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Chapter 3. Water and life, Screenshot (901), 03-water-and-life-34-638 -…
Chapter 3. Water and life
3.3 Acidic & basic conditions affect living Organisms
pH scale
[H+][OH–] = 10^-14
neutral: pH = 7
pH = –log [H+]
Threats to water
CO2 is released by fossil fuel
Acidification of the oceans
“greenhouse” effect
Acid precipitation
Buffers
pH of most living cells ~ 7
minimizes changes in the concentrations of H+ and OH-
acid-base pairs
Definition
BASE
H+ < OH- : basic solution
reduces H+ concentration
ACID
H+ > OH- : acid solution
increases H+ concentration
H+ = OH- : neutral
3.1 Polar covalent bonds in water molecules result in hydrogen bonding.
V shape
Electronegative: O > H.
Polar covalent bonds.
The partially positive hydrogen of one molecule is attracted to the partially negative oxygen of a nearby molecules. => are held by a hydrogen bond.
Liquid form of water:
Hydrogen bonds are very fragile, 1/20 covalent bonds.
The hydrogen bonds form, break, reform frequently.
3.2 For emergent properties of water contribute to Earth’s suitability for life.
The linkages make water more structured than most other liquids.
Cohesion
Hydrogen bonds hold water together
Allows transport of water and dissolved nutrients against gravity in plants.
Adhesion
hydrogen bonds allow to stick to the molecule to stick to the molecules of cell walls.
Surface tension
a measure of how difficult it is to stretch or break the surface of a liquid.
Temperature & Heat.
Kinetic energy, the energy of motion.
Atom & molecules have kinetic energy - always moving.
Thermal energy is diferent from temperature but related to
Temperature
the average kinetic energy of the molecules in a body of matter, regardless of volume
Thermal energy
of a body matter reflects total kinetic energy depends on matter”s volume.
Two objects of different temperature
Thermal energy passess from the warmer to the cooler object until they are the same.
Ex: Liquid receives thermal energy from the ice cube.
A calorie is the amount of heat it take to raise the temperature of 1g H20 by 1C
Also the amount of heat 1g H2O release where it cools by 1 C
Water’s high specific heat.
Water has hydro bonds => the specific heat is higher than other materials.
Heat must be absorbed in order to break hydrogen bonds and released when hydrogen bonds form.
Specific heat => amount of heat that must be absorbed/ lost for 1g that substance to change by 1 C.
Evaporative cooling
This transformation from a liquid to a gas => evaporation.
Molecules of any liquid stay close because they are attracted to one another.
Heat of evaporation is the quantity of heat a liquid must absorb for 1g to convert from liquid => gas state.
Because of hydrogen bonds => high heat vaporization.
Evaporation cooling occurs because the hottest molecules.
Ex: Transpiration cools the leaf.
Floating of ice on liquid water.
Water is less dense as a solid than as a liquid (10% less dense 0 C vs 4 C)
At 4 C , water like other liquids, expanding as it warms & contracting as it cools.
As the temperature all from 4 C -> 0 C, water begins to freeze because molecules move too slowly to break hydrogen bonds.
At 0 C, the molecules become looked into a crystalline lattice, each molecule hydrogen - bonded to 4 partners
The floating ice insulates the liquid water below.
Water: the solvent of life
Solution (ddich)
a liquid that is completely homogeneous mixture of two or more substances.
Solvent(dmoi
the dissolving agent of a solution.
Solute (ctan)
: the substance that is dissolved aqueous solution: one in which water is the solvent.
Water is a versatile (flexible) solvent due to its polarity, which allows it to form hydrogen bonds easily.
The sphere of water molecules around each dissolved ion is called a hydration shell ( hydrat hoa)
Other compound: sugar, protein,... can be dissolved in water.
Hydrophilic and hydrophobic substances.
Hydrophilic ( ua nuoc )
): any substance that has affinity to water.
*Some substances can be hydrophilic without dissolving
Ex: Some molecules in cell are so large that they cannot dissolve.
Hydrophobic
substances that are nonionic & nonpolar( cannot form hydrogen bonds)seem to repel water.
