Geochemistry Exam 2

isotope

An element with a different number of neutrons than expected.

more

Isotopes always have ____ neutrons than protons.

stable isotopes

Isotopes that are not radioactive and do not decay.

both

Some elements, like carbon can have _____ stable and radiogenic isotopes.

less, more

Light isotopes have ___ neutrons than a known standard and heavy isotopes have ___ neutrons.

Pure water with no salt or other chemicals.

What is Vsmow?

Pee dee Belemnite; a geologic formation in the Carolinas that has carbon and a marine deposit of fossils

What is PDB?

equilibrium fractionation

When isotopes of an element are redistributed among chemical substances or phases in a dosed, well-mixed system at equilibrium.

Water evaporation; gas becomes lighter

What is an example of equilibrium fractionation?

heavy/light

The fractionation ratio is..?

heavier, higher, positive

Enriched = ?

lighter, lower, negative

Depleted = ?

((Rsample/Rstandard) - 1) x 1,000

How do you solve for fractionation in change per mil?

fractionation

The distribution of heavy and light isotopes in a thing changes due to some process.

more

Covalent bonds cause fractionation as heavier isotopes form a ____ stable bond than light isotopes.

Ionic

____ bonds have a minimal effect of fractionation.

higher

When it comes to fractionation, heavier isotopes prefer to bond to elements of ______ oxidation states.

solid, liquid

When it comes to fractionation, heavier isotopes form a _____ first so the _____ becomes depleted.

greatest

Fractionation is ________ at lowest temperature.

Dissolves CaCO3

CaCO3 + CO2 > Ca(2+) + H2CO3*

Precipitates stalactite

Ca(2+) + H2CO3* > CaCO3 + CO2

kinetic fractionation

When isotope reacts, diffuses, evaporates faster than another due to the process and catalysts.

lighter

Kinetic fractionation results in the ______ isotope accumulating in the product. 

faster

Lighter molecules react ______.

Rayleigh fractionation

Evaporation/precipitation/condensation cycles on global scale; occurs when a material changes phase

fractionation ratio

How fractionation is changing between two substances relative to each other.

Temperature, latitude, continentality, and humidity

What factors influence isotope ratios?

Formation of rocks, climate (CO2), various photosynthesis pathways, etc.

How can isotopes impact everyday life?

radiogenic isotopes

Isotopes that spontaneously decay into daughter isotopes.

alpha radiation

The type of radioactive decay when a particle is lost with 2 protons, 2 neutrons, and a +2 charge.

alpha radiation

This is an example of what kind of radioactive decay?

beta decay

The type of radioactive decay when an electron is lost; occurs in series with alpha decay.

beta decay

This is an example of what kind of radioactive decay?

positron decay

The types of radioactive decay when there is an emission of positron (positively charged electron).

positron decay

This is an example of what kind of radioactive decay?

positrons

________ form when a proton converts to a neutral state and releases a positive particle. 

gamma

In alpha, beta, and positron decay - ______ radiation is released, stabilizes the nucleus to a lower energy, and a more stable state.

fission decay

Nucleus splits into two or more nuclei; produces an alpha particle.

half-life

The amount of time it takes for some substance to decay to half its original mass.

Pt = P0 x e^-kt

What is the equation for half-life?

zero-order

Do these graphs represent a zero, first, or second-order rate?

Dissolution of some salts

What kind of chemical reactions follow a zero order rate?

First-order

Do these graphs represent a zero, first, or second-order rate?

Population growth, radioactive, hill slope

What things could be represented by a first-order rate?

Carbon-14

What isotope is used in carbon dating?

Burning of fossil fuels and atomic bomb tests

Radiocarbon dating must be corrected for “old carbon” in the form of..?

Acids have H+; bases have OH-; limited to aqueous solution

Arrhenius definition?

Acid is proton donor (gives H+); base is a proton acceptor (accepts H+); conjugate acids and bases

Bronsted-Lowry definition?

Acid dissociation constant (Ka)

When the conjugate pair dissociates, we describe this as..?

-log(Ka)

pka = ?

[H+][OH-]

kw = ?

completely

Strong acids _________ dissociate in water.

large

Strong acids have a ______ Ka.

small

Weak acids have a _____ Ka.

don’t

Weak acids ____ fully dissociate in water.

polyprotic acids

Acids with multiple hydrogens

acid dissociation constant

For every deprotonation step, there is a separate..?

pH

At different __ values, different species are dominant.

base, acid

In each step of a phosphate bjerrum plot, in each step the phosphorus and hydrogen goes from being ____ to an ____.

amphoteric substances

Something that can be an acid or a base depending on pH and the system.

CO2

H2CO3 (carbonic acid) is present everywhere due to the partial pressure of ___ in the atmosphere. 

H2CO3

_______ is critical to controlling the pH of water in a system.

Encompasses the CO2(g) > CO2(aq); CO2(aq) + H2O > H2CO3

What is H2CO3*

Sum of CO2, H2CO3, HCO3, and CO3 in an aqueous system

dissolve inorganic carbon (DIC)

alkalinity

Ability of a solution to accept acidity and not change pH.

titration

Alkalinity is operationally defined by _______, a process that adds acid slowly to a solution while pH is measured after each addition.

meq/L

What are the units for alkalinity?

buffer

A solution or solid that resists change (pH) when something is added.

buffer capacity

Measure of buffering in a solution.

buffered

Karst waters are well..?

charge

Alkalinity is measured in meq because titrations are just a ______ balance. 

buffer zone 1

Very low pH; lots of [H+]; addition of acid is negligible; OH- becomes neutralized because of high [H+]

buffer zone 2

Between pk1 and pk2; add acid (HCO3>H2CO3*); add base (H2CO3>HCO3-); species transfer back and forth and buffer between the two species

buffer zone 3

High pH; lots of [OH-]; well buffered; transfer of species between HCO3- and CO3(2-); any addition of acid is quickly neutralized

constituents

Chemical reactions add __________ or stuff to H2O.

mineral dissolution/precipitation; weathering; reactions in solution

What are some ways that more constituents can be added to water?

water cycle, dissolved vs particulate, mineral solubility/reaction types, water measurements, Eh-pH diagrams

What are the five big picture controls on water chemistry?

total dissolved solids

Measure of all dissolved components in water - organics, inorganics, ions, colloids, in ppm

Non aqueous phase liquids (NAPLs); both dense and light non-aqueous phase liquids (DNAPLs & LNAPLs)

What things in H2O don’t get dissolved?

colloids

Small solids with surface chemistry interactions.

suspended items

Particulates, bacteria, viruses, some colloids

Na+, Ca(2+), Mg(2+), K+

What are the monoatomic ions that can be found in water?

HCO3-, OH-, SO4(2-), PO4(3-)

What are the polyatomic ions that can be found in water?

sorbed species

Things attached to mineral surfaces

ionic charge (z) / ionic radius (r)

Ionic potential is defined by the ratio of electric charge to radius of the ion:

ionic potential

How strongly or weakly the ion will be electrostatically attracted to ions of opposite charge; how strongly or weakly the ion will repel ions of the same charge

strong, high, small

High z/r is associated with _____ bonding, ____ charge, and ____ radius

weaker

Lower z/r generally means ______ bonding.

solubility

Cations with high z/r can form stable complexes which impacts __________ and geological reactions/processes. 

oxygen

Low z/r has weak bonds with _______ if they can form at all. It makes them soluble and enter into solids at relatively low temperatures.

high ionic potential

Charge is more focused; strong bonds with oxygen and repel other cations

K+, Na+, Sr+

What are some examples of low ionic potential monoatomic ions?

NO3-, SO4(2-), PO4(3-)

What are some examples of high ionic potential polyatomic ions?

Al, Ti, Fe, Mn (multiple oxidation states)

What are some examples of intermediate ionic potential transition metals?

transition metals, oxides, and hydroxides

What molecules/atoms have intermediate ionic potential?

solubility

pH controls mineral..?

pH

Not all minerals have the same solubility pattern relative to..?

karst

Consists of specific surface and subsurface features formed by the dissolution of soluble rocks containing adequate porosity with exposure to chemically aggressive water over appropriate time.

Px = nx/ntotal

How do you calculate partial pressure?

acid mine drainage

Generates SO4 from the oxidation of pyrite.