Chapter 2 - Aqueous Chemistry Flashcards
how much of the human body is water?
about 60%. most of it is intracellular water
is water polar or non-polar?
polar
geometry of water
- tetrahedral geometry due to its electronic structure: oxygen positioned in centre while having 2 hydrogens in 2 corners, and the 2 unpaired electrons in the other 2 corners
- sp3 hybridization
hydrogen bond
- type of electrostatic force
- neighbouring water molecules tend to orient themselves so that each partially positive hydrogen is aligned with a partially negative oxygen
- these bonds also exist within a water molecule
- each water molecule can participate in up to 4 hydrogen bonds with up to 4 other water molecules
- lifetime of a hydrogen bond is 10^-12 seconds
why is the structure of water continually flickering?
this is because the lifetime of a hydrogen bond is very short (10^-12 seconds). this causes hydrogen bonds to flicker as they rotate and bend.
some properties of water
polar, highly cohesive, high surface tension
what do strong covalent bonds define?
basic molecular constitutions
what do weak non-covalent bonds define?
3D structures and molecular interactions
forces from strongest to weakest
covalent bond, ionic interaction, hydrogen bond, van Der waal forces
hydrogen donors
N-H, O-H, S-H
hydrogen acceptors
electronegative N, S, O atoms
electronegativity
measure of an atom’s affinity for electrons
in biological conditions, why are weak interactions more desirable/important than strong ones?
- interactions that are too strong become permanent
- this is not good for biological conditions as our biology is constantly changing
- weaker bonds are easier to control and change
what are key players in hydrogen bonding in biomolecules?
hydroxyl group and amine group
types of electrostatic interactions
ionic interaction, hydrogen bonds, van Der Waals interactions, high dielectric constant
types of van Der Waals interactions
dipole-dipole, dipole-induced dipole, London dispersion forces (i.e. induced dipole-induced dipole)
the cumulative effect of small forces
individual small forces have minimal effect. but all of the small forces together are very important and have a great impact on the body.
dielectric constant
a measure of a solvent’s ability to diminish the electrostatic attractions between dissolved ions
what type of biological molecules are readily solubilized/
those that bear polar or ionic groups
hydrophilic
water loving
hydrophobic
water fearing
what does the solvation process depend more on?
- depends more on entropy
- hydration of a non-polar molecule results in water molecules being unable to participate in hydrogen bonding
- this decreases their freedom to move, resulting in a loss of entropy
hydrophobic effect
- exclusion of non-polar substances from an aqueous solution
- entropy driven: there are no attractive forces holding the non-polar molecules together, rather they aggregate because they are driven out by the unfavourable entropy of hydrating non-polar molecules individually
amphiphilic molecules
have both hydrophobic and hydrophilic components
micelle
- one tailed lipid
- solvated surface and hydrophobic core
- formed by amphiphilic molecules
bilayer
- two-tailed lipids
- prevents the diffusion of polar substances
vesicle
lipid bilayer that closes up in order to eliminate its solvent-exposed edges
ionic composition of intracellular fluids
- K+ is present in the highest concentration
- Na+ and Cl- exists in small concentrations
ionic composition of extracellular fluids
- Na+ is present in the highest concentration
- Cl- is present in relatively high concentration
- K+ exists in small concentrations
proton jumping
proton associated with one water molecule appears to jump rapidly through a network of hydrogen bonded water molecules
Kw
- ionization constant
- ionization constant of water is 10^-14 at 25C
K
- dissociation constant
- specifies strength of an acid
- in H2O ≤≥ H+ + OH-, K =([H+]*[OH-)]/[H2O]
relationship between pH and [H+]
pH = -log[H+]
relationship between [H+] and [OH-]
as one increases in concentration, the other decrease, and vice versa
acid
substance that can donate a proton
base
substance that can accept a proton
relationship between pKa and Ka
- pKa = -log Ka
- strong acids have Ka»_space; 1 (i.e. they will deprotonate entirely)
Henderson-hasselbalch equation
pH = pK + log [A-]/[HA]
polypro tic acid
acid that had more than one acidic hydrogen. these acids will have multiple pKa values
effective buffering capacity
within 1 pH unit of its pK
le châtelier’s principle
change in concentration of one reactant will shift concentrations of other reactants in order to maintain equilibrium
pH «_space;pK
[HA]»_space; [A-]
pH»_space; pK
[HA] «_space;[A-]
biological buffers
functional groups of proteins and phosphate groups can do this
most important buffering system in the body
- CO2 in the blood plasma
- overall reaction: CO2 + H2O ≤≥ H+ + HCO3-
- reason for its effectiveness is that it can not only buffer the excess H+ ions, but it can also eliminate them
