Transcript Non-Metals
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 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 • • • • 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 • • • • 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 • • • • • 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 • • • • • • 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 .