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Unit 5 - Practice Quiz

SOL103

1 Which of the following represents the basic structural unit of the silica sheet in silicate clays?

A. Silicon Octahedron
B. Silicon Tetrahedron
C. Aluminum Octahedron
D. Aluminum Tetrahedron

2 What is the ratio of tetrahedral to octahedral sheets in the crystal structure of Kaolinite?

A. 2:1
B. 1:1
C. 2:2
D. 2:1:1

3 Which phenomenon is primarily responsible for the permanent negative charge in 2:1 silicate clays?

A. Protonation of hydroxyl groups
B. Dissociation of carboxyl groups
C. Isomorphous substitution
D. Broken edge bonds

4 Which cation typically dominates the interlayer space of Illite, preventing expansion?

A.
B.
C.
D.

5 According to the Lyotropic series, which of the following cations is most strongly adsorbed by soil colloids?

A.
B.
C.
D.

6 The Cation Exchange Capacity (CEC) of a soil is best defined as:

A. The total weight of clay in the soil
B. The total number of exchangeable anions a soil can hold
C. The sum of total exchangeable cations that a soil can adsorb
D. The percentage of aluminum saturation

7 Which clay mineral typically has the highest Cation Exchange Capacity (CEC)?

A. Kaolinite
B. Illite
C. Vermiculite
D. Chlorite

8 What is the standard unit for expressing Cation Exchange Capacity (CEC) in the SI system?

A. meq/100g
B. cmol(+)/kg
C. ppm
D. mg/kg

9 The swelling and shrinking behavior of Montmorillonite (Smectite) is caused by:

A. Water entering the interlayer space
B. Expansion of individual atoms
C. Breakdown of the crystal lattice
D. Precipitation of salts

10 Calculate the Base Saturation percentage if a soil has a CEC of and the sum of exchangeable basic cations () is .

A. 25%
B. 75%
C. 133%
D. 50%

11 In the silicon tetrahedron, the central silicon ion () is surrounded by how many oxygen ions?

A. 3
B. 4
C. 6
D. 8

12 Which source of charge is considered 'pH-dependent'?

A. Isomorphous substitution in the tetrahedral layer
B. Isomorphous substitution in the octahedral layer
C. Dissociation of hydroxyl (-OH) groups on broken edges
D. Substitution of for

13 Anion Exchange Capacity (AEC) generally increases when:

A. Soil pH increases
B. Soil pH decreases
C. Organic matter content increases
D. CEC increases

14 Which of the following is considered an 'acidic cation' in the context of base saturation?

A.
B.
C.
D.

15 Buffering capacity in soils refers to:

A. The ability to drain water rapidly
B. The resistance to change in soil pH
C. The maximum amount of fertilizer a soil can hold
D. The rate of organic matter decomposition

16 Active acidity in soil is defined as:

A. ions adsorbed on the clay complex
B. ions in the crystal lattice
C. ions present in the soil solution
D. Total acidity minus exchangeable acidity

17 Which soil component contributes most significantly to pH-dependent charge (variable charge)?

A. Sand particles
B. Soil Humus (Organic Matter)
C. Vermiculite
D. Smectite

18 Which equation correctly represents the stoichiometry of cation exchange?

A.
B.
C.
D.

19 In the aluminum octahedron, the coordination number of Aluminum is:

A. 4
B. 6
C. 8
D. 12

20 Which of the following clay minerals is non-expanding?

A. Montmorillonite
B. Vermiculite
C. Kaolinite
D. Beidellite

21 The 'Point of Zero Charge' (PZC) is the pH at which:

A. The soil has no cations
B. The net surface charge of the colloid is zero
C. The CEC is at its maximum
D. The soil becomes highly alkaline

22 Which mechanism creates a permanent charge in Montmorillonite?

A. Substitution of for in the octahedral sheet
B. Substitution of for in the tetrahedral sheet
C. Broken edges
D. Protonation

23 Reserve (or potential) acidity is typically _____ than active acidity.

A. Much lower
B. Exactly the same as
C. Much higher
D. Unrelated to

24 If a soil has a high buffering capacity, adding lime will:

A. Raise the pH very quickly
B. Raise the pH slowly
C. Have no effect
D. Lower the pH

25 Which colloid type is known as 'Amorphous' (non-crystalline)?

A. Kaolinite
B. Allophane
C. Illite
D. Montmorillonite

26 Which of the following is an oxide clay commonly found in highly weathered tropical soils?

A. Gibbsite
B. Smectite
C. Vermiculite
D. Mica

27 The specific surface area is highest in which of the following clays?

A. Kaolinite
B. Illite
C. Montmorillonite
D. Fine sand

28 The conversion factor between and is:

A. 1:10
B. 1:1
C. 10:1
D. 1:100

29 Dispersion of soil colloids is primarily promoted by which cation?

A.
B.
C.
D.

30 Flocculation is the process of:

A. Breaking down clay particles
B. Aggregating individual particles into clumps
C. Leaching cations from soil
D. Measuring soil pH

31 Chlorite is structurally similar to vermiculite but contains an extra layer of:

A. Potassium ions
B. Water molecules
C. Magnesium-hydroxide (Brucite)
D. Silica tetrahedra

32 Which functional group is primarily responsible for the CEC of soil organic matter?

A. Amino groups ()
B. Carboxyl groups ()
C. Silanol groups ()
D. Aluminol groups ()

33 In a 2:1 clay mineral, the '2' refers to:

A. Two octahedral sheets
B. Two tetrahedral sheets
C. Two interlayer spaces
D. Two types of cations

34 A soil with a Base Saturation of 20% would likely have a pH that is:

A. Neutral (7.0)
B. Alkaline (> 7.0)
C. Acidic (< 5.5)
D. Variable

35 Which law states that the ratio of cations on the exchange surface is proportional to the ratio of their activities in the soil solution?

A. Darcy's Law
B. Stoke's Law
C. Ratio Law
D. Beer's Law

36 Why does Kaolinite have a much lower CEC than Smectite?

A. It has high isomorphous substitution
B. It has very little isomorphous substitution and low surface area
C. It contains potassium in the interlayer
D. It is an amorphous colloid

37 Which cation exchange reaction represents the process of acidification?

A.
B.
C.
D.

38 The 'Oscillation Volume' refers to:

A. The volume of water a clay expands into
B. The space where adsorbed cations move around the colloid surface
C. The volume of air in soil pores
D. The shrinkage limit of soil

39 Which of the following creates a 'tetrahedral sheet'?

A. Linking of tetrahedra through sharing of basal oxygen atoms
B. Linking of octahedra through hydroxyl groups
C. Stacking of silica and alumina units
D. Hydration of silicon atoms

40 What is the primary process responsible for the release of ions from Aluminum () in soil solution?

A. Reduction
B. Hydrolysis
C. Oxidation
D. Chelation

41 Which soil texture typically has the lowest buffering capacity?

A. Clay Loam
B. Silty Clay
C. Sand
D. Peat (Organic Soil)

42 Isomorphous substitution usually occurs during:

A. Weathering of existing minerals
B. Fertilizer application
C. The crystallization of clay minerals from molten magma or solution
D. Organic matter decomposition

43 If the concentration of in the soil solution increases, what happens to the adsorbed on the colloid?

A. It decreases
B. It increases
C. It remains unchanged
D. It turns into

44 The negative charge on humus is primarily:

A. Permanent
B. pH-Dependent
C. Positive
D. Neutral

45 Anions like Nitrate () and Chloride () are generally:

A. Strongly adsorbed by silicate clays
B. Repelled by the negative charge of silicate clays
C. Precipitated as solids immediately
D. Converted to cations

46 Which cation is most effective at causing soil particles to disperse, leading to poor structure?

A.
B.
C.
D.

47 A 2:1 clay with high lattice charge located in the tetrahedral sheet, limiting expansion, describes:

A. Kaolinite
B. Smectite
C. Vermiculite
D. Goethite

48 The 'Complementary Ion Effect' describes how:

A. Anions attract cations
B. The ease of replacing a specific ion depends on the strength of adsorption of other ions present
C. pH changes the color of the soil
D. Water molecules complement clay structures

49 Generally, the CEC of a soil usually ___ with an increase in soil organic matter.

A. Decreases
B. Increases
C. Stays the same
D. Fluctuates randomly

50 When measuring soil pH with water, the result represents:

A. Potential Acidity
B. Total Acidity
C. Active Acidity
D. Exchangeable Acidity