1.2 Water: Life's Solvent Flashcards
-Hydrogen bonds form readily between water molecules in both liquid water and ice.
This bonding forms an arrangement known as the ________ _______
water lattice
Most molecules that are the size of water,
such as H2, O2, CO2, HCl, and H2S, are _____ at room temperature.
gases
In liquid water, the hydrogen bonds that hold the _______ together constantly break and reform, allowing water molecules to slip past one another and _______ the lattice in new positions.
This gives liquid water its ______ properties.
lattice; reform; fluid
In ice, the water lattice is a _______ crystalline structure.
rigid
Specific heat definition
Specific heat is the amount of thermal energy that is required to increase the temperature of a given quantity of water by one degree Celsius.
If the boiling point of water were −81 degrees C, most of the water on Earth would be in the _________ state
gaseous
The hydrogen bond lattice of water results in water molecules staying close together—a property called __________.
cohesion
Surface tension definition
Surface tension is the measure of how difficult it is to stretch or break the surface of a liquid
Water molecules on the surface of a body of water can form hydrogen bonds on all sides, except the side that faces the _____.
This creates an _______ in bonding, which produces a force that places the surface water molecules under _______ and makes them more resistant to separation than the molecules below the surface.
air; imbalance; tension
True or false
Surface tension is strong enough to allow small insects, such as water striders, to walk on water
true
Water molecules can also form hydrogen bonds with other polar molecules— a
property called _______.
adhesion
cohesion
water molecules form hydrogen bonds with each other
adhesion
water molecules form hydrogen bonds with other polar molecules
high specific heat capacity
hydrogen bonding causes water to absorb large amounts of thermal energy as its temp increases, or lose large amounts of thermal energy as its temp decreases
high specific heat of vaporization
Hydrogen bonding causes liquid water to
absorb large amounts of thermal energy and
become a vapour (gas).
effect of cohesion
high surface tension
effect of adhesion
capillary action and solubility of polar compounds
effect of high specific heat capacity
temp moderation
effect of high specific heat of vaporization
evaporation and cooling
effect of highest density at 4 degrees celsius
ice floats on water
water molecules are small and strongly ____
polar
The surface coat of water, called a _______ ____, reduces the ________ between the molecules or
ions of another substance and promotes their separation.
hydration shell; attraction
The hydration shell tends to prevent the
ions from ___________.
re-associating
Why do ionic substances or salts dissolve so easily in water?
Sodium chloride dissociates in water because water molecules quickly form hydration shells around the Na+ and Cl- ions of the salt crystals.
The surrounding water molecules REDUCE the attraction between ions so much that they
SEPARATE from their normal crystal lattice structure and enter the surrounding water
lattice as hydrated ions.
Hydrophilic molecules
polar or charged molecules that are strongly attached to water
Hydrophobic molecules
non-polar molecules that are not strongly attached to water
Small hydrophilic substances are _____ soluble in water, while hydrophobic substances have
very _____ solubility in water.
highly; low
What is the autoionization of water?
When two water molecules react, one water molecule transfers an H+ ion to the other molecule, forming a hydronium ion, H3O+, and
a hydroxide ion, OH-
Autoionization always produces _____ numbers of hydronium and hydroxide ions.
equal
When the concentration of hydronium ions, H3O+ in a solution is greater than the
concentration of hydroxide ions, OH- the solution has the properties of a(n) ______.
acid
Acids ______ the hydronium ion con-
centration when dissolved in water
increase
When the concentration of OH- ions in a solution is greater than the concentra-
tion of H3O+ ions, the solution has the properties of a ______
base
Bases _______ the OH- concentration of an aqueous (water-based) solution.
increase
How is the increase in OH- ions accomplished?
Strong ionic bases, such as sodium hydroxide, may contain an OH group and thus dissociate when added to water, releasing OH- ions
Other bases combine directly with H+ ions.
The concentration of H3O+ ions, compared to the concentration of OH- ions, in an aqueous solution determines the ________ of the solution.
acidity
The pH scale is based on ______ to make the values more manageable
logarithms
Each whole number on the pH scale represents a ________ difference in pH.
10-fold
A change of 0.1 or even 0.01 in the pH level of a
cell can drastically affect ___________ _________.
biological reactions
A small change in the pH surrounding
some proteins causes ________ changes that can alter or destroy the functions of the
proteins.
structural
The strength of an acid or base depends on the degree to which it _______ when dissolved in water.
ionizes
A strong acid, such as HCl, and a strong base, such as NaOH, are __________ dissociated in an
aqueous solution.
completely
A weak acid and a weak base ________ ionize in water.
partially
The reaction of a weak acid or a weak base in water is a _______ reaction.
reversible
True or false:
Most acids and bases that are involved in biochemical reactions are strong.
False
They are weak
How did neutralization reaction get its name?
This type of reaction is called a neutralization reaction, since its products, water and salt, are neutral.
Buffer definition
A buffer is a chemical that compensates for relatively small pH changes by absorbing or releasing hydrogen ions.
When a biological reaction releases excess H+
ions, buffers ________ with the H+ ions so they are no longer ______ in the solution.
combine; free
If the concentration of H+ ions in a solution decreases, buffers can _______ H+ ions into the solution to ________ their concentration.
release; increase
Since weak acids and bases dissociate in a reversible reaction in water, most buffers are …
weak acids, weak bases, or a combination of the two.
The hydrogen bonding of water molecules to one another gives water a high ______ ______.
surface tension
Water forms a ______ _______ through hydrogen bonding in liquid water and ice.
lattice structure
As polar molecules or charged ions ______ in solution, they are completely surrounded by water molecules, which _______ the electrostatic interactions between them.
dissolve; reduce
Water is a polar molecule. Explain how the polarity of water accounts for its lattice structure.
The polarity of water helps the formation of hydrogen bonds among water molecules.
Hydrogen bonds create the lattice structure of water.
How does the structure of water account for its properties, such as its boiling point?
High specific heat gives water a high boiling point.
How does the structure of water account for its properties, such as its surface tension?
The lattice structure keeps molecules close causing high surface tension.
How does the structure of water account for its properties, such as its adhesion?
Water has the ability to form H-bonds with other polar molecules, which gives water its adhesion properties.
Potassium bromide, KBr, is an ionic compound. Describe what happens to its ions when it is dissolved in water.
When potassium bromide, KBr, is dissolved in water it dissociates into potassium ions, K+ , and bromine ions, Br– ions.
These ions are enveloped by water molecules to form a surface coat.
Will water form a surface coat around a molecule such as octane?
No, because octane is non-polar, and no bonding will occur.
How does polarity influence water’s role as a solvent?
Polar water molecules can surround polar biological molecules or ions, thus dissolving them.
How do acids and bases differ in terms of how they behave when added to pure water?
Acids when placed in aqueous solution cause the production of hydronium ions, increasing H+ concentration and lowering the pH.
Bases cause the production of hydroxide ions in aqueous solution, increasing OH– concentration, and raising the pH.
What determines whether an acid or a base is classified as strong or weak?
The degree of ionization or dissociation determines its classification.
Strong acids or bases completely dissociate or ionize while a weak acid or base does not.
How do buffers in your cells help to keep your body functioning properly?
Buffers help to maintain proper pH levels in different cells in the body by being able to absorb excess hydronium or hydroxide ions.
Buffers use systems of weak acids or weak bases to accomplish this.
Why would it be inaccurate to say that a buffer is a solution that maintains a constant pH?
A buffer solution is one that maintains a relatively constant pH when H+ or OH– are added.
However, the pH can change slightly. It remains relatively constant not completely constant.
Vitamin C is also known by its chemical name, ascorbic acid. What does this name suggest about its chemical and physical properties?
The name suggests it acts as an acid and would likely generate hydronium ions in aqueous solution.
Why is water so important?
Water is known as the “Universal
Solvent” and helps to dissolve many
substances
Approximately 60% of your body is water
Virtually all cellular processes occur in
water
ALL LIVING THINGS contain water
cohesion
force of
attraction between like
molecules
Water molecules
form hydrogen
bonds with each
other
Which property of water results in surface tension and allows
small insects/spiders to walk on water?
cohesion
adhesion
force of
attraction between
different molecules
Water molecules may
also form hydrogen
bonds with other polar
molecules
Which property of water helps plants transport water (sticks to xylem) and allows water to dissolve polar substances?
adhesion
high specific heat capacity
water
can absorb large amounts of thermal
energy when heated (also releases
large amounts of thermal energy as it
cools)
which property of water helps organisms maintain a constant body temp (holds heat)
high specific heat capacity
high specific heat of vaporization
water absorbs large amounts of
heat as it evaporates
which property of water allows organisms to cool themselves through evaporation (sweating)?
high specific heat of vaporization
true or false:
solid water is less dense than liquid water
true
As water cools the water molecules form a ________
structure that spreads the molecules farther apart
thus ______ density
lattice; lowering
in an aqueous solution, water molecules are strongly _____
They surround other
atoms/molecules and prevent
them from _______
polar; reforming
hydrophilic
polar substances
that are attracted to water
example of a hydrophilic substance
salt
hydrophobic
non-polar
substances that are not attracted
to water
example of a hydrophobic substance
oil
acids
H3O+ ions are responsible for acidity
(H3O+ > OH- = acidic)
Taste Sour, Conduct Electricity, Turns Blue
Litmus paper Red
bases
OH- ions are responsible for alkalinity (basic)
(OH- > H3O+ = Basic)
Taste Bitter, Feel Slippery, Conducts
Electricity, Turns Red Litmus paper Blue
strong acid/base
completely dissociates in
water (ex. 100% of HCl dissociates)
weak acid/base
only a small percentage of
the molecules dissociate in water (ex. 10% of
Ammonia, a base, dissociates in water)
buffer
a chemical that can change pH by accepting or
releasing H+ ions
Since most weak acids/weak bases have _______
reactions they often act as _____
reversible; buffers
