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.
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.
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.
In the molecule below, how many atoms could make hydrogen bonds with water?
10
How many atoms in the pictured molecule can form hydrogen bonds with water molecules?
5
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
What type of bond is found between the oxygen and hydrogens?
polar covalent
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
About _____ molecules in a glass of water are dissociated.
1 in 500,000,000
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?
A- reacts with H+ to become HA
Which answer helps to explain why all living cells need pH buffers?
Amino acid side chains have many carboxyl and amino groups.
The open spaces in water's crystal structure make it possible for ...
Aquatic life to exist at the North Pole
Polar attractions are ...
Forces between atoms with partial charges Weaker than covalent bonds Important because they are numerous.
A water molecule can bond up to ___ other water molecules by ___ bonds.
Four ... hydrogen
Which of these is the correct equation for the dissociation of water?
H2O + H2O <==> H3O+ + OH-
What is the arrow pointing to? O+
Hydrogen ion
What name is given to this molecule? A water molecule that gains a hydrogen
Hydronium ion
What is the arrow pointing to? O-
Hydroxide ion
What name is given to this molecule? A water molecule that loses a hydrogen ion
Hydroxide ion
Which statement is true of water's tensile strength?
It results from hydrogen bonding It helps pull water through plants It involves both cohesion & adhesion
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 factor is important in making it possible to cool yourself by sweating?
Molecules collide with varied angles and speeds. Hydrogen bonds are relatively weak.
Which statement must be mentioned in explaining why amphipathic molecules line up at a water surface?
Polar groups attract one another
Why doesn't oil mix with water?
Polar molecules attract one another
How does the pH of the solution on the right compare with that of the solution on the left? Right: all + charges. Left: all - charges
The solution on the right is basic relative to the solution on the left
Which statement is true of pH buffers?
They consist of weak acids and weak bases.
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
Hydrogen bonds ...
can form between H and N
The tendency of an atom to pull electrons toward itself is referred to as its _____.
electronegativity
What process exerts the pull on water molecules that is relayed from leaf to root via cohesion?
evaporation
To make a buffer, you need to ...
have a weak acid or a weak base half ionized in water
Because organisms are made primarily of water, they resist rapid temperature changes. This useful quality is based on water's _____.
high specific heat
Water is a source of ______________ for chemical reactions in cells.
hydrogen and oxygen atoms
Water has surface tension because ...
hydrogen bonds between surface water molecules resist being stretched.
In a neutral solution the concentration of _____.
hydrogen ions is equal to the concentration of hydroxide ions
