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Specialist Chemistry > Water Composition > Flashcards

Water Composition Flashcards

1
Q

What is the Hydrologic cycle?

A

Movement of water between biosphere, atmosphere, lithosphere, hydrosphere

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2
Q

Rain water composition

A

evaporation from sea, evapotranspiration from land

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3
Q

Bnefits of water

A

excellent solvents for ionic compounds, good for polar organic compounds

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4
Q

3 main natural resources

A
  1. gases dissolve in water Kh=[gas]/partial pressure of gas 2. atmospheric aerosols dissolve, including sulphates. 3. Sea surface bubbles NaCl aerosol -> dissolves
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5
Q

“Average” rainwater compositions?

A

Depends on location, very diluted seawater, human inputs cause changes

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6
Q

Why acidic pH 5.5?

A

Water falls in soils, sediments, dissolved minerals via acid hydrolysis reactions

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7
Q

Acid hydrolysis reaction

A

limestone+acidic natural water, clay mineral produce H+

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8
Q

pH logarithmic scale

A

change in 1 unit means 10 fold change in water acidity

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9
Q

“Boomerang profile” - Temperate region

A

Rich in Ca relative to Na due to hydrolysis reactions

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10
Q

“Boomerang profile” - Tropical region

A

River simillar to rain, low in TDS, rich in Na, shallow soil cover and intense rainfall limits weathering

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11
Q

“Boomerang profile” - Arid region

A

Evaporation of water = less soluble Ca to precipitate = Na rich brine, sea water composition end of process

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12
Q

Temperate

A

TDS 10-20x than rain water, wich in Ca, Mg, hydrogen carbonate and silicates

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13
Q

HCO3

A

derived from carbonic acid (CO2 in rain water( reaction with carbonaceous minerals in rocks

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14
Q

Silicates

A

mix of complexed hydrated silicate chemical species

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15
Q

Water residence time

A

t increases as water slows

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16
Q

Spring and summer surface of heating water

A

surface water less dense than underlying water - results in stratification of water column

17
Q

Water column

A

Deeper water isolated from surface contact with atmosphere for weeks

18
Q

Late autumn and early spring

A

surface cools by lower air temperature with strong wind mixing -> stratification broken

19
Q

Broken Stratification

A

leads to water turnover periods - water surface becomes cool and dense to sink to be replaced - water formerly held at depth

20
Q

Winter

A

strong surface cooling leads to ice formation & weak water stratification

21
Q

What does water stratification and stability allow photosynthetic plankton do?

A

Grow and thrive in the light and nutrient rich surface of water

22
Q

What happens when plankton grow?

A

Surface water nutrients become depleted - deep water nutrients unavailable

23
Q

Deep water

A

cannot mix upward -> leads to crash of plankton bloom

24
Q

Dead plankton cells

A

gravitationally sink, decompose in deep water

25
Q

What nutrients are re-released?

A

N and P -> leads to elevated nutrient concentration in hypoliminion in contrast to depleted low conc. in epiliminion

26
Q

Decomposition

A

leads to dangerously low oxygen levels in deep water -> carbon-rich biogenic particles oxidise

27
Q

Seawater composition

A

Mostly Na+Cl then Mg, S, Ca, K. Rest = ions of elements in periodic table. No units “PSU”

28
Q

Coastal waters

A

sea water influence by fresh water, simillar chemistry to lakes : stratification (thermal & salinity) and nutrient supply

29
Q

Groundwater

A

impermeable -> (2 years) -> AQUIFER - (decades) -> Centuries -> impermeable

30
Q

Oxidising and solution reactions

A

mildly acidic rainwater infiltrates: acid hydrolysis reactions. Filtration process means pathogen content low. Water: Ca, Mg, HCO3 (hard water)

31
Q

Ion exchange (sorption) reaction

A

Clay minerals sorb higher charged ions (Ca2+, Mg2+, SO4 2-), groundwater enriched in monovalent ions (Na+, K+, Cl-), change to “soft water” - low pathogens

32
Q

Saltiness of water

A

becomes salty with age - restricts usefulness for abstraction

33
Q

Reducing reactions

A

Oxygen used in decomposition & reduction reactions, others: NO3- -> N2 and SO4 2- -> S2 (transition metals precipitate)

34
Q

Methanogenesis

A

Alternative, less energetically favourable, CO2 -> CH4 (bacterial mediation)

Specialist Chemistry (22 decks)

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