Chapter 5: water and seawater

what shape is water

bent because it is dipolar from covalent bonds. Small negative charge at O end causes attraction btwn O and H, hydrogen bonding

cohesion

molecules sticking together. high surface tension, high solubility,

electrostatic attraction

produces ionic bond between solutes and water

van der waals forces

weak interactions when molecules close together

heat

transfer of both kinetic and potential energy from one object to another due to temp differences

temperature

direct measure of kinetic energy of molecules in a substance

calorie

amount of heat needed to raise temp of 1 gram of water by 1 degree C

heat capacity

amount of heat required to raise temp of 1 gram by 1 degree C

specific heat

heat capacity per unit mass

latent heats

heat absorbed or released during change of state

latent heat of melting

energy needed to break intermolecular bonds that hold water molecules in place in ice crystals

latent heat of vaporization

amt of heat that must be added to substance at boiling point to break intermolecular bonds from liquid to vapor. 540 calories/g

latent heat of evaporation

conversion of liquid to gas below boiling point. 585 calories/g

latent heat of condensation

cooled water vapor turns to liquid and releases heat to environment (identical to heat of vaporization)

latent heat of freezing

heat released when water freezes. identical to latent heat of melting

marine effect

ability of oceans to moderate temp changes from day to night and during diff seasons along coastlines and islands

continental effect

land areas have greater range of temps from day to night and during diff seasons

Density

mass/unit volume

water density

density of H2O increases as temp decreases. thermal contraction is shrinkage of most substances caused by cold temperatures, molecules lose energy and slow down.

freezing point depression

dissolved solids reduce freezing point of water

what is the salinity of seawater

3\.5% or 35 ppt

how was salinity determined in the early days of science

evaporation, weigh water and evaporated salts. not accurate, bc some salts evaporate with water

principle of constant proportions

chemical analysis via titration. Major dissolved constituents in same proportion regardless of total salinity. Determine one concentration, you can determine all of them bc relative abundance is same.

conversion formula for salinity

salinity (ppt) = chlorinity (ppt) x 1.80655

salinometer

measures water’s electrical conductivity, more dissolved substances increases conductivity

salinity variations

brackish: influx of fresh water from rivers or rain.

hypersaline: high evap conditions, great salt lake salinity 280 ppt

affecting salinity

decrease salinity: runoff, melting icebergs, melting sea ice, precip

increase: sea ice formation, evaporation

earth’s hydrologic cycle

water in diff reservoirs:

97\.2 in world ocean

2\.15 in glaciers and ice caps

.62 in groundwater and soil moisture

.02 in streams and lakes

.001 as water vapor in atm

residence time

average length of time a substance remains dissolved in seawater. ions with long residence time are in high concentration in seawater. short residence time are in low conc. seawater.

acid

releases hydrogen ion in water

base

releases OH ion in water

what is ocean pH

seawater is slightly alkaline. surface water avg is 8.1. pH increases with depth

buffering

keeps ocean from becoming too basic or acidic. Precip or dissolution of CaCO3 buffers ocean pH

surface salinity variation

high latitudes: low salinity, high sea ice melt, precip, runoff. low evap

low latitudes: low salinity high precip and runoff

mid latitudes: high salinity, warm, dry air increases evap (subtropics)

salinity variation with depth

low latitudes: salinity decreases with depth

high latitudes: salinity increases with depth

deep ocean salinity consistent globally

halocline

separates ocean layers of different salinity

seawater density

freshwater is 1.0 g/cm3,

ocean surface water 1.022 to 1.020 g/cm3

ocean layered according to density, decreased temp density increases

pycnocline

abrupt change of density with depth

thermocline

abrupt change of temp with depth

high latitude temp changes

high latitude have no pycnocline, low latitudes do.

high latitudes have no thermocline, low latitudes have a thermocline

temperature and density variations with depth

high and low latitudes have halocline

high lat: halocline shows lower surface salinity, increases with depth. lots of precip, runoff, melting

low lat: halocline reflects high surface salinity

ocean layers

mixed surface: layer above thermocline

upper water: low density, thermocline and pycnocline low middle lat

deep water: below thermocline to ocean floor

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isothermal

no temp variation in water column

isopycnal

no density variation in water column

distillation

used to desalinize water, boiled and condensed, removes salt. Use solar distillation in arid climates

electrolysis

electrode containing freshwater, membrane between fresh and salt water tanks

reverse osmosis

salt water forced through membrane into fresh

freeze separation

water frozen and thawed multiple times