Chapter 3 - Water and Life

Question 1

Four of water’s properties that facilitate an environment for life are…

Answer 1

• Cohesive behavior
• Ability to moderate temperature
• Expansion upon freezing
• Versatility as a solvent

Question 2

Cohesion

Answer 2

The linking together of like molecules, often by hydrogen bonds.

Question 3

Adhesion

Answer 3

The clinging of one substance to another, such as water to plant cell walls by means of hydrogen bonds.

Question 4

Surface tension

Answer 4

The measure of how difficult it is to stretch or break the surface of a liquid. Water has a high surface tension because of the hydrogen bonding of surface molecules.

Question 5

How does Water Moderate Temperature?

Answer 5

• Water absorbs heat from warmer air and releases stored heat to cooler air
• Water can absorb or release a large amount of heat with only a slight change in its own temperature

Question 6

Heat

Answer 6

A measure of the total amount of kinetic energy due to molecular motion

Question 7

Temperature

Answer 7

Measures the intensity of heat due to the average kinetic energy of molecules.

Question 8

Calorie (cal)

Answer 8

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

Question 9

Joule (J)

Answer 9

unit of energy where 1 J = 0.239 cal, or 1 cal = 4.184 J

Question 10

Specific heat

Answer 10

The amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºC.

Question 11

The specific heat of water is…

Answer 11

1 cal/g/ºC Water resists changing its temperature because of its high specific heat. This minimizes temperature fluctuations to within limits that permit life.

Question 12

Water has a high specific heat because…

Answer 12

– Heat is absorbed when hydrogen bonds break – Heat is released when hydrogen bonds form

Question 13

Heat of vaporization

Answer 13

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

Question 14

Evaporative cooling

Answer 14

The process in which the surface of an object becomes cooler during evaporation, a result of the molecules with the greatest kinetic energy changing from the liquid to the gaseous state. Evaporative cooling of water helps stabilize temperatures in organisms and bodies of water.

Question 15

Ice floats in liquid water because…

Answer 15

Hydrogen bonds in ice are more “ordered,” making ice less dense.

Question 16

Water reaches its greatest density at…

Answer 16

4°C

Question 17

Solution

Answer 17

A liquid that is a homogeneous mixture of substances.

Question 18

Solvent

Answer 18

The dissolving agent of a solution.

Question 19

Solute

Answer 19

The substance that is dissolved.

Question 20

Aqueous solution

Answer 20

A solution in which water is the solvent.

Question 21

Water is a versatile solvent due to its…

Answer 21

polarity, which allows it to form hydrogen bonds easily.

Question 22

Hydration shell

Answer 22

This forms when an ionic compound is dissolved in water. Each ion is surrounded by a sphere of water molecules.

Question 23

Can water dissolve Water can also compounds made of nonionic polar molecules?

Answer 23

Yes. Even large polar molecules such as proteins can dissolve in water if they have ionic and polar regions.

Question 24

Hydrophilic Substance

Answer 24

A substance that has an affinity for water.

Question 25

Hydrophobic substance

Answer 25

A substance that has does not an affinity for water. Oil molecules are hydrophobic because they have relatively nonpolar bonds.

Question 26

Colloid

Answer 26

A stable suspension of fine particles in a liquid

Question 27

Molecular Mass

Answer 27

the sum of all masses of all atoms in a molecule.

Question 28

Numbers of molecules are usually measured in…

Answer 28

moles, where 1 mole (mol) = 6.02 x 10²³ molecules

Question 29

Avogadro’s number and the unit dalton were defined such that…

Answer 29

6.02 x 10²³ daltons = 1 g

Question 30

Molarity (M)

Answer 30

The number of moles of solute per liter of solution.

Question 31

Hydrogen ion

Answer 31

A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other. The hydrogen atom leaves its electron behind and is transferred as a proton, or hydrogen ion (H+).

Question 32

Hydronium ion

Answer 32

A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other. The molecule with the extra proton is now a hydronium ion (H₃O+), though it is often represented as H+.

Question 33

Hydroxide ion

Answer 33

A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other. The molecule that lost the proton is now a hydroxide ion (OH–).

Question 34

Water is in a state of dynamic equilibrium in which water molecules dissociate…

Answer 34

at the same rate at which they are being reformed

Question 35

Concentrations of H+ and OH– are _____ in pure water.

Answer 35

equal. Adding certain solutes, called acids and bases, modifies the concentrations of H+ and OH–. Biologists use something called the pH scale to describe whether a solution is acidic or basic.

Question 36

acid

Answer 36

any substance that increases the H+ concentration of a solution. Acidic solutions have pH values less than 7.

Question 37

base

Answer 37

any substance that reduces the H+ concentration of a solution. Basic solutions have pH values greater than 7.

Question 38

In any aqueous solution at 25°C the product of H+ and OH– is constant and can be written as…

Answer 38

[H+][OH–] = 10^–14

Question 39

The pH of a solution is defined by…

Answer 39

the negative logarithm of H+ concentration, written as pH = –log [H+]

Question 40

For a neutral aqueous solution, [H+] is 10^–7, so…

Answer 40

pH = –(–7) = 7

Question 41

Most biological fluids have pH values in the range of…

Answer 41

6 to 8. The internal pH of most living cells must remain close to pH 7.

Question 42

Buffers

Answer 42

substances that minimize changes in concentrations of H+ and OH– in a solution. Most buffers consist of an acid-base pair that reversibly combines with H+.

Question 43

ocean acidification

Answer 43

The process where CO₂ dissolves in sea water to form carbonic acid. CO2 is the main product of fossil fuel combustion. About 25% of human-generated CO₂ is absorbed by the oceans. As seawater acidifies, H+ ions combine with carbonate ions to produce bicarbonate. Carbonate is required for calcification (production of calcium carbonate) by many marine organisms, including reef-building corals.

Question 44

Acid precipitation

Answer 44

rain, fog, or snow with a pH lower than 5.2. The burning of fossil fuels is a major source of sulfur oxides and nitrogen oxides. These compounds react with water in the air to form strong acids that fall in rain or snow. Acid precipitation damages life in lakes and streams and changes soil chemistry on land.