Chapter 2 Aqueous Chemistry

what % of humans are made of water

60% by weight

functions of life requiring water

grow, function, reproduce

breakdown of water in body

40% intracellular

15% extracellular

5% circulatory system

40% non water

H2O geometry

tetrahedral

is water polar or nonpolar, why?

polar, has uneven distribution of charges (partial negative on O, partial positive on H)

how do water molecules interact with each other

via hydrogen bonds

hypothetically and actually, how many hydrogen bonds can a water molecule take part in

theoretically 4: 2 pairs of unshared e-s to ‘accept’ hydrogen, 2 hydrogens to ‘donate’

reality 2: one accepted, one donated

what are the hydrogen bond donors and acceptors in water?

donor: H

acceptor: O

what are the hydrogen bond donor and acceptors in an amine molecule?

donor: H

acceptor: N

what are electrostatic forces and what are the types

noncovalent bonds/forces; include ionic bonds, hydrogen bonds, van der waals interactions

distance between atoms in covalent bonds, force

1 angstrom, 460 kJ/mol

distance between atoms in hydrogen bonds, force

1.8 angstroms, 20 kJ/mol

distance between atoms required for there to be no force/bond

2.7 angstrom

most common functional groups forming hydrogen bonds in biomolecules

hydroxyl groups (-OH), amine groups (NH3)

what is electronegativity

how much an atom likes electrons (affinity for them/will attract)

what are van der waals interactions

interactions between polar molecules that aren’t charged

dipole-dipole interactions, strength

strong van der waals interaction between strongly polar groups, 9 kJ/mol

london dispersion forces, strength

weak van der waals interaction between nonpolar molecules; small fluctuations in electron distributions create temporary separation of charges, 0.3 kJ/mol

why are electrostatic/small forces important despite being weak?

they have a cumulative effect since they are occurring between many many molecules at a time

water’s dielectric constant is…

relatively high

what is the dielectric constant

measure of a solvent’s ability to diminish electrostatic interactions between dissolved ions

why is seawater not drinkable

seawater contains too much salt for our kidneys to process without pulling water from our bodies - as a result, seawater dehydrates our bodies

why is water essential to life/cells

a couple water molecules can fit inside each cell, giving an aqueous environment for them to exist in without too much space - maintains cells’ contents in crowded but fluid state

hydrophilic v hydrophobic

hydrophilic: likes water (polar)

hydrophobic: avoids water (nonpolar)

hydrophobic effect, ex oil in water

exclusion of nonpolar substances from an aqueous solution; ex, a drop of oil in water will be surrounded by a layer of constrained water molecules and stay separate/not form a mixture

change in entropy of water molecules with addition of drop of nonpolar substance, several drops, etc

introduction of nonpolar substance will decrease entropy since some water molecules must ‘protect’ the nonpolar substance, so there are fewer possible molecular arrangements

if there are several drops, initially entropy will decrease as water molecules surround all of the nonpolar substance. due to the hydrophobic effect, thought, the nonpolar molecules will clumb together, requiring fewer water molecules to surround them, so entropy increases.

is the hydrophobic effect a bond?

NO, just an observable phenomenon/interaction

ampiphilic molecules

have both hydrophilic and hydrophobic portions; ex, lipids (polar head, nonpolar tail)

hydrophobic effect & phospholipid bilayer

polar/hydrophilic heads are located towards aqueous cell interior AND exterior, while nonpolar/hydrophobic tails remain inside. this takes two layers of lipids (bilayer) and creates a protective layer around a cell that selectively allows molecules in an out, is a barrier to diffusion (ex, ions or polar substances can’t get through due to hydrophobic/nonpolar core)

hydronium and hydroxide ions

hydronium: H3O+

hydroxide: OH-

water chemical equilibrium

what are some of the fastest biochemical reactions

acid-base reactions

why are acid base reactions so fast

water has a 'jumping proton’ that moves through H-bond connected water molecules → H+ mobility in water is greater than mobility of other ions that must diffuse amongst water molecules

dissociation constant K

K = [H+][OH-]/[H2O]

Kw

ionization constant of water, since the concentration of H2O (55.5 M) is so much greater than [H+] or [OH−] it’s considered constant, redefinition of K

relationship between [H+] and [OH-]

inverse

pH equation

pH = -log [H+']

difference of one pH unit indicates?

10 fold difference in [H+] in a solution, since pH is a logarithmic scale

Ka

= K [H2O] → acid dissociation constant

pKa

= -log (Ka)

what does higher/lower pKa value indicate

lower = stronger acid; acid more fully dissolved in water

henderson-hasselbach equation

pK is ___ to a specific acid

constant

what are buffers

weak acid/conjugate base system (HA/A-) that prevents dramatic changes in pH when acid/base is added to a solution

general buffering capacity of an acid

± 1 pH unit of solution’s pK

major buffering systems in the human body

bicarbonate and phosphate

human physiological pH

6.9-7.4

pK of buffering system involving CO2 in blood

6.1

bicarbonate buffer system, normal conditions

bicarbonate buffer system, excess acid

bicarbonate buffer system, insufficient acid

why do humans need a buffering system

we will not survive if physiological pH is incorrect, but many biochemical reactions produce acid so we need a system to ensure that this acid doesn’t dramatically decreases body pH

long-term vs short-term pH changes in the blood

long-term changes made by the kidneys (hours → days)

short-term changes can be made by changes in pulmonary function, ie heart racing (minutes → hours)

bicarbonate reabsorption in kidneys looks like

bicarbonate production in kidneys looks like

acidosis

blood pH < 7.35

alkylosis

blood pH > 7.45

metabolic acidosis/alkylosis is disease of

kidneys

respiratory acidosis/alkylosis is disease of

lungs