Lecture 2: Non-covalent interactions; acids, bases , and pH

describe water as a solvent

• polarity of H2O breaks electrostatic interactions (increasing entropy → randomness)

• allows high concentration of solutes

describe the hydrophobic effect

• Fatty acids have polar heads and nonpolar tails (amphipathic)

• entropy of H2O cages drive. interactions

• → fewer H2O’s in cage

• highly structured and ordered

hydrophobic effect drives formation of structures ex. lipid bilayer

hydrophobic effect drives protein folding ex. protein chain (disordered) → folded protein (ordered)

• NP inside

• Polar outside

describe water as a reactant: hydrolysis and condensation

hydrolysis: water breaking

condensation: production of water

ex. hydrolysis of a peptide

O=C-NH group = peptide bond

R = special diverse groups

water as a reactant: hydration/dehydration

hydration forward

dehydration reverse

water as a heat buffer

high specific heat of water

• cooling counteracted by heat release

• warming counteracted by heat uptake

perspiration requires heat input to vaporize

water moderates enviornmental temperature

what are the properties of water

• electrical asymmetry

• hydrogen bonding

• polar solvent

  • hydrate ions

  • H-bonds with solutes

• hydrophobic interactions

• reactant - hydrolysis and hydration

• ionization (pH)

formula fo equillibrium constant Keq

[H⁺][OH^-]/[H₂O]

Describe K_w

K_{w =} [H⁺][OH^-] = K_eq [H₂O] = 10^-14 M² @ 1 atm, 25 c)

for pure water (neutral): [H⁺] = [OH^-] = 10^-7 M

ex.

describe the equations for pH and pOH

discuss the pH of common solutions

excess OH basic (alkaline): → strong bases NAOH or Ammoia

[H⁺] = [OH^-] → 7.0 → human blood plasma/cows milk

excess [H⁺] acidic → strong acids human gastric contents HCl

waht are teh definitions of Acid-Base

acid

• proton donor (bronsted)

• electron pair acceptor (lewis)

base

• proton acceptor

• electron pair

describe teh relationship between acid strength and pka

stronger the acid = lower the pKa

what is the henderson hasselbach equation

what is a buffer solution

[H⁺] and pH change very little

micture of a weak acid and its salt buffers pH

titration curves represent henderson-hasselbach equations

@ buffer region pH = pKa

buffering capacity of a buffer is greatest near its pKa

• when [A^-] = [HA]

what is the biological buffering of pH

intracellular and extracellular fluids kept at a constant (6.9-7.4) by buffering systems

• critical for enzymes and other activities

phosphoric acid system

describe the carbonic acid system (principal blood buffer)

exhaling increases pK₁ → respiratory pH control