Lecture 2: pH and Buffers

Question 1

pH

Answer 1

• H+ and OH- ions formed upon dissociation of H2O or other weak acids and bases
• pH = -log[H+]
• At lower pH values, more H+ present to protonate different functional groups
• pH important because functional groups can act as weak acids or bases losing and accepting H+ at diff pH values

Question 2

pKa values

Answer 2

• pKa used to measure strength of an acid
• strong acids have high Kas and low pKa
• pKa tells you the pH at which a functional group loses or gains its H+
• pH < pKa = protonates
• pH = pKa = equal amount
• pH > pKa = deprotonated

Question 3

Henderson-Hasselbach Equation

Answer 3

• Used to determine the pH of a solution depending on the amount of ionization of a weak acid([HA] vs [A-])
• pH = pKa + log [A-]/[HA]
• can be used to determine pH of a mixture of weak acid and conj. base

Question 4

pH and pKa values

Answer 4

• proteins contain functional groups that must be protonated/deprotonated to allow for non-covalent interactions to take place
• Buffers are mixtures of weak acids and conj. bases that can resist changes in pH
• Water is poor buffer due to low [H+] and [OH-]
• Buffers are most effective at +/- 1 pH

Question 5

Importance of pH and Buffers

Answer 5

• pH affects hydrogen bonding and the charge of a molecule, which may be important for the ability to interact with other binding partners
• Buffers are important for maintaining stable pH environment
• Normal pH in humans is 7.4