BIOL-L112 Chapter 3
polarity of water makes it a versatile solvent bc
it forms hydrogen bonds easily
hydrogen bonding is responsible for
water's high specific heat
3 things that help explain why water molecules form hydrogen bonds
1. Attractions form between opposite partial charges 2. There is a partial positive charge on each hydrogen atom and two partial negative charges on the oxygen atom in a water molecule 3. The electrons spend more time around the oxygen atom because oxygen is more electronegative than hydrogen
4 emergent properties of water
1. cohesive behavior 2. ability to moderate temperature 3. expansion upon freezing 4. versatility as a solvent
In the molecule below, how many atoms could make hydrogen bonds with water?
10
___% less dense than liquid water at 4C
10
concentration of H+ and OH- in pure water:
10^-7 each at 25C
what is the max number of hydrogen bonds one molecule of water can form?
4
each molecule of water is bound to
4 neighboring water molecules in a fixed structure
How many atoms in the pictured molecule can form hydrogen bonds with water molecules?
5
most cells are surrounded by water and cells themselves are about _______ water
70-95%
Why isn't this insect drowning?
Surface tension.
alkalosis:
pH of blood is greater than 7.45
acidosis:
pH of blood is less than 7.35
The unequal sharing of electrons within a water molecule makes the water molecule _____.
polar
is ammonia (NH3) a polar or nonpolar molecule?
polar
water is a highly ____ molecule
polar
In this molecule, what type of bond is found between the oxygen and hydrogens?
polar covalent
In a single molecule of water, two hydrogen atoms are bonded to a single oxygen atom by _____.
polar covalent bonds
electronegativity
the attraction of an atom for the electrons in a covalent bond
changes in concentrations of H+ and OH- can drastically affect
the chemistry of the cell
adhesion:
the clinging of one substance to another
cohesion:
the clinging of one substance to itself
The partial negative charge in a molecule of water occurs because _____.
the electrons shared between the oxygen and hydrogen atoms spend more time around the oxygen atom nucleus than around the hydrogen atom nucleus
temperature:
the measure of energy that represents the average kinetic energy of molecules
water's cohesive and adhesive properties enable
the transport of water & dissolved nutrients upwards in plants against the force of gravity
measure temperature directly with a _____
thermometer
why do He, Ne, and Ar have no electronegativity value?
they have a full outer shell
why are water's emergent properties important?
they help make earth an environment that is suitable for life
heat:
total amount of kinetic energy due to random motion of atoms or molecules in a body of matter
the attraction of an atom for the electrons in a covalent bond
two atoms that do not have similar electronegativities.
characteristics of polar molecules
unequal sharing of electrons, frequently asymmetrical, has partial positive and partial negative charges, electronegativity is 0.4-2
water has high heat of
vaporization
water absorbs heat from air that is
warmer
ion and polar regions on the protein's surface attract
water molecules
at equilibrium, _________ water molecules is dissociated
1 out of 554,000,000
to increase temp of water:
1) average kinetic energy of water must increase 2) heat absorbed must be enough to break the hydrogen bonds and increase the molecule's kinetic energy
units of temperature
C,F,K
Right before a predicted overnight freeze, farmers spray water on crops to protect the plants. Use the properties of water to explain how this method works. Be sure to identify why hydrogen bonds are responsible for this phenomenon.
Due to intermolecular hydrogen bonds, water has high specific heat. When water is cooled, many of these bonds are formed, which releases a significant amount of heat. This can provide some protection against freezing of the plants' leaves, thus protecting the cells from damage.
Nitrogen (N) is more electronegative than hydrogen (H). Which of the following is a correct statement about the atoms in ammonia (NH3)?
Each hydrogen atom has a partial positive charge; the nitrogen atom has a partial negative charge.
which element is the most electronegative?
F
The partial negative charge at one end of a water molecule is attracted to the partial positive charge of another water molecule. What is this attraction called?
a hydrogen bond
aqueous solution:
a solution in which water is the solvent
water exists in the natural environment in:
all 3 physical states
why is it important that life floats?
allows life to exist under frozen surfaces
specific heat:
amount of heat absorbed or lost when 1g of a substance changes its temp by 1C
heat of vaporization:
amount of heat needed to convert 1g of liquid to gaseous state
units of heat
calorie- amount of heat it takes to raise the temp of 1g water 1C
Hydrogen bonds ...
can form between H and N.
Which property of water is responsible for the formation of raindrops?
cohesion property
Water molecules can form hydrogen bonds with _____.
compounds that have polar covalent bonds
water releases heat to air that is
cooler
an increase in pH means that the concentration of H+ has
decreased
solvent:
dissolving agent of a solution (water)
The tendency of an atom to pull electrons toward itself is referred to as its _____.
electronegativity
characteristics of nonpolar molecules
equal sharing of electrons, usually symmetrical, have little or no partial charges, electronegativity is 0-0.4
water's high heat of vaporization leads to
evaporate cooling
Polar attractions are ...
forces between atoms with partial charges, weaker than covalent bonds, important because they are numerous.
A water molecule can bond to up to _____ other water molecules by ____ bonds.
four; hydrogen
when in liquid form, hydrogen bonds are
fragile and short lived
hottest molecules are most likely to leave as
gas, leaving behind cooler molecules
the faster a molecule moves, the ______ its kinetic energy
greater
liquid water is at its
greatest density at 4C
The brackets are indicating a(n) _____ bond.
hydrogen
What name is given to the bond between water molecules?
hydrogen
polarity enables water to form
hydrogen bonds
floating ice _____
insulates liquid below
water's ability to moderate temp stems from ___
its high specific heat
anything that moves has
kinetic energy
atoms and molecules have
kinetic motion
solution:
liquid that is a completely homogenous mixture of 2 or more substances
heat does depend on _____
matter's volume
temperature does not depend on _____
matter's volume
adding acids and bases will
modify the concentrations of H+ and OH- of a solution
the lower the pH of a solution, the __
more acidic the solution
a calorie of heat causes a relatively small change in temp bc
much of the heat is used to break hydrogen bonds before the molecules can move faster
can heat be measured with a device directly?
no
does a partially negative charged oxygen atom have to be present in a hydrogen bond?
no
water can also dissolve compounds made of
nonionic polar molecules
is oxygen (O2) a polar or nonpolar molecule?
nonpolar
Bonds between two atoms that are equally electronegative are _____.
nonpolar covalent bonds
Sulfur is in the same column of the periodic table as oxygen, but has electronegativity similar to carbon. Compared to water molecules, molecules of H2S will _____.
not form hydrogen bonds with each other
A covalent bond is likely to be polar when ________.
one of the atoms sharing electrons is more electronegative than the other atom
hydrophilic:
one that has affinity for water (NaCl, glucose, some proteins)
hydrophobic:
one that repels water (olive oil)
free H+ and OH- are ____
rare yet biologically important
when blood pH drops (acidosis):
reaction will proceed to left to maintain pH homeostasis. more H2CO3 forms and H+ decreases, pH increases
when blood pH increases (alkalosis):
reaction will proceed to right to maintain pH homeostasis. more H2CO3 dissociates and H+ increases, pH decreases
What type of bond joins the carbon atom to each of the hydrogen atoms?
single (nonpolar) covalent
Rubbing alcohol swab on the skin feels cool because ________.
skin transfers heat to the liquid alcohol and the alcohol evaporates
absorbs & releases large amounts of heat w _____ changes in temperature
slight
sugar dissolves when stirred in water. sugar is the
solute
sugar dissolves when stirred in water. sweetened water is the
solution
sugar dissolves when stirred in water. water is the
solvent
hydration shell:
sphere of water molecules that surrounds solutes when they are dissolved in water
acid:
substance that increases the H+ concentration of a solution
solute:
substance that is dissolved (NaCl)
buffers:
substance that keep in the pH of biological fluids relatively constant
base:
substance that reduces the H+ concentration of a solution
true statement pertaining to sweat:
sweating cools the body by converting water into gas
which has more heat: water in a lukewarm swimming pool or boiling water in a teacup?
swimming pool
which has the highest temperature: water in a lukewarm swimming pool or boiling water in a teacup?
teacup
does a partially positive charged hydrogen atom have to be present in a hydrogen bond?
yes
