ĐỀ CƯƠNG HÓA HỌC ĐẤT TIẾNG ANH

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 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 in soils

+ Haber-Bosch/industrial N fixation

The Haber Process combines nitrogen from the air with hydrogen derived mainly

from natural gas (methane) into ammonia

1rststep catalyzed by Nitrosomonas

2 NH4++ 3 O2  2 NO2-+2 H2O+ 4 H+

2ndstep catalyzed by Nitrobacter

2 NO2-+ O2  2

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

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 2

a Present soil colloid classification

b Present concepts of adsorption, absorption, desorption, adsorbate, adsorbent

a Hiện phân loại keo đất

b Khái niệm hiện tại của 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

• 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

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

• 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 3

a Present Jackson-Sherman weathering stages

b State soil organic matter classification

a, Present Jackson-Sherman weathering stages

a Hiện tại 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

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 cơ

Question 4

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 các khái niệm phí vĩnh viễn cấu trúc, phí proton , phí phức tạp bên trong khối cầu, phí phức tạp lật đổ Giới.

b Trình bày một cấu trúc của keo đất

c Xin giải thích sự khác biệt giữa hấp phụ vật lý và 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

Question 5

a Present soil phases in term of chemical composition

b Please write the structure of a ring phyllosilicate

a Giai đoạn đất đá được trong nhiệm kỳ của thành phần hóa học

b Hãy viết cấu trúc của một phyllosilicate vòng

(e) Phyllosilicates (sheet silicates)

-Phyllosilicates, or sheet silicates, are an important group of minerals that includesmicas, chlorite, serpentine, talc, clay minerals

- The basic structure of the phyllosilicates is based on interconnected six memberrings of SiO4-4tetrahedra that extend outward in infinite sheets

- Each tetrahedra is bound to three neighboring tetrahedra via three basal bridgingoxygens

Question 6

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 của cấu trúc phí vĩnh viễn của chất keo sét trong đất

b Loại hấp phụ hiện tại của đất

c Cho biết significances hấp phụ của đất trong 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

• 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 7

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 hiện nay

b Khái niệm nhà nước của keo đất , các hạt nano , các hạt đất sét , hạt đất.

c Xin giải thích vai trò của các nhóm chức bề mặt của chất keo sét

a

SOIL ELEMENTS

1.1.1 Earth structure

• Very high surface area per unit mass

(specific surface area)

• Common examples of colloidal

suspensions

– Jello

– Milk

4

Characteristics of Soil Colloids

• High surface area

– Smectites & vermiculites: 1 g = 800 m2

– Range: 10 - 800 m

2

g

–1

• Electrically charged surface

– Usually net negative surface charge

– In low pH soils dominated by sesquioxides, allophane, imogolite, surfaces may be net positive

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

• 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 8

a State concepts of solution, solute, solvent, mixtures

b Present the types of soluble complexes in soils

a Khái niệm nhà nước của dung dịch, chất tan , dung môi , hỗn hợp

b Trình bày các loại phức hòa tan trong 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 inminor 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 do not combine chemically, but remain the same individual substances They can be separated by physical means such as temperature

• Two types of mixtures:

• 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 9

a Present nitrogen cycle within the earth system

b Explain the terms of nanoparticles, clay particles, soil particles

a Chu kỳ nitơ có mặt trong hệ thống trái đất

b Giải thích các điều khoản của các hạt nano , các hạt đất sét , hạt đất.

c Đất đá được phân loại chất hữu cơ

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 chính hiện tại của keo đất

b So sánh sự khác biệt giữa hấp phụ hóa học và hấp phụ vật lý

3.1.4 Properties of soil colloids

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

b Hiện tại 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