Water- lecture #3 Flashcards
when do polar covalent bonds form?
when two atoms involved in a covalent bond do not have equal electronegativity
Carbon is more electron loving than hydrogen, what does that mean for sharing of electrons?
electrons are equally shared in between the two atoms
oxygen is more electron loving than hydrogen, what does that mean for the sharing of electrons?
electrons are not equally shared in between the two atoms and are held more closely to the oxygen nucleus
when the electrons are not equally shared in between the two atoms what happens to the charge?
a resulting partial charge on the hydrogen (+) atom and a partial negative (-) charge on the electron loving atom
what are polar molecules?
molecules that contain unequal sharing of electrons
in a bond with Na+ and water (H2O) what gets created?
solvation cage
this cage gets created because the (-) oxygen stays closer to the (+) nucleus, therefore all the hydrogens end up outside the solvation cage
what are the top 3 elements most greedy for electrons?
florine
oxygen
nitrogen
what kind of bonds are used in water molecules?
hydrogen bonds using the oppositely charged atoms
the partial positive charge on the hydrogen atom is attracted to what?
the partial negative charge on atoms within OTHER molecules
are hydrogen bonds stronger than covalent and ionic bonds?
no, they are weaker
hydrogen bonds create molecular networks, these networks occur between what types of molecules?
identical and different molecules
what are the two important properties of water?
cohesion of water molecules
temperature moderation
does hydrogen bonding keep water molecules close or far from one another? what does this create?
close
creates a complex structure
what is cohesion?
hydrogen bonding keeping water molecules close to one another
(water likes to stick to itself)
what does cohesion allow for?
water to move against gravity from root to shoot in plants
(water likes to stick to other things)
water is also subject to adhesion, what does that mean?
The molecules hydrogen bond to the walls of the vessels in the plant preventing them from falling back down
what is temperature moderation?
Water absorbs heat from air that is warmer and releases heat to air that is cooler
what type of energy is associated with motion?
kinetic energy
if the atoms and molecules move fast, what does that do to kinetic energy?
increases
what is heat a measure of?
the total kinetic energy of a body
how does heat transfer?
from hotter object to a cooler object
what happens to the molecules in the cooler object when heat is transferred from hot to cold?
start to speed up because of the gain of kinetic energy
is heat volume independent or volume dependent?
volume dependent
is temperature volume independent or volume dependent?
volume independent
temperature is the average what of molecules?
kinetic energy
what is a calorie?
the amount of heat needed to raise the temperature of 1 gram of water by 1oC
1 cal= how many joules?
4.184 Joules
what is specific heat?
the amount of heat that must be absorbed/lost in order to change the temperature of 1 gram of a substance by 1 degree C
does water have a high or low specific heat?
very high specific heat compared to other substances
why does water have such a high specific heat?
hydrogen bonding
heat needs to be used in order to break those hydrogen bonds, after the hydrogen bonds are broken the heat can then be used to increase the temperature of the water
what happens when water is cooled?
heat is released as hydrogen bonds are reformed between water molecules
results in a decreased speed of the molecules
what does evaporation of a substance do to temperature?
moderates temperature
what is something that is incredibly sensitive to temperature?
living systems
what occurs in evaporation?
molecules with the greatest energy (the hottest) leave the substance
remaining liquid is cooler as a result of this loss
what are examples of evaporation?
sweating, boiling water
why is water an excellent solvent?
It can dissolve many ionic compounds such as NaCl
The ions (Na+, Cl-) remain dissolved in the water and form a solution
why does the solution form between Na+ and Cl-
This solution forms because the partial positive regions within the water molecules surround the negative ions (Cl-) and the partial negative regions within the water molecule surround the positive ions (Na+)
This holds the ions in solution
what are the 3 primary states water exists in?
solid, liquid, gas (water vapor)
what is the most dense between solid, liquid and gas?
solid
what is density?
the number of particles (molecules) per unit area
what is the one exception to density?
water
what has a smaller density, ice or liquid water
ice, this explains why ice cubes float in water (due to hydrogen bonds)
what happens when water freezes?
each water molecule forms four hydrogen bonds with adjacent water molecules resulting in the creation of a crystal lattice
are the hydrogen bonds developed with freezing temperature weak or stable?
extremely stable
in liquid water are hydrogen bonds stable or less stable?
less stable and continually break and reform
what is a solution?
a liquid consisting of a uniform (homogenous) mixture of two or more substances
what is a solvent?
dissolving agent
example: water
what is a solute?
dissolved substance
example: sugar, salt
when water is the solvent the solution is referred to as what type of solution?
aqueous solution
why is water such a great solvent?
because of the polarity of the molecules
what happens to NaCl in water?
it dissociates forming Na+ and Cl- ions
what does the partial positive (+) charge on the hydrogen and the partial negative (-) charge from oxygen (from water) interact with in respect to NaCl
partial positive: Cl-
partial negative: H+
what is a non-ionic material?
polar molecules that have unequal charge distribution
what are examples of non-ionic materials?
proteins and sugars
can non-ionic materials dissolve in water?
yes
can non-ionic materials participate in hydrogen bonding with water?
yes
are hydrophilic substances water loving or water hating?
water loving (have an affinity for water)
do hydrophilic substances dissolve in water?
yes, if not too large
if hydrophilic substances are too large what do they form?
a colloid
what is a colloid?
stable suspension of fine particles in a liquid
are hydrophilic substances polar or non-polar?
polar
are hydrophobic substances water loving or water hating?
water hating (zero affinity for water)
are hydrophobic substances polar or non-polar?
non-polar (non-ionic)
what is an example of a hydrophobic substance?
oil
oil and water will not mix
what is the equation for glucose?
C6 H12 O6
how many daltons does carbon weigh?
12
how many daltons does hydrogen weigh?
1 dalton
how many daltons does oxygen weigh?
16 daltons
what is the weight of glucose in daltons?
180 daltons
6x12= 72 daltons (carbon)
12x1= 12 daltons (hydrogen)
6x16=96 daltons (oxygen)
what is molar mass?
the number of grams one mole of a substance weighs
glucose is 180g/mole
what is molarity?
the number of moles of solute/ liter of solution
what can be said about this
H2O <—————> H+ + OH-
the hydrogen ion has left its electron behind
(free in solution as an H+ ion)
OH- that results is the hydroxide ion
what can be said about this
H2O <—————> H+ + OH-
the hydrogen ion has left its electron behind
(free in solution as an H+ ion
OH- that results is the hydroxide ion
what can be said about this
2 H2O <——————> H3O+ + OH-
the lost proton attaches to the second water molecule
in pure water H+ = what?
H+ = OH-
an addition of acid or base will do what to the balance of H+ = OH-?
disrupt this balance
do acids dissociate when placed in water?
yes, they release H+ ions
the more HCl that is added to water will cause what?
more H+ to be present following dissociation
if theres a high amount of H+ in the solution what happens to the pH of the solution?
lower pH (more acidic)
do bases dissociate in water?
yes, they release OH- ions
the OH- that is generation from the dissociation of NaOH binds to what?
H+
if theres a high amount of OH- in the solution, what will that do to the pH?
higher pH (more basic)
what does a double sided arrow indicate
(<———->)
weak acid will have incomplete dissociation
what is the pH scale measured on a scale of?
0-14
if the amount of H+ in solution is equal to the amount of OH- in solution, what does that indicate about the pH?
pH is 7
solution is neutral
on the pH scale, what is considered to be acidic?
pH 1 to 6 is acidic
on the pH scale what is considered to be basic?
pH 8-14
what will the addition of H+ do to OH- in a solution?
cause the OH- to decrease
what will the addition of OH- do to H+ in a solution?
cause the H+ to decrease
what does a difference of 1 pH unit represent in respect to H+ concentration?
1000x difference in H+ concentration
what is a buffer?
substances that allow a solution to offset large and potentially dangerous changes in pH from occuring
what is threatened by very small changes in pH?
living systems
what is an example of a buffer found in the blood?
carbonic acid (H2CO3)
H2 CO3 <————> H+ + HCO3-
if blood pH drops what will bind to the excess H?
HCO3
H2 CO3 <————> H+ + HCO3-
if blood pH increases what will bind to the excess OH-
H+
H2 CO3 <————> H+ + HCO3-
what is the result of these buffers?
the blood pH will not change dramatically
