Chapter 3: Water and Life

what four properties of water facilitate an environment for life?

cohesive behavior, ability to moderate temperature, expansion upon freezing, and versatility as a solvent

what type of bonds are in a water molecule?

polar covalent

where do the electrons of a water molecule spend more time?

near the oxygen

the water molecule is a ______ molecule

polar

what allows water molecules to form hydrogen bonds with each other?

polarity

what is cohesion?

a phenomenon were hydrogen bonds hold water molecules together

what results from cohesion?

high surface tension

what is surface tension?

a measure of how difficult it is to stretch or break the surface of a liquid

what contributes to the transport of water and dissolved nutrients against gravity in plants?

cohesion

what is adhesion?

an attraction between different substances

what is an example of adhesion?

the attraction between water and plant cell walls

what helps to counter the downward pull of gravity?

adhesion

water ______ heat from warmer air

absorbs

water ______ stored heat to cooler air

releases

water can absorb or release a large amount of ______ with only a slight change in its own temperature

heat

what is kinetic energy?

energy of motion

what is thermal energy?

the kinetic energy associated with random motion of atoms or molecules

what is temperature?

represents the average kinetic energy of the molecules in a body of matter

what is heat?

thermal energy in transfer from one body of matter to another

______ is the amount of heat required to raise the temperature of 1g of water by 1°C

a calorie (cal)

______ is the amount of heat released when 1g of water cools by 1°C

a calorie (cal)

the “calories” on food packages are actually what?

kilocalories (kcal)

how many calories are equal to 1 kilocalorie?

1000

what is a unit of energy?

Joule (J)

how many calories is a Joule equal to?

0.239

how many Joules are equal to 1 calorie?

4.184

what is specific heat?

the amount of heat that must be absorbed or lost for 1g of that substance to change its temperature by 1°C

how does water resist changes in its temperature?

high specific heat

what is responsible for water’s high specific heat?

hydrogen bonding

heat is absorbed when hydrogen bonds ______

break

heat is released when hydrogen bonds ______

form

the high specific heat of water minimizes what?

temperature fluctuations to within limits that permit life

when can a large body of water absorb and store a huge amount of heat?

from the sun in daytime and during summer while warming up only a few degrees

when does water gradual cool the air?

at night and during the winter water gradual cools

in what type of areas does water moderate air temperature?

coastal

what is evaporazation (or vaporization)?

transformation of a substance from liquid to gas

what is heat of vaporization?

heat a liquid must absorb for 1g to be converted to gas

what is evaporative cooling?

the process where, as a liquid evaporates, its remaining surface cools

why is evaporative cooling beneficial?

it helps stabilize temperatures in organisms and bodies of water

what is an example of evaporative cooling?

an elephant spraying water on itself

is water less dense as a liquid or as a solid?

solid

at 0°C, water molecules are locked into a ______

crystalline lattice

what keeps water molecules far enough apart to make the ice ~10% less dense than liquid water?

hydrogen bonds

at what temperature does water reach its greatest density?

4°C

if ice was more dense than liquid water what would be the result?

all bodies of water would eventually freeze solid, making life impossible on Earth

what is a solution?

a liquid that is a completely homogeneous mixture of substances

what is a solvent?

the dissolving agent of a solution

what is a solute?

the substance that is dissolved

what is an aqueous solution?

one in which water is the solvent

due to its polarity, water is a ______

versatile solvent

what is a hydration shell?

sphere of water molecules that surround the each ion of an ionic compound when it is dissolved in water

water can also dissolve compounds made of ______

nonionic polar molecules

what types of regions are required for large molecules, such as proteins, to dissolve in water?

ionic and polar

what is a hydrophilic substance?

one that has an affinity for water

what is a hydrophobic substance?

one that does not have an affinity for water

what is an example of a hydrophobic substance?

oil molecules

what makes a substance hydrophobic?

nonpolar bonds

what are the major ingredients of cell membranes?

hydrophobic molecules related to oils

to pass through the cell membrane, what does a molecule have to be?

small and nonpolar

most chemical reactions in organisms involve ______ dissolved in water

solutes

what do we use to calculate the number of solute molecules in an aqueous solution when carrying out experiments?

mass

what is molecular mass?

the sum of all masses of all atoms in a molecule

1 mole is equal to how many molecules?

6.02 × 10²³

how many daltons are equal to 1g?

6.02 × 10²³

what is molarity (M)?

the number of moles of solutewhich plane per liter of solution

which planet in our solar system has been found to have water?

Mars

what is the name for a hydrogen atom that leaves its electron behind and is transferred as a proton?

hydrogen ion (H⁺)

what is the name for the molecule that lost a proton?

hydroxide ion (OH^-)

what is the name for the molecule with an extra proton?

hydronium ion (H₃O⁺), but it’s often represented as H⁺

what state is water in?

dynamic equilibrium in which water molecules dissociate at the same rate at which they are being reformed

changes in the concentrations of which ions can drastically affect the chemistry of a cell?

H⁺ and OH^-

when are the concentrations of H⁺ and OH^- equal?

in pure water

what types of solutes modify the concentrations of H⁺ and OH^-?

acids and bases

what do scientists use to describe whether a solution is acidic or basic?

pH scale

what is an acid?

a substance that increases the H⁺ concentration of a solution

what is a base?

a substance that reduces the H⁺ concentration of a solution

what type of acids and bases dissociate completely in water?

strong

what types of acids and bases reversibly release and accept back hydrogen ions?

weak

for any aqueous solution at 25°C, the product of H⁺ and OH^- is constant and can be written as what?

[H⁺][OH^-] = 10^-14

what is the equation used to find pH?

-log[H⁺]

what is the pH of a neutral solution?

7

acidic solutions have pH values ______

less than 7

basic solutions have pH values ______

greater than 7

most biological fluids have pH values in the range of ___ to ___

6, 8

the internal pH of most living cells is close to what?

7

what are buffers?

substances that minimize changes in concentrations of H⁺ and OH^- in a solution

what do most buffer solutions contain?

a weak acid and its corresponding base

what is an example of a human activity that threatens water quality?

burning fossil fuels

what is the main product of fossil fuel combustion?

carbon dioxide

about what percentage of human-generated CO₂ is absorbed by the oceans?

25

what is ocean acidification?

the process in which CO₂ dissolved in seawater forms carbonic acid

as seawater acidifies, H⁺ ions combine with carbonate ions to produce ______

bicarbonate ions

______ is required for calcification (production of calcium carbonate) by many marine organisms, including reef-building corals

carbonate

what statement about water is true?

a. if you had 10 mL of water, it would take 10 kcal of heat to raise the temperature by 1 degree Celsius

b. ice water is more dense than liquid water

c. plants transport water from the roots to the leaves by using cohesion and adhesion

d. water molecules in the gas phase have more hydrogen bonds relative to water molecules in liquid water

e. all of the above

c. plants transport water from the roots to the leaves by using cohesion and adhesion

which statement about evaporative cooling is true?

a. when you sweat, water molecules that leave the liquid phase and enter the gas phase have more kinetic energy relative to water molecules that remain in the liquid phase

b. an elephant covering its body with water on a hot day in Central Africa is an example of evaporative cooling

c. during evaporative cooling the surface of an object’s temperature becomes lower

d. the process of evaporative cooling involves kinetic energy of molecules

e. all of the above

e. all of the above

what statement about a long hydrocarbon chain (molecule with only carbon and hydrogen is true?

a. it is classified as a polar molecule

b. it has polar covalent bonds

c. two hydrocarbon chain molecules could participate in Van der Waals interaction

d. long hydrocarbon chains are very soluble in water

e. all of the above

c. two hydrocarbon chain molecules could participate in Van der Waals interaction

which statements about water are true?

a. water is most dense at 4 degrees Celsius

b. liquid water is more dense than ice water

c. liquid water has a low specific heat relative to most other liquids

d. water molecules in the gas phase participate in 4 hydrogen bonds

e. all of the above

a. water is most dense at 4 degrees Celsius

b. liquid water is more dense than ice water

how many hydrogen bonds does ice state of water have?

4

how many hydrogen bonds does gas state of water have?

0