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Hydrogen Class 11 Notes Chemistry

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 Page 1


? Hydrogen	 is	 the	 first	 element	 in	 the	 periodic	 table	 and	 also	 the	 lightest
element	known.	Electronic	configuration	of	Hydrogen	is	1s
1
.
? Isotopes of hydrogen :
(i)	Protium	(
1
1
H)
(ii)	Deuterium	(
1
2
H or 
1
2
D)
(iii)	 T ritium	(
1
3
H or 
1
3
T)
? Preparation of Dihydrogen :
(i)	Laboratory	preparation	:	Zn	+	2H
+
 ? 	Zn
2+
	+	H
2
.
(ii)	Commercial	preparation	:	By	electrolysis	of	acidified	water .
(iii)	 High	 purity	 dihydrogen	 is	 obtained	 by	 electrolysing	 warm	 aqueous
barium	hydroxide.
? Properties :
* Reaction	with	halogen:	H
2
	+	X
2
 ??	2HX	[X	=	F ,	Cl,	Br ,	I]
* Reaction	with	oxygen:	H
2
(g)	+	O
2
(g) ?? 
D
2H
2
O(l) DH
ø
=	–	285.9	kJ	mol
–1
* Reaction	with	nitrogen:	3H
2
(g)	+	N
2
(g) ?? 
D
2NH
3
(g) DH
ø
=	–92	kJ	mol
–1
* Reaction	with	alkali	metals:	H
2
(g)	+	2M(g)	?? 
D
2MH(s)
It	 is	 relatively	 inert	 at	 room	 temperature	 due	 to	 the	 high	 H-H	 bond	 enthalpy .
? Uses of Dihydrogen :
(i)	For	synthesis	of	 Ammonia	(NH
3
)
Page 2


? Hydrogen	 is	 the	 first	 element	 in	 the	 periodic	 table	 and	 also	 the	 lightest
element	known.	Electronic	configuration	of	Hydrogen	is	1s
1
.
? Isotopes of hydrogen :
(i)	Protium	(
1
1
H)
(ii)	Deuterium	(
1
2
H or 
1
2
D)
(iii)	 T ritium	(
1
3
H or 
1
3
T)
? Preparation of Dihydrogen :
(i)	Laboratory	preparation	:	Zn	+	2H
+
 ? 	Zn
2+
	+	H
2
.
(ii)	Commercial	preparation	:	By	electrolysis	of	acidified	water .
(iii)	 High	 purity	 dihydrogen	 is	 obtained	 by	 electrolysing	 warm	 aqueous
barium	hydroxide.
? Properties :
* Reaction	with	halogen:	H
2
	+	X
2
 ??	2HX	[X	=	F ,	Cl,	Br ,	I]
* Reaction	with	oxygen:	H
2
(g)	+	O
2
(g) ?? 
D
2H
2
O(l) DH
ø
=	–	285.9	kJ	mol
–1
* Reaction	with	nitrogen:	3H
2
(g)	+	N
2
(g) ?? 
D
2NH
3
(g) DH
ø
=	–92	kJ	mol
–1
* Reaction	with	alkali	metals:	H
2
(g)	+	2M(g)	?? 
D
2MH(s)
It	 is	 relatively	 inert	 at	 room	 temperature	 due	 to	 the	 high	 H-H	 bond	 enthalpy .
? Uses of Dihydrogen :
(i)	For	synthesis	of	 Ammonia	(NH
3
)
(ii)		 For 	production	of	Methanol	(CH
3
OH)
(iii)		 In	oxyhydrogen	torches
(iv) 		 In	a	fuel	cell.
? Hydrides
(i)  Ionic or salt like or saline hydrides are 	 formed	 with 	 most	 of	 the
s -block	 eleme nts.	 Significant	 covalent	 character	 is	 found	 in	 LiH,	 BeH
2
and	MgH
2
.
(ii)  Covalent or Molecular hydrides are 	 formed	 with 	 most	 of	 the	p -block
elements.	 There 	are	further 	classified	as	:
(a)  Electron deficient hydrides are 	 formed	 by	 group	 13	 elements	e.g. ,
B
2
H
6
.	 They	acts	as 	Lewis	acid.
(b) 		Electron Precise hydrides 	 are	 formed	 by	 group 	 14	 elements 	e.g. ,
CH
4
.
(c)		 Electron rich hydrides have	 lone	 pair	 of	 electrons 	 on	 central 	 atoms
of	 the	 molecules. 	 Elements	 of	 group	 15-17	 form	 these	 types	 of	 hydrides.
NH
3
,	 HF	 has	 high	 m.p./b.p.	 due	 to 	 presence 	 of	 intermolec ular	 hydrogen
bonding.
(iii)  Metallic or Non-stoichiometric or Interstitial hydrides are 	 formed
by	d	and	f 	-block	elements.	For	example	La	H
2.87
	or	NiH
0.6–0.7
.
? Water : (H
2
O)
Hard water : Hard 	 water 	 contains 	 calciu m	 and	 magnesium	 salts 	 in	 the
form	 of	 hydrogencarbonate,	 chloride 	 and	 sulphate.	 Hard	 water	 does	 not
give	lathers	with 	soap.
Soft water : W ater 	 free 	 from 	 soluble	 salts	 of	 calcium	 and 	 magnesi um	 is
soft	water .
Types of Hardness :
Temporary hardness i s 	 due 	 t o	 presence 	 of	 ca l ci um 	 or	 m agnesium
hydrogen	carbonate 	in	water .
T emporary 	hardness 	can	be	removed	by	:
(i)	Boiling
(ii)	Clark’ s	Method
Permanent hardness :
Such	 hardness	 is	 due	 to	 presence	 of	 calcium	 or	 magnesium	 chlorides	 and
sulphates.
Page 3


? Hydrogen	 is	 the	 first	 element	 in	 the	 periodic	 table	 and	 also	 the	 lightest
element	known.	Electronic	configuration	of	Hydrogen	is	1s
1
.
? Isotopes of hydrogen :
(i)	Protium	(
1
1
H)
(ii)	Deuterium	(
1
2
H or 
1
2
D)
(iii)	 T ritium	(
1
3
H or 
1
3
T)
? Preparation of Dihydrogen :
(i)	Laboratory	preparation	:	Zn	+	2H
+
 ? 	Zn
2+
	+	H
2
.
(ii)	Commercial	preparation	:	By	electrolysis	of	acidified	water .
(iii)	 High	 purity	 dihydrogen	 is	 obtained	 by	 electrolysing	 warm	 aqueous
barium	hydroxide.
? Properties :
* Reaction	with	halogen:	H
2
	+	X
2
 ??	2HX	[X	=	F ,	Cl,	Br ,	I]
* Reaction	with	oxygen:	H
2
(g)	+	O
2
(g) ?? 
D
2H
2
O(l) DH
ø
=	–	285.9	kJ	mol
–1
* Reaction	with	nitrogen:	3H
2
(g)	+	N
2
(g) ?? 
D
2NH
3
(g) DH
ø
=	–92	kJ	mol
–1
* Reaction	with	alkali	metals:	H
2
(g)	+	2M(g)	?? 
D
2MH(s)
It	 is	 relatively	 inert	 at	 room	 temperature	 due	 to	 the	 high	 H-H	 bond	 enthalpy .
? Uses of Dihydrogen :
(i)	For	synthesis	of	 Ammonia	(NH
3
)
(ii)		 For 	production	of	Methanol	(CH
3
OH)
(iii)		 In	oxyhydrogen	torches
(iv) 		 In	a	fuel	cell.
? Hydrides
(i)  Ionic or salt like or saline hydrides are 	 formed	 with 	 most	 of	 the
s -block	 eleme nts.	 Significant	 covalent	 character	 is	 found	 in	 LiH,	 BeH
2
and	MgH
2
.
(ii)  Covalent or Molecular hydrides are 	 formed	 with 	 most	 of	 the	p -block
elements.	 There 	are	further 	classified	as	:
(a)  Electron deficient hydrides are 	 formed	 by	 group	 13	 elements	e.g. ,
B
2
H
6
.	 They	acts	as 	Lewis	acid.
(b) 		Electron Precise hydrides 	 are	 formed	 by	 group 	 14	 elements 	e.g. ,
CH
4
.
(c)		 Electron rich hydrides have	 lone	 pair	 of	 electrons 	 on	 central 	 atoms
of	 the	 molecules. 	 Elements	 of	 group	 15-17	 form	 these	 types	 of	 hydrides.
NH
3
,	 HF	 has	 high	 m.p./b.p.	 due	 to 	 presence 	 of	 intermolec ular	 hydrogen
bonding.
(iii)  Metallic or Non-stoichiometric or Interstitial hydrides are 	 formed
by	d	and	f 	-block	elements.	For	example	La	H
2.87
	or	NiH
0.6–0.7
.
? Water : (H
2
O)
Hard water : Hard 	 water 	 contains 	 calciu m	 and	 magnesium	 salts 	 in	 the
form	 of	 hydrogencarbonate,	 chloride 	 and	 sulphate.	 Hard	 water	 does	 not
give	lathers	with 	soap.
Soft water : W ater 	 free 	 from 	 soluble	 salts	 of	 calcium	 and 	 magnesi um	 is
soft	water .
Types of Hardness :
Temporary hardness i s 	 due 	 t o	 presence 	 of	 ca l ci um 	 or	 m agnesium
hydrogen	carbonate 	in	water .
T emporary 	hardness 	can	be	removed	by	:
(i)	Boiling
(ii)	Clark’ s	Method
Permanent hardness :
Such	 hardness	 is	 due	 to	 presence	 of	 calcium	 or	 magnesium	 chlorides	 and
sulphates.
Permanent 	hardness	can 	be	removed	by	:
(i)	 T reatment 	with 	washing	soda
(ii)		 Calgon’ s	method
(iii)		 Ion	exchange 	m ethod.
Demineralised or Deionised water : 	 W ater	 free	 from	 all	 soluble	 mineral	 	
salts 	is	known	as	demineralised water.
? Hydrogen Peroxide (H
2
O
2
)
Preperation :
(i)	 By	 electrolytic	 oxidation 	 of	 acidified	 sulphate	 solutions 	 at 	 high	 current
density .
(ii)	2-Ethylanthraquinol H
2
O
2
	+	(oxidised	product)
? Physical Properties
(i)	Miscible	with	water 	in	all	proportions.
(ii) 	 A 	 30%	 of 	 H
2
O
2
	 solution 	 is 	 marked 	 as	 ‘100	 volume’ 	 hydrogen	 peroxide .
? Chemical Properties :
(i)	It 	acts	as	an	oxidising	as	well	as	reducing	agent.
(ii) Oxidising action in acidic medium :
2Fe
2+
(aq)	+	2H
+
	(aq) 	+	H
2
O
2 
(aq) 	?	2Fe
3+
	(aq)	+	2H
2
O(l)
(iii) Reducing action in acidic medium :
2MnO
4
–
	+ 	6H
+
	+	5H
2
O
2
 ?	2Mn
2+
	+	8H
2
O	+	SO
2
? Storage of H
2
O
2 
:
(i)	 Stored 	 in	 wax-linked	 glass	 or	 plastic 	 vess els 	 in	 dark. 	 Urea 	 can 	 be	 added
as	a	stabiliser .
(ii)	 It 	 is	 kept	 aw ay	 from	 dus t 	 becaus e 	 dus t 	 can 	 induce 	 explosive
decomposition	of	the	compound.
? Uses of H
2
O
2
 :
(i)	 As	an	antiseptic	it	is	sold	in	the	market 	name 	perhydrol .
(ii)	In	synthesis	of	hydroquinone.
(iii)	 As	a	bleaching	agent.
Page 4


? Hydrogen	 is	 the	 first	 element	 in	 the	 periodic	 table	 and	 also	 the	 lightest
element	known.	Electronic	configuration	of	Hydrogen	is	1s
1
.
? Isotopes of hydrogen :
(i)	Protium	(
1
1
H)
(ii)	Deuterium	(
1
2
H or 
1
2
D)
(iii)	 T ritium	(
1
3
H or 
1
3
T)
? Preparation of Dihydrogen :
(i)	Laboratory	preparation	:	Zn	+	2H
+
 ? 	Zn
2+
	+	H
2
.
(ii)	Commercial	preparation	:	By	electrolysis	of	acidified	water .
(iii)	 High	 purity	 dihydrogen	 is	 obtained	 by	 electrolysing	 warm	 aqueous
barium	hydroxide.
? Properties :
* Reaction	with	halogen:	H
2
	+	X
2
 ??	2HX	[X	=	F ,	Cl,	Br ,	I]
* Reaction	with	oxygen:	H
2
(g)	+	O
2
(g) ?? 
D
2H
2
O(l) DH
ø
=	–	285.9	kJ	mol
–1
* Reaction	with	nitrogen:	3H
2
(g)	+	N
2
(g) ?? 
D
2NH
3
(g) DH
ø
=	–92	kJ	mol
–1
* Reaction	with	alkali	metals:	H
2
(g)	+	2M(g)	?? 
D
2MH(s)
It	 is	 relatively	 inert	 at	 room	 temperature	 due	 to	 the	 high	 H-H	 bond	 enthalpy .
? Uses of Dihydrogen :
(i)	For	synthesis	of	 Ammonia	(NH
3
)
(ii)		 For 	production	of	Methanol	(CH
3
OH)
(iii)		 In	oxyhydrogen	torches
(iv) 		 In	a	fuel	cell.
? Hydrides
(i)  Ionic or salt like or saline hydrides are 	 formed	 with 	 most	 of	 the
s -block	 eleme nts.	 Significant	 covalent	 character	 is	 found	 in	 LiH,	 BeH
2
and	MgH
2
.
(ii)  Covalent or Molecular hydrides are 	 formed	 with 	 most	 of	 the	p -block
elements.	 There 	are	further 	classified	as	:
(a)  Electron deficient hydrides are 	 formed	 by	 group	 13	 elements	e.g. ,
B
2
H
6
.	 They	acts	as 	Lewis	acid.
(b) 		Electron Precise hydrides 	 are	 formed	 by	 group 	 14	 elements 	e.g. ,
CH
4
.
(c)		 Electron rich hydrides have	 lone	 pair	 of	 electrons 	 on	 central 	 atoms
of	 the	 molecules. 	 Elements	 of	 group	 15-17	 form	 these	 types	 of	 hydrides.
NH
3
,	 HF	 has	 high	 m.p./b.p.	 due	 to 	 presence 	 of	 intermolec ular	 hydrogen
bonding.
(iii)  Metallic or Non-stoichiometric or Interstitial hydrides are 	 formed
by	d	and	f 	-block	elements.	For	example	La	H
2.87
	or	NiH
0.6–0.7
.
? Water : (H
2
O)
Hard water : Hard 	 water 	 contains 	 calciu m	 and	 magnesium	 salts 	 in	 the
form	 of	 hydrogencarbonate,	 chloride 	 and	 sulphate.	 Hard	 water	 does	 not
give	lathers	with 	soap.
Soft water : W ater 	 free 	 from 	 soluble	 salts	 of	 calcium	 and 	 magnesi um	 is
soft	water .
Types of Hardness :
Temporary hardness i s 	 due 	 t o	 presence 	 of	 ca l ci um 	 or	 m agnesium
hydrogen	carbonate 	in	water .
T emporary 	hardness 	can	be	removed	by	:
(i)	Boiling
(ii)	Clark’ s	Method
Permanent hardness :
Such	 hardness	 is	 due	 to	 presence	 of	 calcium	 or	 magnesium	 chlorides	 and
sulphates.
Permanent 	hardness	can 	be	removed	by	:
(i)	 T reatment 	with 	washing	soda
(ii)		 Calgon’ s	method
(iii)		 Ion	exchange 	m ethod.
Demineralised or Deionised water : 	 W ater	 free	 from	 all	 soluble	 mineral	 	
salts 	is	known	as	demineralised water.
? Hydrogen Peroxide (H
2
O
2
)
Preperation :
(i)	 By	 electrolytic	 oxidation 	 of	 acidified	 sulphate	 solutions 	 at 	 high	 current
density .
(ii)	2-Ethylanthraquinol H
2
O
2
	+	(oxidised	product)
? Physical Properties
(i)	Miscible	with	water 	in	all	proportions.
(ii) 	 A 	 30%	 of 	 H
2
O
2
	 solution 	 is 	 marked 	 as	 ‘100	 volume’ 	 hydrogen	 peroxide .
? Chemical Properties :
(i)	It 	acts	as	an	oxidising	as	well	as	reducing	agent.
(ii) Oxidising action in acidic medium :
2Fe
2+
(aq)	+	2H
+
	(aq) 	+	H
2
O
2 
(aq) 	?	2Fe
3+
	(aq)	+	2H
2
O(l)
(iii) Reducing action in acidic medium :
2MnO
4
–
	+ 	6H
+
	+	5H
2
O
2
 ?	2Mn
2+
	+	8H
2
O	+	SO
2
? Storage of H
2
O
2 
:
(i)	 Stored 	 in	 wax-linked	 glass	 or	 plastic 	 vess els 	 in	 dark. 	 Urea 	 can 	 be	 added
as	a	stabiliser .
(ii)	 It 	 is	 kept	 aw ay	 from	 dus t 	 becaus e 	 dus t 	 can 	 induce 	 explosive
decomposition	of	the	compound.
? Uses of H
2
O
2
 :
(i)	 As	an	antiseptic	it	is	sold	in	the	market 	name 	perhydrol .
(ii)	In	synthesis	of	hydroquinone.
(iii)	 As	a	bleaching	agent.
1. Auto–protolysis of water: 	 W ater	 accepts 	 a	 proton	 from 	 other	 water
molecule 	 to	 from 	 H
3
O
+
	 and	 OH
–
	 this	 porous	 is	 called	 auto	 –	 protolysis 	 of
water
H
2
O(l)	+	H
2
O(l)	
? 
? 
 H
3
O
+
	(aq)	+	OH
–
	(aq)
Its 	 significance	 is	 that	 water 	 can	 act	 as	 acid	 as	 well 	 as	 base	 i.e.	 it 	 is
amphoteric 	in	nature.
2. Hydrogen economy:– It 	 is	 transportation 	 and 	 storage 	 of	 ener gy 	 in	 the	 form
of	 liquid	 or	 gaseous	 hydrogen.	 Advantage	 of	 hydrogen	 economy	 is	 that
ener gy	 is	 transmitted	 in	 the	 form 	 of	 dihydrogen 	 and	 not	 as	 electric	 power
3. Hydrogenation:– It	 is 	 a	 process 	 of	 converting 	 polyunsaturated	 oils	 in
edible 	fats.
V egetable	oil 	+ 	H
2
 
Ni
473K
	 V anaspati	ghee 	(fat).
4. Syngas:– It 	 is	 a 	 mixture 	 of 	 CO 	 and 	 H
2
	 in	 1:1	 ratio 	 and 	 also	 known	 as 	 water
gas	or	syntnesis	gas.
C(s)	+	H
2
O(g)		
1270K
Ni
	CO
2
	+	H
2
(g)
							Carbon			 Carbon	monoxide 	
5. W ater 	gas	shift 	reaction.
CO HO
673 K
iron chromate as catalyst
CO H
22 2
++
6. Full-cell:– 	 Fue l 	 c e l l 	 i s	 a 	 c e l l 	 i n	 whi c h 	 c he m i c a l 	 e ne r gy 	 of 	 fue l 	 i s 	 c onve rt e d
into 	electrical	ener gy .
7. Structure of water:– 	 It 	 is 	 bent	 molecule	 in	 gas	 phase 	 with	 HOH 	 bond
angle 	104.5°	and	O–H	bond	length	of	95.7	pm	as	shown	if	figure
Page 5


? Hydrogen	 is	 the	 first	 element	 in	 the	 periodic	 table	 and	 also	 the	 lightest
element	known.	Electronic	configuration	of	Hydrogen	is	1s
1
.
? Isotopes of hydrogen :
(i)	Protium	(
1
1
H)
(ii)	Deuterium	(
1
2
H or 
1
2
D)
(iii)	 T ritium	(
1
3
H or 
1
3
T)
? Preparation of Dihydrogen :
(i)	Laboratory	preparation	:	Zn	+	2H
+
 ? 	Zn
2+
	+	H
2
.
(ii)	Commercial	preparation	:	By	electrolysis	of	acidified	water .
(iii)	 High	 purity	 dihydrogen	 is	 obtained	 by	 electrolysing	 warm	 aqueous
barium	hydroxide.
? Properties :
* Reaction	with	halogen:	H
2
	+	X
2
 ??	2HX	[X	=	F ,	Cl,	Br ,	I]
* Reaction	with	oxygen:	H
2
(g)	+	O
2
(g) ?? 
D
2H
2
O(l) DH
ø
=	–	285.9	kJ	mol
–1
* Reaction	with	nitrogen:	3H
2
(g)	+	N
2
(g) ?? 
D
2NH
3
(g) DH
ø
=	–92	kJ	mol
–1
* Reaction	with	alkali	metals:	H
2
(g)	+	2M(g)	?? 
D
2MH(s)
It	 is	 relatively	 inert	 at	 room	 temperature	 due	 to	 the	 high	 H-H	 bond	 enthalpy .
? Uses of Dihydrogen :
(i)	For	synthesis	of	 Ammonia	(NH
3
)
(ii)		 For 	production	of	Methanol	(CH
3
OH)
(iii)		 In	oxyhydrogen	torches
(iv) 		 In	a	fuel	cell.
? Hydrides
(i)  Ionic or salt like or saline hydrides are 	 formed	 with 	 most	 of	 the
s -block	 eleme nts.	 Significant	 covalent	 character	 is	 found	 in	 LiH,	 BeH
2
and	MgH
2
.
(ii)  Covalent or Molecular hydrides are 	 formed	 with 	 most	 of	 the	p -block
elements.	 There 	are	further 	classified	as	:
(a)  Electron deficient hydrides are 	 formed	 by	 group	 13	 elements	e.g. ,
B
2
H
6
.	 They	acts	as 	Lewis	acid.
(b) 		Electron Precise hydrides 	 are	 formed	 by	 group 	 14	 elements 	e.g. ,
CH
4
.
(c)		 Electron rich hydrides have	 lone	 pair	 of	 electrons 	 on	 central 	 atoms
of	 the	 molecules. 	 Elements	 of	 group	 15-17	 form	 these	 types	 of	 hydrides.
NH
3
,	 HF	 has	 high	 m.p./b.p.	 due	 to 	 presence 	 of	 intermolec ular	 hydrogen
bonding.
(iii)  Metallic or Non-stoichiometric or Interstitial hydrides are 	 formed
by	d	and	f 	-block	elements.	For	example	La	H
2.87
	or	NiH
0.6–0.7
.
? Water : (H
2
O)
Hard water : Hard 	 water 	 contains 	 calciu m	 and	 magnesium	 salts 	 in	 the
form	 of	 hydrogencarbonate,	 chloride 	 and	 sulphate.	 Hard	 water	 does	 not
give	lathers	with 	soap.
Soft water : W ater 	 free 	 from 	 soluble	 salts	 of	 calcium	 and 	 magnesi um	 is
soft	water .
Types of Hardness :
Temporary hardness i s 	 due 	 t o	 presence 	 of	 ca l ci um 	 or	 m agnesium
hydrogen	carbonate 	in	water .
T emporary 	hardness 	can	be	removed	by	:
(i)	Boiling
(ii)	Clark’ s	Method
Permanent hardness :
Such	 hardness	 is	 due	 to	 presence	 of	 calcium	 or	 magnesium	 chlorides	 and
sulphates.
Permanent 	hardness	can 	be	removed	by	:
(i)	 T reatment 	with 	washing	soda
(ii)		 Calgon’ s	method
(iii)		 Ion	exchange 	m ethod.
Demineralised or Deionised water : 	 W ater	 free	 from	 all	 soluble	 mineral	 	
salts 	is	known	as	demineralised water.
? Hydrogen Peroxide (H
2
O
2
)
Preperation :
(i)	 By	 electrolytic	 oxidation 	 of	 acidified	 sulphate	 solutions 	 at 	 high	 current
density .
(ii)	2-Ethylanthraquinol H
2
O
2
	+	(oxidised	product)
? Physical Properties
(i)	Miscible	with	water 	in	all	proportions.
(ii) 	 A 	 30%	 of 	 H
2
O
2
	 solution 	 is 	 marked 	 as	 ‘100	 volume’ 	 hydrogen	 peroxide .
? Chemical Properties :
(i)	It 	acts	as	an	oxidising	as	well	as	reducing	agent.
(ii) Oxidising action in acidic medium :
2Fe
2+
(aq)	+	2H
+
	(aq) 	+	H
2
O
2 
(aq) 	?	2Fe
3+
	(aq)	+	2H
2
O(l)
(iii) Reducing action in acidic medium :
2MnO
4
–
	+ 	6H
+
	+	5H
2
O
2
 ?	2Mn
2+
	+	8H
2
O	+	SO
2
? Storage of H
2
O
2 
:
(i)	 Stored 	 in	 wax-linked	 glass	 or	 plastic 	 vess els 	 in	 dark. 	 Urea 	 can 	 be	 added
as	a	stabiliser .
(ii)	 It 	 is	 kept	 aw ay	 from	 dus t 	 becaus e 	 dus t 	 can 	 induce 	 explosive
decomposition	of	the	compound.
? Uses of H
2
O
2
 :
(i)	 As	an	antiseptic	it	is	sold	in	the	market 	name 	perhydrol .
(ii)	In	synthesis	of	hydroquinone.
(iii)	 As	a	bleaching	agent.
1. Auto–protolysis of water: 	 W ater	 accepts 	 a	 proton	 from 	 other	 water
molecule 	 to	 from 	 H
3
O
+
	 and	 OH
–
	 this	 porous	 is	 called	 auto	 –	 protolysis 	 of
water
H
2
O(l)	+	H
2
O(l)	
? 
? 
 H
3
O
+
	(aq)	+	OH
–
	(aq)
Its 	 significance	 is	 that	 water 	 can	 act	 as	 acid	 as	 well 	 as	 base	 i.e.	 it 	 is
amphoteric 	in	nature.
2. Hydrogen economy:– It 	 is	 transportation 	 and 	 storage 	 of	 ener gy 	 in	 the	 form
of	 liquid	 or	 gaseous	 hydrogen.	 Advantage	 of	 hydrogen	 economy	 is	 that
ener gy	 is	 transmitted	 in	 the	 form 	 of	 dihydrogen 	 and	 not	 as	 electric	 power
3. Hydrogenation:– It	 is 	 a	 process 	 of	 converting 	 polyunsaturated	 oils	 in
edible 	fats.
V egetable	oil 	+ 	H
2
 
Ni
473K
	 V anaspati	ghee 	(fat).
4. Syngas:– It 	 is	 a 	 mixture 	 of 	 CO 	 and 	 H
2
	 in	 1:1	 ratio 	 and 	 also	 known	 as 	 water
gas	or	syntnesis	gas.
C(s)	+	H
2
O(g)		
1270K
Ni
	CO
2
	+	H
2
(g)
							Carbon			 Carbon	monoxide 	
5. W ater 	gas	shift 	reaction.
CO HO
673 K
iron chromate as catalyst
CO H
22 2
++
6. Full-cell:– 	 Fue l 	 c e l l 	 i s	 a 	 c e l l 	 i n	 whi c h 	 c he m i c a l 	 e ne r gy 	 of 	 fue l 	 i s 	 c onve rt e d
into 	electrical	ener gy .
7. Structure of water:– 	 It 	 is 	 bent	 molecule	 in	 gas	 phase 	 with	 HOH 	 bond
angle 	104.5°	and	O–H	bond	length	of	95.7	pm	as	shown	if	figure
8. Calgon:– It 	 is	 sodium	 polymetaphosp hate	 (NaPO
3
)
n
	 it 	 is	 used 	 to	 remove.
Permanent 	hardness	of	water .
9. De-ionized water:– Pure	 di-mineralised 	 (ionized 	 water)	 free 	 from	 all
soluble 	 mineral 	 matter	 is	 obtained	 by	 passing	 water	 successively 	 through
a	cation 	exchanger	(in	the	H
+
	 form)	and	an	anion	exchanger	for	 removal
by	cation 	and	anions
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FAQs on Hydrogen Class 11 Notes Chemistry

1. What is hydrogen and why is it important?
Ans. Hydrogen is the lightest and most abundant element in the universe. It is important because it can be used as a clean and efficient source of energy. Hydrogen can be used in fuel cells to produce electricity, and it can also be used as a fuel for vehicles, heating, and industrial processes.
2. How is hydrogen produced?
Ans. Hydrogen can be produced through various methods. The most common method is steam methane reforming, where methane reacts with steam to produce hydrogen and carbon dioxide. Other methods include electrolysis, where electricity is used to split water into hydrogen and oxygen, and biomass gasification, where organic matter is heated to produce hydrogen gas.
3. What are the advantages and disadvantages of using hydrogen as an energy source?
Ans. The advantages of using hydrogen as an energy source include its clean and renewable nature, as it produces only water vapor when used in fuel cells. It is also highly efficient and can be stored for long periods of time. However, the main disadvantage is the high cost of production and infrastructure development. Hydrogen is also highly flammable and requires careful handling.
4. How is hydrogen used in transportation?
Ans. Hydrogen can be used to power vehicles through fuel cell technology. In a fuel cell, hydrogen reacts with oxygen to produce electricity, which powers an electric motor. This eliminates the need for combustion and reduces emissions. Hydrogen fuel cell vehicles have the advantage of longer driving ranges and shorter refueling times compared to electric vehicles.
5. What are the current challenges in the widespread adoption of hydrogen as an energy source?
Ans. The widespread adoption of hydrogen faces several challenges. Firstly, the cost of hydrogen production needs to be reduced to make it more competitive with other energy sources. Additionally, a hydrogen infrastructure needs to be developed, including production, storage, and distribution facilities. Safety concerns related to hydrogen storage and handling also need to be addressed. Finally, increasing public awareness and acceptance of hydrogen as an energy source is crucial for its widespread adoption.
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