$to $\mathrm{H}_2 \mathrm{O}$ to form $\mathrm{H}_3 \mathrm{O}^{+}$ion.
$\mathrm{H}_2 \mathrm{O}_2$ oxidizes Ferrous sulphate to Ferric sulphate in acidic medium.
Question 22.
What is meant by binary hydride? Give example.
Answer:
A binary hydride is a compound formed by hydrogen with other electropositive elements including metals and non-metals, e.g., $\mathrm{LiH}$ or $\mathrm{MgH}_2$.
Question 23.
What are ternary hydrides? Give example?
Answer:
Ternary hydrides are compounds in which the molecule is constituted by hydrogen and two types of elements, e.g., $\mathrm{LiBH}_4$ or $\mathrm{LiAlH}_4$.

Question 24.
What arc the different types of hydrides?
Answer:
The hydrides are classified as Ionic, Covalent and Metallic Hydrides.
Ionic hydride $-\mathrm{LiH}$
Covalent hydride $-\mathrm{CH}_4$
Metallic hydride - $\mathrm{TiH}$
Question 25.
Why metallic hydrides are called interstitial hydrides? Give one example.
Answer:
Metallic hydrides are usually obtained by hydrogenation of metals and alloys in which hydrogen occupies the interstitial sites (voids). Hence, they are called interstitial hydrides. e.g., $\mathrm{PdH}$.
Question 26.
What is hydrogen bonding?
Answer:
When a hydrogen atom $(\mathrm{H})$ is covalently bonded to a highly electronegative atom such as fluorine (F) or oxygen $(\mathrm{O})$ or nitrogen $(N)$, the bond is polarized in such a way that the hydrogen atom is able to form a weak bond between the hydrogen atom of a molecule and the electronegative atom of a second molecule. The bond thus formed is a hydrogen bond and it is denoted by dotted lines $(\ldots \ldots)$
Question 27.
What are the types of hydrogen bonding? Give example.
Answer:
There are two types of hydrogen bonding.
- Intramolecular hydrogen bonding: It can occur with a molecule. e.g., o-nitrophenol.
- Intermolecular hydrogen bonding: It is formed between two molécules of same type or different type. e.g., $\mathrm{H}_2 \mathrm{O}$.

Question 28 .
Explain about the type of bonding present in hydrogen fluoride?
Answer:
In hydrogen fluoride (HF), for example, one molecule is strongly attracted to the fluorine on its neighboring hydrogen. In both liquid and solid, hydrogen fluoride forms long hydrogen bonded zig-zag chains as a consequence of the orientation of the lone pairs on the fluorine atoms.

Question 29.
Ice is less dense than water at $0^{\circ} \mathrm{C}$. Justify this statement.
Answer:
In ice, each oxygen atom is surrounded tetrahedrally by through hydrogen bonds to four water molecules. That is, the presence of two hydrogen atoms and two lone electron pairs (on oxygen) in each water molecule results in a three - dimensional structure. The arrangements creates an open structure, which in turn accounts for the fact that ice is less dense than water at $0^{\circ} \mathrm{C}$.
Question 30.
Draw the structure of -
1. Acetic acid
2. Water.
Answer:
1. Acetic acid:

2. Water: 

Question 31.
Write a note about gas hydrates.
Answer:
Gas hydrates are a kind of inclusion compounds, where gas molecules arc trapped in the crystal lattice having voids of right size, without being chemically bonded. An interesting hydrate is that of the hydronium ion $\left(\mathrm{H}_2 \mathrm{O}\right)$ in the gas-phase, similar to methane hydrate. Each water molecule is bonded to three others in the dodecahedron.
Question 32.
Give the advantages of future fuel - Hydrogen.
Answer:
Hydrogen is considered as a potential candidate for this purpose as it is a clean burning fuel. Hence, hydrogen can directly be used as a fuel and can replace existing gasoline (petrol) diesellkerosene powered engines, and indirectly be used with oxygen in fuel cells to generate electricity. One major advantage of using hydrogen is that the combustion product is essentially free from pollutants; the end product formed in both cases is water.
Question 33.
What do you understand by the term non-stoichiometric hydrides'? Do you expect this type of hydrides to be formed by alkali metals? Justify your answer.
Answer:
Those hydrides which do not have fixed composition are called non-stoichiometric hydrides, and the composition varies with temperature and pressure. This type of hydrides are formed by $\mathrm{d}$ and f-block elements. They cannot be formed by alkali metals because alkali thetal hydrides form ionic hydrides.
Question 34.
How does the atomic hydrogen or oxy - hydrogen torch function for cutting and welding purposes? Explain.
Answer:
When hydrogen is burnt in oxygen the reaction is highly exothermic, it produces very high temperature nearly $4000^{\circ} \mathrm{C}$ which is used for cutting and welding purposes.

Question 35.
How does $\mathrm{H}_2 \mathrm{O}_2$ behave as bleaching agent?
Answer:
Bleaching action of $\mathrm{H}_2 \mathrm{O}_2$ is due to the oxidation of colouring matter by nascent oxygen.
$
\mathrm{H}_2 \mathrm{O}_2 \rightarrow \mathrm{H}_2 \mathrm{O}_{(\mathrm{l})}+\mathrm{O}_{(\mathrm{g})}
$
Question 36.
Can we use concentrated sulphuric acid and pure zinc in the preparation of dihydrogen?
Answer:
Cone. $\mathrm{H}_2 \mathrm{SO}_4$ cannot be used because it acts as an oxidizing agent also and gets reduced to $\mathrm{SO}_2$ $\mathrm{Zn}+2 \mathrm{H}_2 \mathrm{SO}_4$ (Conc.) $\rightarrow \mathrm{ZnSO}_4+2 \mathrm{H}_2 \mathrm{O}+\mathrm{SO}_2$
Pure $\mathrm{Zn}$ is not used because it is non-porous and reaction will be slow. The impurities in $\mathrm{Zn}$ help in constitute of electrochemical couple and speed up reaction.
Question 37.
Write the chemical reactions to show the amphoteric nature of water.
Answer:
Water is amphotenc in nature and it behaves both as an acid as well as base. With acids stronger than itself (e.g., $\mathrm{H}_2 \mathrm{~S}$ ) it behaves as a base and with bases stronger than itself (e.g., $\left.\mathrm{NH}_3\right)$ it acts as an acid
1. As a base $: \mathrm{H}_2 \mathrm{O}_{(1)}+\mathrm{H}_2 \mathrm{~S}_{(\mathrm{aq})} \rightarrow \mathrm{H}_3 \mathrm{O}_{(\mathrm{aq})}+\mathrm{HS}^{-}{ }_{(\mathrm{aq})}$
2. As an acid : $\mathrm{H}_2 \mathrm{O}_{(\mathrm{l})}+\mathrm{NH}_{3(\mathrm{aq})} \rightarrow \mathrm{OH}_{(\mathrm{aq})}^{-}+\mathrm{NH}_4^{+}{ }_{(\mathrm{aq})}$
Question 38 .
Why is hydrogen peroxide stored in wax-lined plastic coloured bottles?
Answer:
The decomposition of $\mathrm{H}_2 \mathrm{O}_2$ occurs readily in the presence of rough surface (acting as catalyst). It is also decomposed by exposure of light. Therefore, wax-lined smooth surface and coloured bottles retard the decomposition of $\mathrm{H}_2 \mathrm{O}_2$.
3 - Mark Questions
Question 1.
Compare the properties of ortho and para hydrogen.
Answer:

Question 2.
Compare the properties of isotopes of hydrogen

Answer:

Question 3.
Draw the structure of the isotopes of hydrogen and distinguish them.
Answer:

Question 4.
Explain the different methods of preparation of Tritium with equation.
Answer:
It occurs naturally as a result of nuclear reactions induced by cosmic rays in the upper atmosphere.
${ }_7^{14} \mathrm{~N}+{ }_0^1 \mathrm{n} \rightarrow{ }_6^{12} \mathrm{C}+{ }_1^3 \mathrm{H}$
${ }_1^2 \mathrm{H}+{ }_1^2 \mathrm{H} \rightarrow{ }_1^3 \mathrm{H}+{ }_1^1 \mathrm{H}$
${ }_3^6 \mathrm{Li}+{ }_0^1 \mathrm{n} \rightarrow{ }_2^4 \mathrm{He}+{ }_1^3 \mathrm{H}$
Question 5.
How would you prepare hydrogen in the laboratory?
Answer:
Small amounts of hydrogen are conveniently prepared in laboratory by the reaction of metals, such as zinc, iron and tin, with dilute acid.
$
\mathrm{Zn}_{(\mathrm{s})}+2 \mathrm{HCl}_{(\mathrm{aq})} \rightarrow \mathrm{ZnCl}_2(\mathrm{~s})+\mathrm{H}_2(\mathrm{~g})
$
In principle, any metal with a negative standard reduction potential will react with an acid to generate hydrogen.

Question 6.
What happens when hydrogen reacts with -
1. $\mathrm{O}_2$
2. $\mathrm{Cl}_2$
3. $\mathrm{Na}$ ?
Answer:
1. $2 \mathrm{H}_{2(\mathrm{~g})}+\mathrm{O}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{H}_2 \mathrm{O}_{(\mathrm{l})}$ - Water
2. $\mathrm{H}_{2(\mathrm{~g})}+\mathrm{Cl}_{2_{(\mathrm{g})}} \rightarrow 2 \mathrm{HCl}_{(\mathrm{g})}-$ Hydrogen Chloride
3. $2 \mathrm{Na}_{(\mathrm{s})}+\mathrm{H}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{NaH}_{(\mathrm{s})}$-Sodium hydride
Question 7.
Write a note about ortho water and para water.
Answer:
1. Water exists in space in the interstellar clouds, in proto-planetary disks, in the comets and icy satellites of the solar system, and on the Earth.
2. In particular, the ortho-to-para ratio (OPR) of water in space has recently received attention. Like hydrogen, water can also be classified into ortho- $\mathrm{H}_2 \mathrm{O}$ and para- $\mathrm{H}_2 \mathrm{O}$, in which the directions are antiparallel.

3. At the temperature conditions of the Earth ( $300 \mathrm{~K})$, the OPR of $\mathrm{H}_2 \mathrm{O}$ is 3 .
4. At low temperatures below $(<50 \mathrm{~K})$ the amount of para- $\mathrm{H}_2 \mathrm{O}$ increases. It is known that the OPR of water in interstellar clouds and comets has more para- $\mathrm{H}_2 \mathrm{O}(\mathrm{OPR}=2.5)$ than on Earth.
Question 8.
Water $i$ s an amphoteric oxide. Justify this statement.
Answer:
1. Water is an amphoteric oxide. It has the ability to act an acid as well as a base. That is, water shows this behavior when it reacts with hydrogen chloride and ammonia.
2. When water reacts with ammonia, it behaves as an acid.

3. When water reacts with hydrogen chloride, behaves as a base.

So water is an amphoteric oxide.
Question 9.
Distinguish between Hard water and Soft water.
Answer:
Hard water:
- Presence of magnesium and calcium in the form of bicarbonate, chloride and sulphate in water makes hard water.
- Cleaning capacity of soap is rcduced when used in hard water.
- When hard water is boiled deposits of insoluble carbonates of magnesium and calcium are obtained.
Soft water:
- Presence of soluble salts of calcium and magnesium in water makes it soft water.
- Cleaning capacity of soap is more when used in soft water.
- When soft water is boiled, there is no deposition of salts.
Question 10.
Explain the action of soap with hard water.
Answer:
- The cleaning capacity of soap is reduced when used in hard water.
- Soaps are sodium or potassium salts of long chain fatty acids.
- When soap is added to hard water, the divalent magnesium and calcium cations present in hard water react with soap.
- The sodium salts present in soaps are converted to their corresponding magnesium and calcium salts which are precipitated as scum or precipitate.
$
\mathrm{M}^{2+}+2 \mathrm{RCOONa}(\mathrm{RCOO})_2 \mathrm{M}_{(\mathrm{s})}+2 \mathrm{Na}_{(\mathrm{aq})}{ }^{+}
$
Where, $\mathrm{M}$ Ca or $\mathrm{Mg}$;
$
\mathrm{R}=\mathrm{C}_{17} \mathrm{H}_{35} \text {. }
$

Question 11.
Describe about ion exchange method of softening water (or) Explain Zeolite (or) Permutit process.

Answer:
1. Hardness can be removed by passing through an ion-exchange bed like zeohtes or resin containing column. Thus, the zeolites work as water softener.
2. Zeolites are hydrated sodium alumini-silicates with a general formula, $\mathrm{NaO} \cdot \mathrm{Al}_2 \mathrm{O}_3 \cdot \mathrm{xiO}_2 \cdot \mathrm{yH}_2 \mathrm{O}(\mathrm{x}=2-10, \mathrm{y}=2-6)$. They have high ion exchange capacity.
3. The complex structure can represented as $\mathrm{Na}_2-\mathrm{Z}$ with sodium as exchangeable cations. This method is called zeolite or permutit process.
4. Zeolites have porous structure in which the monovalent sodium ions are loosely held and can be exchanged with hardness producing divalent metal ions (Ca or $\mathrm{Mg}$ ) in water.

$
\mathrm{Na}_2-\mathrm{Z}_{\text {(s) }}+\mathrm{M}^{2+} \text { (aq) } \rightarrow \mathrm{M}-\mathrm{Z}_{\text {(s) }}+2 \mathrm{Na}^{+} \text {(aq) }
$
5. When exhausted, the materials can be regenerated by treating with aqueous sodium chloride. Hard minerals caught in the zeolite are released and they get replenished with sodium ions.

$
\mathrm{M}-\mathrm{Z}_{(\mathrm{s})}+2 \mathrm{NaCl}_{(\mathrm{aq})} \rightarrow \mathrm{Na}(\mathrm{s})-\mathrm{Z}_{(\mathrm{s})}+\mathrm{MCl}_{2(\mathrm{aq})}
$
Question 12.
Explain about the exchange reactions of deuterium oxide.
Answer:
When compounds containing hydrogen are treated with $\mathrm{D}_2 \mathrm{O}$, hydrogen undergoes an exchange for Deuterium.

Question 13.
Complete the following reactions.
$
\mathrm{A1}_4 \mathrm{C}_3+\mathrm{D}_2 \mathrm{O} \rightarrow \text { ? }
$
$\mathrm{CaC}_2+\mathrm{D}_2 \mathrm{O} \rightarrow ?$

$\mathrm{Mg}_3 \mathrm{~N}_2+\mathrm{D}_2 \mathrm{O} \rightarrow ?$

$\mathrm{Ca}_3 \mathrm{P}_2+\mathrm{D}_2 \mathrm{O} \rightarrow \text { ? }$

Answer:

Question 14.
What are the uses of hydrogen peroxide?
Answer:
- $\mathrm{H}_2 \mathrm{O}_2$ is used in water treatment to oxidize pollutants.
- $\mathrm{H}_2 \mathrm{O}_2$ is used as a mild antiseptic.
- $\mathrm{H}_2 \mathrm{O}_2$ is used as a bleach in textile, paper and hair-care industry.
Question 15.
Prove that $\mathrm{H}_2 \mathrm{O}_2$ act as reducing agent $i \mathrm{n}$ alkaline medium.
Answer:
In alkaline conditions, $\mathrm{H}_2 \mathrm{O}_2$ act as a reducing agent.
$
\begin{aligned}
& 2 \mathrm{KMnO}_{4(\mathrm{aq})}(\text { Potassium permanganate })+3 \mathrm{H}_2 \mathrm{SO}_{4(\mathrm{aq})}+5 \mathrm{H}_2 \mathrm{O}_{2(\mathrm{aq})} \rightarrow \mathrm{K}_2 \mathrm{SO}_4+2 \mathrm{MnSO}_4+8 \mathrm{H}_2 \\
& \mathrm{O}_{(\mathrm{l})}+5 \mathrm{O}_{2(\mathrm{~g})}
\end{aligned}
$
Question 16.
Write a note about saline (or) ionic hydride.
Answer:
Ionic hydrides composed of an electropositive metal, generally, an alkali or alkaline-earth metal (except beryllium and magnesium) formed by transferring of electrons from metal to hydrogen atoms. They can be prepared by the reaction of elements at about $400^{\circ} \mathrm{C}$. These are salt-like, highmelting, white, crystalline solids having hydride ions $\left(\mathrm{H}^{-}\right)$and metal cations $\left(\mathrm{M}^{\mathrm{n+}}\right)$.
$2 \mathrm{Li}_{(\mathrm{s})}+\mathrm{H}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{LiH}_{(\mathrm{s})}(\mathrm{Lithiuinhydride)}$
$2 \mathrm{Ca}_{(\mathrm{s})}+\mathrm{H}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{CaH}_{2(\mathrm{~s})}($ Calcium hydride $)$

Question 17.
What are metallic hydrides? Explain about it.
Answer:
- Metallic hydrides are obtained by hydrogenation of metals and alloys in which hydrogen occupies the interstitial sites (voids). Hence, they are called interstitial hydrides.
- The hydrides show properties similar to parent metals and hence they are also known as metallic hydrides.
- They arc mostly non-stoichiometric with variable composition ( $\mathrm{TiH}_{1.5-1.8} 18$ and $\mathrm{PdH}_{0.6}$ 0.8 )
- Some are relatively light, inexpensive and thermally unstable which makes them useful for hydrogen storage applications. Example, $\mathrm{TiH}_2, \mathrm{ZrH}_2, \mathrm{ZnH}_2$.
Question 18 .
What are intra molecular hydrogen bonding? Explain with an example.
Answer:
1. Intramolecular hydrogen bonds are those which occur within one single molecule. This occurs between two functional groups within a molecule.

2. An intramolecular hydrogen bond (dashed lines) joins the $\mathrm{OH}$ group to the doubly bonded oxygen atom of the carboxyl group on the same molecule. e.g., Salicylic acid.

3. Salicylic acid act as an analgesic and antipyretic.
Question 19.
What are intermolecular hydrogen bonds? Explain with example.
Answer:
1. Intermolecular hydrogen bonds occur between two separate molecules. They can occur between any numbers of like or unlike molecules as long as hydrogen donors and acceptors are present in positions in which they can interact.
2. For e.g., Intermolecular hydrogen bonds can occur between ammonia molecules alone, between water molecules alone or between ammonia and water.

Question 20.
Explain about the importance of hydrogen bonding in proteins.
Answer:
- Hydrogen bonds occur in complex biomolecules such as proteins and in biological systems.
- For example, hydrogen bonds play an important role in the structure of deoxyribonucleic acid (DNA), since it holds together the two helical nucleic acid chains.
- In these systems, hydrogen bonds are formed between specific pairs, for example. with a thymine unit in one chain bonding to an adenine unit in another; similarly, a cytosine unit in one chain bonds to a guanine unit in another.
- Intramolecular hydrogen bonding also plays an important role in the structure of polymers, both synthetic and natural.
Question 21.
What are Clatharate hydrate? Explain it with suitable example.
Answer:
- Gas hydrates $j n$ which the guest molecules are not bonded chemically but retained by the structure of host is called Clatharates.
- Water forms clatharate hydrates, e.g., methane hydrate $\left(\mathrm{CH}_4 20 \mathrm{H}_2 \mathrm{O}\right)$ which arc a type of ice that will bum when a lit match is held to it.
- The structure of methane hydrate is made of linked polyhedra that contains 20 hydrogen bonded water molecules forming a cage in which methane molecule is trapped.
- Deposits of methane clatharates occur naturally in deep sea bed.

- Hydrates are commonly obtained when water is frozen in presence of a gas such as argon, methane, etc.
- Most gases form hydrates under high pressure.
Question 22.
What are crystalline hydrates? Explain it with example.
Answer:
1. In these, hydrogen bonding is very important. Often the water molecules serve to fill in the interstices and bind together structure.
2. A specific example is $\mathrm{CuSO}_4 5 \mathrm{H}_2 \mathrm{O}$.
3. Although there are five water molecules for every divalent copper ion, only four are coordinated to the cation, it's six-coordination being completed from sulphate anions. The fifth water molecule is held in place of hydrogen bonds, $\mathrm{O}-\mathrm{H}-\mathrm{O}$, between it and two coordinated water molecules and then coordinate sulphate anion.
4. Water forms hydrated salts during crystallization. Examples, $\mathrm{Na}_2 \mathrm{CO}_3 \cdot 10 \mathrm{H}_2 \mathrm{O}$, $\mathrm{FeSO}_4 \cdot 7 \mathrm{H}_2 \mathrm{O}$.
5. The water present in the hydrates is called as water of hydration.
Question 23.
What do you understand by -
1. Electron-deficient
2. Electron-precise
3. Electron-rich compounds of hydrogen? Provide justification with suitable examples.

Answer:
1. Electron deficient hydrides:
Compounds in which central atom has incomplete octet, are called electron deficient hydrides. For example, $\mathrm{BeH}_2, \mathrm{BH}_3$ are electron deficient hydrides
2. Electron precise hydrides:
Those compounds in which exact number of electrons are present in central atom or the central atom contains complete octet are called precise hydrides e.g., $\mathrm{CH}_4, \mathrm{SiH}_4, \mathrm{GeH}_4$ etc. are precise hydrides.
3. Electron rich hydrides:
Those compounds in which central atom has one or more lone pair of excess electrons are called electron rich hydrides. e.g., $\mathrm{NH}_3, \mathrm{H}_2 \mathrm{O}$.
Question 24.
What causes the temporary and permanent hardness of water?
Answer:
Temporary hardness of water is due to the presence of bicarbonates of calcium and magnesium in water i.e., $\mathrm{Ca}\left(\mathrm{HCO}_3\right)_2$ and $\mathrm{Mg}\left(\mathrm{HCO}_3\right)$ in water. Permanent hardness of water is due to the presence of soluble chlorides and suiphates of calcium and magnesium i.e., $\mathrm{CaCl}_2, \mathrm{CaSO}_4, \mathrm{MgCl}_2$ and $\mathrm{MgSO}_4$

Question 25.
Write chemical reaction to show the amphoteric nature of water.
Answer:
Water is amphoteric in nature because it acts as an acid.

Question 26.
What is the difference between the terms 'hydrolysis' and 'hydration'?
Answer:
Hydrolysis is a chemical reaction in which a substance reacts with water under neutral, acidic or alkaline conditions.

Hydration on the other hand is the property of a chemical compound to take up molecules of water of crystallization and get hydrated.

5-Mark Questions
Question 1.
Explain about the different industrial preparation of hydrogen.
Answer:
In the large scale, hydrogen is produced currently by steam reforming of hydrocarbons. Steam and methane reacts with each other in the presence of nickel catalyst at $35 \mathrm{~atm}$ and at a temperature of $800^{\circ} \mathrm{C}$ gives hydrogen.

Steam is passed over a red hot coke to produce carbon monoxide and hydrogen.
$
\mathrm{C}_{(\mathrm{s})}+\mathrm{H}_2 \mathrm{O}_{(\mathrm{g})} \rightarrow \underbrace{\left.\mathrm{CO}_{(\mathrm{g})}+\mathrm{H}_2 \mathrm{~g}\right)}_{\text {Water gas }}
$
Water is reduced to hydrogen with carbon monoxide by passing over iron oxide catalyst at $400^{\circ} \mathrm{C}$.
$
\mathrm{CO}_{(\mathrm{g})}+\mathrm{H}_2 \mathrm{O}_{(\mathrm{g})} \rightarrow \mathrm{CO}_{2(\mathrm{~g})}+\mathrm{H}_{2(\mathrm{~g})}
$
Hydrogen is produced as a by-product in oil refining industry during the cracking of long chain hydrocarbons.
$
\mathrm{C}_6 \mathrm{H}_{12(\mathrm{~g})} \rightarrow \mathrm{CH}_{66(\mathrm{~g})}+3 \mathrm{H}_{2(\mathrm{~g})}
$
Hydrogen is also obtained in the manufacture of chlonne and sodium hydroxide via electrolysis of a concentrated solution of sodium chloride.
Question 2.
Explain about the uses of hydrogen compounds.

Answer:
- The hydrogen compounds such as sodium borohydride $\left(\mathrm{NaBH}_4\right)$ and lithium aluminium hydride $\left(\mathrm{LiAlH}_4\right)$ are commonly used as reducing agents in organic chemistry.
- Hydrides such as sodium hydride $(\mathrm{NaH})$ and potassium hydride $(\mathrm{KH})$ are used as strong bases in organic synthesis.
- Calcium hydride is used as desiccant to remove moisture from organic solvents.
- Hydride complexes are catalysts.
- Atomic hydrogen and oxy-hydrogen torches for cutting and welding.
- Hydrogen is used in fuel cells for generating electrical energy.
- Liquid hydrogen is used as a rocket fuel as well as in space research.
- Metallic hydrides are used in battery applications.
Question 3.
Describe the process of water softening and purification.
Answer:
1. An idealised image of water softening process involves replacement of cations such as $\mathrm{Mg}$, $\mathrm{Ca}$ and $\mathrm{Fe}$ in water with sodium ions.by a cation exchange zeolite. The ion exchange zeolites or resins are used to replace the $\mathrm{Mg}$ and $\mathrm{Ca}$ ions found in hard water with sodium ions.
2. They can be recharged by washing it with a solution containing a high concentration of sodium ions.
3. The calcium and magnesium ions migrate from the zeolite or resin being replaced by sodium ions from the solution until a new equilibrium is reached. That is, the salt is used to recharge an ion exchange medium, which itself is used to soften the water.
4. A couple of other methods, namely chelating method and reverse osmosis are also used to soften hard water. Chelating method employs a polydentate ligand such as EDTA, while reserve osmosis uses high pressure to force the water through a semi-permeable membrane.
5. In the case of water purification application, ion exchange zeolites or resins are used to remove toxic (eg., copper) and heavy metal (e.g., cadmium or lead) ions from solution,

Question 4.
(a) How is $\mathrm{H}_2 \mathrm{O}_2$ prepared?
(b) Explain about the structure of $\mathrm{H}_2 \mathrm{O}_2$.
Answer:
(a) Hydrogen peroxide can be made by adding a metal peroxide to dilute acid.
$
\mathrm{BaO}_{2(\mathrm{~s})}+\mathrm{H}_{(\mathrm{s})} \mathrm{SO}_4 \rightarrow \mathrm{BaSO}_{4(\mathrm{~s})}+\mathrm{H}_2 \mathrm{O}_{2(\mathrm{aq})}
$
(b) Structure of $\mathrm{H}_2 \mathrm{O}_2$

1. $\mathrm{H}_2 \mathrm{O}_2$ has a non-polar structure. The molecular dimensions in the gas phase and solid phase differ as shown in the figure.
2. Both in gas phase and solid phase, the $\mathrm{H}_2 \mathrm{O}_2$ molecule adopt a skew configuration due to repulsive interaction of the $-\mathrm{OH}$ bonds with lone pairs of electrons on each oxygen atom.
3. Indeed, it is the smallest molecule known to show hindrance rotation about a single bond. in solid phase, the dihedral angle is sensitive and hydrogen bonding decreasing from 111.50 in the gas phase to $90.2^{\circ}$, in the solid phase.
4. Structurally, $\mathrm{H}_2 \mathrm{O}_2$ is represented by the dihydroxyl formula in which the two O-H groups do not lie in the same plane. In the solid phase of molecule, the dihedral angle reduces to $90.2^{\circ}$ due to hydrogen bonding and the $\mathrm{O}-\mathrm{O}-\mathrm{H}$ angle expands from $94.8^{\circ}$ to $101.9^{\circ}$.
5. One way of explaining the shape of hydrogen peroxide is that the hydrogen atoms would lie on the pages of a partly opened book, and the oxygen atoms along the spin.
Question 5.
Explain about Hydrogen sponge.
Answer:
1. Hydrogen sponge (or) Metal hydride e.g., palladium-hydrogen system is a binary hydride $(\mathrm{PdH})$
2. Upon heating, $\mathrm{H}$ atoms diffuse through the metal to the surface and recombine to form molecular hydrogen. Since no other gas behaves this way with palladium, this process has been used to separate hydrogen gas from other gases:
$
2 \mathrm{Pd}_{(\mathrm{s})}+\mathrm{H}_{2(\mathrm{~g})} \rightleftharpoons 2 \mathrm{PdH}_{(\mathrm{s})}
$
3. The hydrogen molecule readily adsorb on the palladium surface, where it dissociates into atomic hydrogen. The dissociated atoms dissolve into the interstices or voids (octahedral or tetrahedral) of the crystal lattice.

4. Technically, the formation of metal hydride is by chemical reaction but it behaves like a physical storage method, i.e., it is absorbed and released like a water sponge. Such a reversible uptake of hydrogen in metals and alloys is also attractive for hydrogen Storage and for rechargeable metal hydride battery applications.
Question 6.
How are reducing agents in synthetic organic chemistry prepared?
Answer:
Hydrogen has a tendency to react with reactive metals like lithium, sodium to give corresponding hydrides.
$2 \mathrm{Li}+\mathrm{H}_2 \rightarrow 2 \mathrm{LiH}$
$2 \mathrm{Na}+\mathrm{H}_2 \rightarrow 2 \mathrm{NaH}$
These hydrides are used as reducing agents in synthetic organic chemistry. It is also used to prepare important hydrides such as lithium aluminium hydride and sodium boro hydride (organic reducing agents).
$
4 \mathrm{LiH}+\mathrm{AlCl}_3 \rightarrow \mathrm{Li}\left[\mathrm{AIH}_4\right]+3 \mathrm{LiCl}
$

$
4 \mathrm{NaH}+\mathrm{B}\left(\mathrm{OCH}_3\right)_3 \rightarrow \mathrm{Na}\left[\mathrm{BH}_4\right]+3 \mathrm{CH}_3 \mathrm{ONa}
$
Question 7.
How does water react with -
1. $\mathrm{SiCl}_4$
2. $\mathrm{P}_4 \mathrm{O}_{10}$
Answer:
1. Water reacts with $\mathrm{SiCl}_4$ to give silica.

2. Water reacts with $\mathrm{P}_4 \mathrm{O}_{10}$ to give ortho phosphoric acid.

Question 8 .
Explain about the structure of $\mathrm{CuSO}_4 .5 \mathrm{H}_2 \mathrm{O}$

Question 9.
How is hydrogen peroxide prepared on industrial scale?
Answer:
On an industrial scale, hydrogen peroxide is prepared by auto oxidation of of 2-alkyl antliraquinol.

Question 10 .
How is hydrogen peroxide is used to restore the white colour of old paintings.
Answer:
Hydrogen peroxide is used to restore the white colour which was lost due to the reaction of hydrogen suiphide in air with the white pigment $\mathrm{Pb}_3(\mathrm{OH})_2\left(\mathrm{CO}_3\right)_2$ to form black colored lead suiphide ( $\mathrm{PbS}$ ) Hydrogen peroxide oxidises black coloured lead suiphide to white coloured lead sulphate, there by restoring the colour.
$
\mathrm{PbS}+4 \mathrm{H}_2 \mathrm{O}_2 \rightarrow \mathrm{PbSO}_2+4 \mathrm{H}_2 \mathrm{O}
$