Properties of water Flashcards
what are the basic properties of water?
three states
H2O
polar bond
hydrogen bonds
why is water essential for life?
circulates all time in varying states
scarce and valuable
by 2025 more than 1/2 world pop could face water based vulnerability
what % of the planet does water make up?
70%
97% is salt, 1% fw
what does water do?
Carries minerals and chemicals
Aids dispersal of sediments/seeds
Sculpts landscape
Transparent - aquatic plants can live within the water. Very productive system
Absorbs energy (heat) - solid to gas
Releases energy gas (heat) - solid
Important for buffering planet against temp extremes
what are the properties of water because of hydrogen bonds?
Cohesive behaviour - similar molecules attract each other
Resists change in temp
High heat of vaporization
Expands when freezes - less dense
High adhesion
High solubility of chemical compounds in water
what does water being a solvent show?
polar
attracts positive and negative ions
what is seawater made up of?
ratio of abundant components almost components change in salinity by removing/adding pure water chloride ions (55%) sodium (31%)
what is the heat capacity?
the amount of heat required to change the temp by a given amount
Expressed in joules per K
what is specific heat capacity?
heat capacity per unit mass of a body - energy needed to change 1kg by 1C
what is heat not the same as?
temperature
what is latent heat?
The amount of energy released/absorbed by a substance during a change of state that occurs without changing its temp
what is the change in energy with heat?
no change in kinetic energy
where does energy come from?
Energy released comes from the potential energy stored in the bonds between the particles
what happens when water absorbs/releases heat?
only slight change in its own temp
what is the change in temp in the oceans?
large difference between night/day, but little change in oceans
why do gases and liquids not mix?
cohesion forces greater than adhesion forces
Intermolecular attractions in every direction (H bond) force is negligible (cancel out)
This not the case on the surface molecules - here net force is downwards as the intermolecular attractions with the air molecules is negligible. Water molecules cohere strongly at surface
The compression resistance of the liquid will limit the downward force and a compressed layer forms at the surface
equation for pressure?
p = F/A
Units expressed as kg/A
what does water pressure at a given depth depend on?
mass of water above that depth
at 1m depth what is the mass of water above?
1 cubic meter
what is pressure reported at?
10,000Pa, 1dbar, 0.1bar
whats the equation for density?
(p) the mass per unit volume (kg/m^3))
what effects density?
temp (biggest effect), salinity and pressure
what happens with change in density?
water parcels moving (convection, thermohaline circulation)
what’s the density of water like in the med?
little freshwater in, high evaporation rate so salinity much higher and so much denser - sinks when meets atlantic and moves over sea floor
what happens to water below 0C?
form hexagonal crystals which cause water to expand
what happens to water between 0-4C?
added energy will break some H bonds of long chains and H20 molecules will move up more freely
- Water expands, density decreases
what happens above 4C?
more energy breaks H bonds, water moves more freely, water expands, density decreases
what happens to water between 0-4C with high salinity?
less molecules available to form chains, the more salt dissolved in water. So density not increasing between 0-4 for waters with salinities higher than 25 psu
why does ice float?
Hexagonal structure less compact - lower density than liquid water
Density decreases as the freezing point is reached - ice floats
When all molecules crystaline structure density about 8% less than liquid
whats the surface freezing point in the ocean?
around -1.9C
what is negative buoyancy?
an abject has density greater than surrounding fluid (experiencing downward force proportional to volume)
what is positive buoyancy?
object with density lower than surrounding fluid - tends to float
why is the density of aqueous organisms so sensitive to small changes?
density of water similar to body density
a change of 10 in air changes by what on land/in sea?
1% and 20%
which buoyancy type are fats and oils?
positive
which buoyancy type is a whale ear bone?
negative
what is the adaptation of the cuttefish?
cuttlebone - controls amount of gas and fluid within rigid structure
- Day - negatively buoyant to hide in sediment
Dark - neutrally buoyant to hunt
what does the swim bladder do?
walls have blood vessels not permeable to gases. The quantity of gas in bladder allows fish to maintain preferred depth
- Dorsal side of fish - helps stay up right - Sounds production
adaptations of squid?
exchange sodium ions for NH3 ions creating lower density fluid, increasing the osmotic pressure allowing the organism to control its buoyancy
what are the adaptations of crustaceans (copeopods)?
- During summer moths eat diatoms which leave bodies high in fat
- Winter - go through diapause (at depths below 500m)
- When they descend to start diapause the fat solidifies (usually around 500m depth) theory - stop descending when they become neutrally buoyant (kind of like dormancy)
- This strategy uses low amounts of energy to stay at perfect depth for months (up to 6) at a time - dormancy to hide
what are the adaptations of sperm whales?
before diving cold water enters spermaceti organ solidifying wax increasing the density so the whale can dive
during hunting wax warms and melts, increasing buoyancy so the whale can surface easily
