Aqueous Reactions

H-bond donor

Hydrogen is attached to an electronegative atom (O or N)

H-bond acceptor

Has a lone pair on an electronegative atom

Water is a good solvent for

• H-bonds accepters + donors

• polar

• ions

Water is a poor solvent for

• nonpolar

hydrophobic effect

• water maximizes h-bonding by forming an ordered structure → unfavorable to entropy

• water forms a cage-like structure around a nonpolar aggregate: burial of nonpolar surface

• there is a lower surface area of water increasing the free water which brings up entropy

enzyme-substrate binding

The substrate squeezes water out from between the enzyme and substrate, so nonpolar surfaces interact and water entropy increases.

amphipathic molecules

molecules that have nonpolar and polar groups

micelles

amphipathic molecules associate their nonpolar chains with each other and polar heads associate with water

self organization

formation happens on its own

water ionization

H2O ←→ H+ + OH-

allows water to participate directly in chemical reactions with solutes dissolves in it

ionization constant of water

Kw= [H+][OH-]

pH equation

pH= -log[H+]

strong acid or base

ionize completely to their conjugate base or acid (acid: HCl, HNO3, H2SO4), (base:NaOH, KOH)

Weak acid

• less likely to give up H+

• does not ionize completely

acid equilibrium constant

Ka= ([H+][A-])/[HA]

pka

pka=-log(Ka)

• low = stronger acid

• high= weaker acid

polyprotic acid

can give up more than one proton in a sequence

Henderson hasselbalch

pH= pka + log[A-]/[HA]

pH=pka

when [HA]=[A-]

titration curve

• defined by the Henderson-Hasselbalch equation

• tells you the ratio of [HA] to [A-]

• pH of the solution of the acid as a function of added strong base

Buffer

• a solution of a conjugate acid-base pair at a pH where both species have a significant concentration (near pka)

• resists change in pH

• will add H+ to make OH- into H2O

• will add H+ to make HA