276 Exam Flash Cards

studied byStudied by 1 person
0.0(0)
get a hint
hint

what are the 8 substances that make up the chemical composition of water?

1 / 251

encourage image

There's no tags or description

Looks like no one added any tags here yet for you.

252 Terms

1

what are the 8 substances that make up the chemical composition of water?

H20, pH, major cations, major anions, organic matter, trace metals, particles, biological materials.

New cards
2

Give 4 examples of chemical reactions

sorption-desorption, acid-base, precipitation-dissolution, redox

New cards
3

Give 2 examples of biological processes

uptake and release, photosynthesis and respiration

New cards
4

What is the equation for advection

concentration x mean velocity

New cards
5

What are 2 types of diffusion

Eddy turbulence and molecular

New cards
6

What is the equation for diffusion

concentration gradient x diffusion coefficient

New cards
7

3 key facts regarding thermal stratification

Bottom waters horizontally mixed, surface waters mixed by convection, eddy diffusion controls vertical transport

New cards
8

Define eddy diffusion

The diffusion process where substances are mixed due to eddy motion

New cards
9

Example of eddy diffusion

Manganese- released from sediment and diffuses through the stratified bottom layers, well mixed in surface waters.

New cards
10

What is the exponential decay curve equation

C = Coe^-Q/v

New cards
11

What does the exponential decay curve equation show?

How the concentration of a substance decreases with time

New cards
12

What are steady-state conditions, an example and exception

Where the total mass in the compartment equals the rate of input or output. Chemical equilibrium, except slow processes such as weathering

New cards
13

What are non steady-state conditions, an example and exception

Where there is a change in concentration over time, for example in lakes. Chemical disequilibrium, except very fast reacting element under input-output balance

New cards
14

Define residence time

The mean time period that any constituent remain in a specified compartment.

New cards
15

What is the average residence time in the oceans compared to windermere

4000 years to 1 year

New cards
16

What are 3 factors that affect the distribution of substances

Reaction rate, residence time, internal mixing

New cards
17

What does an increase in the residence time suggest

A more complex reaction that is heterogeneous and involves physical mixing

New cards
18

What is the shape of a water molecule

4 tetrahedrally orientated sp3 orbitals

New cards
19

How is polarity produced in the water molecule (2 factors)

A difference in electronegativity between O and H, and the distribution of lone electron pairs

New cards
20

What is a hydrogen bond

electrostatic attraction between H and O

New cards
21

in separate H2O molecules, which links 4-8 molecules so it has a higher effective molecular weight

New cards
22

What substances are soluble

Ionic and polar covalent substances

New cards
23

What substances are insoluble

covalent substances (e.g. PCB)

New cards
24

What 2 factors is solubility linked to

Hydration and the dielectric effect of water (as water has no charge, it electrostatically insulates charged ions in a solution).

New cards
25

What is the size of truly dissolved substances and example

less than 1 nm, viruses

New cards
26

What is the size of colloids and example

1 nm - 1 macrometer, bacteria and algae

New cards
27

What is the size of particulates

More than 1 micrometer

New cards
28

2 factors about transport and location of colloids

Suspension of small particles, dispersed in water with dissolved substances

New cards
29

Define stokes law

where the velocity of gravitational settling is proportional to diameter squared

New cards
30

For particles less than 1 micrometer, why can they not compete with other forces (examples)

because their velocity is too small to compete with Brownian motion and turbulence

New cards
31

4 key properties of colloids

very large specific surface area, reactive, mobile and act as intermediates in solution (particle coagulation)

New cards
32

3 examples of colloids

Sulphide minerals, organic materials, clay minerals

New cards
33

Define chemical speciation

substances with different chemical and physical forms with different chemical and biological properties

New cards
34

When is the Physical form important in speciation

Metal ion in solution vs metal adsorbed to clay particles

New cards
35

When is the Physical form unimportant in speciation and example

Free hydrated metal ions vs metal complexes with inorganic ligands, free hydrated Fe2+ behaves differently to Fe(II)-humic complex (forms insoluble FeS)

New cards
36

What happens with chemical speciation in algae

Only free ions are taken up by the algae (Free Ion Activity Model)

New cards
37

Two examples of chemical speciation and biological uptake

Zn Uptake by Algae, zinc concentration in the water was linear to zn2+ in the blue-green algae. Al Uptake by Fish, Al is bad for fish, in high pH and more humic-rich waters, less Al3+ available so fish are safe

New cards
38

What is chemical speciation important for (biological)?

important for bioavailability of substances

New cards
39

What are the key biological substances that affect the chemical composition of natural waters

micro-organisms such as planktonic algae and bacteria

New cards
40

2 major factors that affect chemical speciation, and example

pH and dissolved organic compounds, Metal ion plus humic acid = metal humic species

New cards
41

What size is the filter for filtration

0.1-1 micrometer

New cards
42

2 problems with filtration

Dissolved substances generally includes the colloidal fraction, and size fractions are also affected by other properties

New cards
43

What 4 factors affect the size fractions in filtration

non-uniform pore sizes, clogging, adsorption onto filter and apparatus, colloidal aggregation

New cards
44

Describe the example of measuring total dissolved substances by colorimetry

Phosphate analysis, acidified molybdate reagent. Produces reduced phospho-molybdate complex that absorbs long wave-length visible light. Intensity of blue colour is proportional to concentration. Includes free orthophosphate and inorganically complexed orthophosphate.

New cards
45

Describe the example of measuring total dissolved substances by atomic absorption spectrometry

Sample is sprayed into the flame and atomised. Light with suitable wavelength is shone through the flame. Light is absorbed by the atoms of the sample. The amount of light absorbed is proportional to the concentration of the element in the sample.

New cards
46

How are free ions analysed?

By Ion Selective Electrode (ISE). A membrane electrode possesses a certain selectivity towards a given ion or ions

New cards
47

Define free hydrated metal ions

No ligands other than the water molecules

New cards
48

Define complexes

Central ion or atom surrounded by ligands

New cards
49

Define ligands

Molecules or ions in metal complexes

New cards
50

How do you measure free ions?

Using a ion selective electrode (ISE)

New cards
51

Define an ion selective electrode

A membrane electrode that possesses a certain selectivity towards a given ion or ions

New cards
52

How do you measure labile species

Anodic stripping voltametry (ASV) or diffusive gradient in thin films (DGT)

New cards
53

Define labile species

Species that can dissociate in response to pertubation

New cards
54

4 advantages of DGT

In situ, time-integrated, measures labile and bio-available species, not affected by environmental conditions

New cards
55

What is the equation used by DGT

C = m delta g / DAt

New cards
56

3 reasons why the concentration of labile species measured using DGT be smaller than using a filter?

Diffusion coefficient could be smaller, complexes may dissociate slowly, DGT doesn't measure colloids

New cards
57

what 5 things does DGT measure?

metals, radionuclides, nutrients, antibiotics, pesticides

New cards
58

What is the main dissolved constituent in natural waters?

inorganic ions

New cards
59

What 3 things does the concentration of inorganic ions depend on?

crustal abundances, aqueous chemistry, biological effects

New cards
60

Give 3 examples of very soluble metal ions

Calcium, sodium, magnesium

New cards
61

Give 2 examples of not very soluble metal ions

Aluminium and iron

New cards
62

Define ionic potential

a charge density term indicating the ionizing power of the ion

New cards
63

What is the equation for ionic potential

ionic potential (z/r) = Ionic charge (z) / ionic radius (r)

New cards
64

What does the interaction strength of elements in dissolved water depend on?

ionic potential

New cards
65

What happens to ions when there is a low ionic potential (under 3) and a low cation electronegativity (under 1.2)

Large, low-charge, electropositive ions surrounded by water molecules with little interaction between ion and water

New cards
66

What happens to ions when there is a medium ionic potential (3-12) and a medium cation electronegativity (1.2-1.9)

Small, highly-charged, electropositive ions, interaction between ion and water, bond to oxygen by abstracting OH liberating hydrogen ion, form uncharged and insoluble hydroxides (Fe, Al)

New cards
67

What happens to ions when there is a high ionic potential (over 12) and a high cation electronegativity (over 1.9)

Smaller, more highly-charged, electronegative ions, interaction between ion and water, bond to oxygen by abstracting O liberating hydrogen ion, form large and stable anions

New cards
68

The elements present in highest concentrations relative to their crustal abundances are...

group 1 metals and the larger group 2 metals, elements with large ionic potentials which form soluble oxyanions, and group 7 anions

New cards
69

Where is dissolved organic carbon (DOC) usually present

In humic substances

New cards
70

What is the master variable in natural waters?

pH

New cards
71

What is the pH of freshwater

5-11

New cards
72

What is the pH of seawater

around 8

New cards
73

define chemical equilibrium and exceptions

The state of dynamic balance where the rates of opposing reactions are equal and the concentrations remain unchanged. exception: very Slow Reaction such as weathering of aluminium-silicate rock, concentration of species unchanging, non-equilibrium

New cards
74

How are equilibrium reactions quantified

using the equilibrium constant (k) derived from the law of mass action

New cards
75

Give the mass action expression for A + B -> C + D

k = [C] [D] / [A] [B]

New cards
76

Define non-ideal behaviour

Where the concentration of a species is not the same as the actual concentration due to electrostatic interactions between ionic species

New cards
77

Define a homogeneous reaction

where the reaction involves only one phase for example gaseous,

New cards
78

What is the constant concentration of most natural and sea water?

55.5 M dm-3

New cards
79

What 3 things can a mass action expression determine?

whether a system is at equilibrium, which way it will go if not at equilibrium, determines the equilibrium concentration of a species

New cards
80

What effects do temperature and pressure have on k?

significant, pressure only significant for gas phase and in deep waters

New cards
81

6 examples of reactions that can be shown by mass action expressions

Dissociation, acid-base, complexation, redox, gas solution, precipitation-dissolution

New cards
82

Define Henry's law

The mass of gas dissolved by a given volume of liquid at a fixed temperature is proportional to the partial pressure of gas

New cards
83

K for a precipitation-dissolution reaction is called a...

Solubility product Ksp

New cards
84

What happens in the mass action equations when k values are obtained from any set of standard tables?

The effective concentrations of an pure solid or liquid are omitted

New cards
85

What happens when the concentration product is larger than Ksp?

Solution is supersaturated, non-equilibrium

New cards
86

What happens when the concentration product is the same as Ksp?

Solution is saturated, equilibrium

New cards
87

What happens when the concentration product is smaller than Ksp?

Solution is undersaturated, non-equilibrium

New cards
88

Define an acid

An acid is a substance that can donate a proton to any other substance in aqueous solution (i.e. a proton donor

New cards
89

Define a base

A base is a substance that can accept a proton from another substance in aqueous solution (i.e. proton acceptor)

New cards
90

Define amphoteric and example

displays both acid and base properties (HCO3-)

New cards
91

Define polyprotic acids and example

can donate more than one proton e.g. H2SO4

New cards
92

Define polyprotic base and example

can accept more than one proton e.g. OH-

New cards
93

What is K for strong acid and bases

infinite

New cards
94

What is K for weak acid and bases

small (e.g. 10^-6.5)

New cards
95

Give the equation for working out pH from hydrogen ions

pH = -log10 [H+]

New cards
96

The net electric charge of neutral waters is...

0, anions = cations

New cards
97

Write out mass action expression for dissociation of water

k = [H+] [OH-]

New cards
98

Effect of pH on reactions - protons and equilibrium

proton transfer usually very rapid in aqueous solution, equilibrium concepts applicable where dissolved species involved.

New cards
99

2 main sources of CO2 for water

Respiration and the atmosphere

New cards
100

K1 for the dissociation of carbonic acid

k1 = [HCO3-] [H+] / [H2CO3]

New cards

Explore top notes

note Note
studied byStudied by 20 people
Updated ... ago
4.0 Stars(1)
note Note
studied byStudied by 144 people
Updated ... ago
5.0 Stars(2)
note Note
studied byStudied by 4 people
Updated ... ago
5.0 Stars(1)
note Note
studied byStudied by 11009 people
Updated ... ago
4.9 Stars(52)
note Note
studied byStudied by 63 people
Updated ... ago
4.0 Stars(1)
note Note
studied byStudied by 8 people
Updated ... ago
5.0 Stars(1)
note Note
studied byStudied by 2 people
Updated ... ago
5.0 Stars(1)
note Note
studied byStudied by 77 people
Updated ... ago
5.0 Stars(1)

Explore top flashcards

flashcards Flashcard39 terms
studied byStudied by 2 people
Updated ... ago
5.0 Stars(1)
flashcards Flashcard31 terms
studied byStudied by 11 people
Updated ... ago
5.0 Stars(1)
flashcards Flashcard40 terms
studied byStudied by 133 people
Updated ... ago
5.0 Stars(1)
flashcards Flashcard52 terms
studied byStudied by 15 people
Updated ... ago
5.0 Stars(1)
flashcards Flashcard37 terms
studied byStudied by 14 people
Updated ... ago
5.0 Stars(7)
flashcards Flashcard49 terms
studied byStudied by 5 people
Updated ... ago
5.0 Stars(1)
flashcards Flashcard31 terms
studied byStudied by 2 people
Updated ... ago
5.0 Stars(1)
flashcards Flashcard306 terms
studied byStudied by 5 people
Updated ... ago
5.0 Stars(1)