Tuesday, 5 January 2010

Chemistry notes - Planet Earth

Examples of resources in the Earth: coal, natural gas, metals, NaCl and limestone… Matters are something that has mass. Mixtures – 2+ pure substances which haven’t joint chemically Pure substances: Elements: Can’t be broken into anything simpler by chemical methods. Compound: Composed of 2+ elements joined chemically together. Some examples of compounds and their uses: Ammonia ( NH3) – glass cleanser, fertilizer Calcium carbonate ( CaCO3) – calcium supplement tablets Sodium hydroxide ( NaOH) : drain cleanser Mixture VS compound: Mixed together in any proportion. VS In a fixed ratio. No chemical change when it’s formed VS Energy is usually released when forming the compound (chemical change occurred) Similar properties with the original substances that made up the mixture VS Can have very different chemical properties then the elements that it contains Don’t have a sharp BP/MP (it varies) VS Have a definite/sharp/unique MP/BP Can be separated by physical method VS Have to be separated through chemical method. (e.g. electrolysis) Method of separation 1) Decantation Let the residue sinks in the bottom of the beak and pour the decant away through the glass rod. It’s suitable for separating insoluble liquid from a liquid. 2) Filtration Pour the mixture into a filter funnel with filter paper through the glass rod. Residue is in the beaker underneath and the filtrate left in the filter paper. It’s suitable for separating insoluble liquid from a liquid. (e.g. separate sand from sea water) 3) Evaporation. Heat the mixture in a evaporating dish by Bunsen flame. When solution is evaporated, solid remains. It’s used to separate dissolved solid from a solution. (e.g. NaCl from Sea Water) 4) Crystallization Method I: Heat the mixture, some solvent boils away, but hot solution can hold more solute. Cool it down and the solution can’t hold such solute, crystal formed. Method II: Pour the mixture in a beaker with cover, let the solvent evaporate under room temperature, it will over-saturated and from crystals. It’s used to separate dissolved solid from a solution. (e.g. from Water) 5) Distillation (evaporation + crystallization) Evaporate the solution in a distillation flask, a tube with condenser receives the solution vapour and turn it into liquid, and collected by the conical flask. It’s suitable to separate dissolved solid from a solution. 6) Fractional distillation Remove impurities such as dust, water vapour and ; compress the air in a high pressure (by the Ideal Gas Law it’ll get hotter), then it’s cooled in a cool chamber (by water), it’s expanded (by IGL it’s cooler). Repeated this step until the air is liquefied. Pump the air into the fractioning column, the temperature is slowly increased. The B.P. of , and are , and respectively, therefore is collected in the bottom of the tower, followed and . It’s suitable to separate two miscible liquids. 7) Sublimation Put the mixture in a beaker covered by a evaporating dish. Heat the beaker until it sublimes. Those sublimed gas will become solid again in the bottom of the dish. It’s suitable to separate mixture of two solids which one of them can sublime. Physical properties are something that can be measured without changing the chemical composition of the substance. No new substances are formed during physical change. Chemical properties describe the ability of a substance to form new substances. One or more new substances is formed in chemical change. In another way, energy is absorbed or released. Test for oxygen: (glowing splint test) Oxygen relights glowing splint. Test for hydrogen: (burning splint test) Hydrogen gives a “pop” sound when burning. Test for water: Water turns dry cobalt(II) chloride paper from blue to pink. Test for some metals (flame test): If it’s not clean, dip it into conc. solution, heat it until no characteristic flame is shown. Dip the clean wire into (fresh) conc. solution (or dip it into conc. solution, heat it until no characteristic flame is shown.), then dip it into the solid sample power and heat it. 1) Sodium ion gives golden yellow flame. 2) Calcium ion gives brick-red flame. 3) Potassium ion gives lilac flame. 4) Copper ion gives bluish green flame. Test for chloride: add (dilute) nitric acid followed by silver nitrate solution, gives white ppt (participate). Four layers of Earth’s atmosphere: troposphere, stratosphere, mesosphere and ionosphere. Composition of atmosphere – 78% of , 21% of , 0.9% of noble gases, 0.03% of , variant amount of and some other gases. Sea covers over 70% surface area of the Earth. It dissolved different salts. Most salts are brought by rivers. Composition of sea salt (3.5% of the sea water): about 68% of , 15% of , 11% of , 3% of and some other salt. A solution forms when a substance (solute) dissolves in another (solvent). Dilute solution contains a very small amount of solute in given amount of solution. When solute increase, it becomes concentrated, and finally saturated. Saturated solution means it can’t dissolve anymore solute in a given temperature. Electrolysis of water 2H2O -> 2H2 + O2 sea water -> Hydrogen + Chloride + Sodium Hydroxide Particle theory of matter – all substances are made up by very small particles. Limestone – calcium carbonate ( CaCO3) 1) Heat and limewater(calcium hydroxide) Heating calcium carbonate gives calcium oxide (quick lime) and carbon dioxide: CaCO3 -> CaO + CO2 Adding water to calcium oxide gives lime water (slaked lime in solution): CaO+H2O -> Ca(OH)2 Test for carbon dioxide: turns lime water from colourless to milky: Ca(OH)2+H2O -> CaCO3 + H2O Excess carbon dioxide makes it becomes colourless again: CaCO3+H2O+CO2->Ca(HCO3)2 2) Acid Adding (dilute) hydrochloric acid gives calcium chloride, water and carbon dioxide: CaCO3+2HCl->CaCl2+H2O+CO2 Use of limestone 1) Crushed limestone (CaCO3) – extraction of iron; construction material for road and buildings. 2) Powered limestone (CaCO3, grinded) – neutralize acidity of soil and sulphur dioxide in flue gas of power stations; making glass. 3) Quicklime (CaO) – making steel with Fe, neutralize acidity in soil; drying agent in industry. 4) Slaked lime (Ca(OH)2) – neutralize acidity in soil and lake affected by acid rain. 5) Cement (limestone heating with shale) – ingredients of concrete. Formation of limestone cave Solid rock broke down and changed into other materials by weathering, its surface is wearied away while the movement of products of weathering that changed their location is called erosion. Rainfalls becomes carbonic acid with carbon dioxide in air (H2O+CO2→H2CO3) (Note that the reaction can occur the inverse direction here) while carbonic acid dissolves the underground limestone deposits to form calcium hydrogencarbonate: CaCO3+H2CO3→Ca(HCO3)2 (Ca(HCO3)2 is the main cause of hard water.) The underground limestone is dissolved in this way over millions of years to form underground holes called limestone caves. Formation of limestone CaCO3 exists naturally in 3 forms: chalk, limestone and marble, depends on their hardness. When sea animals die, their skeletons and shells (mainly contains CaCO3) sink into the mud at the bottom of the oceans. After many years layers built up and pressure from top layers changes the bottom layers to chalk. Earth movements such as earthquake may lift the layer to Earth’s surface. They changes to limestone and marble under. higher pressure and heat Sorry for the chemical equation. >_>

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