Biology Chapter 3- Homework

Buffers work best when... the pH is nearly neutral. nearly all of the buffer molecules are dissociated. about half of the buffer molecules are dissociated. nearly all of the buffer molecules are undissociated. the ratio of H+ to OH- is close to 1.0.

about half of the buffer molecules are dissociated.

Which property of water allows a paper towel to pick up a puddle of water? water's high heat of vaporization water's high surface tension adhesion of water molecules to other kinds of molecules

adhesion of water molecules to other kinds of molecules

Sodas typically contain flavorings, coloring agents, sugar, and carbon dioxide dissolved in water. The best term to describe this mixture would be __________. a solute an aqueous solution a solvent an aqueous solvent a suspension

an aqueous solution

Many of water's emergent properties, such as its cohesion, high specific heat, and high heat of vaporization, result from the fact that water molecules __________. -are extremely large -tend to repel each other -are very small -are attracted to each other by partial negative and positive charges on the oxygen and hydrogen atoms, respectively -are in constant motion

are attracted to each other by partial negative and positive charges on the oxygen and hydrogen atoms, respectively

Hydrogen bonds... can form between H and N. are covalent bonds. occur within a water molecule. share electrons between the two bonded atoms. All of the above.

can form between H and N.

The tendency of an atom to pull electrons toward itself is referred to as its _____. ionic potential covalency electronegativity polarity tonicity

electronegativity

What process exerts the pull on water molecules that is relayed from leaf to root via cohesion? precipitation gravity antigravity evaporation

evaporation

A water molecule can bond to up to _____ other water molecules by ____ bonds. two... polar covalent three... ionic two... hydrogen four... polar covalent four... hydrogen

four... hydrogen

Because organisms are made primarily of water, they resist rapid temperature changes. This useful quality is based on water's __________. -properties as a solvent. -cohesion -buffering activity -high specific heat -lower density in the solid phase

high specific heat

Is the thermal energy of a full bathtub higher or lower than the thermal energy of a pot of freshly brewed coffee (even though the coffee has a higher temperature than the bathwater)? Why? higher; high kinetic energy lower; low temperature higher; greater volume lower; low density

higher; greater volume

What kind of bonds are responsible for the unique cohesion, surface tension, and adhesion properties of water molecules? -hydrogen bonding -polar covalent bonding -hydrophobic bonding -ionic bonding

hydrogen bonding

Water molecules have a polarity, which allows them to be electrically attracted to other water molecules and other polar molecules by weak chemical bonds known as _____. See Concept 3.1 (Page) ionic bonds polar covalent bonds hydrogen bonds nonpolar covalent bonds Van der Waals interactions

hydrogen bonds

Water has surface tension because... -there is positive pressure inside the water mass. -molecules at the surface make more hydrogen bonds. -hydrogen bonds between surface water molecules resist being stretched. -cohesion forces are weaker at the surface. -water tends to evaporate from the surface.

hydrogen bonds between surface water molecules resist being stretched.

In a neutral solution the concentration of _____. -hydrogen ions is greater than the concentration of hydroxide ions -hydrogen ions is equal to the concentration of hydroxide ions water -molecules is less than the concentration of hydroxide ions water -molecules is less than the concentration of hydrogen ions hydrogen -ions is less than the concentration of hydroxide ions

hydrogen ions is equal to the concentration of hydroxide ions water

Melting of ice and thus reduced feeding opportunities for polar bears is occurring because of the ________. -increase in phytoplankton population -constant breaking and reforming of hydrogen bonds in water -drying up of lakes and streams -increase in CO2 and other greenhouse gases in the atmosphere

increase in CO2 and other greenhouse gases in the atmosphere

An acid is a substance that __________. contains hydrogen is a versatile solvent forms covalent bonds with other substances reduces the hydrogen ion concentration of a solution increases the hydrogen ion concentration of an aqueous solution

increases the hydrogen ion concentration of an aqueous solution

Which of the following statements correctly describes the property of hydrophobic substances such as vegetable oil? -polar substances that repel water molecules -polar substances that have an affinity for water -nonpolar substances that repel water molecules -nonpolar substances that have an attraction for water molecules

nonpolar substances that repel water molecules

Sulfur is in the same column of the periodic table as oxygen but it is less electronegative than oxygen. Compared to water molecules, how will the H2S molecules behave? -not be able to form hydrogen bonds with each other -have greater cohesion to other H2S molecules -have a greater tendency to form hydrogen bonds with each other -have a higher capacity to absorb heat for the same change in temperature

not be able to form hydrogen bonds with each other

We can be sure that a mole of table sugar and a mole of vitamin C are equal in their number of atoms. volume. mass. number of molecules.

number of molecules.

The unequal sharing of electrons within a water molecule makes the water molecule _____. change easily from a liquid to gaseous form hydrophobic have a low surface tension polar ionic

polar

What kind of bond is formed between the two hydrogen atoms and the single oxygen atom? nonpolar covalent bonds polar covalent bonds hydrogen bonds ionic bonds

polar covalent bonds

When carbon dioxide in the atmosphere dissolves with the raindrops, what is the expected change in pH of the raindrops? slightly basics lightly acidic same as pure water depends on the altitude where rain drops are formed

slightly acidic

To act as an effective coolant in a car's radiator, a substance has to have the capacity to absorb a great deal of heat. Which physical property is the best indicator for a good coolant? heat of vaporization density at room temperature specific heat pH

specific heat

Rank, from low to high, the pH of blood, stomach acid, and urine. blood, urine, and stomach acid stomach acid, urine, blood stomach acid, blood, and urine urine, blood, stomach acid

stomach acid, urine, blood

A solution of pH 7 is ________ than a solution of pH 8. 100% less acidic ten times as acidic twice as acidic 100% more acidic

ten times as acidic

Electronegativity is the negative charge surrounding the nucleus of an atom. the repulsion of electrons in one atom for electrons in another atom. the number of electrons in the outermost electron shell. the attraction of an atom for the electrons in a covalent bond.

the attraction of an atom for the electrons in a covalent bond.

Consider two solutions: solution X has a pH of 4; solution Y has a pH of 7. From this information, we can reasonably conclude that ________. solution Y has no free hydrogen ions (H+) the concentration of hydrogen ions in solution Y is 1000 times as great as the concentration of hydrogen ions in solution X the concentration of hydrogen ions in solution X is 3 times as great as the concentration of hydrogen ions in solution Y the concentration of hydrogen ions in solution X is 1000 times as great as the concentration of hydrogen ions in solution Y

the concentration of hydrogen ions in solution X is 1000 times as great as the concentration of hydrogen ions in solution Y

The partial negative charge in a molecule of water occurs because ________. -one of the hydrogen atoms donates an electron to the oxygen atom -the oxygen atom has two pairs of electrons in its valence shell that are not neutralized by hydrogen atoms -the electrons shared between the oxygen and hydrogen atoms spend more time around the oxygen atom nucleus than around the hydrogen atom nucleus -the oxygen atom donates an electron to each of the hydrogen atoms

the electrons shared between the oxygen and hydrogen atoms spend more time around the oxygen atom nucleus than around the hydrogen atom nucleus

Which property of water allows dogs to cool themselves by panting? the formation of covalent bonds between water molecules water's high heat of vaporization water's high surface tension

water's high heat of vaporization

How would you describe a buffer solution? weak acid and its conjugate base strong acid and its conjugate base strong base and its conjugate acid weak base and its conjugate acid

weak acid and its conjugate base

Which of the following helps most to explain why water has a high specific heat? (a) A water molecule can make 4 hydrogen bonds. (b) The water molecule has exceptionally strong covalent bonds. (c) Water temperature is exceptionally sensitive to heat. Both (a) and (b). Both (b) and (c).

(a) A water molecule can make 4 hydrogen bonds.

A polar covalent bond between two atoms results from the presence of two ions close to each other. the shape of the molecule that has the bond. two atoms that do not have similar electronegativities. whether the bond is single or not.

two atoms that do not have similar electronegativities.

Which property of water allows a water strider to walk on water? -the formation of covalent bonds between water molecules -adhesion of water molecules to other kinds of molecules -water's high surface tension

water's high surface tension

Which of the following is a hydrophobic material? table salt wax paper sugar

wax

Identify all correct statements about the ionization of water. Check all that apply. (a) Dissociation of water produces equal numbers of OH- and H+. (b) Water ionizes to form hydroxide and hydronium ions. (c) Dissociation of water produces equal masses of OH- and H+. (d) Dissociation of water is reversible. (e) Dissociation of water is not reversible. (f) Water ionizes to form peroxide and hydronium ions.

(a) Dissociation of water produces equal numbers of OH- and H+. (b) Water ionizes to form hydroxide and hydronium ions. (d) Dissociation of water is reversible.

Polar attractions are... (a) forces between atoms with partial charges. (b) weaker than covalent bonds. (c) important because they are numerous. (a) and (b) are true. (c) is false. (a), (b), and (c) are correct.

(a), (b), and (c) are correct.

Why doesn't oil mix with water? (a) Nonpolar molecules repel water molecules. (b) Polar molecules repel nonpolar molecules. (c) Polar molecules attract one another. (d) Nonpolar molecules attract one another. Both (a) and (d).

(c) Polar molecules attract one another.

Which statement is true of pH buffers? (a) They consist of strong acids and strong bases. (b) They keep the pH of the blood constant. (c) They consist of weak acids and weak bases. Both (a) and (b). Both (b) and (c).

(c) They consist of weak acids and weak bases.

Water is a source of ______________ for chemical reactions in cells. (a) hydrogen atoms (b) oxygen atoms (c) energy Both (a) and (b) (d)- (a), (b), and (c).

(c) energy Both (a) and (b)

To make a buffer, you need to... (a) combine equal amounts of a strong acid and a strong base in water. (b) put either a strong acid or a strong base in water. (c) adjust the pH to 7.0. (d) have a weak acid or a weak base half ionized in water. Both (a) and (c).

(d) have a weak acid or a weak base half ionized in water.

Which statement is true of water's tensile strength? (a) It results from hydrogen bonding. (b) It helps to pull water through plants. (c) It involves both cohesion and adhesion. Both (a) and (b). (d)- (a), (b), and (c).

(d)- (a), (b), and (c).

What is the charge on a hydronium ion? 1- 1+ 0 2- 2+

1+

A pH of 6 is how many times more acidic than a pH of 9? 303 100 300 1,000

1,000

Select the statement that best describes a buffer. A buffer resists change in pH by accepting hydrogen ions when acids are added to the solution and donating hydrogen ions when bases are added. Buffered solutions are always neutral with a pH of 7.A buffer prevents the pH of a solution from changing when an acid or base is added. A buffer stabilizes the pH of a solution by preventing acids or bases from dissociating. A buffer causes acidic solutions to become alkaline and alkaline solutions to become acidic.

A buffer resists change in pH by accepting hydrogen ions when acids are added to the solution and donating hydrogen ions when bases are added.

Which of the following can be attributed to water's high specific heat? -Oil and water do not mix well. -A lake heats up more slowly than the air around it. -Ice floats on water. -Sugar dissolves in hot tea faster than in iced tea.

A lake heats up more slowly than the air around it.

Which answer helps to explain why all living cells need pH buffers? Amino acid side chains have many carboxyl and amino groups. Hydrogen bonds only form at medium pH values. Nucleic acids must have positive charges to form double helices. ATP will not deliver energy if it is ionized.

Amino acid side chains have many carboxyl and amino groups.

Which factor is important in making it possible to cool yourself by sweating? Think carefully! (a) Molecules collide with varied angles and speeds. (b) Hydrogen bonds are relatively weak. (c) Water has more energy at the body surface. Both (a) and (b). (a), (b), and (c).

Both (a) and (b).

Which of these is the correct equation for the dissociation of water? H2O <==> H+ + OH- H2O + H2O <==> H3O+ + OH- H2O + OH-<==> H2O+ H+<==> H2O + H2O+ H2O + H2O+<==> H2O + OH-

H2O + H2O <==> H3O+ + OH-

How would acidification of seawater affect marine organisms? It will increase dissolved carbonate concentrations and promote faster growth of corals and shell-building animals. It will increase dissolved carbonate concentrations and hinder growth of corals and shell-building animals. It will decrease dissolved carbonate concentrations and hinder growth of corals and shell-building animals. It will decrease dissolved carbonate concentrations and promote faster growth of corals and shell-building animals.

It will decrease dissolved carbonate concentrations and hinder growth of corals and shell-building animals.

How does the way a buffer stabilizes pH during addition of acid differ from the way the same buffer stabilizes pH during addition of base? In one case the buffer is strong; in the other case it's weak. It's the same reaction running backward or forward. In one case it adds H+; in the other case it adds OH-. The same buffer can't work for both acid and base.

It's the same reaction running backward or forward.

Which of the following is considered to be a strong base (alkali)? NH3 + H+ ↔↔ NH4+ HCl →→ H+ + Cl- NaOH →→ Na+ + OH- H2CO3 ↔↔ HCO3- + H+

NaOH →→ Na+ + OH-

Which statement must be mentioned in explaining why amphipathic molecules line up at a water surface? Polar groups repel water. Polar groups attract one another. Nonpolar groups attract one another. Nonpolar groups repel water. All of the above.

Polar groups attract one another.

Increased atmospheric CO2 concentrations might have what effect on seawater? Seawater will become more acidic, and carbonate concentrations will increase. Seawater will become more acidic, and carbonate concentrations will decrease. There will be no change in the pH of seawater, because carbonate will turn to bicarbonate. Seawater will become more alkaline, and carbonate concentrations will decrease.

Seawater will become more acidic, and carbonate concentrations will decrease.

Which answer best describes why does ice float in liquid water? -Stable hydrogen bonds keep water molecules of ice farther apart than water molecules of liquid water. -The high surface tension of liquid water keeps the ice on top. -The ionic bonds between the molecules in ice prevent the ice from sinking. -The crystalline lattice of ice causes it to be denser than liquid water.

Stable hydrogen bonds keep water molecules of ice farther apart than water molecules of liquid water.

Which of the following reasons explains why a steam burn is more severe than a hot water burn? -Steam can penetrate the skin. -Steam contains more energy than water. -Water evaporates and leaves the surface faster and helps in cooling. -Burns caused by liquids are always milder.

Steam contains more energy than water.

Why isn't this insect drowning? The insect is very light. It is difficult to change the temperature of water. The insect is swimming. Surface tension. The insect is flying just above the water surface.

Surface tension.

Dissolving is best described as... molecules breaking into ions. a mingling of molecules and/or ions. breaking covalent bonds. a change from a solid to a liquid. a separation of molecules into neutral atoms.

a mingling of molecules and/or ions.