Geochem Exam Two

please for the love of God let me get at least an 85

Retrograde Solubility of Gases in Water

Colder temperatures = more dissolution

Warmer Temperatures = less dissolution

Why does solution not equal activity?

Electrostatic interactions between charged ions and formation of hydration shells around ions

If activity equals 1

Then activity = molarity

What is a hydration shell?

When water is attracted to an ion and blocks other reactions from occurring

Salting Out

Precipitation of Minerals

i.e. SiO2+2H2O < — H4SiO4

Salting In

Increases activity coefficient and decreases the molarity

i.e. CaCO3 —> Ca+2 + CO3-2

Saturation index

How saturated a certain mineral is in an aqueous solution

N2 saturation of seawater

High activity coefficient and low molarity

N2 saturation of freshwater

Low activity coefficient and high molarity

If SI = 1

equilibrium

If SI greater than 1

super saturated

If SI is less than 1

Undersaturated

What is an acid

A substance that produces H+ in an aqueous solution.

What is a base

A substance that produces OH- in an aqueous solution

Global Carbon Cycle Equation

Total carbon = Organic carbon + inorganic carbon

Particulate matter is

less than 0.45 microns

Carbonic Acid System

Most common source of acidity in water is dissolved carbon dioxide that enters the water through equilibrium with the atmosphere
CO2+H20=H2CO3

Bjerrun Plot

Shows the relative speciation at a given pH

Buffer

Something resistant to changing pH. Steeper parts of plots indicate the most buffering capacity.

Open carbonic acid system

when the system is in equilibrium with the atmosphere (exposed to gas/atm)

Closed carbonic acid system

when the system is isolated from the atmosphere (groundwater or deep oceans)

How are speleothems formed?

A decreased in pCo2 created from the cave creates speleothems. Higher temperatures in the cave create precipitation with high CO2

Where do phytoplankton remove CO2 in the ocean?

Top depths

Why does the Pacific Ocean have a higher pH and more CO2?

Thermohaline circulation brings more organic carbon to the pacific ocean.

Highest calcite concentration in the ocean is located

At the top of the ocean

Lysocline

Where calcium begins to dissolve in the ocean

Compensation Depth

Where calcium completely dissolves in the ocean

As+3

More mobile and toxic than other forms of arsenic

Pollutants in pristine conditions

Flows from Oxygen —> Methane stages

Pollutants in polluted conditions

Flows from Methane → Oxygen stages

Chemosynthesis

the way some organisms obtain energy from redox reactions.

Steady State Water Profile

Oxygen in = Oxygen out

Solutes move from high to low concentration

Fick’s first law of diffusion

Determines how fast (the flux) things are moving

O2 + H2S

An acid is generated when H2S is exposed to oxygen and oxygenates very quickly

Redox

Oxic respiration —> Denitrification —> Manganese reduction —> Iron reduction —> Sulfate reduction
More positive delta g along progression

Mnemonic for redox stages

Otters Don’t Make Iron Swords

Redox Steps

Ther are no traces of previous redox stages if the process was fully completed

Bacteria & Oxidation

Redox would still occur without bacteria but they are a catalyst

Pyrite Formation

Between Iron reduction and sulfate reduction CHECK WITH ELLA

Autochthonous Mineral

Formed/produced in the environment

Allochthonous Mineral

was transported into the environment.

Eh-pH Diagrams

show redox equilibrium with pH as a factor

Preserving Water Samples

Acids can be added to samples, so cations don’t dissolve out. Sample can then be preserved

Oxidation

The removal of electrons from an atom of an element, often by oxygen that causes an increase in valence.

Reduction

The addition of electrons to an element that decreases valence.

Half Reactions

Splits redox equations for balancing into oxidation and reduction half reactions.

Electromotive Force

Delta G: determines if a reaction happens spontaneously or not.

Acid Mine Drainage

Overflow of acidic water that is very acidic and transports heavy metals

Slowest step in acid mine drainage process

Oxygen

Passive Treatments for acid mine drainage

Artifical wetland construction

Active Treatments for acid mine drainage

chemical additives like calcium carbonate to neutralize acidity.

Depletion of oxygen is caused by

oxygen being taken up as we burn fossil fuels. or through eutrophication in water

What was the missing carbon sink?

Northern Hemisphere Forests

How did we find the missing carbon sink?

Burned fossil fuels are a known, so we tested ocean water for CO2.

More O2

Biosphere grows

Less O2

Decreasing biosphere (deforestation)

CO2 and Acids in ocean

More CO2 makes more carbonic acid which decreased ph and increases pco2. Less gas solubility.

Stratification due to CO2

Warmer temperatures slow thermohaline circulation and freshwater melt caps impact O2 dissolution.

Cl as a pollution indicator

Used since it does not have a terrestrial source.

Weathering

Various physical and chemical processes that lead to the decomposition of minerals and the breakdown of rocks into soil.

Types of weathering

Oxidation, congruent dissolution by water, congruent dissolution by acid attack, incongruent dissolution by acid attack.

Calculating Pollution

Man Made Pollution = Total - Natural

Sometimes uses two-member end model and reverse engineer composition

Land temperatures can be reconstructed with

Pollen and lake levels

O2, CO2, and Nitrogen are not ideal for paleoclimate studies because

they are not constant in concentration

Noble Gasses (Ne, Kr, Xe) are helpful for paleoclimate studies because they are

ideal for solubility and remain relatively constant. Use gas dissolution of these in water as proxy.

Cultural Eutrophication

the process of excessive nutrient enrichment in a water body that gets accelerated by human activities (N,P)

Oligotrophic Conditions

Low phosphorous, nitrogen, chlorophyll and higher secchi disc depth

Eutrophic Conditions

High phosphorous, nitrogen, chlorophyll and low secchi disc depth

Limiting Nutrient

An essential nutrient for the growth and development of an organism.

Limiting nutrients for phytoplankton

Nitrogen or Phosphorous

Liebig’s Law of Minimum

The nutrient present in the least relative amount is the limiting nutrient

Limiting Nutrient for Freshwater Lakes

Phosphorous is the limiting nutrient for most freshwater lakes in North America. More chlorophyll → more phosphorous loading

Adsorption

Electrostatic phenomena that effects ions. Lower pH creates more adsorption. PO4- wants positive sources to bind to since opposites attract.

Low pH Adsorption

H+ dominates and surface has a net positive charge

High pH Adsorption

OH- dominates and the surface has a net negative charge

Internal Loading Indirect reduction

Caused by sulfur reducing bacteria

Internal Loading Direct reduction

caused by iron reducing bacteria

Both direct and indirect reduction

release phosphate

Carbonates

suck up phosphates

Why is Hawaii an ideal place to study nutrient cycling?

Temperature/Precipitation, parent material, plants and animals, topographic and soil are all known and well constrained to study changes over time

Proximate Limiting Nutrient

Any nutrient whose addition enhances growth in the short term

Ultimate Limiting Nutrient

elements with the ability to transform a community or ecosystem.

P, Ca, K and Ms decrease over time due to

weathering

For the first 22,000 years what is the limiting nutrient

Nitrogen

After 22,000 years what is the limiting nutrient

Phosphorous

Without a rejuvenation event phosphorous limitation can lead to

retrogression

How was Ca traced to be coming from dust?

Using Sr87/Sr86 as a tracer

In less than 100,00 years

the atmosphere is the dominant source of nutrients

Objectives of environmental cleanup

Most toxic components are captured, stored and controlled

Cinnabar

contains mercury which is very insoluble and does not weather or release mercury.

What are natural concentrations of mercury?

50 ppb in rocks

What mobilizes mercury

Mining, burning fossil fuels and anthropogenic activities.

Organic forms of mercury (methylated mercury) are

more bio reactive and dangerous since they bind tightly and inhibit molecular processes

Most dangerous forms of mercury

CH3-Hg+ and (CH3)2-Hg

Minamata Bay

Mercury was used to make glue and methylate mercury polluted the area. Fish consumption led to the spread of wooden puppet syndrome.

Mercury methylation

Occurs during bacterial reduction during the sulfate reduction phase.

Modern Sources of mercury exposure

seafood, breathing in vapors, old dental fillings, medical treatments and religious rituals

US Emissions of mercury

Gold mines, burning hazardous waste, chlorine production, institutional boilders

Global Mercury Emissions

Coal burning and small-scale gold production in China and India

Grasshopper Effect of Mercury

Remitted mercury that gets deposited and reenters atmosphere. Makes it hard to determine preindustrial mercury levels.