Soil Chemistry Quiz - Soil Properties and pH

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Questions and Answers

What is the general pH range where phosphorus is most available to plants?

7.0-8.5

3.5-4.5

5.5-7.0 (correct)

4.5-5.5

How does the cation exchange capacity (CEC) of soil relate to its ability to hold nutrients?

Lower CEC indicates a greater nutrient retention ability.

CEC is unrelated to nutrient holding capacity.

Higher CEC allows for more nutrient retention. (correct)

Higher CEC indicates a lower ability to hold nutrients.

What characteristic distinguishes montmorillonite as a clay mineral?

It forms dense aggregates.

It is primarily composed of quartz.

It is non-swelling when wetted.

It has a high cation exchange capacity. (correct)

Which of the following statements is true regarding residual acidity in soil?

Residual acidity requires more lime to be neutralized than active acidity. Signup and view all the answers

Why is Al3+ classified as an acid cation?

It hydrolyzes water and releases H+ ions. Signup and view all the answers

What is the effect of acid rain on well-buffered soils?

It may not significantly alter the pH due to buffering capacity. Signup and view all the answers

In which fraction of soils are secondary minerals most prevalent?

Clay Signup and view all the answers

What does the CEC of 16 cmolc/kg suggest about a soil's nutrient-holding capacity?

It indicates high nutrient-holding efficiency. Signup and view all the answers

The swelling and shrinking of certain silicate clay minerals is primarily due to what factor?

Movement of soil solution in and out of the interlayers Signup and view all the answers

What does a soil pH of 7 indicate about its H+ ion concentration?

It contains a very low H+ concentration Signup and view all the answers

Which clay type would be least suitable for a foundation due to its high capacity to adsorb ions?

Montmorillonite Signup and view all the answers

What happens to pH-dependent charge as soil pH decreases?

It decreases overall Signup and view all the answers

Calculating the moles of positive charge in 50 g of Ca2+ (m.w.=40 g/mol) leads to which result?

2.5 mol Signup and view all the answers

How many Mg2+ ions are contained in 1 mole of Mg2+?

6.02 x $10^{23}$ Signup and view all the answers

Why might the CEC of a soil remain unchanged between pH 5.0 and 8.2?

Isomorphic substitution maintains constant charge Signup and view all the answers

Which type of clay is most associated with enhancing soil fertility?

Smectite Signup and view all the answers

What primarily contributes to the electronegative charge on 2:1 type silicate clays?

Isomorphic substitution of a metallic atom in the clay's crystal structure Signup and view all the answers

What is the primary reason for the negative charges associated with smectitic clay crystals?

Isomorphic substitution of Mg for Al in the octahedral sheet Signup and view all the answers

Which of the following formulas correctly represents Base Saturation in soil?

$\frac{Total; of; base; cations}{Effective; CEC}*100$ Signup and view all the answers

If a soil contains 10% clay and 1.5% humus, what is the importance of the CEC of each material?

High CEC of humus directly correlates with higher nutrient availability Signup and view all the answers

What is a characteristic effect of protonation of hydroxy groups in highly acidic soil conditions?

Development of positive charges on soil colloids Signup and view all the answers

How many moles of positive charge are contained in 1 mole of Al3+?

3 molc Signup and view all the answers

Given an H+ ion concentration of 0.000000063, what is the resulting soil pH?

7 Signup and view all the answers

Which of the following is a characteristic of soil colloids?

Very small size Signup and view all the answers

Study Notes

Question 1

Swelling/shrinking of silicate clay minerals primarily due to the movement of soil solution in and out of the crystal interlayers, and expansion/contraction in the interlayers due to ions like K+
Cations are attracted to negative charges on internal surfaces

Question 2

A soil with pH 7 has a H+ concentration of 0.0000001

Question 3

For a very stable foundation with low adsorption capacity, choose kaolinite

Question 4

pH-dependent charge decreases as soil pH decreases

Question 5

50 g of Ca2+ (molar mass = 40 g/mol) contains 1.7 moles of positive charge

Question 6

One mole of Mg2+ contains 6.02 x 10^23 Mg2+ ions

Question 7

Similar CEC values at different pH levels likely due to a lack of significant charge differences across the pH range

Question 8

Illite clay provides the best fertility for soils

Question 9

Information unavailable to answer the question

Question 10

Poorly buffered soils require more lime than well-buffered soils to adjust pH

Question 11

Electronegative charge on 2:1 type silicate clays primarily due to isomorphic substitution of one metallic atom for another in the crystal structure of the clay.

Question 12

Negative charges associated with smectite clay crystals mainly due to isomorphic substitution

Question 13

Information in table required to calculate Base Saturation of the soil (values for various cations are given)

Question 14

Alkaline soil with 10% clay and 1.5% humus has a CEC of 11 cmolc/kg

Question 15

Building a foundation on smectite-rich soil is not always a good idea

Question 16

Soil colloids characterized by very small size

Question 17

Positive charges on soil colloids under highly acidic conditions are likely due to protonation of some hydroxy groups by excess H+ ions.

Question 18

One mole of Al3+ contains 3 moles of positive charge

Question 19

pH of soil with H+ concentration of 0.000000063 is 6.5

Question 20

Residual acidity in clay loam soil requires considerably less lime than active acidity in the same soil.

Question 21

Phosphorus is generally most available to plants in a soil pH range of 4.5 - 5.5

Question 22

Information missing to determine the answer

Question 23

CEC of soil is 20.5

Question 24

Acid rain's impact on well-buffered soils is likely to be minimal

Question 25

Spatial variation is checking soil pH at multiple spots in a field to account for variations in field conditions

Question 26

Secondary minerals are most prominent in the silt fraction of soils

Question 27

Soil colloid with a high cation exchange capacity (CEC) and tendency to swell when wetted is most likely of monmorillinite

Question 28

Humus is similar to 2:1 type minerals in its ability to adsorb cations

Question 29

Cation exchange capacity of vermiculite increases as pH increases is False

Question 30

Soil with a high CEC is likely to be highly buffered

Question 31

External surfaces of 2:1 type clays are typically much more extensive than their internal surfaces

Question 32

Information unavailable to answer the question

Question 33

A octahedral sheet is characterized by a plane of aluminum atoms surrounded by oxygen and hydroxyl groups

Question 34

Information unavailable to answer the question

Question 35

Farmers can significantly decrease soil pH by using NH4+-based fertilizers

Question 36

Information missing to determine the answer

Question 37

For a liming material with a CaCO3 equivalent of 0.90, 7,407 lbs of material are needed to achieve the same liming effect as 1.5 tons of 100% CaCo3.

Question 38

Soils developed in marine marshes become extremely acidic when drained due to oxidation of sulphides

Question 39

Elemental sulfur is the most appropriate for decreasing soil pH to grow azaleas

Question 40

A soil with 30% clay would have the greatest potassium-fixing capacity due to 2:1 clays

Question 41

Information unavailable to answer the question

Question 42

Finely ground dolomitic limestone is favored when needing to significantly reduce exchangeable Al3+ in the soil

Question 43

The Calcium Carbonate Equivalent of MgCO3 is 0.93.

Question 44

Soil pH can vary with soil depth is True

Question 45

A soil with a CEC of 40 cmolc/kg would likely be highly buffered

Question 46

100 kg of 95% pure CaO is approximately 97.5% as effective as 100 kg of 100% pure CaCO3

Question 47

Effectiveness of lime based only on size is 0.44 lbs reactive material/lb total lime

Question 48

Information unavailable to answer the question

Question 49

Applying 4 tons of lime to a sandy soil would likely lead to a higher pH than intended

Question 50

The Calcium Carbonate Equivalent of CaMg(CO3)2 is 0.54

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Description

Test your knowledge on soil chemistry with this comprehensive quiz focusing on silicate clay minerals, pH levels, and cation exchange capacity. Explore how changes in pH affect soil properties and the characteristics of various clay minerals. Ideal for students studying soil science or environmental chemistry.