Semester 1 Final: Water and the Fitness of the Environment

Question 1

structure of water

Answer 1

Two hydrogen atoms joined by a single polar covalent bond to one oxygen atom (H2O)

Question 2

polarity

Answer 2

the oxygen region has the partial negative charge (δ-) & the hydrogen region has the partial positive charge (δ+)
• Electrical attraction between the charged sides creates hydrogen bonds between water molecules - slightly positive hydrogen of one molecule is attracted to the slightly negative oxygen of a nearby molecule

Question 3

cohesion

Answer 3

Water creating hydrogen bonds with other water molecules
– Essential for water transport in plants (cohesion helps hold together the column of water with the xylem)
– Surface tension is a result of cohesion

Question 4

adhesion

Answer 4

clinging of one substance to another

• in water transport, adhesion of water to the cells helps counter the downward pull of gravity during transpiration
• capillary action, meniscus

Question 5

high specific heat

Answer 5

the amount of heat that must be absorbed/lost for one gram of the substance to change temperature by 1°C.
(1 cal/g/°C)
when heat is absorbed, hydrogen bonds are broken, when hydrogen bonds form, heat is released - a large quantity of heat is absorbed or lost for each degree temperature change
-regulate temperature fluctuations on land, stabilize ocean temperatures

Question 6

heat of vaporization

Answer 6

the quantity of heat a liquid must absorb for one gram of the liquid to be converted from liquid to gaseous state

• hydrogen bonds must be broken before the molecules can make an exodus from liquid
• moderate Earth’s climate

Question 7

evaporative cooling

Answer 7

essential to regulate lakes & maintain homeostasis
-water surface becomes cooler as evaporation occurs because the molecules with the greatest kinetic energy evaporate as gas

Question 8

Expansion during Freezing

Answer 8

Water expands as it freezes becoming less dense due to its crystalline structure from hydrogen bonds
• Ice floating at the top of lakes and ponds insulates the water below preventing them from freezing solid

Question 9

High Solubility

Answer 9

the partial negative charge of oxygen region attracts cations while the partial positive charge of hydrogen regions are attracted to anions
-water molecules surround the individual ions, forming hydration shells

Question 10

dissociation of water

Answer 10

• creates acidic and basic conditions
• Two water molecules connected by a hydrogen bond: a hydrogen atom will move from one molecule to join the other while leaving behind its electron. This creates a hydronium ion (H3O+) and a hydroxide ion (OH-).

Question 11

acids

Answer 11

a substance that increases the H+ concentration of a solution

Question 12

bases

Answer 12

a substance that reduces the hydrogen ion concentrations of a solution

Question 13

weak and strong bases

Answer 13

weak bases directly accept H+ ions

strong bases release OH- ion to bond with H+ ion to form water

Question 14

strong acids and bases

Answer 14

permanent dissociation

Question 15

buffers

Answer 15

A substance that
minimizes changes in the
concentration of OH and H+ in a solution
-accept H+ ions from a solution when too acidic and donates H+ ions when too basic
-most are comprised of a weak acid and corresponding base