non-metals
DESCRIPTION
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. Poor conductors of heat and electricity - PowerPoint PPT PresentationTRANSCRIPT
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Non-Metals
Prepared December 2007
Alrick Moodie
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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
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Properties of Non-Metals
• Poor conductors of heat and electricity
• Brittle , not malleable and ductile
• Dull in colour
• Low in sonority
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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
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Common Non-metals
We will be looking at :
• Hydrogen
• Chlorine
• Oxygen
• Carbon
• Sulphur
• Nitrogen
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Hydrogen
It is a diatomic gas H2
It is colourless and odourless . It is almost insoluble in water and is the lightest known substance .
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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
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Uses of Hydrogen
• Manufacture of ammonia , nitric acid and nylon
• Manufacture of margarine and other hydrogenated oils
• In welding
• As fuel
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Laboratory Preparation
• Hydrogen can be prepared by reacting an acid with a metal
Zn + 2HCl ZnCl2 + H2
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Diagram of the Laboratory Preparation of Hydrogen
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The Water Cycle
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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
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Plants absorb water and loses it through a process called transpiration
Animals also intake water and lose through excretion ( sweat , urine or breathing )
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Uses of water
• Domestic purposes e.g. drinking , washing , cooking , cleaning
• Irrigation of crops
• Generation of electricity
• Industrial processes
• Recreational activities
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WATER VAPOUR IN AIR
GROUND WATER
DOMESTIC & INDUSTRIALPROCESSES
UNDERGROUND WATER
SEAS
PLANTS
ANIMALS
PRECIPITATION
PERCOLATION
RUN OFF
EVAPOURATION
FEEDING
EXCRETION
TRANSPIRATION
ABSORPTION
DRINKING
EVAPOURATION
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Chlorine
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Chlorine
It is a diatomic gas Cl2It is a greenish-yellow gas with a choking odour . It is more dense than air and is slightly soluble in water .
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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 )
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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
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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)
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Oxygen
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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 .
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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 .
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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 .
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Uses of Oxygen
• In welding apparatus
• Rocket fuels
• Steel manufacture
• Breathing equipment
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Laboratory Preparation
Oxygen is prepared by the catalytic decomposition of hydrogen peroxide .
2H2O2 (aq) 2H2O (l) + O2 (g)
MnO2 is the catalyst used
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Carbon
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Carbon exists as many natural occurring allotropes ; diamond , graphite , charcoal and coke .
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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 .
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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 .
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Preparation
Carbon dioxide is prepared by the reaction of a carbonate and a dilute acid .
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Uses of Carbon dioxide
• As a refrigerant
• As a fire suppressant
• In sodas
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Carbon cycle
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Sulphur
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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 .
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Chemical Properties
• Burns in air to form sulphur dioxide
• Combines with most metals to form sulphides .
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Uses
• Manufacture of sulphuric acid
• Manufacture of gunpowder and matches
• Manufacture of fungicides and pesticides
• Vulcanization of rubber
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Sulphur is obtained by the Frasch process where the sulphur is mined directly from the earth in its elemental form .
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Sulphuric acid
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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 .
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Uses
• Manufacture of fertilizers
• Manufacture of white paint
• Manufacture of soaps and detergents
• Refining of petroleum
• Vulcanization
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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)
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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)
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Nitrogen
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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 .
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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 .
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Uses & Manufacture
• As a refrigerant
• As an inert atmosphere in packaging
• Manufacture of ammonia
Nitrogen is obtained by fractional distillation of air .
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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
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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
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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)
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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)
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Uses of Ammonia
• Water purification
• Cleaning agent
• Refrigerant
• Manufacture of fertilizers
• Manufacture of nitric acid
• Manufacture of nylon
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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 VIITurns 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 .