Flashcards for JEE Chemistry - Hydrogen Class 11

 Page 1


Hydrogen
Flash cards
Page 2


Hydrogen
Flash cards
Introduction
Hydrogen is the first element of the Periodic Table. It is a 
powerful polarising agent, polarises NH
3
and H
2
O to NH
4
+
, 
H
3
O
+
, [H(H
2
O)
n
]
+
.
Page 3


Hydrogen
Flash cards
Introduction
Hydrogen is the first element of the Periodic Table. It is a 
powerful polarising agent, polarises NH
3
and H
2
O to NH
4
+
, 
H
3
O
+
, [H(H
2
O)
n
]
+
.
Chemistry of Hydrogen (Continued)
(1) Preparation of hydrogen :
(a) By reaction of water on metals
e.g. 2 Na + 2 H
2
O ?2NaOH + H
2
(b) By the reaction of water on hydrides
e.g. CaH
2
+ 2H
2
O ?Ca(OH)
2
+ 2H
2
Page 4


Hydrogen
Flash cards
Introduction
Hydrogen is the first element of the Periodic Table. It is a 
powerful polarising agent, polarises NH
3
and H
2
O to NH
4
+
, 
H
3
O
+
, [H(H
2
O)
n
]
+
.
Chemistry of Hydrogen (Continued)
(1) Preparation of hydrogen :
(a) By reaction of water on metals
e.g. 2 Na + 2 H
2
O ?2NaOH + H
2
(b) By the reaction of water on hydrides
e.g. CaH
2
+ 2H
2
O ?Ca(OH)
2
+ 2H
2
Chemistry of Hydrogen (Continued)
(1) Preparation of hydrogen :
(c) By the electrolysis of water
When electricity is passed through water containing a little 
acid or alkali (to make it conducting), hydrogen is obtained at 
the cathode and oxygen at the anode.
2H
2
O + H
2
SO
4
? 2 H
3
O
+
+ SO
4
2–
At cathode :
2H
3
O
+
+ 2e¯ ? 2 H
2
O + 2H
H + H ?H
2
At anode : 2SO
4
2 –
+ 2H
2
O ?2H
2
SO
4
+ O
2
+ 2e
Page 5


Hydrogen
Flash cards
Introduction
Hydrogen is the first element of the Periodic Table. It is a 
powerful polarising agent, polarises NH
3
and H
2
O to NH
4
+
, 
H
3
O
+
, [H(H
2
O)
n
]
+
.
Chemistry of Hydrogen (Continued)
(1) Preparation of hydrogen :
(a) By reaction of water on metals
e.g. 2 Na + 2 H
2
O ?2NaOH + H
2
(b) By the reaction of water on hydrides
e.g. CaH
2
+ 2H
2
O ?Ca(OH)
2
+ 2H
2
Chemistry of Hydrogen (Continued)
(1) Preparation of hydrogen :
(c) By the electrolysis of water
When electricity is passed through water containing a little 
acid or alkali (to make it conducting), hydrogen is obtained at 
the cathode and oxygen at the anode.
2H
2
O + H
2
SO
4
? 2 H
3
O
+
+ SO
4
2–
At cathode :
2H
3
O
+
+ 2e¯ ? 2 H
2
O + 2H
H + H ?H
2
At anode : 2SO
4
2 –
+ 2H
2
O ?2H
2
SO
4
+ O
2
+ 2e
Chemistry of Hydrogen (Continued)
(1) Preparation of hydrogen :
(d) From acids :
Zn + dil. H
2
SO
4
? ZnSO
4
+ H
2
Mg + dil. H
2
SO
4
?MgSO
4
+ H
2