Biology 120 > Geochemistry > Flashcards

Geochemistry Flashcards

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1
Q

Name the Basic Hydrocarbon Groups and their defining structure.

A
  1. Apliphatic: straing and branched chain structure
  2. Naphthene: cyclic aliphatic
  3. Aromatic: one six-carbon ring
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2
Q

Name the types of chemical weathering and explain them.

A
  1. Dissolution: dissolve mineral into its ions with water (ex. Halite, NaCL = Na+ + Cl-
  2. Acid dissolution: use acid to dissolve minerals into its ions (ex Calcite and carbonic acid, 2CaCO3+H2CO3 = 2HCO3- + 2Ca2+)
  3. Oxidation-reduction: electron transfer (ex. iron sulfide + oxygen, FeS2 + 15O2 +14H2O = 16H+ + 8SO4- + 4Fe(OH)3)
  4. Hydrolysis: “water splitting” (ex Feldspar, KAlSi3O8 + H20 + H+ = Al2Si2O5(OH)4 +SiO2 +K+)
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3
Q

What are the 4 sections of a piper diagram?

A
  1. Calcium Sulfate Waters
  2. Sodium Chloride Water
  3. Sodim Bicarbonate Waters
  4. Calcium Bicarbonate Waters
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4
Q

State the weaknesses of the Piper diagram

A
  1. Only take 7 major ions into account
  2. Must ignore any other ions so the sum is 100%
  3. Also doesn’t work for anoxic of low-O2 waters, where reduced ions like Fe2+ or S2- can dominate
  4. Not all groundwaters follow the chemical evolution sequence ex. waterloo region groundwater : HCO3- dominated but medium to high TDS
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5
Q

How does TDS change with age of groundwater

A

As age increases (go deeper) TDS is higher

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6
Q

How do the dominant ions in groundwater change with age

A

Young: Ca and Mg, HCO3
Medium: Ca and Mg, SO4
Old: Na, Cl

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7
Q

What is water hardness?

A

The ability of relatively insolubleminerals to precipitate out of water. Sum of 2+ ions that form CaCO3, CaMg(CO3)2, CaSO4 precipitates

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8
Q

How do you remove hardness in a water sample?

A
  1. Increase water temperature, ex. boiling
  2. Use water softener, ex cation-exchange resin to replace Ca and Mg with Na
  3. Water filters with activated carbon (less effective)
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9
Q

What are the classifications of DOM

A
  1. Labile: easy to break down, high energy yield for bacteria
  2. Refractory: not easy to break down
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10
Q

What is turbidity and how is it measured?

A
  • measure of water clarity, measured by light penetration
  • usually correlates to TSS
  • approximated in the field by using a Secchi disc to measure the maximum depth at which a Secchi disc can be seen in the water
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11
Q

Which is not a major dissolved ion in natural fresh waters.

HCO3, Na+, K+, H4SiO4, SO42-, Ca2+, Mg2+, Cl-

A

H4SiO4

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12
Q

You are giver a concentration of Na+ of 23.6 mg/L, what is the normality (Na Molar mass = 23.0g/mol)

A

1.03meq/L

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13
Q

A water sample has a hardness of 4.5 meq/L, what is the hardness in mg/L as CaCO3. Molar mass CaCO3=100.1g

A

225.2

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14
Q

What factors affect the activity coefficient

A
  1. concentration of all ions and chare in the solution
  2. Charge of the ion
  3. Diameter of the ion
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15
Q

How does activity change with increased salinity?

A

Activity is equal to 1 in pure water, decreases as salinity increases except for brines

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16
Q

Calculate the ionic stength of a solution of 0.01 mol MgCl2 dissolved in 1 L of water.

A

0.03

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17
Q

How are ionic strength and activity coefficients related?

A

The greater your ionic strength the lower the activity coefficient.

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18
Q

Calculate the activity coefficient for Mg2+ at 25C if the ionic strength is equal to 0.03

A

0.572

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19
Q

Calculate the activity for Mg2+ if you add 0.01 mol MgCl2 to 1 L of water using an activity coefficient of 0.5722

A

0.00572

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20
Q

what is the definition of pKa

A

the pH at which half of the acid has dissociated into H+ and A-

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21
Q

Calculate the pH of water in equilibrium with atmospheric CO2 at 25C.
[CO2] in atmosphere = 405ppm-v
Kh for CO2 = 10^(-1.47)M/L

A

[H2CO3]=1.37E-5

pH=5.61

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22
Q

What is total alkalinity?

A

Tatal alkalinity = [HCO3 2-] - [CO3 2-] + [OH-] - [H+]

Main anions minus their respective cations

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23
Q

Calculate the ionic strength of a soilution of 0.1 mol CaCl2 dissolved in 1.5L of water.

A

IDK

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24
Q

What is Electromotive Force?

A

Force generated by a redox reation, measured in volts.

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25
Calculate the electromotive force of the following reaction when aZn=0.01 and aLi=0.2. will the reaction continue in the forward direction? (E0=2.238 V)
Er=2.210V | This reaction will proceed in the forward reaction.
26
``` Which of the pairs are stable at low Eh? O2 or O2- H2S or SO4 2- NO3 - or NH4 + Fe2+ or Fe3+ Cr(III) or Cr (VI) Mn2+ or Mn4+ Cu+ or Cu2+ ```
``` O2- SO4 2- NH4 + Fe2+ Cr(III) Mn2+ Cu+ ```
27
Describe the Eh of the following reaction in terms of pH and pO2. 2H+ +0.5O2 +2e = H2O deltaGr= -237.1
E0=1.23V | Eh= 1.23 - 0.0592pH + 0.0148pO2
28
Outline the steps you need to take to make an Eh-pH diagram
1. Take the half equation and balance. Is this a redox reaction? a. no, find delta G0, find K, find the pH where the two species are at equal activity, plot this vertical line. Done! b. yes, keep e- on the left and find delta G0, find Eho, find Eh. Do you have H+ in your reaction? b1. no, you can find a value for Eh, this will form a horizontal line. Done! b2. yes, must rearrage the Eh equation to express as a function of pH, this will form a sloped line. Done!
29
Which reaction will happen preferentially between two different compatible ions?
The ion that reacts to produce the greatest amount of energy will react first.
30
Name and order the reduction cascade.
``` Aerobic respiration Denitrification Manganese reduction Iron reduction Sulfate reduction Methanogenesis ```
31
Under what conditions do we observe reduction cascades IRL?
when O2 in water is used up and not replenished. (closed system) ex. -groundwater plue with contaminants - porewater in sediment - hypolimnion (bottom) of stratified lake
32
How does salinity affect redox reactions?
An increased salinity increases electrical conductivity which facilitates redox reactions such as rusting
33
What caused the flint water crisis?
- high DOM in water source - used high levels of Cl2 to reduce DOM, already a lot of Cl- from road salt - DOM+Cl2 can be toxic, less Cl2 was left in "clean" water so more diseases were spread - High salinity also increased the rate of oxidation of Pb in pipes - Pb poisoning in those drinking the water
34
What could have prevented the flint water crisis?
- anti-corrosive agents should have been added (prevents rusting of pipes so would have resulted in less Pb) - Pb pipes replaced
35
What is an oxidizing agent?
Reactant that is intially in an oxidized state
36
what is a reducing agent?
reactant that contains excess electrons to donate
37
Which is the electron acceptor in | 4FeS2 +15O2 +14H2O = 4Fe(OH)3 + 8SO4 2- + 16H+
O2
38
In which direction will a reaction with a positive E0 proceed?
to the right
39
What is the oxidation state of carbon in graphite?
0
40
True or false: an environmental system with a high Eh means there are lots of chemicals that will accept an electron
True
41
True or false: electromotive force can be measured using only a half reaction
False
42
True or false: The reduction of O2 to H2O is part of anaerobic respiration
False
43
True or false: Denitrification during a redox casade can help reduce nitrate containation in groundwaters
True
44
True or false: Methanogenesis will occur before denitrifacation in a redox cascade since it yields higher energy
False
45
True or false: Groundwater is usually isolated from the atmosphere, so its pH is usually lower that stream water
False: stream water reacts with atmosphere so more acidic, lower pH
46
``` What is E0 for the complete reaction 2Pu3+ + 3Zn2+ + 2Pu Pu3+ +3e- = Pu Eh=-2.07V Zn2+ + 2e- = Zn Eh=-0.763V Is this reaction spontaneous? ```
E0=-1.307V, the reaction is not spontaneous
47
What is mass-dependent isotope fractionation?
- The idea that heavy and light isotopes of the same elements react in the same reactions at different rates. - product has different heavy/light isotope ratio than reactants
48
Which isotope is less abundant: heavy or light?
Heavier ones are less common with the exception of 3He/4He
49
A Nitrate sample has a 15N/14N ratio of 0.003800, express as delta15N. 15N/14?N standard=0.003677
33.5 permil
50
Name and describe the two kinds of isotopic change fractionation that can occur during reactions
1. Reversible reactions - fractionation measured at equilibrium - abiotic process - "equilibrium fractionation" 2. Irreversible reactions - fractionation depends on rate of reaction - often biotic chemical reactions - "kinetic fractionation"
51
The oxygen isotopic fractionation factor for the condensation of water at 298K is 1.0092. Calculate the delta value for vapor in a cave in equilibtium with liquid water with a delta value of -5 permil
-14.07 permil
52
determin the isotopic enrighment factor if the isotopic fractionation factor is equal to 1.0092
9.2permil
53
True or false: an enrichment factor >1 is enriched in the heavy isotope
True
54
True or false: isotopic fractionation typically is more extreme if rates are slower
True
55
A rain cloud with an initial delta 18O of 12permil is 90% rained out by the time it gets to Ontario. a) If the fractionation factor for condenstaion is 1.0092, what will the delta 18O be in the cloud? b) What is the delta 18O value for the rain formed?
a) -32.7permil | b) -23.8
56
Is the fraction factor larger or smaller as temperature increases?
The fractionation factor will decrease as temperature increases
57
True or false: a lower delta 18O and delta 2H value from an ice sample indicates a period of ice age.
True
58
On a global meteoric water line graph, where would you expect to see water from winter snow?
bottom end of the GMWL
59
What does it mean when the fractionation factor is less than 1?
the products have a lower ratio than the reactants
60
If the standard 18O/16O value is 0.002005, what is the delta 18O value for a sample with a ratio of 0.001995?
-5 permil
61
True or false: most abiotic reactions which affect stable isotope ratios undergo equilibtium fractionation because they are irreversible.
False | - the reactions are reversible in euqilibrium fractionation
62
What process(es) produce heavier elements than iron?
s process in large stars and the r process
63
True or false: even numbered atomic number elements have a lower abundance than odd numbered elements
False
64
How does the central temperature of a massive star change over time?
It increases over the lifetime of the star
65
What is the total mass of the products of a nuclear fusion reaction compared to the total mass of reactants?
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