Transcript Non-Metals - Scientific Research Council

Non-Metals
Prepared December 2007
Alrick Moodie
What are non-metals ?
• Non-metals are those substances which
are not metals i.e. they do not ionize by
electron loss and do not show the
characteristics of metals
Properties of Non-Metals
•
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•
Poor conductors of heat and electricity
Brittle , not malleable and ductile
Dull in colour
Low in sonority
Chemical Properties
• React with air/oxygen to give covalent
acidic oxides ( although a few give neutral
oxides e.g. CO )
• React with metals to form ionic
compounds
• Do not react with dilute acids
• Do not react with water except chlorine
• Tend to be oxidizing agents
Common Non-metals
We will be looking at :
• Hydrogen
• Chlorine
• Oxygen
• Carbon
• Sulphur
• Nitrogen
Hydrogen
It is a diatomic gas H2
It is colourless and odourless . It is almost
insoluble in water and is the lightest known
substance .
Chemical Properties of Hydrogen
• It has a neutral pH
• It burns in air/oxygen
• It combines with reactive metals to give
hydrides : Mg + H2  MgH2
• It can act as a reducing agents e.g. in the
extraction of metals
CuO + H2  Cu + H2O
Uses of Hydrogen
• Manufacture of ammonia , nitric acid and
nylon
• Manufacture of margarine and other
hydrogenated oils
• In welding
• As fuel
Laboratory Preparation
• Hydrogen can be prepared by reacting an
acid with a metal
Zn + 2HCl  ZnCl2 + H2
Diagram of the Laboratory
Preparation of Hydrogen
The Water Cycle
Water vapour in the atmosphere
condenses and form water droplets and
precipitation occurs . If temperature is low
we will get snow or hail ( ice ) .
The water on the ground :
• percolates and go underground
• runs off into rivers and the seas
• evaporates
Plants absorb water and loses it through a
process called transpiration
Animals also intake water and lose
through excretion ( sweat , urine or
breathing )
Uses of water
• Domestic purposes e.g. drinking , washing
, cooking , cleaning
• Irrigation of crops
• Generation of electricity
• Industrial processes
• Recreational activities
EXCRETION
WATER VAPOUR IN AIR
EVAPOURATION
TRANSPIRATION
EVAPOURATION
ANIMALS
DRINKING
PRECIPITATION
GROUND WATER
FEEDING
RUN OFF
SEAS
PERCOLATION
ABSORPTION
PLANTS
UNDERGROUND WATER
DOMESTIC & INDUSTRIAL
PROCESSES
Chlorine
Chlorine
It is a diatomic gas Cl2
It is a greenish-yellow gas with a choking
odour . It is more dense than air and is
slightly soluble in water .
Chemical Properties of Chlorine
• Readily combines with metals to form
chlorides : Mg + Cl2  MgCl2
• It is a powerful oxidizing agent
• It bleaches substances ( in the presence
of moisture )
Uses of Chlorine
• Manufacture of plastics e.g. PVC
• Sterilize water e.g. drinking supplies ,
swimming pools
• Preparation of cleaning fluids and
bleaching agents
• Manufacture of hydrochloric acid
Laboratory Preparation
• Chlorine can be the oxidation of conc.
Hydrochloric acid by potassium
manganate VII
HCl (l) + KMnO4(s)
 KCl (aq) + MnCl2 (aq) + H2O (l) + Cl2 (g)
Oxygen
Oxygen is the most abundant element on
Earth . Approximately 50% of the earth’s
crust is composed of oxygen containing
compounds , while 20% of the atmosphere
is free oxygen gas .
Oxygen is a diatomic gas O2 although in
the upper atmosphere it exists in the
allotrope form as ozone O3 .
It is a colourless odourless gas which is
slightly soluble in water and has the same
density as air .
Chemical Properties
• It has a neutral pH of 7
• Supports combustion
• Combines with most elements to form
oxides
• It is involved in biological processes of
respiration .
Uses of Oxygen
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In welding apparatus
Rocket fuels
Steel manufacture
Breathing equipment
Laboratory Preparation
Oxygen is prepared by the catalytic
decomposition of hydrogen peroxide .
2H2O2 (aq)  2H2O (l) + O2 (g)
MnO2 is the catalyst used
Carbon
Carbon exists as many natural occurring
allotropes ; diamond , graphite , charcoal
and coke .
Chemical Properties of Carbon
• Readily burns in oxygen to form carbon
dioxide . In limited supply of air carbon
monoxide is formed .
• It is a powerful reducing agent at high
temperatures .
Carbon Dioxide
Carbon dioxide is a colourless , odourless
gas which is slightly soluble in water .
It is more dense than air and is slightly
acidic .
The presence of carbon dioxide can be
determined by the formation of a
precipitate with calcium hydroxide .
Preparation
Carbon dioxide is prepared by the reaction
of a carbonate and a dilute acid .
Uses of Carbon dioxide
• As a refrigerant
• As a fire suppressant
• In sodas
Carbon cycle
Sulphur
Sulphur is found in the earth’s crust as a
free element and as sulphides and
sulphates .
The free sulphur occurs as two allotropes ,
monoclinic and rhombic .
Chemical Properties
• Burns in air to form sulphur dioxide
• Combines with most metals to form
sulphides .
Uses
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Manufacture of sulphuric acid
Manufacture of gunpowder and matches
Manufacture of fungicides and pesticides
Vulcanization of rubber
Sulphur is obtained by the Frasch process
where the sulphur is mined directly from
the earth in its elemental form .
Sulphuric acid
Concentrated sulphuric acid is a
colourless , odourless , oily liquid . It is a
powerful dehydrating liquid .
Diluting conc. sulphuric acid is a very
exothermic reaction and must be done
cautiously .
Uses
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Manufacture of fertilizers
Manufacture of white paint
Manufacture of soaps and detergents
Refining of petroleum
Vulcanization
Manufacture
Sulphuric acid is manufactured by the
Contact process which has three stages .
1. Sulphur is burned in air to form sulphur
dioxide S (s) + O2 (g)  SO2 (g)
2. The sulphur dioxide is oxidized to
sulphur trioxide
2SO2 (g) + O2 (g)  2SO3 (g)
3. The sulphur trioxide is dissolved in
concentrated sulphuric acid to form
oleum which is diluted to form sulphuric
acid .
H2SO4 (aq) + SO3 (g)  H2S2O7 (l)
H2S2O7 (l) + H2O (l)  2H2SO4 (aq)
Nitrogen
Nitrogen forms 78% of the air by volume .
It is a colourless , odourless gas which is
insoluble in water and has the same
density as air .
Nitrogen is notoriously inert . However it
will combine with oxygen at high
temperatures to form nitrous oxides . This
occurs during lightning discharges and in
the engines of vehicles .
It will also combine with hydrogen under
certain conditions of temperature and
pressure to form ammonia .
Uses & Manufacture
• As a refrigerant
• As an inert atmosphere in packaging
• Manufacture of ammonia
Nitrogen is obtained by fractional
distillation of air .
Ammonia
Ammonia is a colourless gas with a
pungent , choking smell . It is less dense
than air and is very soluble in water .
Chemical formula NH3
Dissolved ammonia is called aqueous
ammonia NH3 (aq) or ammonium
hydroxide NH4OH
Chemical properties
• Dissolves in water to give a weakly alkali
solution . It is the only common alkali gas .
• Combines directly with acids to form
ammonium salts
• Acts as a reducing agent
Laboratory Preparation
Ammonia can be prepared by heating an
ammonium salt with an alkali .
2NH4Cl (s) + Ca(OH)2 (s)
 2NH3 (g) + CaCl2 (aq) + 2H2O (l)
Industrial Preparation
Ammonia is prepared by the Haber
Process . Purified Nitrogen and Hydrogen
gases are passed over a finely divided iron
catalyst at 350 – 400 oC and a pressure of
250 to 300 atmospheres .
N2 (g) + 3H2 (g)  2NH3 (g)
Uses of Ammonia
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Water purification
Cleaning agent
Refrigerant
Manufacture of fertilizers
Manufacture of nitric acid
Manufacture of nylon
Gas
Colour
Odour
Test
Hydrogen
None
None
Gives a pop with a lighted splint .
No effect on litmus
Oxygen
None
None
Relights a glowing splint .
No effect on litmus
Carbon dioxide
None
None
Turns lime water cloudy then colourless
Ammonia
None
Pungent
Dense white fumes formed when in contact with
hydrogen chloride .
Turns moist red litmus blue .
Sulphur dioxide
None
Choking
Reduces potassium dichromate and manganate VII
Turns moist blue litmus red .
Hydrogen
chloride
None
Irritating
Dense white fumes formed when in contact with
ammonia .
Turns moist blue litmus red .
Chlorine
Yellow-green
Irritating
Moist blue litmus turns red and then bleached .
Nitrogen
dioxide
Brown
Irritating
Moist blue litmus turns red .
Water vapour
None
None
Cobalt chloride paper turns from blue to pink .