1- Properties of Water

Question 1

Discuss the characteristics of H2O molecules that are believed to be responsible for its anomalous “behavior.”

Answer 1

First, water has a higher than normal boiling point for a molecule of its molecular weight.

Water also has a higher than normal freezing point compared to other molecules.

The heat capacity of water is high.

Water has a density anomaly in that ice will float in water that is only a few degrees above freezing.

Question 2

Name the chemical species represented by the formula H30+.

Answer 2

Hydronium ion.

Question 3

Define the equilibrium constant

Answer 3

The equilibrium constant relates the individual ion concentrations to the concentration of the aqueous compound. This constant is a good measure of the amount of dissociation of the compound into its ionic components

Question 4

List the ways in which [H+] can influence biological systems.

Answer 4

Protons influence biological systems in 6 ways:

1. H+ affects the rate of enzyme-catalyzed reactions
2. Membrane permeability
3. Stability and “native conformation” of proteins and macromolecules
4. Molecular transport rates through membranes, both charged and uncharged
5. Absorption, transport, and metabolism of drugs; drugs have varying dissociation rates based oh pH
6. Hydrophobicity or hydrophilicity of a compound.

Question 5

Name the two most important buffer systems in the body. Which is more important? Why?

Answer 5

Phosphate and bicarbonate are two of the most important buffer systems in the body. While phosphate has a pK closer to the desired pH of 7 (pK=6.7), bicarbonate (pK=6.1) is a more effective buffer because there is more of it in the human body.

Question 6

What are the pK’s of the bicarbonate and phosphate systems?

Answer 6

Phosphate pK=6.7

Bicarbonate pK=6.1

Question 7

Define “acid” and “base” as usually used in biological systems.

Answer 7

Acid: proton donor
Base: proton acceptor

Question 8

Write the Henderson-Hasselbalch equation, and describe its utility for a physician.

Answer 8

PH=pK + log [base]/[acid]

For a physician, this equation allows a convenient way to relate the concentrations of each of the conjugated pairs to the pH of its surrounding environment.

Question 9

What are the relative concentrations of conjugate acid/base when pH equals pK?

Answer 9

The pH is equal to pK only when the concentrations of each conjugate pair are equal to each other (50/50 in solution).

The relative [conjugate acid] is equal to base when pH=pK
The relative [conjugate base] is equal to acid when pH=pK.

Question 10

10. Given the structure of a molecule, and the pK’s of its ionizable groups, be able to (qualitatively) describe the molecule’s titration curve.

Answer 10

DRAW FIGURES