Sci 2.1-2.6 Summary - Water Cycle & Pollution (PDF)

1 er at (w te sta gas d an ) ter (wa te sta uid liq e), (ic Water exists in three physical states: solid state vapour or steam). 2 The table below summarizes the changes in states of water: Temperature at which the process Change in states Process Energy absorbed by ShsOroe or released occurs...

1 er at (w te sta gas d an ) ter (wa te sta uid liq e), (ic Water exists in three physical states: solid state vapour or steam). 2 The table below summarizes the changes in states of water: Temperature at which the process Change in states Process Energy absorbed by ShsOroe or released occurs solid (ice) i Melting - - , Freezing liquid (water) | (steam) s — — S S i o 5 : 100 °C (boiling point) mae ‘ Absorbed —_ Temperatures below gas (water vapour) | the boiling point | ADIOEDN i 7 _ | e - - 19 gas . A bsorbed | liquid ferster) — solid (ice) . , t O 0 °C (freezing point) R L , Evaporation # — (water) S— b -4 iqui Boiling : . (meltin point)t 0 °C (melting Released - — | s Mmoo RN { liquid (water) d 1 — | —_— | Condensation 8a° | | (water vapour e g (water) Temperatures at or P 1S . below the boiling point Released 1 The water cycle involves the following processes: I N B T o e e A o A T B D SN S B N AT e N LS R T A TS S N A AL mvn!\mclzmuwnw.vz\‘rg Evaporatlon E~ Water in the sea, rivers and } - on land evaporates and é becomes water vapour. Prec1p1tat10n Water droplets in the cloud ! fall as rain. @2 The rate of evaporation of water is higher when e the surface area exposed to air is larger, e the humidity is lower, e the temperature is higher, e the air speed is higher. Condensation f The water vapour cools down and condenses, forming | | | clouds. Transportation Clouds may be carried to other places by the wind. (33 1 A solute dissolves in a solvent to form a solution. 2 In general, the rate of dissolving of a solute in water is higher when e the water is stirred, e the temperature of water is higher, e the size of solute is smaller. Solubility of a substance refers to the amount of the substance that can be dissolved in a fixed amount of water at a given temperature. (@24 Different substances have different solubilities in water. (55 The solubility of a substance in water changes with temperature. 1 Natural water contains soluble impurities (e.g. mineral salts), insoluble impurities (e.g. sand and plant debris) and microorganisms. 2 If we drink or use natural water directly, the impurities and microorganisms in the water may harm our health. 3 The types of impurities removed by different methods of water purification in the laboratory: (‘v’ refers to the impurity that can be removed; ‘X" refers to the impurity that cannot be removed.) Type of impurities removed Insoluble impurities Soluble impurities | Microorganisms Sedimentation Distillation ———— e —— v — — e | v P v - - ——————————— e e v —— S Chlorine, ozone and ultraviolet light can be used to kill microorganisms in water. Adding fluoride to drinking water can help prevent tooth decay. Fluoride cannot kill microorganisms. @3 The water treatment process in Hong Kong involves sedimentation, filtration, adding chlorine and fluoridation. ' o Lv . human waste animal waste Human and animal waste may carry harmful microorganisms. If we eat seafood from waters polluted with harmful microorganisms, we may get diseases such as cholera”. If we swim in polluted water, we may get eye or skin diseases. Detergents and fertilizers may contain nutrients” that promote the growth of algae. If the population of algae increases rapidly, a red tide” may result. >, - = ..... ~ detergents fertilizers ........ Sy, Fig 2.43 Ared tide During a red tide, the algae may use up the oxygen in water. Other living things in the water may die because of a lack of oxygen. If the algae produce toxins, the toxins will kill sea animals. If we eat the seafood contaminated with the toxins, we may get poisoned. These chemicals may be taken by sea animals. If we eat the contaminated seafood, these chemicals may build up in our body over time and may cause health problems. 1 it. ve er ns co to t an rt po im is It . ce ur so re l ra Fresh water is a precious natu 2 e, st wa d li so s, ie or ct fa d an s rm fa s, me ho om fr r te Water pollution is mainly caused by waste wa and oil spills from accidents. @3 o int ed rg ha sc di is it re fo be s rk wo t en tm ea tr ge wa se in d te ea tr In Hong Kong, waste water is the sea. @4 for tre Cen ent atm Tre te Was al mic Che the to t sen is als mic Waste water containing harmful che tment.