BIOC 503 - Water Lecture 2

heterolytically

O-H bonds are polar and can dissociate ___

proton, hydroxide

water dissociation produces a __ H+ and a __ ion OH-

reversible

water dissociation is a rapid ___ process

unionized, left, low

most water molecules remain ___ , thus the equilibrium lies strongly to the ___ and have a low Keq value.

For the same reason water has a very __ electrical conductivity.

temperature

the extent of dissociation depends on temperature

hydronium ions

protons are not free in soln, they are immediately hydrated to form ____ = water molecules with protons associated with one of the lone pairs on the oxygen

proton hopping

the covalent and hydrogen bonds are interchangeable, allowing for an extremely fast mobility of protons in water via ___

faster than true diffusion of water and explains the high ionic mobility of H+ compared to other monovalent cations like Na+ or K+

used in binding sites of many proteins

equilibrium constant

relates concentrations of participating species in an equilibrium process

Kw

ionic product of water constant

___ = [H+]*[OH-] = 1.0×10^-14

10^-7

In pure water [H+]=[OH-]=___

pH

negative logarithm of the hydrogen ion concentration

• can be negative or above 14, the 0-14 scale is just practical (14 because of Kw)

7

pH of a neutral solution

CO2

pure water does not stay pure long as atmospheric __ gets dissolved and forms carbonic acid

negative

if [H+] > 1M, then the pH will be ___

above 14

if [H+] < 10^-14, then the pH is __

10

log are using a base of ___ and thus are cancelled when put as the exponent of ___.

Angstrom

10^-10

strong

__ acids and bases FULLY dissociate in water, thus the concentration of dissociated ions is the same as the one of the initial acid/base

partially

weak electrolytes dissociate ___ in water

Ka

the extent of dissociation is determined by the acid dissociation constant ___

• can calculate pH is __ is known

initial acid concentration stays the same

In weak acid cases, the use of quadratic equation is necessary to find pH from Ka and initial acid concentration.

However, assumption that the ____ can be made when the amount of dissociated species is much LESS than the amount of undissociated acid. x < [total acid]

-log(Ka)

pKa measures acidity

pKa = ____

• amino acid amino group pKa ~9.60

• amino acid carboxy group pKa ~ 2.34

buffers

mixture of weak acids and their conjugate bases (anions)

Their function is to resist change in pH

pH = pKa

buffering capacity id the greatest at ___, aka when there is a 50:50 ratio of acids:anions forms.

1

buffering capacity is LOST when the pH differ from pKa by more than __ pH unit(s)

plateau

the __ of a weak acid titration curve is the point where there is a 50:50 ratio of acid to anion, aka where pH = pKa.b

buffering region

on a titration curve, the region of the curve including the plateau and the gradual incline/decline on both sides (until it starts increasing/decreasing much faster aka sharper curves)

Handerson-Hasselbach

___ equation

[H+] = Ka [HA]/[A]

take negative log of everything

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

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

maintenance of intracellular pH is vital to all cells

• enzyme-catalyzed rxns have optimal pH

• solubility of polar molecules depends on H-bond donors and acceptors

  • equilibrium between CO2 gas and dissolved HCO3- depends on pH

Buffer systems IN VIVO based on

• phosphate (mM concentration range)

• bicarbonate (important for blood plasma)

  • histidine (efficient buffer at neutral pH)

buffers IN VITRO based on

___ sulfonic acids of cyclic amines such as HEPES, PIPES, or CHES