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ENVB 210 > Chemosphere III > Flashcards

Chemosphere III Flashcards

1
Q

What happens to plants visually when they lack N?

A

They turn yellow.

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2
Q

What is the cause of algal blooms?

A

Excessive phosphates and nitrates present in agricultural runoff into lakes.

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3
Q

Are environmental pollutants more likely to be anions or cations? Why?

A

They are more likely to be anions, because they’re more mobile in soil. Cations will stick in soil more and be harder to leach out.

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4
Q

The retention of ions is called […]

A

Sorption

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5
Q

For sorption of ions to be possible, what 2 factors are needed?

A
  1. A source of charge (colloids) to attract the ions.
  2. A source of ions
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6
Q

Name 4 possible sources of ions in soil

A
  1. Released from organic matter
  2. Inputs from (slightly acidic) rain
  3. Chemical inputs (fertilizers, pesticides, sewage, etc.)
  4. Weathering of plant material.
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7
Q

How will ions in behave in sandy, low OM, and 1:1 clays? Why?

A

The ions will get leached out, because the soil in all these cases has little to no charge and thus can’t attract ions as strongly.

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8
Q

How will ions behave in soil with added organic matter?

A

They will mostly be retained because OM is very strongly negatively charged.

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9
Q

When ions are not sorbed to the soil, what state are they in?

A

They are hydrated and diffuse, as they are attached to the dipolar water molecules.

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10
Q

When ions are sorbed to the soil, what are the two possible forms they can take?

A

They can either form an outer sphere complex or an inner sphere complex.

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11
Q

What is an outer sphere complex?

A

It is when hydrated ions are bridged to the charged colloid surface by water. These ions are loosely held and are thus exchangeable.

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12
Q

What is an inner sphere complex?

A

It is when non-hydrated ions are adsorbed directly to the colloid and are not easily released. The are more strongly bonded and are thus not typically exchangeable.

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13
Q

What is cation exchange?

A

The interchange between a cation in solution and another cation on the surface of a colloid.

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14
Q

What are the major 3 exchangeable cations in soil?

A

Ca2+, Mg2+, K+

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15
Q

Give 3 examples of exchangeable anions.

A

Cl-, PO43-, NO3-

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16
Q

Explain the significance of N in agricultural systems.

A

It is essential for plant health but is very inefficiently uptake, with many losses to the atmosphere and leaching.

17
Q

What form of nitrogen is best uptaken by plants? Why?

A

NH4+ because it will adsorb to the negatively charged colloids.

18
Q

What is the effect of nitrification inhibitors on nitrogen production?

A

Nitrification inhibitors suppress bacterial conversion of NH4+ to NO3-, which helps reduce N losses in the soil by promoting adsorption.

19
Q

What are the 4 principles governing cation exchange?

A
  1. Reversibility
  2. Charge equivalence
  3. Ratio law
  4. Cation selectivity
20
Q

Explain the principle of reversibility in cation exchange.

A

The cation exchange reaction is rapid and reversible, and can occur many times.

21
Q

Explain the principle of charge equivalence in cation exchange.

A

The exchange of cations occurs on a charge-for-charge basis. For example, if 2 H+ adsorb to the colloid, it must exchange a 2+ ion (like Ca2+)

22
Q

Explain the principle of ratio law in cation exchange.

A

The same ratio of ions must be present in solution and on the colloid. For example, if Mg is added to the solution, ions will exchange until the same ratio of Mg to everything else is present in both the colloid surface and solution.

23
Q

Explain the principle of cation selectivity in cation exchange?

A

Ions that are held more tightly will exchange less frequently.

24
Q

What factors determine how tightly ions get adsorbed to the soil colloid?

A

It depend on charge, where higher charge = more strongly held, and radius, where larger radius = more weakly held.

25
Q

Rank the following ions in order of their strength of adsorption: K+, NH4+, Li+, Al3+, Ca2+, Na+, Sr2+, Mg2+

A

Al3+ > Sr2+ > Ca2+ > Mg2+ > K+ = NH4+ > Na+ > Li+

26
Q

The less tightly held cations are, the […] likely they are to be leached out.

A

More

27
Q

What is CEC?

A

The total amount of exchangeable cations that a particular soil can adsorb at a given pH.

28
Q

Name 3 factors influencing CEC.

A
  1. Cation saturation
  2. Complementary cations
  3. Type of colloid
29
Q

Explain how cation saturation affects cation exchange.

A

Cation saturation refers to the proportion of CEC satisfied by a given cation. Higher saturation on exchange complex = more exchangeable and available compared to other ions of the same charge.

30
Q

Explain how complementary cations affect cation exchange.

A

If a loosely held ion on the exchange complex is surrounded by more tightly held ions, the loosely held ion is more likely to be exchanged.

31
Q

In a situation where K+ is surrounded by Na+ vs surrounded by Al3+, which K+ is more likely to be exchanged and why?

A

The K+ surrounded by Al3+ is more likely to be exchanged due to the complementary cations rule, where a loosely held ion surrounded by more tightly held ions is more likely to be exchanged.

32
Q

How do plants utilize H+ in cation exchange?

A

Plant roots leak H+ and CO2 which dissociates into HCO3- and H+. These H+ ions can be released and exchanged with cations on clay colloids, allowing for the takeup of cationic nutrients.

33
Q

Is CEC high or low for the following colloid types? 1:1 layer silicate, 2:1 smectite (expandable), 1:1 illite (non-expandable), organic matter, Fe and Al oxides, allophane

A

Low, high, low, high, low, high

34
Q

How does pH affect CEC?

A

In colloids with a pH-dependent charge, at a low pH, H+ binds more tightly and doesn’t exchange as well, lowering CEC.

35
Q

In tropical areas, plants are usually deficient in what nutrient? Why?

A

The plants are typically P deficient because P sorbs very tightly to the positively-charged colloids at low pHs, preventing it from being uptaken.

36
Q

Where is global P sorption potential the highest? How can this be changed?

A

At tropical latitudes, as the soil is very acidic and thus holds on to P very tightly. In these regions, the soil pH can be increased to allow more P take up by plants.

37
Q

Plants with a phosphorus limitation appear […]

A

Purple.

ENVB 210 (16 decks)

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