AP Bio Unit 1 (properties of water)

water: polar covalent (electrons not equally shared), oxygen has slightly negative charge and hydrogen has a partial positive charge
Electronegativity: tendency of an atom to attract electrons to itself
Polar molecules tend to attract one another. Polar molecules repel non-polar (uncharged / neutral) molecules. Based on their interactions with water, other polar vs. non-polar molecules have received certain names.
Hydrophilic molecules = water loving / polar molecules that dissolve in water (ex: sugars, DNA, proteins)
Hydrophobic molecules = water fearing / nonpolar molecules that tend to cluster in water (ex: fats… remember, oil and water do not mix!… also, the interactions between water and phospholipid molecules, a type of fat, enable cell membranes to form)
why are water molecules able to form hydrogen bonds with one another?: polarity → negative oxygen at end of one water molecule attracts the positive hydrogen at the end of another molecule (opposites attract)
can hydrogen bonds form between different molecules?: yes, if they are both polar and is a highly electronegative atom (slight negative charge within polar molecule) ex: nitrogen, oxygen, or fluorine → definition of hydrogen bonding is H—NOF.
How many hydrogen bonds can one water molecule make?: maximum of four hydrogen bonds with four other water molecules
A single hydrogen bond is weaker than a single covalent or ionic bond but
Why is water known as the universal solvent?: can dissolve other polar or ionic (fully charged) substances to make a solution
What happens when water dissolves salt (NaCl)?: Na+ and Cl- split apart, negative oxygen ends of water molecules surround the Na+ (because opposites attract) and the positive hydrogen ends of water molecules surround the Cl- (hydration shell)
What causes cohesion in water?: hydrogen bonding
What quality does water have as a result of cohesion?: surface tension
Examples of Cohesion and Surface Tension in water: Water droplets bead up, water strider insects can “walk on water” by spreading their weight and using the surface tension of the water
Why causes adhesion in water?: polarity of water and ability to form hydrogen bonds
Examples of Adhesion: water forms a meniscus (dip) in a graduated cylinder because the water molecules closest to the sides of the tube are attracted to the glass and are pulled up
Cohesion and Adhesion of water molecules causes capillary action, the ability of water to move through a narrow passageway.
What happens when water cools and freezes to form ice?: movement of water slow down (allows more hydrogen bonds to form between water molecules and pushes them farther apart) -→ makes ice less dense than liquid water
Whats an environmental benefit of ice?: ice floats on the surface of a lake or pond, it insulates the water in the pond and prevents it from being exposed to the cold air. This protects organisms in aquatic ecosystems over the winter.
Why does water have a high specific heat?: because hydrogen bonds must be broken to raise the temperature of water and create more movement / kinetic energy between the water molecules
What is specific heat?: amount of energy required to raise the temperature of 1 gram of a substance 1 degree Celsius
How is pH measured molecularly?: measures the hydrogen ion (H+) concentration of a substance
How does a change in pH change H+ ion concentration?: each difference in one pH unit represents a 10X difference in the H+ concentration (ex: pH 2 has 1000 times more H+ ions than a pH 5)
What is the ration of H+ ion to OH- ions in an acid?: high amount of H+ ions and a low amount of OH- ions (pH less than 7)
What is a base (alkaline)?: a substance that has a high amount of OH- ions and a low amount of H+ ions (pH greater than 7)
How often do water molecules dissociate and into what? : occasionally dissociate (come apart and form charged ions) →one water molecule may dissociate into H+ and OH-, or two water molecules will dissociate into H3O+ (hydronium ion) and OH-
How do our bodies maintain constant pH levels (homeostasis)?: carbonic acid-bicarbonate buffer system
What are buffers?: weak acids and their related base (or vice versa) that act by combining reversibly with H+, can donate H+ to solutions when concentrations fall and remove H+ from solutions when concentrations increase. Because they minimize changes in the concentrations of H+ and OH-, they counteract major changes in pH. Buffer systems are one way that the body attempts to maintain homeostasis (stable internal conditions).
What happens when H+ concentration in blood falls (pH rises)?: the reaction “shifts” to the right and more carbonic acid dissociates, creating more H+ and lowering the pH.
What happens when H+ concentration in blood rises (pH falls)?: reaction “shifts” to the left and bicarbonate combines with excess H+ to form carbonic acid (removes the excess H+ and raises the pH)
How does Co2 in atmosphere affect ocean acidity?: CO2 in the atmosphere combines with water to form carbonic acid. As the H+ ion concentration increases (pH drops) the H+ will bind to carbonate ions, decreasing calcification.

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