Biology; Chapter 3
Which of the following helps most to explain why water has a high specific heat?
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.
Though you add heat, the temperature of boiling water remains constant because ...
it takes energy to break hydrogen bonds. At boiling, 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.
A pH of 6 is how many times more acidic than a pH of 9?
1,000 A pH of 6 is 10 times more acidic than 7, which is 10 times more acidic than 8, which is 10 times more acidic than 9. 10 x 10 x 10 = 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. In this fashion, buffers minimize the change in the pH of a solution.
Why doesn't oil mix with water?
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.
The unequal sharing of electrons within a water molecule makes the water molecule _____.
polar The electrons spend more time with the oxygen of the water molecule than with the hydrogens of water. Thus, the oxygen has a net negative charge and the hydrogens have a net positive charge.
In this molecule, what type of bond is found between the oxygen and hydrogens?
polar covalent While oxygen shares electrons with hydrogen, the electrons spend more time with the oxygen than with the hydrogens.
Which of these bonds is weakest?
Hydrogen Bonds are weaker than covalent bonds because they do not involve sharing of electrons, and they are weaker than ionic bonds because they involve the attraction of partial (not full) opposite charges.
Which statement is true of water's tensile strength?
It results from hydrogen bonding. It helps to pull water through plants. It involves both cohesion and adhesion. 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.
Which factor is important in making it possible to cool yourself by sweating?
Molecules collide with varied angles and speeds. Hydrogen bonds are relatively weak. 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 must be mentioned in explaining why amphipathic molecules line up at a water surface?
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.
How does the pH of the solution on the right compare with that of the solution on the left?
The solution on the right is basic relative to the solution on the left. The solution on the right has a lower concentration of hydrogen ions relative to hydroxide ions than does the solution on the left.
Which statement helps to explain why ice is less dense than liquid water?
Water molecules make hydrogen bonds at definite angles. Cold molecules move less than warm molecules. 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.
Dissolving is best described as ...
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.
The open spaces in water's crystal structure make it possible for ...
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.
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 _____.
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 _____.
electronegativity
Each water molecule is joined to _____ other water molecules by ____ bonds.
four ... hydrogen
Because organisms are made primarily of water, they resist rapid temperature changes. This useful quality is based on water's _____.
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.
Water is a source of ______________ for chemical reactions in cells.
hydrogen atoms oxygen atoms Many reactions incorporate O and H from water into biological molecules. This happens when you digest starch and protein, for example.
Water has surface tension because ...
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.
What is the arrow pointing to?
hydrogen ion The arrow is indicating a single proton, a hydrogen ion (H+).
In a neutral solution the concentration of _____.
hydrogen ions is equal to the concentration of hydroxide ions
What is the arrow pointing to?
hydroxide ion The arrow is indicating a hydroxide ion (OH-).
Why isn't this insect drowning?
surface tension The high surface tension of water allows the insect to remain on the surface.
