AP Bio Unit 1 (properties of water)

pH drops

pH drops

As the H+ ion concentration increases (________) the H+ will bind to carbonate ions, decreasing calcification.

x 10 7 M

In pure water, [H+]= [OH]=- 1.0 ________, which means pH= 7 (neutral)

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

-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

The substance that dissolves (ex

NaCl, table salt) is known as the solute

When water dissolves salt (NaCl), Na+ and Cl

split apart

The 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)

Once the Na+ and Cl

are isolated from each other and are no longer able to form the compound NaCl, we say that the salt has dissolved in the water

Examples of Cohesion and Surface Tension

Water droplets bead up, water strider insects can "walk on water" by spreading their weight and using the surface tension of the water

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

Note

Heat capacity is a more general term for specific heat and refers to the amount of energy required to change the temperature of a substance by a particular amount

Note

Vaporization, or the transformation of a substance from a liquid to a gas, is also known as evaporation

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)

An acid is a substance that has a high amount of H+ ions and a low amount of OH

ions (pH less than 7)

A base (alkaline) is a substance that has a high amount of OH

ions and a low amount of H+ ions (pH greater than 7)

There are two equations used to compare pH and H+ and OH

concentrations

Brackets around an ion-ex

[H+]-signify the concentration of that ion

Equation 1

pH = -log10[H+]

Example

if [H+] = 1 x 10-7, then pH = 7

Equation 2

[H+] x [OH-] = 10-14

Example

if [H+] = 1 x 10-9, then [OH-] = 10-5

The system involves the use of HCO3

(bicarbonate, a weak base and H+ acceptor) and H2CO3 (carbonic acid, a weak acid and H+ donor) to minimize changes in blood pH

H2CO3 ← → HCO3

• H+

How do polar and non polar molecules interact with each other?

Polar molecules tend to attract one another.  Polar molecules repel non-polar (uncharged / neutral) molecules.

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

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

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?

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.

Polar

H-N,O,F = polar, non symmetrical

Non polar

molecule made of one element (monoatomic atom), carbon and hydrogen bond = non polar, symmetrical