Biology

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. (When you heat water, much of the heat is used to break hydrogen bonds. Only the remaining heat can increase molecular motion, raising the temperature. )

The open spaces in water's crystal structure make it possible for ... (a) aquatic life to exist at the North Pole. (b) water to have a low boiling point. (c) life to occur in hot springs. Both (b) and (c). (a), (b), and (c).

(a) aquatic life to exist at the North Pole. (The openings in the lattice make ice less dense than liquid water, so it floats. That causes water to freeze from the top down, so there's always liquid in which organisms can live. )

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

(a), (b), and (c). (Because of hydrogen bonding, water coheres to itself and adheres to cell walls. That makes it possible to pull water through plants without breaking the water column. )

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. (Water molecules cling to one another and won't part to make room for uncharged (nonpolar) molecules. There's no repulsion. )

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

-hydrogen ions is equal to the concentration of hydroxide ions

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

Both (a) and (b) (Many reactions incorporate O and H from water into biological molecules. This happens when you digest starch and protein, for example. )

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). (Random collisions allow some molecules to accumulate more energy than other molecules. The weakness of hydrogen bonds lets those molecules escape, leaving the cooler molecules behind. )

Which statement helps to explain why ice is less dense than liquid water? (a) Water molecules make hydrogen bonds at definite angles. (b) Cold molecules move less than warm molecules. (c) Hydrogen bonds lengthen in the cold. All of the above. Both (a) and (b).

Both (a) and (b). (The ice lattice has open spaces because of the angles at which hydrogen bonds form. Heat energy can break water molecules free of the lattice so they move into the openings. )

Because organisms are made primarily of water, they resist rapid temperature changes. This useful quality is based on water's _____. See Concept 3.2 (Page 46) lower density in the solid phase high specific heat ability to form colloids buffering activity cohesion

High specific heat (Water has a high specific heat, meaning that a relatively large amount of heat must be added or removed in order to get the temperature of the water to change significantly.)

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

Polar groups attract one another. ( Polar water molecules pull together, holding the polar parts of the amphipathic molecules and squeezing out the nonpolar parts. That leaves the nonpolar parts waving in the air. )

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

a mingling of molecules and/or ions. (When sugar dissolves in water, the sugar molecules remain intact but mingle with water molecules. When salt (NaCl) dissolves, its Na+ and Cl- ions separately mingle with water. )

Many of water's emergent properties, such as its cohesion, its high specific heat, and its high heat of vaporization, result from the fact that water molecules _____. See Concept 3.2 (Page 45) -tend to repel each other -are attracted to each other by partial negative and positive charges on the oxygen and hydrogen atoms, respectively -are very small -are extremely large -are in constant motion

are attracted to each other by partial negative and positive charges on the oxygen and hydrogen atoms, respectively (The formation of hydrogen bonds between the positive and negative regions of different water molecules accounts for most of water's unique properties.)

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

electronegativity

Each water molecule is joined to _____ other water molecules by ____ bonds. two ... polar covalent two ... hydrogen four ... hydrogen three ... ionic four ... polar covalent

four ... hydrogen

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

hydrogen bonds between surface water molecules resist being stretched. (The hydrogen bonds between surface water molecules are normally slightly stretched. Like a stretched sheet of rubber, the surface tends to contract and resists being penetrated. )

Though you add heat, the temperature of boiling water remains constant because ... it takes energy to break covalent bonds. water has a constant boiling temperature. it takes energy to break hydrogen bonds. it takes energy to circulate water. None of the above. The temperature rises during boiling.

it takes energy to break hydrogen bonds ( all the added heat is used to break hydrogen bonds. Free of the water mass, the departing steam carries away all the added energy, with none left over to raise the temperature. )

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

polar

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

water's high heat of vaporization (Evaporative cooling takes place when molecules with the greatest kinetic energy leave a fluid as gas molecules. Because of water's high heat of vaporization, a large amount of heat must be absorbed for 1 gram of water to be converted from liquid to gas. The dog loses this heat as the water on its tongue evaporates, allowing him to cool down by panting. To understand why this answer is correct, read about evaporative cooling.)