Water (Unit 1) Flashcards
Water
A molecule where the structure allows it to interact with other molecules
What type of bond is water?
Water has polar covalent bonds, that are more attracted to oxygen than hydrogen
What are the 4 abilities of water that allow it to facilitate life?
Cohesive behavior
Ability to moderate temperature
Expansion upon freezing
Versatility as a solvent
Cohesion
hydrogen bonds hold water molecules
together; helps the transport of water against gravity
in plants
Adhesion
an attraction between different
substances, for example, between water and plant
cell walls
Water Names .
H20, hydroxide, hydrogen dihydrogen monoxide
Surface Tension
a measure of how difficult it is to
break the surface of a liquid
Surface Tension of water?
Water has an unusually high surface tension due to hydrogen bonding between the molecules at the air-water interface and to the water below.
Explain the moderation of temperature by water
Water absorbs heat from warmer air and releases
stored heat to cooler air
Water can absorb or release a large amount of heat
with only a slight change in its own temperature
Thermal energy
kinetic energy associated with random motion of
atoms or molecules
Kinetic energy
the energy of motion
Temperature
represents the average kinetic energy
of the molecules in a body of matter
Heat
Thermal energy in transfer from one body of matter to another
Calorie (cal)
the amount of heat required to
raise the temperature of 1 g of water by 1ºC
It is also the amount of heat released when 1 g of water cools by 1ºC
Kilocalories
1 kcal = 1,000 cal
Joule
1 cal = 4.184 J
Specific Heat
The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºC
Water resists changing its temperature because of its high specific heat
Why does water have a high specific heat?
This can be traced to hydrogen bonding
Heat is absorbed when hydrogen bonds break
Heat is released when hydrogen bonds form
Evaporation (or vaporization)
transformation of a
substance from liquid to gas
Heat of vaporization
the heat a liquid must
absorb for 1 g to be converted to gas
evaporative cooling
As a liquid evaporates, its remaining surface cools
Function of Evaporative Cooling
helps stabilize
temperatures in organisms and bodies of water
Why does ice float in water?
Ice floats in liquid water because hydrogen bonds in ice are more “ordered,” making ice less dense than
water
When does water reach its greatest density?
Water reaches its greatest density at 4ºC
Solution
a liquid that is a completely homogeneous mixture of substances
Solvent
the dissolving agent of a solution
Solute
the substance that is dissolved
Aqueous solution
solution in which water is the solvent
Why is water a versatile solvent?
This is because of polarity.
Hydration Shell
When an ionic compound is dissolved in water, each
ion is surrounded by a sphere of water molecules
called a hydration shell
What is the condition for a substance to dissolve in water?
Large polar molecules such as proteins
can dissolve in water if they have ionic and polar regions
Hydrophilic
A hydrophilic substance is one that has an
affinity for water
Hydrophobic
A hydrophobic substance is one that does not have
an affinity for water
Hydrophobic Substance example?
Oil molecules are hydrophobic because they have relatively nonpolar bonds
Molecular Mass
the sum of all masses of all
atoms in a molecule
Mole
Numbers of molecules are usually measured in
moles
Avogadro’s Number
6.02 × 1023 daltons = 1 g
Molarity
the number of moles of solute
per liter of solution
How do the bonds in water act?
A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other
Hydrogen Ion
A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other
Hydroxide
ion (OH–)
The molecule that lost the proton
Hydronium ion (H3O+)
The molecule with the extra proton is now a
hydronium ion (H3O+), though it is often represented as H+
What is water’s dynamic state?
Water is in a state of dynamic equilibrium in which water molecules dissociate at the same rate at which they are being reformed
Concentrations of H+ and OH–
Concentrations of H+ and OH– are equal in
pure water
Ph
Biologists use the pH scale to describe whether a
solution is acidic or basic (the opposite of acidic)
Concentration of hydrogen ions
Acid
An acid is a substance that increases the H+
concentration of a solution
Bases
A base is a substance that reduces the H+
concentration of a solution
Behavior of acids and bases in water
Strong acids and bases dissociate completely
in water
How do you tell the ph of a solution?
The pH of a solution is defined by the negative
logarithm of H+ concentration, written as
pH = –log [H+]
How many hydrogen ions increase/decrease when you change ph
Every time you change the ph by 1 it is different by a factor of 10
Buffer
- don’t like to change PH
Buffers are substances that minimize changes in
concentrations of H+ and OH– in a solution
