MasteringBiology Chapter 3
Which of the following helps most to explain why water has a high specific heat?
(a) A water molecule can make 4 hydrogen bonds.
Which statement is true of pH buffers?
(c) They consist of weak acids and weak bases.
Buffers work best when ...
about half of the buffer molecules are dissociated.
Though you add heat, the temperature of boiling water remains constant because ...
it takes energy to break hydrogen bonds.
Which property of water allows dogs to cool themselves by panting?
water's high heat of vaporization
A pH of 6 is how many times more acidic than a pH of 9?
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.
Why isn't this insect drowning?
Surface tension.
Look at the figure showing the pH values of some familiar aqueous solutions. What is the difference between H+ concentration in an acidic solution such as lemon juice (pH 2) and a basic solution such as household bleach (pH 13)?
The H+ concentration of lemon juice is higher than the H+ concentration of household bleach by a factor of 1011 (100 billion).
The unequal sharing of electrons within a water molecule makes the water molecule _____.
polar
In this molecule, what type of bond is found between the oxygen and hydrogens?
polar covalent
Water has surface tension because ...
hydrogen bonds between surface water molecules resist being stretched.
The open spaces in water's crystal structure make it possible for ...
(a) aquatic life to exist at the North Pole.
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).
A buffer consists of undissociated acid (HA) and the ion made by dissociating the acid (A-). How does this system buffer a solution against decreases in pH?
(b) A- reacts with H+ to become HA.
Why doesn't oil mix with water?
(c) Polar molecules attract one another.
To make a buffer, you need to ...
(d) have a weak acid or a weak base half ionized in water.
Which answer helps to explain why all living cells need pH buffers?
Amino acid side chains have many carboxyl and amino groups.
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)
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 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).
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?
It's the same reaction running backward or forward.
Which statement must be mentioned in explaining why amphipathic molecules line up at a water surface?
Polar groups attract one another.
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.
Dissolving is best described as ...
a mingling of molecules and/or ions.
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 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
In a neutral solution the concentration of _____.
hydrogen ions is equal to the concentration of hydroxide ions
