Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
SCIENCE - II TERM (2014 – 2015) STD 7 Chemistry in Your Life In this chapter, you will learn about: Compounds and their uses including organic compounds such as hydrocarbons Man-made materials and their uses Useful compounds Compounds are the substances that are formed by elements combining in a fixed proportion. Let us learn about some compounds which are used in daily life. Fertilizers Fertilizers are substances applied to the soil to promote plant growth. The main elements present in a fertilizer are nitrogen, phosphorus and potassium. Generally, the decaying organic matter present in the soil, supply all these minerals to the plants. But if the natural nutrient supply is not present or is insufficient, then fertilizers must be added to the soil. Fertilizers like urea and ammonium phosphate supply nitrogen to the soil. Potassium sulphate supplies potassium to the soil. Pesticides Pesticides are chemicals that are used to destroy pests such as rats, insects and disease causing organisms like bacteria, fungi, algae and viruses that destroy plants. Some common pesticides are DDT, BHC heptachlor and methyl parathion. Bordeaux mixture is used to control fungus on grapes, melons and other berries. It is also used in swimming pools to control growth of algae. Though pesticides are used to reduce the levels of pest damage, some of them are harmful. Some pesticides like DDT (dichlorodiphenyltrichloroethane) do not break down easily in the environment and accumulate in food chains and spread to other ecosystems. These pesticides also cause contamination of water, which if consumed causes health problems like birth defects, nerve damage and cancer. To reduce harmful effects of pesticides the following steps should be taken: 1. Washing: You must wash all fruits and vegetables under tap water before consuming them. This helps to remove bacteria and traces of chemicals from the surface of fruits and vegetables. 2. Peeling and trimming: Peel off the skin of fruits and vegetables to remove bacteria and pesticides. 1 Discard outer leaves of leafy vegetables. Trim fat from meat and poultry and fish as pesticides accumulate in fats. 3. Food sources: Consume a variety of foods from different sources of production. This will not only reduce the exposure to a single pesticide but will also give a better mix of nutrients. Naturally occurring compounds: Silicon compounds Silicon is an element possessing properties typical to metals and non-metals. Uses of silicon: Silicon plastic (silastic) is used for artificial skin grafts to protect healing skin. Silica (sand) is the main ingredient used for making glass, cement, porcelain and glazes. It is also found in human skeleton. Silicon combines with oxygen to form silicones which are resistant to heat and moisture. Silicones are widely used to coat kitchenware to make non-stick surfaces for oil free cooking. Silicon is also used in the electronics industry to make semiconductors. Limestone and marble Limestone and marble are naturally occurring rocks. They are different forms of calcium carbonate. There are several uses of these rocks. A few are given below: 1. White marble is used to make statues and monuments. Eg: The Taj Mahal is made of white marble. 2. Ground calcium carbonate is used as a coating pigment for paper because of its high brightness. It is used in plastics because it imparts stiffness and strength. It is used in paints because it has high brightness, and is weather resistant. 3. Limestone is used to make slaked lime which is used for white washing in buildings. Paints Paints are liquids which after application to the surface forms a solid film. They help to protect metallic surfaces from corrosion, or to decorate the surface. Paints have three main components: 1. Pigments which add colour: Titanium oxide and zinc oxide are commonly used pigments. Zinc oxide provides anti-corrosive coatings for various metals. Titanium oxide is replacing lead pigments which were used earlier and are highly toxic. 2. Binders: The binders bind the pigments and make the paint more durable. 3. Solvents: These adjust the fluidity of the paints. Water is the solvent in water based paints while oil based paints have solvents like alcohol or turpentine. 4. Gypsum and plaster of Paris (POP):Both gypsum and plaster of Paris are different forms of calcium sulphate. When heated, gypsum changes to POP. This is used to make statues, chalks for writing on black boards and casts for setting fractured bones in humans. 2 Organic compounds The compounds present in living matter are called organic compounds. The main elements present in organic compounds are carbon, hydrogen and oxygen. Nitrogen and sulphur may also be present. Some important compounds are hydrocarbons, carbohydrates and proteins. Carbohydrates Carbohydrates are complex organic substances which form the bulk of your diet. They are the energy suppliers in daily diet. The common carbohydrates are glucose, sucrose, lactose, fructose, cellulose and starch. Sucrose Sugar Lactose Milk Cellulose Walls of plant cells Starch Potato, corn, rice, wheat Proteins Proteins are complex organic compounds containing nitrogen in addition to carbon, hydrogen and oxygen. Proteins are another important constituent of your diet which is required for body building. Nuts, milk, beans, chicken and pulses are rich in proteins. Almost all organs of the body contain a protein called collagen which gives strength to the body. Man-made materials Materials that are not produced naturally but are created by humans using various methods are synthetic in nature. Some examples of man-made materials are plastics, medicines, soaps and detergents, glass, etc. Plastics: Small building blocks of the same or different kind when joined together they form a long chain molecule of high molecular mass called a polymer. The process of forming these long chains of molecules is called polymerization. Carbohydrates like starch and cellulose, proteins, jute, silk, cotton and wool are all natural polymers. Plastics are man-made polymers. They are not affected by acids or alkalis. Plastics degrade very slowly and on burning produce harmful greenhouse gases. Plastics are of two types: 1. Thermosetting plastics: These plastics can melt and take shape only once. After they have solidified, they stay solid and cannot be melted and remoulded. For example, Melanine is used for making unbreakable cups, saucers and crockery. Formica is used for making smooth surface on table tops. Bakelite is used for making electrical plugs and switches. 2. Thermoplastics: These plastics can be melted and remoulded repeatedly. For example, Polyethylene or polythene is used to make carry bags for milk and water. Polyvinyl chloride (PVC) used to make raincoats, soles of shoes, water and gas pipes, electrical wires, etc. 3 Polystyrene in the form of foam is commonly called thermocole and is used as packaging material. Nylon is used as a synthetic fibre Cement Cement is an important synthetic material used in the construction of buildings, dams, bridges and other structures. This cement can be used for various other purposes. Such as: 1. When mixed with sand and water it is used for plastering and to bind bricks and stones together. 2. When mixed with water, sand and gravel, forms a hard, solid mass called concrete. Concrete is used to make sleepers in railway tracks and the framework for certain parts of the buildings. Steel rods when embedded in wet concrete form reinforced concrete. This is much stronger than concrete and forms the load bearing frame work in pillar construction for example, bridges Bridge made out of reinforced cement Glass Glass is an amorphous (or non-crystalline) solid material which is a mixture of silica, soda and lime. It is not a solid, gas or a liquid substance. Generally, it is classified as a rigid liquid, maintaining liquid properties while acting like a solid. At very high temperatures, glass is melted into the liquid form and now can be moulded into various forms. It can be easily recycled and can be used in several forms such as in making window panes, electric bulbs, greenhouses, etc. Greenhouse Electric bulbs Types of glass: Glass is generally defined as a transparent, shiny substance that breaks very easily. You see several things around you which are made of glass. For example, window panes, eyeglasses, etc. The type of glass used for preparation of all these objects is different. There are many kinds of glass. 1. Type of glass Characteristic features Uses Commercial / soda-lime glass Most common commercial glass, less expensive. Soft, breaks and cracks easily. Not resistant to high temperatures. Window panes, bottles 4 2. Lead glass (commonly called Crystal) Contains lead in addition. Sparkles when cut. 3. Pyrex glass / Borosilicate Resistant to heat and chemicals. Can be shaped and blown easily 4. 4.Optical glass 5. Fibreglass Consists of tiny glass fibres which are loosely packed together in a wool-like mass. It can be used like wool or cotton fibres to make glass yarn, tape, cloth etc. 6. Laminated safety glass Tough and strong and does not develop cracks or shatter like ordinary glass. 7. Tempered safety glass Used in all-glass doors, side and rear windows of automobiles. 8. Bullet proof glass It is a single piece of glass that has been given special heat treatment. It is several times stronger than ordinary glass. When it does break, the whole piece of glass collapses into small, dulledged fragments. Thick, multilayer laminated glass. This can stop bullets. 9. Laboratory glassware It is made from heat resistant glass to withstand rapid change in temperature. It is also more resistant to chemical attack than ordinary glass. This type of glass darkens when exposed to ultraviolet rays and returns to their clear state when the rays are removed Making beakers, flasks, test tubes and special chemical apparatus. 10. Photochromic glass Tableware. Radiation shielding glass in nuclear industry because lead absorbs harmful radiations. For cooking and serving utensils, lab apparatus because it can withstand high temperatures. Eyeglasses, microscopes, telescopes. Electrical insulation, chemical filtration. Aeroplane wings and bodies, automobile bodies, curtain material because it is fireresistant and washable. Automobile windshields Security purposes Used for windows, sunglasses and instrument controls. 5 Soaps and detergents A soap is a salt of sodium or potassium with fatty acids like stearic, oleic and palmitic acid present in oils and fats. Soaps are made from the breakdown of oils or fats by sodium or potassium hydroxide, they form respective salts of fatty acids. This process is called saponification. Perfumes and colours are added to the soaps before they are moulded and dried into cakes. SOAPS Hard soaps Soft soaps Contain sodium Contain potassium Uses: Shaving, washing clothes Uses: As bath soaps Detergents: Detergents are made from petroleum products. Compared to soaps, they have better cleansing action and form lather even in hard water unlike soaps. In hard water soaps form a white precipitate or scum which sticks to the clothes giving it an unclean appearance and even results in wastage of soap. However, unlike soaps, the biggest disadvantage of detergents is that they are non-biodegradable in nature and they cause water pollution. Medicines: Medicines are chemicals used to treat a diseased condition without affecting the patient. Some medicines are extracted from plants or animals but some others need to be made artificially from chemicals. There are different type of medicines used for different purposes. Type of medicine Uses Examples 1. Antacids For acidity Milk of Magnesia 2. Analgesics Give relief from pain Aspirin, Crocin 3. Antipyretics Bring down fever, reduce pain Paracetamol 4. Antiseptics To prevent infection on cuts and wounds Dettol 5. Antibiotics Used to kill or prevent the growth of Penicillin disease causing microorganisms 6. Anti-histamines For allergies and hypersensitive Benadryl reactions and colds *************************************************************************************** KSD 6