CHAPTER 8 HYDROGEN AND THE ACTIVE METAL

by • 14/07/2011 • 9th class ChemistryComments (1)1064

Q:1) How hydrogen is prepared commercially and give its properties?
Ans) Commercial hydrogen is relatively less pure and can be prepared by following methods.
1) Passing steam over red hot coke:- By passing steam over red hot coke we get.
C+H2OCO+H2
carbon monoxide can be separate from the gaseous mixture by liquefying at a temperature of -200c.

2) By the electrolysis of water:- The purest but expensive hydrogen is obtained by the electrolysis of water in the presence of little acid.
2H2O2H2+O2
3) By thermal decomposition:- Hydrogen is prepared by thermal decomposition of natural gas.
CH4C+2H2
4) Pure and relatively in expensive hydrogen is prepared by passing steam aver red hot ion.
3Fe+4H2O Fe3O4+4H2
5) By heating a mixture of natural gas steam the presence of a suitable catalyst nickel.
CH4+H2O3H2+CO
Properties of hydrogen:
a) Physical properties:-
1) Hydrogen has got three isotopic forms known as protium ,deuterium and tritium.
2) At room temperature hydrogen is a colorless, tasteless and odorless gas.
3) Molecular hydrogen is the lightest of all gases.
b) Chemical properties:-
1) Reducing agent: Hydrogen is a very reducing agent it can reduce metallic oxides to metal easily ,e.g.
CuO+H2Cu+H2O

2)Reaction with non metal: Hydrogen react with non metal like oxygen and nitrogen on heating.
2H2+O22H2O
3) Reaction with halogen: Hydrogen immediately react with halogen to give halides.
H2+Cl22HCl

 

 

Q:2) How aluminum is extracted from its ore. give its physical and chemical properties?
Ans) Preparation:- It is prepared industrially by a process called the hall beroult process.
purification of ore:- naturally occurring bauxite contain impurities like silica and oxides of iron. the first step is obtained aluminum therefore involves the purification of the mineral. the natural bauxite is reacted with a hot concentrated solution of sodium hydroxide and form soluble sodium aluminates .the impurities remain undissolved and ore removed by filtration. aluminum hydroxide is then precipitate from the solution and is heated to regenerate pure aluminum oxide..
electrolysis of aluminum:- the pure aluminum oxide obtained by the above process is dissolved in a molten mixture of cryolite and calcium fluoride at 950c. this molten mixture is electrolyzed in a specially designed cell with carbon anode. the final result can be represented by the following simplified electrode reaction.
Al2O32Al+3O
aluminum is liberated at the cathode and oxygen is liberated at the anode however the atomic oxygen released at the carbon anode reacts with anode itself to produce carbon dioxide gas.
thus the carbon anodes constantly consumed during the process and they must be replaced at suitable intervals.
PROPERTIES OF ALUMINIUM:-
PHYSICAL PROPERTIES :-
1)Aluminum has a silvery white lustrous shine.
2)It is a good reflector of heat and light.
3)It is a good conductor of heat and electricity.
4)It has a melting point 66C
CHEMICAL PROPERTIES :-
ACTION OF AIR :-Dry has no action .but in most air when aluminum powder is strongly heated it forms aluminum oxide.
ACTION OF WATER :-Cold water has no effect on pure aluminum. but aluminum powder decompose water at 100C liberating and forms.
REACTION WITH ALKALIS :-Aluminum react vigorously with strong alkalis eg to form aluminates along with hydrogen .

 

Q3) What are isotopes? describe the isotopes of hydrogen?
Ans) Isotopes are atom of same element with same atomic number but different mass number.
Isotopes of hydrogen: There are three isotopes of hydrogen i.e.
1)Protium or ordinary hydrogen
2)Deuterium
3)Tritium
1) Protium(ordinary hydrogen):- It most frequently occur in nature. it is represented by 1H1. it has one electron in the nucleus and one electron in the k shell. it occur to 99.98%.
2) Deuterium(heavy hydrogen):- It occur to very little extent. ordinary hydrogen contain about 1 part of deuterium in 7000 part of it. it is represented by 1H2 or D. it has one electron and one neutron in the nucleus and one electron revolves in the k shell. it is usually present in the form of D2O (heavy water) in ordinary water is small amount.
3) Tritium: It is the heaviest isotopes of hydrogen and very varely occur in nature. it is represented by 1H3 or T . it has one proton and two neutron in the nucleus and one electron revolve in the k shell. it has radio active form of hydrogen.

 

 

Q4) How is sodium hydroxide manufactured electrolytically. Give its important application.
A) sodium hydroxide commonly known as caustic soda is commonly manufactured by the electrolysis of solution sodium chloride which is commonly known as brine.
in this electrolytic process nelson cell is used. in this cell anode consist of graphite rod and a u shaped perforated steel cathode used. brine is added in the u tube which on electrolysis gives chloride anode and sodium at cathode sodium react with water to form sodium hydroxide(caustic soda).
application of sodium hydroxide:
1)It is an important laboratory reagent.
2) It is used in paper industry.
3) It is used in the refining of petroleum and oils.

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One Response to CHAPTER 8 HYDROGEN AND THE ACTIVE METAL

  1. muhammad says:

    pleas do me a favour i need a full note of chemistry to downloud

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