1. Pratt & Cornely Chapter 2
Aqueous Solutions
Pratt & Cornely
Chapter 2

2. Water
Polarity
Transient interactions

3. Intermolecular Forces
Relative strength of IMF
Permanent dipole
London dispersion forces

4. H-bonding 1/10 the strength of some covalent bonds Donor/acceptor
~2.3 H-bonds/ water molecule

5. Transient Interactions
Intermediate strength of H-bonds key to function
Medium for Brownian Motion

6. Solvation Dielectric constant Solvation shell
Ionic, polar, and nonpolar compounds

7. Hydrophobic Effect
The exclusion of nonpolar substances from aqueous solution
DG = DH – TDS
Cage-like structure of water molecules minimized upon aggregation
Powerful structural determination

8. Structure of Biomolecules
Increased order in protein
Decreased order overall
How?

9. Amphipathic Compounds
Structures determined by hydrophobic effect
Micelles
Bilayer
Vesicle

10. Compartmentalization
Formation of cells and organelles
Limits diffusion of molecules unless small and nonpolar (O2, CO2)
Essential for life: don’t reach equilibrium!

11. Problem 27
Which of these substances might be able to cross a bilayer? Explain.
CO Ca+2

12. Autoionization of Water
Proton jumping: faster than diffusion limit

13. Kw, The Ion Product of Water

14. Reciprocal Relationship

15. pH of Neutral Water

16. Problem 34
Like all equilibrium constants, the value of Kw is temperature dependent. What is the pH of a neutral solution at 30 oC, where Kw = 1.47 x 10-14?

17. pH of Solutions
If acid is added to water, the concentration of hydronium increases and pH decreases
If base is added to water, the concentration of hydronium decreases (ion product of water) and the pH increases
Addition of MORE acid vs. addition of a STRONGER acid

18. Strong Acid Complete dissociation
What is the pH of a 0.01 M HCl solution?
You add a drop of HCl to make a 1 x 10-8 M solution. What is the pH?
What is your assumption?

19. Weak Acids
Strong
Weak

20. Weak Acid Dissociation Constants
Weak acids have low [pdts], therefore low Ka
Low Ka = high pKa
Weaker acids have __________ Ka values and __________ pKas

22. Henderson-Hasselbalch
Proton Acceptor
Proton Donor

23. Qualitative Understanding
Relationship of
Solution pH
Strength of acid
Ratio of CB to CA
Solve quantitatively, but understand qualitatively

24. Quantitative Understanding
What percent of molecules in an imidazole buffer are protonated at pH 7.2?

25. Buffers

27. Understand Figures
Be able to explain what is happening as you trace the line from left to right in this figure.
Key Tool in biochemistry:
Buffer

28. Buffer Capacity Depends on pKa of CA/CB mix
Depends on concentration of CA/CB

29. Making a Buffer
Problem 63: An experiment requires a HEPES buffer, pH 8.0. Write an equation for dissociation of HEPES. What is its effective buffer range? Describe how you would make 1.0 L of 0.10 M HEPES buffer (MW = g/mol) using 6.0 M HCl.

30. Polyprotic Acids
Must be able to match the pKa with the appropriate proton
Assumptions are legitimate if the pKa values are more than ~3 units from each other

31. What is/are the major ionization state(s) for succinic acid at pH 3
What is/are the major ionization state(s) for succinic acid at pH 3.2, 4.2, 5.2, and 6.2?

32. Blood Buffer
Physiological pH 7.4
Closed vs. Open systems
Acidosis

33. Kidney Function
Kidneys fight acidosis caused by common metabolic processes
Reclaims excreted bicarbonate by excreting acid
Forms new bicarb by CO2 producing metabolism