Dr.Atikah,MSi,Apt Jurusan Kimia FMIPA Universitas Brawijaya (UB) 2012 04/12/2012Kimia Lingkungan Air-11.

Presentasi berjudul: "Dr.Atikah,MSi,Apt Jurusan Kimia FMIPA Universitas Brawijaya (UB) 2012 04/12/2012Kimia Lingkungan Air-11."— Transcript presentasi:

1 Dr.Atikah,MSi,Apt Jurusan Kimia FMIPA Universitas Brawijaya (UB) 2012 04/12/2012Kimia Lingkungan Air-11

2 Referensi From Green Chemistry and the Ten Commandments of Sustainability, Stanley E. Manahan, ChemChar Research, Inc., 2006 manahans@missouri.edu Manahan, Stanley E. "ENVIRONMENTAL SCIENCE, TECHNOLOGY, AND CHEMISTRY"Environmental Chemistry, Boca Raton: CRC Press LLC, 2000 04/12/2012Kimia Lingkungan Air-12

3  Air, dengan rumus kimia tampak sederhana H 2 O, merupakan substansi sangat penting dalam semua bagian dari lingkungan.  Air mencakup sekitar 70% keberadaanya di semua bidang lingkungan dari permukaan bumi, dengan lautan sebagai reservoir terbesar  Keberadaan air mulai dari :  air asin, air atas tanah sebagai air permukaan di danau dan sungai,  air bawah tanah sebagai air tanah,  di atmosfer sebagai uap air,  dalam ice caps kutub seperti es padat, dan. 04/12/2012Kimia Lingkungan Air-13

4 Keberadaan air juga terdapat dalam banyak segmen anthrosphere seperti dalam boiler atau sistem distribusi air kota Air merupakan bagian penting dari semua sistem kehidupan dan Merupakan media dari mana kehidupan berevolusi dan di mana ada kehidupan 04/12/2012Kimia Lingkungan Air-14

5 Air yang digunakan manusia harus cukup keberadaannya dan bersih Oleh karena itu kita perlu mengukur kuantitas dan kualitas air dalam rangka untuk memahami di mana masalah air terjadi Air dapat menjadi "terbarukan" jika penggunaan air < dibandingkan air yang dapat di Recharge (pengisisn kembali air) Air dapat menjadi "terbarukan" jika Polusi air < dari Pembersihan air 04/12/2012Kimia Lingkungan Air-15

6 H 2 O: RUMUS MOLEKUL SEDERHANA, MOLEKUL KOMPLEKS  Siku struktur molekul air (lihat slide berikutnya)  Molekul air  polar Muatan Positif berakhir pada anion Muatan Negatif berakhir pada kation  Molekul air membentuk ikatan hidrogen 04/12/2012Kimia Lingkungan Air-16

7 Water Molecule Water’s properties can best be understood by considering the structure and bonding of the water molecule: The water molecule is made up of two hydrogen atoms bonded to an oxygen atom. The three atoms are not in a straight line; instead, as shown above, they form an angle of 105°. Because of water’s bent structure and the fact that the oxygen atom attracts the negative electrons more strongly than do the hydrogen atoms, the water molecule behaves like a dipole having opposite electrical charges at either end.

8 The properties of water are due to the polar nature of the water molecule and its ability to form hydrogen bonds. The Water Molecule 04/12/2012Kimia Lingkungan Air-18

9 SIFAT PENTING AIR Air memiliki sifat yang sangat penting karena perannya sebagai: Pelarut, media kehidupan, perilaku lingkungan, dan penggunaan di industri, mengikuti dasar karakteristik molekul air: 04/12/2012Kimia Lingkungan Air-19

10 Sifat Air sebagai Senyawa yang Unik Sebagai media reaksi kimia, air sangat penting dalam kehidupan makhluk hidup Sifat khusus air adalah: bersifat polar, cenderung membentuk ikatan hidrogen serta mampu menghidrasi ion-ion logam Sifat air disajikan dalam Tabel 3.1 04/12/2012Kimia Lingkungan Air-110

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12 Apabila garam NaCl dilarutkan ke dalam air, maka akan dihasilkan ion positif Na + dan ion negatif Cl-, ion ion positif Na + dikelilingi oleh molekul air, dimana gugus negatifnya berujung pada ion-ion positif dan anion klorida dikelilingi molekul air dengan gugus positifnya berujung pada ion-ion negatif seperti yang terlihap pada Gambar 3.4. This kind of attraction for ions is the reason why water dissolves many ionic compounds and salts that do not dissolve in other liquids.

13 Polar water molecules

14 Ikatan Hidrogen Air Sifat kedua dari air adalah kemampuannya membentuk ikatan hidrogen

15 Ikatan Hidrogen dalam Molekul Air Ikatan Hidrogen air membantu agar molekul-molekul solut dan ion-ion berada dalam larutan Hal ini terjadi jika terjadi ikatan Hidrogen yang terbentuk antara molekul air dengan atom hidrogen, nitrogen, oksigen dalam molekul solut (see Figure 3.5). Ikatan Hidrogen juga membantu mengikat partikel- partikel kecil (partikel koloid) tetap dalam bentuk suspensi dalam air

16 Sifat Air Sebagai Pelarut yang Baik Sebagai pelarut, molekul air merupakan media transpor dasar untuk nutrisi dan limbah yang dihasilkan dalam proses-proses kehidupan Karena memiliki tetapan dielektrik yang tinggi maka air merupakan pelarut yang baik dan kebanyakan senyawa-senyawa ionik berdissosiasi dalam air menghasilkan ion-ion Air juga memiliki kapasitas panas tertinggi diantara cairan atau padatan (l cal x g - 1 x deg -1 ) 04/12/2012Kimia Lingkungan Air-116

17 Sifat Air Sebagai Pelarut yang Baik Karena tingginya kapasitas panas yang dimiliki air maka untuk mengubah temperatur massa air diperlukan panas cukup besar Oleh karena itu badan air bersifat dapat menstabilkan efek temperatur pada daerah geografis berdekatan Sifat kapasitas panas dari air mencegah perubahan besar temperatur secara tiba-tiba dalam badan air sehingga melindungi organisme akuatik akibat terjadinya schock tiba-tiba akibat perubahan temperatur air 04/12/2012Kimia Lingkungan Air-117

18 Sifat Air Sebagai Pelarut yang Baik Kenyataan sifat air ini menyababkan es mengapung, Yang beruntung konsekuensi dari fakta ini adalah bahwa es mengapung, bahkan tubuh besar beberapa molekul air dapat membeku. Gambaran sirkulasi secara vertikal air danau merupakan faktor penentu senyawa kimia dan biologi yang berada di dalamnya yang sebagian besar dibentuk oleh keunikan hubungan densitas- temperatur molekul air 04/12/2012Kimia Lingkungan Air-118

19 SIFAT PENTING AIR Sebagai pelarut yang baik untuk garam, asam, basa, dan Dengan zat yang memiliki atom H, O, dan N mampu membentuk ikatan hidrogen Sebagai pelarut dalam cairan biologis, seperti darah atau urin Sebagai media mineral dan transportasi mineral terlarut dalam geosfer yang mengangkut nutrisi ke akar tanaman dalam tanah Banyak digunakan dalam industri Air memiliki tegangan permukaan sangat tinggi Cairan air seperti tetes hujan menunjukkan sifat fisk seperti penutup lapisan tipis membran bebek mengapresiasi sifat air karena memungkinkan mereka mengambang diatas permukaan air 04/12/2012Kimia Lingkungan Air-119

20 SIFAT PENTING AIR Seekor bebek akan tenggelam dalam air yang ditambahkan deterjen telah untuk menurunkan tegangan permukaan, menyebabkan burung bernasib sangat menyedihkan Air bersifat transparan terhadap cahaya sinar tampak dan UV yang memungkinkan terjadinya fotosintesis pada ganggang di bawah permukaan air Air membeku pada 0 o C dan memiliki kerapatan maksimum pada temperatur 4 o C, sehingga menyebabkan badan air bertingkat dengan bagian lebih dingin, lapisan padat berada di bagian lebih bawah air 04/12/2012Kimia Lingkungan Air-120

21 Sifat Panas Air yang Penting High heat capacity of 4.184 joules per gram per ˚ C (J/g- ˚C) Very high heat of fusion of 334 joules per gram (J/g) Very high heat of vaporization of water is 2,259 J/g, water vapor carries latent heat 04/12/2012Kimia Lingkungan Air-121

22 Karakteristik Panas Air yang Penting Sifat fisik yang paling penting dari air yang sering diperdebatkan adalah perilaku dengan panas. Air cair memiliki kapasitas panas dari 4,184 joules per gram per ˚ C (J / g ˚ C), yang berarti bahwa 4,184 joule energi panas yang dibutuhkan untuk menaikkan suhu 1 gram air cair sebesar 1 ˚ C. Ini menunjukkan kapasitas panas yang sangat tinggi untuk menstabilkan suhu daerah di dekat badan air. Kapasitas panas tinggi air adalah karena adanya fakta bahwa molekul air sangat terikat bersama oleh ikatan hidrogen 04/12/2012Kimia Lingkungan Air-122

23 Karakteristik Panas Air yang Penting Besarnya energi panas diperlukan untuk memecahkan ikatan hidrogen air sehingga molekul air dapat bergerak lebih cepat pada suhu tinggi Air juga memiliki panas fusi sangat tinggi yakni 334 joule per gram (J / g). Ini berarti diperlukan panas yang sangat tinggi untuk memecahkan bagian molekul air yang terikat secara ikatan hidrogen dalam molekul es dalam rangka mengubah es menjadi cairan air 04/12/2012Kimia Lingkungan Air-123

24 Karakteristik Panas Air yang Penting Es yang meleleh, asalkan baik es padat dan air cair berada bersama-sama, maka suhu tetap pada suhu leleh, yaitu suhu konstan pada 0 ˚C. Panas ditambahkan ke sistem digunakan untuk memecah molekul terpisah dalam es padat, bukan untuk meningkatkan suhu. Panas penguapan air adalah 2,259 J/g. Artinya 2.259 joule energi panas yang dibutuhkan untuk menguapkan 1 gram air cair Panas ini merupakan suhu penguapan tertinggi bagi kebanyakan cairan 04/12/2012Kimia Lingkungan Air-124

25 Karakteristik Panas Air yang Penting Panas penguapan ini memiliki pengaruh besar pada badan air dan pada cuaca. Dengan menyerap panas begitu banyak, air berubah dari cair ke uap, Air menstabilkan suhu atmosfer. Namun, panas laten yang terkandung dalam uap air dilepaskan ketika uap mengembun, seperti apa yang terjadi saat hujan. panas yang dilepas ini menghangatkan massa udara menyebabkan massa udara meningkat, yang merupakan kekuatan pendorong di belakang badai dan angin topan. 04/12/2012Kimia Lingkungan Air-125

26 Karakteristik Panas Air yang Penting Panas laten dalam bentuk uap air diuapkan dari lautan di dekat khatulistiwa yang terbawa menjauh dari khatulistiwa dalam bentuk massa udara dan dilepaskan ketika uap air terkondensasi membentuk hujan. 04/12/2012Kimia Lingkungan Air-126

27 Air yang digunakan oleh manusia terutama adalah air permukaan dan air tanah Meskupun sumber air berbeda beda satu sama lainnya secara nyata Secara teoritis air yang dapat digunakan sekitar 4.6 x 10 12 liter per hari, atau hanya 23 sentimeter per tahun. Pada saat ini air yang dapat digunakan di USA sekitar 1.6 x 10 12 liter per hari, atau 8 sentimeterdari rata-rata curah hujan tahunan. Jumlah ini merupakan kenaikan 10 kali penggunaan dari 1.66 x 10 11 liter per hari pada pergantian abad. 04/12/2012Kimia Lingkungan Air-127

28 Trend dalam penggunaan air di U.SA Pendorong tren dalam penggunaan air di AS, merupakan hasil dari: upaya konservasi air, terutama di industri dan pertanian Daur ulang air, termasuk penggunaan melalui beberapa tingkatan membutuhkan kualitas air semakin rendah Penggantian irigasi semprot dengan aplikasi langsung dari air untuk tanah termasuk irigasi kontrol penggunaan air 04/12/2012Kimia Lingkungan Air-128

29 7.3. WATER DISTRIBUTION AND SUPPLY 04/12/2012Kimia Lingkungan Air-129

30 conserve water Since about 1980, however, water use in the U.S. has shown an encouraging trend with total consumption down by about 9% during a time in which population grew 16%, according to figures compiled by the U.S. Geological Survey. This trend, which is illustrated in Figure 3.2,

31 4.4. Water Utilization (in U.S.) 04/12/2012Kimia Lingkungan Air-131

32 conserve water It has been attributed to the success of efforts to conserve water, especially in the industrial (including power generation) and agricultural sectors. Conservation and recycling have accounted for much of the decreased use in the industrial sector. Irrigation water has been used much more efficiently by replacing spray irrigators, which lose large quantities of water to the action of wind and to evaporation, with irrigation systems that apply water directly to soil. Trickle irrigation systems that apply just the amount of water needed directly to plant roots are especially efficient

33 Distribution Problem of Water A major problem with water supply is its nonuniform distribution with location and time. As shown in Figure 3.3, precipitation falls unevenly in the continental U.S. This causes difficulties because people in areas with low precipitation often consume more water than people in regions with more rainfall. Rapid population growth in the more arid southwestern states of the U.S. during the last four decades has further aggravated the problem

34 Distribution Problem of Water.

35 THE CHARACTERISTICS OF BODIES OF WATER The physical condition of a body of water strongly influences the chemical and biological processes that occur in water. Surface water occurs primarily in streams, lakes, and reservoirs. Wetlands are flooded areas in which the water is shallow enough to enable growth of bottom-rooted plants. Estuaries are arms of the ocean into which streams flow. The mixing of fresh and salt water gives estuaries unique chemical and biological properties. Estuaries are the breeding grounds of much marine life, which makes their preservation very important

36 THE CHARACTERISTICS OF BODIES OF WATER

37 Water’s unique temperature-density relationship results in the formation of distinct layers within nonflowing bodies of water, as shown in Figure 3.6. During the summer a surface layer (epilimnion) is heated by solar radiation and, because of its lower density, floats upon the bottom layer, or hypolimnion. This phenomenon is called thermal stratification.

38 THE CHARACTERISTICS OF BODIES OF WATER When an appreciable temperature difference exists between the two layers, they do not mix but behave independently and have very different chemical and biological properties. The epilimnion, which is exposed to light, may have a heavy growth of algae. As a result of exposure to the atmosphere and (during daylight hours) because of the photosynthetic activity of algae, the epilimnion contains relatively higher levels of dissolved oxygen and generally is aerobic. In the hypolimnion, bacterial action on biodegradable organic material may cause the water to become anaerobic (lacking dissolved oxygen). As a consequence, chemical species in a relatively reduced form tend to predominate in the hypolimnion.

39 THE CHARACTERISTICS OF BODIES OF WATER The shear-plane, or layer between epilimnion and hypolimnion, is called the thermocline During the autumn, when the epilimnion cools, a point is reached at which the temperatures of the epilimnion and hypolimnion are equal. This disappearance of thermal stratification causes the entire body of water to behave as a hydrological unit, and the resultant mixing is known as overturn. An overturn also generally occurs in the spring. During the overturn, the chemical and physical characteristics of the body of water become much more uniform, and a number of chemical, physical, and biological changes may result. Biological activity may increase from the mixing of nutrients. Changes in water composition during overturn may cause disruption in water-treatment processes.

40 BADAN AIR DAN KEHIDUPAN DI AIR Stratifikasi thermal badan air menunjukkan sifat sebagai berikut: Pada lapisan bagian atas badan air (lapisan epilimnion) lebih hangat, kurang padat, kaya oksigen dan lapisan lebih bawah (hypolimnion), dingin lebih padat, dan miskin oksigen (Gambar 7.4) sangat mempengaruhi kimia dan biologi air Lapisan Epiliminion sering mendukung tinggi pertumbuhan alga secara fotosintetik Lapisan epilimnion yang kaya oksigen umumnya mengandung konsentrasi tinggi spesies kimia teroksidasi, yang biasanya memiliki kandungan oksigen yang tinggi, misal: CO2 dan HCO3 - untuk karbon, NO3 untuk nitrogen, dan SO4 2- untuk sulfur 04/12/2012Kimia Lingkungan Air-140

41 BADAN AIR DAN KEHIDUPAN DI AIR Lapisan hypolimnion sering kekurangan O dan cenderung mengandung senyawa kimia cenderung tereduksi mengurangi isi species dengan kandungan oksigen rendah dan H tinggi, termasuk CH4, NH3 (atau NH4 + ), dan H2S masing-masing untuk karbon, nitrogen, dan beleran Di bawah kondisi reduksi lapisan hypolimnion, besi dapat hadir sebagai Fe larut, sedangkan di hypolimnion itu ada apadatan Fe(OH)3 atau Fe2O3 04/12/2012Kimia Lingkungan Air-141

42 BADAN AIR DAN KEHIDUPAN DI AIR 04/12/2012Kimia Lingkungan Air-142

43 Sources and Uses of Water: The Hydrologic Cycle The world’s water supply is found in the five parts of the hydrologic cycle(Figure 3.1). About 97% of Earth’s water is found in the oceans. Another fraction is present as water vapor in the atmosphere (clouds). Some water is contained in the solid state as ice and snow in snowpacks, glaciers, and the polar ice caps. Surface water is found in lakes, streams, and reservoirs. Groundwater is located in aquifers underground.

44 04/12/2012Kimia Lingkungan Air-144

45 The Hydrologic Cycle: There is a strong connection between the hydrosphere, where water is found, and the lithosphere, which is that part of the geosphere accessible to water. Human activities affect both. For example, disturbance of land by conversion of grasslands or forests to agricultural land or intensification of agricultural production may reducevegetation cover, decreasing transpiration (loss of water vapor by plants) and affecting the microclimate. The result is increased rain runoff, erosion, and accumulation of silt in bodies of water. The nutrient cycles may be accelerated, leading to nutrient enrichment of surface waters. This, in turn, can profoundly affect the chemical and biological characteristics of bodies of water.

46 Where Earth’s Water is Found  About 97% of Earth ’ s water is in oceans  Most of the remaining water is in the form of solid snow and ice  Less than 1% of Earth ’ s water as water vapor and clouds in the atmosphere, as surface water in lakes, streams, and reservoirs, and as groundwater in underground aquifers

47 7.4. Bodies of Water and Life in Water Stratification of a Body of Water Strongly Affects Chemical and Biological Processes

48 Living Organisms inWater Sebuah badan air normal akan menyediakan habitat bagi sejumlah besar organisme mulai dari bersel tunggal ganggang sampai ikan. Sehingga badan air dapat dianggap sebagai sebuah ekosistem,biasanya didasarkan pada pasokan makanan yang terdiri dari biomassa yang dihasilkan secara photosynthetic oleh ganggang dan tanaman yang hidup di dalamnya: 04/12/2012Kimia Lingkungan Air-148

49 Biologically Mediated Processes in Water  Specialized bacteria in water can utilize oxidized chemical species with high oxygen contents other than molecular O 2 for oxygen sources.  Example: Nitrate ion, NO 3 -, acts as an oxidizing agent in the bacterially-mediated biodegradation of biomass:  C 6 H 12 O 6 + 3NO 3 - + 6H +  6CO 2 + 3H 2 O + 3NH 4 + (7.4.3)  By mediating chemical reactions, such as the one above, microorganisms, particularly bacteria, largely determine the chemistry that occurs in water.  Dissolved oxygen in water is very important.  Biodegradable organic pollutants cause biochemical oxygen demand, BOD.

50 7.5. CHEMICAL PROCESSES IN WATER  Biochemical processes including photosynthesis  2HCO 3 - (sunlight energy)  {CH 2 O} + O 2 + CO 3 2- (7.5.1)  {CH 2 O} represents biomass  Acid-base reactions  CO 3 2- + H 2 O  HCO 3 - + OH - (7.5.2)  Precipitation reactions  Ca 2+ + CO 3 2-  CaCO 3 (s) (7.5.3)  Oxidation-reduction reactions, usually carried out by bacteria are generally ones in which chemical species gain or lose oxygen  Example: Oxidation of S in H 2 S  H 2 S + 2O 2  SO 4 2- + 2H + (7.5.4)

51 CHEMICAL PROCESSES IN WATER Many chemical and biochemical reactions occur in water in the environment. Theseare discussed here on the basis of their chemical classification. Several of these were shown by example reactions in Figure 7.4 1. The photosynthesis reaction, which utilizes sunlight energy to produce biomass, 04/12/2012Kimia Lingkungan Air-151

52 CHEMICAL PROCESSES IN WATER is shown here for the conversion of inorganic carbon from dissolved HCO3- ion to organic carbon (biomass) abbreviated as {CHO}. This reaction produces biomass that can be acted upon biochemically by other organisms to form the basis of a number of important biochemical processes in water 04/12/2012Kimia Lingkungan Air-152

53 CHEMICAL PROCESSES IN WATER 2. The carbonate ion, CO3 2- generated by photo- synthesis reacts with water removing a hydrogen ion, H, from the water molecule and producing OH - ion. Reactions involving the exchange of H+ or the generation or consumption of OH- are acid-base reactions. This reaction generates OH- ion, so it makes the water more basic. The carbonate ion generated by photosynthesis may become involved in another kind of reaction as exemplified by its reaction with dissolved calcium ion, Ca 2+, in water, to produce solid CaCO3 04/12/2012Kimia Lingkungan Air-153

54 CHEMICAL PROCESSES IN WATER This is a precipitation reaction. CaCO3 is limestone, and it is this kind of reaction, beginning with the CO3 2- generated by photosynthesis, that is responsible for large formations of limestone rock throughout the world. 3. Oxidation-reduction reactions (see Section 4.7), usually carried out by bacteria, are common in natural waters. The bacterially- mediated reaction of sulfate ion, SO4 2- acting as an oxidizing agent in the O 2 - deficient bottom regions of a body of water to oxidize biodegradable organic matter, {CH 2 O} 04/12/2012Kimia Lingkungan Air-154

55 CHEMICAL PROCESSES IN WATER Reaksi : is one in which the sulfate ion loses oxygen (is reduced). As the H 2 S gas bubbles up through the water, it may contact molecular oxygen and other kinds of bacteria that cause it to undergo the following reaction in which the sulfur is oxidized with the addition of oxygen atoms to produce SO4 2 -ion: 04/12/2012Kimia Lingkungan Air-155

56 7.6. FIZZY WATER FROM UNDERGROUND  Natural waters contain dissolved gases.  Dissolved oxygen required by fish  Dissolved carbon dioxide in some mineral waters  Carbon dioxide in Lake Nyos in the African country of Cameroon which asphyxiated 1,700 people in 1986 Henry ’ s Law for gas solubilities states that the solubility of a gas in a liquid is proportional to the partial pressure of that gas in contact with the liquid. Gas solubility decreases with increasing temperature

57 Oxygen in Water  At 25˚ C the concentration of oxygen dissolved in water is only about 8 milligrams per liter of water (mg/L)  Readily consumed by biodegradation of biomass (abbreviated {CH 2 O}) by oxygen-utilizing bacteria:  {CH 2 O} + O 2   CO 2 + H 2 O (7.6.1)  Only about 8 mg of {CH 2 O} consumes 8 mg of O 2

58 7.7. (WEAK) ACID FROM THE SKY  An acid is a substance that contains or produces H + ion in water, whereas a base is a substance that accepts H + ion in water or contains or produces hydroxide ion, OH -  Whether water is acidic or basic is expressed by pH:  pH = -log [H + ] (7.7.1)  [H + ] is the molar concentration of H + in water, that is, the number of moles of this ion per liter of water. [H + ], mol/Llog[H + ]pH 0.100-1.001.00 1.00  10 -3 -3.003.00 1.00  10 -5 -5.005.00 1.00  10 -9 -9.009.00

59 Acid in Water (Continued) The value of [H + ] in pure water at 25˚ C is 1.00  10 -7 mol/L and the pH is 7.00. The concentration of dissolved carbon dioxide, [CO 2 (aq)], in water in equilibrium with 370 ppm atmospheric air at 25˚ C is 1.21  10 -5 mol/L. Makes water slightly acidic because CO 2 + H 2 O  H + + HCO 3 - (7.7.2) [H + ] = 2.3  10 -6 mol/L corresponding to a slightly acidic pH of 5.6 Such water is neutral, neither acidic nor basic. Water with a pH less than 7.00 is acidic, whereas water with a pH greater than 7.00 is basic. The average global concentration of CO 2 gas in air in the year 2001 was about 370 parts per million by volume, and going up by about 1 ppm per year.

60 7.8. WHY NATURAL WATERS CONTAIN ALKALINITY AND CALCIUM Water alkalinity is the ability of water to react with and neutralize acid (H + ). Due to presence of bicarbonate ion, HCO 3 -, which can react as follows with H + ion: HCO 3 - + H +   CO 2 (aq) + H 2 O (7.7.3) Water hardness in the form of dissolved Ca 2+ ion Both water hardness and alkalinity are acquired when water containing dissolved CO 2 reacts with limestone, CaCO 3 : CO 2 (aq) + CaCO 3 (s) + H 2 O   Ca 2+ (aq) + 2HCO 3 - (7.7.4)

61 Atmospheric CO 2 dissolved in water, and from biodegradation HCO 3 - dissolved in water Solid carbonates (CaCO 3 ) in mineral formations in contact with water Carbon Dioxide and Carbonate Species in Water

62 7.9. METALS IN WATER Metal ions in water are present as hydrated ions, such as Ca(H 2 O) 6 2+. Bound water molecules can be displaced reversibly by other species. Such species include chelating agents, which can bond to metal ions in 2 or more places to form a metal chelate. One such chelating agent is the nitrilotriacetate anion used in some cleaning formulations and capable of bonding to a metal ion on 4 separate sites Chelates tend to be particularly stable, and they are very important in natural water systems. Chelates are involved in life systems; for example, blood hemoglobin is a chelate that contains Fe 2+ ion bonded simultaneously to 4 N atoms on the hemoglobin protein molecule

63 Humic Substances in Water  Water in nature may contain naturally-occurring chelating agents called humic substances that are complex molecules of variable composition left over from the biodegradation of plant material.  Humic substances bind with Fe 2+ ion to produce gelbstoffe (German for “ yellow stuff ” ) which is very difficult to remove by water treatment processes.  Humic substances produce trihalomethanes, such as chloroform, HCCl 3 during disinfection of water by chlorine

64 Most important chemical and biochemical processes in water occur at interfaces between water and another phase (usually solid) 7.10. Water Interactions With Other Phases

65  Sediments are variable mixtures of minerals, clay, silt, sand, and organic matter Formed by Erosion Sloughing of banks into water Washed in from watersheds  Chemical reactions, for example, as the result of photosynthesis: Ca 2+ + 2HCO 3 - + h  {CH 2 O}(s) + CaCO 3 (s) + O 2 (g)  Deposits solid CaCO 3 (limestone)  Deposits biomass, {CH 2 O} Sediments

66  Very small particles suspended in water  Size ranging from very large molecules up to about 1  m  Scatter light (Tyndall effect)  Unique characteristics High surface/volume High interfacial energy High surface/charge Colloids in Water

67 Behavior and stability of colloids are important in aquatic chemical phenomena  Formation of sediments  Dispersion and agglomeration of bacterial cells  Dispersion and removal of pollutants  Waste treatment processes

68 AQUATIC LIFE The living organisms (biota) in an aquatic ecosystem may be classified as either autotrophic or heterotrophic. Autotrophic organisms utilize solar or chemical energy to fix elements from simple, nonliving inorganic material into complex life molecules that compose living organisms. Algae are the most important autotrophic aquatic organisms because they are producers that utilize solar energy to generate biomass from CO2 and other simple inorganic species.

69 AQUATIC LIFE Heterotrophic organisms utilize the organic substances produced by autotrophic organisms as energy sources and as the raw materials for the synthesis of their own biomass. Decomposers (or reducers) are a subclass of the heterotrophic organisms and consist of chiefly bacteria and fungi, which ultimately break down material of biological origin to the simple compounds originally fixed by the autotrophic organisms.

70 AQUATIC LIFE The ability of a body of water to produce living material is known as its productivity. Productivity results from a combination of physical and chemical factors. High productivity requires an adequate supply of carbon (CO2), nitrogen (nitrate), phosphorus (orthophosphate), and trace elements such as iron Water of low productivity generally is desirable for water supply or for swimming.

71 AQUATIC LIFE Relatively high productivity is required for the support of fish and to serve as the basis of the food chain in an aquatic ecosystem. Excessive productivity results in decay of the biomass produced, consumption of dissolved oxygen, and odor production, a condition called eutrophication

72 AQUATIC LIFE Life forms higher than algae and bacteria—fish, for example—comprise a comparatively small fraction of the biomass in most aquatic systems. The influence of these higher life forms upon aquatic chemistry is minimal. However, aquatic life is strongly influenced by the physical and chemical properties of the body of water in which it lives. Temperature, transparency, and turbulence are the three main physical properties affecting aquatic life. Very low water temperatures result in very slow biological processes, whereas very high temperatures are fatal to most organisms. The transparency of water is particularly important in determining the growth of algae. Turbulence is an important factor in mixing processes and transport of nutrients and waste products in water. Some small organisms (plankton ) depend upon water currents for their own mobility.

73 Dissolved oxygen (DO Dissolved oxygen (DO) frequently is the key substance in determining the extent and kinds of life in a body of water. Oxygen deficiency is fatal to many aquatic animals such as fish. The presence of oxygen can be equally fatal to many kinds of anaerobic bacteria. Biochemical oxygen demand, BOD, discussed as a water pollutant, refers to the amount of oxygen utilized when the organic matter in a given volume of water is degraded biologically.

74 Carbon dioxide Carbon dioxide is produced by respiratory processes in water and sediments and can also enter water from the atmosphere. Carbon dioxide is required for the photosynthetic production of biomass by algae and in some cases is a limiting factor. High levels of carbon dioxide produced by the degradation of organic matter in water can cause excessive algal growth and productivity. The salinity of water also determines the kinds of life forms present. Irrigation waters may pick up harmful levels of salt. Marine life obviously requires or tolerates salt water, whereas many freshwater organisms are intolerant of salt.

75 04/12/2012Kimia Lingkungan Air-175