A1.1 Water Flashcards
Water as the medium for life
Life on earth began in the ocean (+ vesicles)
Substances dissolved in water -> chem. reactions between solutes.
Molecules bent rather than linear -> Hydrogen on the same side and form one pole. H2O is dipolar.
Electronegativity
A chemical property that describes the tendency of an atom to attract electrons toward itself.
Electronegativity of H2O
O pulls H electrons towards it. O = δ- (partial neg.) and H = δ+
Hydrogen bonding
Electrostatic attraction between H atom in a polar molecule and a small electroneg. atom (O, N, or F) in another.
Cohesion
Alike molecules sticking togehter due to intermolecular forces of attraction (e.g. hydrogen bonds).
Conduction of water in the xylem
Cohesion allows transport of water w/ help of tension.
Roots = soil particles + water attract
Leaves = water evap. atm. and attraction water molecules + cell wall of leaf cells.
Why does water move upwards in the xylem?
Pulling forces in the leaves > forces in the roots.
Surface tension (water)
An elastic-like membrane that forms because water molecules are more attracted to each other in hydrogen bonding than to air particles.
Why does surface tension make it possible for objects to float?
Cohesion between water molecules > attraction between water and floating object. (some animals use this to inhabit water surfaces)
Object break through -> many hydrogen bonds must be broken simultaneously.
Adhesion
When hydrogen bonds form between water and the surface of a solid composed of polar molecules. -> Water sticks to the surface.
Capillary action
When liquid flows through narrow spaces without external forces, rather, the liquid’s movement is aided by intermolecular forces between the liquid and solid surface(s).
Occurs: adhesion to the walls > cohesive forces liquid molecules.
Capillary action glass tube
As air is replaced by water, many H bonds form between glass and water, releasing energy.
Why can porous solides such as paper exert strong suction forces through adhesion?
They have a large amount of surface area to attract water.
How water can rise up from an underground source, even though gravity tends to pull it down?
Water is attracted to many chemical substances in soil. If soil is porous, water is drawn by capillary action through dry soil, wetting it.
Capillary action usefulness in leaves
Water evaporates from cell walls -> lost to atm. -> adhesive forces draw water out nearest xylem vessel.
This keeps the walls moist -> can absorb CO2 needed for photosynthesis. Also generates low pressures that draw water up xylem vessels.
Capillary action usefulness refill xylem
Xylem vessel becomes air-filled -> adhesion between water + wall of vessel helps vessel to refill with water.
Solvent
Substance capable of dissolving other substances.
Solute
A dissolved substance (present in a smaller amount than the solvent in a solution).
Solution
A mixture of one or more solutes dissolved in a solvent.
Water important solvent properties
H2O polar -> forms shells around charged + polar molecules. Prevents clumping so they remain in solution.
Partial neg. attracted to cations + partial pos. attracted to anions -> both dissolve.
H2O forms H-bonds w/ polar molecules.
Hydrophilic
Substances chemically attracted to water. All dissolve in water (polar or charged).
Substances that water adheres to but does not dissolve (e.g. cellulose) also hydrophilic.
Hydrophobic
Not repelled by water but not attracted -> more attracted to other hydrophobic subst.
Non-polar + not charged. -> Insoluble in water but may dissolve in other solvents.
All lipids are hydrophobic.
Water as a medium for metabolism
Cytoplasm = is an aqueous solution and solvent is water. Solutes move around + interact.
