HÓA HỌC ĐẤT Question 1 a. Present a nitrogen cycle within the earth system. b. Present organic matter classification in soils. c. Write a cellulose molecular structure with four sugar monosaccharides a. Trình bày một chu kỳ nitơ trong hệ thống trái đất . b . Phân loại chất hữu cơ có trong đất . c . Viết một cấu trúc phân tử cellulose với bốn monosacarit đường a. From the diagram of global nitrogen cycle, we can summarize key processes: Stock of soil nitrogen depends on N fixation processes and decay processes of organic N compounds. Major fixation processes consist of biological fixation and Haber Bosh process. Decay processes include immonification (mineralization), nitrification, denitrification. The slides below will present major processes of N cycle
HÓA HỌC ĐẤT Question a Present a nitrogen cycle within the earth system b Present organic matter classification in soils c Write a cellulose molecular structure with four sugar monosaccharides a Trình bày chu kỳ nitơ hệ thống trái đất b Phân loại chất hữu có đất c Viết cấu trúc phân tử cellulose với bốn monosacarit đường a From the diagram of global nitrogen cycle, we can summarize key processes: Stock of soil nitrogen depends on N fixation processes and decay processes of organic N compounds Major fixation processes consist of biological fixation and Haber -Bosh process Decay processes include immonification (mineralization), nitrification, denitrification The slides below will present major processes of N cycle in soils 1 + Haber-Bosch/industrial N fixation The Haber Process combines nitrogen from the air with hydrogen derived mainly from natural gas (methane) into ammonia N2+ 3H2 2NH3(ΔH = −92.4 kJ·mol−1) + Ammonification /mineralization Nitrogen enters the soil through the decomposition of protein in dead organic matter Amino acids + 11/2O2 CO2+ H2O + NH3+ 736kJ This process liberates a lot of energy which can be used by the saprotrophic microbes + Nitrification Two step reactions that occur together : 2 1rststep catalyzed by Nitrosomonas NH4++ O2 NO2-+2 H2O+ H+ 2ndstep catalyzed by Nitrobacter NO2-+ O2 NO3+ Denitrification Denitrification is a natural soil microbial process where nitrate (NO3 - ) is converted to nitrogen (N) gases that are lost to the atmosphere b b Present organic matter classification in soils 3 c Write a cellulose molecular structure with four sugar monosaccharides • Polysaccharides, the polymers of sugars, have storage and structural roles • The structure and function of a polysaccharide are determined by its sugarmonomers and the positions of glycosidic linkages Question 4 a Present soil colloid classification b Present concepts of adsorption, absorption, desorption, adsorbate, adsorbent a Hiện phân loại keo đất b Khái niệm hấp phụ , hấp thụ , hấp phụ , adsorbate , vật liệu hấp phụ a, Soil colloids can be classified by crystal structure + Crystalline Silicate Clays • Dominant colloid in most soils (not andisols, oxisols or organic soils) • Crystals layered as in a book • 2-4 sheets of tightly-bonded O, Si and Al atomsin each layer Kaolinite • Kaolinite is one of the most widespread clay mineral in soils, being most abundant in warm moist soils • It is formed by acid weathering and in soils of volcanic origin • Hydroxyl plane is exposed: removal or addition of hydrogen ions cproduce positive or negative charges (hydroxylated surface also binds with anions) • Hydroxyls of octahedral sheet are alongside oxygens of the tetrahedral sheet: hydrogen bonding results, with no swelling in kaolinit Smectite group: • Smectite includes montmorillonite, beidellite, nontronite It occurs widely in moderately weathered soils Montmorilloniteis most common smectite in soils • Interlayer expansion may occur as H2O fills spaces between layers in dry clay • Smectites have a large amount of negative charge due to isomorphous substitution • Mg2+often replaces Al3+in the octahedral sheet • Al3+sometimes replaces Si4+in the tetrahedral sheet • Weak O: cation linkages between layers leads to plasticity, stickiness, swelling and a very high specific surface area Vermiculite group • It is formed as a alteration product of muscovite and biotite mica It has a wide particle size range • Very high negative charge due to frequent substitution of of Si4+ions with Al3+in the tetrahedral sheets •Cation exchange capacity is higher in vermiculitesthan in any other clay • Swelling occurs, but less than in smectites due to strongly adsorbed H2O molecules, Al-hydroxy ions and cations, which act more as bridges than wedges + Non-crystal colloids • Not organized into crystalline sheets • Both + and – charges; can adsorb anionssuch as phosphate • High water-holding capacity • Malleable (change in shape) when wet, but not sticky • Often form in volcanic soils (especially in Andisols) + Fe, Al oxides • Oxides include hydroxides, oxyhydroxides occurs as discrete particles, coatings on other soil surfaces • Hydroxylation of oxide minerals can be structural or occurs by chemisorption of water in an aqueous medium • Edge hydroxyl groups on oxide and clay minerals are most abundant and reactive surface functional groups in soils • Gibbsite is crystalline Al oxides common in soils It occurs as non-crystalline Al oxides with similar structure and chemical properties, but smaller particles than crystalline Al oxides • Iron oxides are found in most soils and provide soil horizons with their red, yellow, brown colors Goethite is the most common Fe oxides, FeO(OH) in template, subtropical and tropical soils Hematite (Fe2O3) occurs commonly in warm climate soils Variable Charge (pH-dependent) Hydrous oxides get their charge from surface protonation and deprotonation >AlO-+ H+←→ >AlOH + H+←→ AlOH2+ Negative Neutral Positive pH decreasing > Hydrous oxides are positively charged in some very acid soils and help retain anions + Humic colloids • A non-crystalline, organic substance • Very large, organic molecules • 50% C, 40% O, 5% H, 3% N and sometimes S • Structure highly variable 6 • Very large negative charge due to three types of -OH groups (H+ions gained or lost) (i) carboxyl group COOH (ii) phenolic hydroxyl group (due to partial decomposition of lignin by microorganisms) (iii) alcoholic hydroxyl group b, Present concepts of adsorption, absorption, desorption, adsorbate, adsorbent • Adsorption is a physical process that involves the transfer of solutes from the liquid phase to the surface of a solid matrix • Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface • Absorption is the filling of pores in a solid • When both adsorption and absorption processes take place simultaneously, the process is called sorption • Desorption: The process of removal of an adsorbed substance from the surface on which it is absorbed Adsorbent, adsorbate - The substance on the surface of which adsorption takes place is called adsorbent - The substance which is being adsorbed on the surface of another substance, called adsorbate Question a Present Jackson-Sherman weathering stages b State soil organic matter classification a, Present Jackson-Sherman weathering stages a Hiện Jackson - Sherman thời tiết giai đoạn 1.5.2 Jackson-Sherman Weathering • The relationship between weathering intensity and the mineral assemblages present in the clay fraction of a soil is described in 7 the weathering sequence of Jackson et al (1948) and Jackson and Sherman (1953) • Jackson reasoned that the mineral composition of the clay-sized fraction could be employed to establish the weathering stage of a soil • Common minerals found in the clay fraction of a soil are identified by an index number Low numbers represent minerals easily weathered Whereas high numbers represent minerals relatively resistant to weathering and abundant in old soils The clay fraction of a soil is typically composed of three to five dominant minerals b Đất nhà nước phân loại chất hữu 8 Question a Present the concepts of permanent structural charge, proton charge, inner-sphere complex charge, ouster-sphere complex charge b Present a structure of soil colloids c Please explain differences between physical adsorption and chemical adsorption a Trình bày khái niệm phí vĩnh viễn cấu trúc, phí proton , phí phức tạp bên khối cầu, phí phức tạp lật đổ Giới b Trình bày cấu trúc keo đất c Xin giải thích khác biệt hấp phụ vật lý hấp phụ hóa học (a) Permanent structural charge Isomorphous subsitution of layer colloids creates negative charge of particle surface This charge is termed permanent structural charge, σ0 In addition, reaction between surface funtional groups with solution ions generates proton charge σH, inner complex charge σis, ouster complex charge σos 9 10 10 11 11 Question 12 12 a Present soil phases in term of chemical composition b Please write the structure of a ring phyllosilicate a Giai đoạn đất đá nhiệm kỳ thành phần hóa học b Hãy viết cấu trúc phyllosilicate vòng (e) Phyllosilicates (sheet silicates) -Phyllosilicates, or sheet silicates, are an important group of minerals that includes micas, chlorite, serpentine, talc, clay minerals - The basic structure of the phyllosilicates is based on interconnected six member rings of SiO4-4tetrahedra that extend outward in infinite sheets - Each tetrahedra is bound to three neighboring tetrahedra via three basal bridging oxygens Question a Explain the origin of permanent structural charge of soil clay colloids b Present adsorption types of soils c Indicate the significances of soil adsorption in soil management a Giải thích nguồn gốc cấu trúc phí vĩnh viễn chất keo sét đất b Loại hấp phụ đất c Cho biết significances hấp phụ đất quản lý đất b 3.2.1 Adsorption concepts • Adsorption is a physical process that involves the transfer of solutes from the liquid phase to the surface of a solid matrix • Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface • Absorption is the filling of pores in a solid 13 13 • When both adsorption and absorption processes take place simultaneously, the process is called sorption • Desorption: The process of removal of an adsorbed substance from the surface onwhich it is absorbed Adsorbent, adsorbate - The substance on the surface of which adsorption takes place is called adsorbent - The substance which is being adsorbed on the surface of another substance, called adsorbate Sorption process 3.2.2 Adsorption types Physical adsorption: Van der Waals attraction between adsorbate and adsorbent The attraction is not fixed to a specific site and the adsorbate is relatively free to move on the surface This is relatively weak, reversible, adsorption capable of multilayer adsorption Chemical adsorption: Some degree of chemical bonding between adsorbate and adsorbent characterized by strong attractiveness Adsorbed molecules are not free to move on the surface There is a high degree of specificity and typically a monolayer is formed The process is seldom reversible Question a Present soil element classifications b State concepts of soil colloids, nanoparticles, clay particles, soil particles c Please explain roles of surface functional groups of clay colloids a Phân loại nguyên tố đất b Khái niệm nhà nước keo đất , hạt nano , hạt đất sét , hạt đất c Xin giải thích vai trò nhóm chức bề mặt chất keo sét a SOIL ELEMENTS 1.1.1 Earth structure 14 14 B, soil colloids Very small, chemically surface reactive particles • Usually < µm diameter • Very high surface area per unit mass (specific surface area) • Common examples of colloidal suspensions – Jello – Milk Characteristics of Soil Colloids • High surface area – Smectites & vermiculites: g = 800 m – Range: 10 - 800 m g –1 • Electrically charged surface – Usually net negative surface charge – In low pH soils dominated by sesquioxides, allophane, imogolite, surfaces may be net positive 15 15 nanoparticles A nanoparticle (or nanopowder or nanocluster or nanocrystal) is a microscopic particle with at least one dimension less than 100 nm clay particles soil particles c Please explain roles of surface functional groups of clay colloids Siloxane surface group: • It associates with silica tetrahedral sheet of a phyllosilicate • Siloxane acts as a Lewis base 16 16 • At the edge of octahedral sheet, OH groups are coordinated to Al+3 At the tetrahedral sheet, OH groups are coordinated to Si+4 • OH groups coordinated to Si+4dissociate only protons But, OH groups coordinated to Al+3dissociate and bind protons These edge OH groups called silanol (SiOH), aluminol (AlOH) Clay minerals have both aluminol, silanol OH group Question a State concepts of solution, solute, solvent, mixtures b Present the types of soluble complexes in soils a Khái niệm nhà nước dung dịch, chất tan , dung môi , hỗn hợp b Trình bày loại phức hòa tan đất a, Solvents are generally liquid , are derivatives , used to dissolve or disperse other substances ( note the two terms dissolved and dispersed , not by just dissolved Koh is not enough ) - - > defined by the university level Solute is dissolved substances or dispersed in a solvent (also called a distributed environment ) Solutions define as a homogeneous mixture of two or more substances in a aqueous phase Usually a solid is dissolved in a liquid, but liquids can be dissolved in other liquids Gases can be dissolved in a liquid as well • Component (substance) present in greater proportion is called the solvent, the one in minor proportion is called the solute • Examples of solution, oceans are salt water solutions—water is the solvent, salt is the solute Sweet tea in another example — sugar is the solute and water is the solvent Solutions as Mixtures • A combination of two or more substances that not combine chemically, but remain the same individual substances They can be separated by physical means such as temperature • Two types of mixtures: Heterogeneous mixtures Homogeneous mixtures Heterogeneous Mixtures • “Hetero” means different 17 17 • It consists of visibly different substances or phases (solid, liquid, gas) • A suspension is a special type of heterogeneous mixture of larger particles that eventually settle Soil solution may be defined as heterogeneous mixture Homogeneous Mixtures • “Homo” means the same • has the same uniform appearance and composition throughout; maintain one phase (solid, liquid, gas) • Commonly referred to as solutions b Present the types of soluble complexes in soils • A soluble complex (complex ion) consists of a central metal ion surrounded by ligands Aligand is molecule or ion which donates a pair of electrons forming a coordinate bond (dative bond) Coordinate bond is one of the bonded atoms has provided both electrons for the covalent bond Question a Present nitrogen cycle within the earth system b Explain the terms of nanoparticles, clay particles, soil particles c Present soil organic matter classification 18 18 a Chu kỳ nitơ có mặt hệ thống trái đất b Giải thích điều khoản hạt nano , hạt đất sét , hạt đất c Đất đá phân loại chất hữu a, Present nitrogen cycle within the earth system b Explain the terms of nanoparticles, clay particles, soil particles c Present soil organic matter classification Question 10 a Present major characteristics of soil colloids b Compare differences between chemical adsorption and physical adsorption a Đặc điểm keo đất b So sánh khác biệt hấp phụ hóa học hấp phụ vật lý 3.1.4 Properties of soil colloids Sizes, shapes Surface area Surface charge Tension surface Colloid coagulation and dispersion 19 19 Physical adsorption: Van der Waals attraction between adsorbate and adsorbent The attraction is not fixed to a specific site and the adsorbate is relatively free to move on the surface This is relatively weak, reversible, adsorption capable of multilayer adsorption Chemical adsorption: Some degree of chemical bonding between adsorbate and adsorbent characterized by strong attractiveness Adsorbed molecules are not free to move on the surface There is a high degree of specificity and typically a monolayer is formed The process is seldom reversible Question 11 a State soil element classifications b Present Jackson-Sherman weathering stages a Phân loại nguyên tố đất Nhà nước 20 20 b Hiện Jackson - Sherman thời tiết giai đoạn • The relationship between weathering intensity and the mineral assemblages present in the clay fraction of a soil is described in the weathering sequence of Jackson et al (1948) and Jackson and Sherman (1953) • Jackson reasoned that the mineral composition of the clay-sized fraction could be employed to establish the weathering stage of a soil • Common minerals found in the clay fraction of a soil are identified by an index number Low numbers representminerals easily weathered Whereas high numbers represent minerals relatively resistant to weathering and abundant in old soils The clay fraction of a soil is typically composed of three to five dominant minerals 21 21 Question 12 a Present the terms of solute, solvent, homogeneous mixtures, heterogeneous mixtures b Explain interaction between water molecules and ions in forming hydrated complex ions c Write an example of cation exchange reaction of Ca-Na in soils a Trình bày điều khoản chất tan , dung môi , hỗn hợp đồng , hỗn hợp đồng b Giải thích tương tác phân tử nước ion việc hình thành ion phức tạp ngậm nước c Viết ví dụ phản ứng trao đổi cation Ca- Na đất a, Câu b II-Calculations Question 14: Use of Langmuir Equation in estimating adsorption capacity 22 22 23 23 Question 13: Calculate CEC using colloid formula and negative charge method 24 24 Tính CEC sử dụng công thức dung dịch keo phương pháp tiêu cực phí 25 25 ... ligands Aligand is molecule or ion which donates a pair of electrons forming a coordinate bond (dative bond) Coordinate bond is one of the bonded atoms has provided both electrons for the covalent