low temp Geochemistry

What is the significance of water as a solvent?

Water is a good solvent because most major components in cells dissolve in it.

At what temperature does water attain its greatest density?

Water attains its greatest density at 4 °C.

Why does ice float on water?

Ice is less dense than liquid water because the formation of ice requires water molecules to move apart.

What property of water allows it to have the highest heat capacity?

The dipolarity of water allows it to absorb large amounts of energy before boiling.

What happens to water's melting and boiling points if it were not dipolar?

It would melt at -110 °C and boil at -80 °C.

What factors affect the solubility and dissolution rate of solids in water?

The chemistry of the solid, structure of the solid, temperature, and pressure.

What are hydration shells?

Hydration shells are layers of water molecules that surround ions in solution.

How does ionic potential relate to ion bonding with water?

Ionic potential measures charge density; higher ionic potential creates stronger bonds with water molecules.

What is the formula for ionic strength?

Ionic strength (I) = 1/2 * Σ(mᵢ * zᵢ²), where mᵢ is molality and zᵢ is charge.

What is the relationship between activity and concentration in dilute solutions?

In dilute solutions, activity equals concentration (a = m).

What occurs in concentrated solutions regarding water activity?

Some water molecules are used to form hydration shells, resulting in activity of water being less than 1.

What is speciation in the context of aqueous solutions?

Speciation refers to the form in which an element exists in water, including simple ions and polyatomic ions.

What does the solubility product (Ksp) represent?

Ksp is the maximum amount that can dissolve in pure water at 25 °C and 1 atm.

What does a Saturation Index (SI) greater than 0 indicate?

SI > 0 indicates precipitation (supersaturation).

What are the three types of solutions based on particle size?

True solution (

What is Ostwald Ripening?

A process where larger particles grow at the expense of smaller ones, minimizing surface energy.

What are the types of calcite based on surface area?

Biogenic calcite (2-8 m²/g), commercial calcite (0.1-2 m²/g), and experimental calcite (0.1-20 m²/g).

What is the significance of small particles in environmental chemistry?

Small particles have large reactive surfaces and different thermodynamic behaviors critical for contaminant sorption.

What are some examples of inorganic pollutants?

Mercury, lead, cadmium, chromium, arsenic, nitrates, sulfates, ammonia, fluoride, and phosphates.

What health issues can excess phosphates cause?

Hypocalcemia, calcification of tissues, chronic kidney disease, osteoporosis, and cardiovascular disease.

What is sorption?

Sorption is the physiochemical attachment of one substance to another, including adsorption and absorption.

What is the Electric Double Layer (EDL)?

The EDL forms on mineral surfaces in contact with fluid, consisting of surface charge, Stern layer, and diffuse layer.

What happens to trace metals when Fe-sulfides oxidize?

The pH decreases, making many trace metals highly soluble at low pH.

How does CO₂ affect carbonate equilibria?

CO₂ dissolves in water proportionally to its partial pressure, affecting calcium ion precipitation.

What is the crystal structure of calcite and aragonite?

Calcite has a rhombohedral structure, while aragonite has an orthorhombic structure.

Water is a good solvent.

Most major cellular components dissolve in water.

What happens to pure water's conductivity when ions dissolve?

It increases.

At what temperature is water densest?

4 °C.

Why does ice float?

Because ice is less dense; molecules move apart when freezing.

Why does water have a high heat capacity?

Because its dipolarity allows strong bonding.

If water were not dipolar what would its melting/boiling points be?

-110 °C and -80 °C.

What controls a solid's solubility?

Chemistry, structure, temperature, and pressure.

What forms around ions in water?

Hydration shells.

What affects hydration shell strength?

Charge, radius, pH, Eh, temperature, pressure, salinity.

What is ionic potential?

Charge / ionic radius.

What does high ionic potential mean?

Stronger bonding with water; harder to dehydrate.

Why must ions lose hydration shells?

To enter mineral structures.

What is activity?

Activity = γ × m.

What is ionic strength?

I = ½ Σ mᵢ zᵢ².

How do ions behave in dilute solution?

Activity ≈ concentration, γ = 1.

How do ions behave in concentrated solution?

Less free water, ion pairs form, γ < 1.

How do ions behave in highly concentrated solution?

Solvent unavailable, γ > 1.

What is speciation?

the form an element takes in solution.

What controls speciation?

pH and redox (Eh).

What is pH?

-log[H⁺].

What is Eh?

-log[e⁻].

What is the solubility product (Ksp)?

Maximum dissolved amount at set conditions.

What does a high Ksp mean?

High solubility.

When is equilibrium reached?

Dissolution = precipitation.

What is the SI formula?

SI = log(IAP / Ksp).

What does SI > 0 mean? S

upersaturation → precipitation.

What does SI = 0 mean?

Equilibrium.

What does SI < 0 mean?

Undersaturation → dissolution.

What is a true solution?

No solids (<1 nm).

What is a colloidal solution?

Nanoparticles (1-100 nm) that don't settle.

What is a suspension?

Particles >100 nm that settle.

What is Ostwald ripening?

Small particles dissolve and redeposit on larger ones.

Why does Ostwald ripening occur?

To reduce surface energy.

Why are nanoparticles important?

High surface area → high reactivity.

Why do clays transport easily?

They are <1 µm with high surface area.

Why are clays plastic?

They attract dipolar water.

Why are clay surfaces reactive?

They have negative surface charge.

What is delamination?

Separation of clay layers to increase surface area.

What is sorption?

Attachment of a substance to a surface.

What is adsorption?

Attachment on the surface.

What is absorption?

Entry into mineral structure.

What is ion exchange?

One ion swaps with another on a surface.

What is surface precipitation?

New minerals grow on a surface.

What is the electric double layer?

Surface charge + Stern layer + diffuse layer.

What is the point of zero charge?

pH where surface has no net charge.

What affects adsorption?

Surface area, chemistry, pH, solubility, temperature, competing ions.

Why do sulfide ores release metals?

Oxidation lowers pH and increases solubility.

Which arsenic species is more toxic?

As³⁺.

Why is lead dangerous? T

oxic at any concentration.

What does long-term copper exposure do?

Damages liver and kidneys.

Why is cadmium dangerous?

Highly toxic.

What controls CO₂ dissolution?

Proportional to pCO₂.

How does pH affect calcite precipitation?

Lower pH → more Ca²⁺ needed.

What does calcite do in seawater?

Buffers pH to ~8.2.

Which is more soluble: calcite or aragonite?

Aragonite (1.5× more).

How do their structures differ?

Calcite = rhombohedral; aragonite = orthorhombic.

How does Mg²⁺ affect calcite growth? I

nhibits calcite → promotes aragonite.

Why does calcite dissolve in deep oceans?

Higher pressure increases solubility.

Ions with high ionic potential tend to be which type of species?

Anions like carbonate sulfate and phosphate that retain oxygen from their hydration shell.

Ions with low ionic potential tend to be what?

Hydrated cations whose hydration shell can sometimes be removed more easily.

What does "inner hydration shell" mean?

The closest layer of water molecules around an ion forming the strongest interactions.

What does the extended activity coefficient equation include besides ionic strength?

An extra term with εᵢⱼ mⱼ to include interactions with counterions.

In the extended activity coefficient equation what does j stand for?

The counterion.

What do speciation diagrams show?

The activity of different species of an element in solution as a function of pH Eh temperature or pressure.

Do speciation diagrams show all species or only some?

Only the most dominant species.

What is the solubility product Ksp physically?

The equilibrium constant for a solid dissolving in water at given conditions usually 25 °C and 1 atm.

How does mineral structure affect solubility at non-ambient conditions? Different structures dissolve more or less releasing different amounts of ions.

How is mineral stability related to solubility?

The more insoluble a mineral the more stable it is.

What is a true solution size range?

Contains no solid particles smaller than about 1 nm.

What is a colloidal solution size range?

Contains solid nanoparticles about 1-100 nm that do not settle.

What is a suspension size range?

Contains particles larger than about 100 nm that can settle.

What is nanocalcite?

Very fine calcite CaCO₃ with high surface area and clean surface.

Typical surface area of biogenic calcite?

About 2-8 m² per gram and usually not perfectly pure.

Typical surface area of commercial calcite?

About 0.1-2 m² per gram and often impure.

Typical surface area of experimental calcite?

About 0.1-20 m² per gram and often impure.