Acids, Bases, and Buffers

Question 1

Law of Mass Action

Answer 1

Rate of rxn is partially determined by concentrations of reactants and products in addition to the equilibrium constant.
If product or reactant concentrations greatly increase, the rxn will move in other direction
K=Kf/Kr=[R1][R2]/[P1][P2]

Question 2

Define pH

Answer 2

Concentration of H+ in solution, measured -log[H]. Given that Keq of water is 1.810^-16, [H][OH]=110^-14 so pH + pOH =14

Question 3

Define pKa

Answer 3

pKa=-log(Ka)=-log([H+][A-]/[HA])
This is the acid dissociation constant, gives the strength of the acid, lower pKa means less acid is bound at equilibrium so the acid is stronger.

Question 4

Henderson Hasselbach Equation

Answer 4

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

So pH=pKa at 50% dissociation

Question 5

Bicarbonate Buffer System H-H equation

Answer 5

Bicarb buffer system regulates physiologic pH by taking up extra protons or hydroxyls without drastically changing the pH. This is an open system helped by CO2 exchange and bicarbonate excretion.

pH=6.1+log([HCO3-]mM/(0.3*PCO2mmHg)

Question 6

Normal Blood pH

Answer 6

Arterial: 7.34-7.44
Venous: 7.28-7.42

Question 7

Normal Bicarbonate Concentration

Answer 7

[HCO3-] 24mM

Question 8

Normal PCO2

Answer 8

40mmHg

Question 9

Why do weak acids make good buffers? What is maximal pH range for buffers?

Answer 9

Weak acids are good buffers because they are only partially associated at physiologic pH, meaning there is undissociated acid and conjugate base to take up extra H or OH.
Buffers work best within 1 pH (0.1 to 10 [A-]/[HA]) of pKa because acid is 50% dissociated when pH=pKa

Question 10

Acid Base Problems

Answer 10

See Handout

Question 11

Important Weak Bases

Answer 11

Purines, Pyrimidines, amphetamines, procianamide, nortriptylene, local anesthetics