Unit 17 and 18 Sample Quiz

A soil at pH 6.0 contains ________ H+ as it would have at pH 7.0.

10 times as much

The concentration of hydrogen ions at pH 5 is ________ times greater than pH 7.

100

What is the % Na+ saturation, if the following are held on the cation exchange sites: 3 meq H+ 11 meq Ca++ 1 meq Mg++ 2 meq K+ 3 meq Na+

15%

What is the % Mg++ saturation in a Histic epipedon having the following exchangeable ions: Ca++ = 37 meq/100 g Mg++ = 12 meq/100 g K+ = 3 meq/100 g Na+ = 1 meq/100 g Zn++ = 1 meq/100 g H+ = 7 meq/100 g

20%

What is the % K+ saturation of a soil having the following exchangeable ions: Ca++ = 37 meq/100 g Mg++ = 12 meq/100 g K+ = 3 meq/100 g H+ = 8 meq/100 g

5%

The hydrogen-base balance is most important in influencing soil pH between:

5.5-7.0

Most of the world's productive agricultural soils are found with a pH range of _____.

5.5-8.0

A soil holds 10 meq Ca, 4 meq Mg, 2 meq Al, 5 meq H, and 1 meq NH4. The percent base saturation of this soil is _________.

68%

What is the percent base saturation, if a soil contains: Ca++ = 10 meq/100 g Mg++ = 4 meq/100 g H+ = 5 meq/100 g NH4+ = 1 meq/100 g Al+++ = 2 meq/100 g

68%

A soil holds 10 meq Ca, 4 meq Mg, 2 meq K, 1 meq Al, 5 meq H, and 1 meq of other basic ions on the CEC. The percent base saturation of this soil is:

74%

Most of the world's productive agricultural soils have a pH value below:

8.0

If a soil contains 1 meq NH4+, 13 meq Ca++, 3 meq H+, 6 meq Mg++ and 1 meq Al+++, the percent base saturation is:

83%

What is the percent base saturation, if a soil contains: 1 meq NH4+1 3 meq Ca++ 3 meq H+ 6 meq Mg++ 1 meq Al+++

83%

A soil holds 12 meq Ca++, 6 meq Mg++, 2 meq K+, 4 meq H+ and 3 meq of other basic ions on the CEC. The percent base saturation is approximately:

85%

What is the percent base saturation, if the following are held on the cation exchange sites: 3 meq H+ 11 meq Ca++ 1 meq Mg++ 2 meq K+ 3 meq Na+

85%

What is the percent base saturation, if the following are held at the cation exchange sites: 3 meq NH4+ 18 meq Ca++ 2 meq H+

91.3%

Below a pH of 5.5, calcium and magnesium are replaced on exchange sites by:

Al and H.

In the determination of base saturation, Al is not considered a base. This is because:

Al ions react to increase soil acidity.

The most common basic cations on the cation exchange complex of Iowa soils are:

Ca & Mg

In the lyotropic series, which cation will have the strongest bonding to the clay surface?

Ca++

The cation exchange system of the soil holds ______ more tightly than the other ions listed here.

Ca++

Which of these ions is held most tightly by cation exchange sites of soil colloids?

Ca++

1). Which of the following is the most commonly used liming material?

CaCO3

The ratio of reserve to active ions in the soil varies with: A.) nature of the parent material B.) amount of weathering C.) leaching D.) all of the above

D.) all of the above

3). The lyotropic series describes the bonding strength between cations and the clay surface. The strength s on: A.) valence (number of chargers) B.) hydrated size C.) solubility of the ions D.) all the above E.) A and B

E.) A and B

The ratio of reserve to active ions in the soil is: A.) 10,000:1 B.) 30,000:1 C.) 70,000:1 D.) 100,00:1 E.) all of these are possible depending on environmental factors

E.) all of these are possible depending on environmental factors

(T/F) In a soil having both active and reserve ions, the reserve ions would be most susceptible to leaching.

False.

A soil with a low buffering capacity would be slower to show pH change than a soil with a high buffering capacity.

False.

The soil pH test measures:

H+ concentration in the active zone

Leaching of bases from soil tends to cause:

H+ concentration to increase.

Which of the following liming materials will increase soil pH with no detrimental effects to the soil but is hazardous to handle?

Mg(OH)2

From an understanding of the lyotrophic series, we know that cations are bonded to the clay minerals with different bond strengths. Of the following which cation is held most tightly?

Mg++

You would expect ______ to be leached most readily from soil.

Na

A soil pH of 7.0 corresponds approximately to a base saturation of:

Percent base saturation cannot be determined from a pH value alone.

Consider two soils of the same clay mineral type. Soil A has a CEC of 22 meq/100g with 24% base saturation. Soil B has a CEC of 28 meq/100g and 35% base saturation. Which soil has a higher pH?

Soil B

A soil with a low buffering capacity would be faster to show pH change than a soil with a high buffering capacity.

True

The number of ions on reserve always exceeds the number of ions in the active zone.

True

Soils with excess calcium carbonate have pH values ranging from 7 to 8.3.

True.

pH determinations measure the:

active H+

Reserve hydrogen ions:

are in equilibrium with active hydrogen ions.

A base saturation of 75% means that 75% of the exchange sites are occupied by:

bases.

The most common basic cation on the soil exchange complex is:

calcium

Calcium carbonate works as a liming material because:

carbonate reacts to ultimately form CO2 and H2O.

When calcium carbonate is added to the soil the calcium replaces the hydrogen and carbonic acid is formed. The carbonic acid does not lower the pH because:

carbonic acid is unstable and quickly breaks down to form carbon dioxide and water.

The buffering capacity of a soil is dependent mostly on its:

cation exchange capacity.

The order of ions in the lyotropic series is usually determined by:

charge and hydrated size of ions.

Cations in the soil move readily back and forth between the soil solution and:

charged sites on clay surfaces.

An Iowa soil with a pH of 9.0:

contains more OH- ions than a neutral soil

When a soil has a base saturation of 50%, this means that:

half of the exchange sites are occupied by basic cations.

a highly buffered soil:

has a high cation exchange capacity

The buffer capacity of the soil is a measure of the ability of the soil's active zone to resist a change in pH. A high cation exchange capacity _________ the buffering capacity of the system.

increases

Percent base saturation:

increases at high pH

The concentration of calcium is highest in the reserve zone because:

it is held strongest to the clay surface.

A soil with a large amount of reserve ions usually has a buffering capacity that is:

large.

The number of reserve cations held by the soil colloids is usually _________ the number of active cations in the soil solution.

many thousands of times as large as

A liming material with a low _______ will have a high _______.

molecular weight; neutralizing value

The main reason lime is added to the soil is to:

raise the pH.

As hydrogen ion concentration in the soil increases:

soil pH decreases.

The soil pH test measures:

the H+ concentration in the active zone.

The cation exchange capacity of the soil is a measure of:

the number of negative charges on the clay surface.

Cations held in insoluble compounds are important because:

they give a measure of long-term soil fertility.

The number of active ions in a soil is usually ____________ the number of reserve ions in a soil.

thousands of times smaller than

Active ions are found in (on) the:

water film around the clay particles.