Chapter 2
Water
2 Water
2.1 Weak Interactions in Aqueous Systems
2.2 Ionization of Water, Weak Acids, and Weak Bases
2.3 Buffering against pH Changes in Biological Systems
2.4 Water as a Reactant
2.5 The Fitness of Aqueous Environment for Living Organisms
2.1 Weak Interactions in Aqueous Systems
Hydrogen bonding gives water its unusual properties. Water forms hydrogen bonds with polar solutes. Water interacts electrostically with charged molecules. Entropy increases as crystalline substances dissolve. Nonpolar gases are poorly soluble in water. N
2.2 Ionization of Water, Weak Acids, and Weak Bases
Pure water is slightly ionized. The ionization of water is expressed by equilibrium constant. The pH scale designates the H+ and the OH- concentrations. Weak acids and bases have characteristic acid dissociation constants. Titration curves reveal the pKa
2.3 Buffering against pH Changes in Biological Systems
Buffers are mixtures of weak acids and their conjugate bases. The Henderson-Hasselbalch equation relates pH, pKa, and buffer concentration. Weak acids or bases buffer cells and tissues against pH changes. Untreated diabetes produces life-threatening acido
2.4 Water as a Reactant
...
2.5 The Fitness of Aqueous Environment for Living Organisms
...
Memorize the Henderson-Hasselbach equation.
pH = pKa + log([A-]/[HA])
View Video segment on Cystic fibrosis
Almost always develops in early childhood. Genes make proteins. People are getting into the protein business. The proteome. From the letters we can learn the genes; from there we learn the proteins. We have so many fewer genes than we teach our students.
After reviewing the chapter, you should be able to:
Describe the properties of water. Know what intermolecular forces and thermodynamic considerations are as they relate to cells. Explain pH and pKa.
Describe the properties of water.
Water is a highly polar molecule, capable of forming hydrogen bonds with itself and with solutes.
Know what intermolecular forces and thermodynamic considerations are as they relate to cells.
Hydrogen bonds are fleeting, primarily electrostatic, and weaker than covalent bonds. Water is a good solvent for polar (hydrophilic) solutes, with which it forms hydrogen bonds, and for charged solutes, with which it interacts electrostatically. Nonpolar
Explain pH
The pH of an aqueous solution reflects, on a logarithmic scale, the concentration of hydrogen ions: pH = log 1/[H+] = -log[H+]. The greater the acidity, the lower the pH.
K eq
0
Explain pKa.
The pKa expresses, on a logarithmic scale, the relative strength of a weak acid or base: pKa = log 1/Ka = -log Ka. The stronger the acid, the lower its pKa; the stronger the base, the higher its pKa.
Write a paragraph describing water's role in the formation of the symptoms of cystic fibrosis. Consider the properties of water and intermolecular forces in your response.
A defect in the CFTR gene causes cystic fibrosis (CF). This gene makes a protein that controls the movement of salt and water in and out of your body's cells. The protein creates a chute that allows salt to enter and leave the cell. In people who have cys
Review Slides
Review Slides
1.6 Is synthetic vitamin C as good as the natural vitamin C?
The properties of the vitamin-like any other compound-are determined by it chemical structure. Because vitamin molecules from the two sources are structurally identical, their properties are identical, and no organism can distinguish between them. If diff
1.7 Identification of Functional Groups. Name the following groups: -NH3+, -OH, -P(OH)O2-, -COO-, -CO-NH-, and -CHO.
Amino, hydroxyl, phosphoryl, carboxyl, amide, and aldehyde.
1.8 Drug Activity and Stereochemistry. Why do the two enantiomers have such radically different bioactivity
The bioactivity of a drug is the result of interaction with a biological "receptor," a protein molecule with a binding site that is also chiral and stereospecific. The interaction of the D isomer of a drug with a chiral receptor site will differ from the
1.12 Components of Complex Bimolecules. Figure 1-10 shows the major components of complex biomolecules. For each of the three important biomolecules below (shown in their ionized forms at physiological pH), identify the constituents. (See pg 12)
a) Guanos
Three phosphoric acid groups (linked by two anhydride bonds), esterified to an alpha-D-ribose (at the 5' position), which is attached at C-1 to guanine.
1.12 Components of Complex Bimolecules. Figure 1-10 shows the major components of complex biomolecules. For each of the three important biomolecules below (shown in their ionized forms at physiological pH), identify the constituents. (See pg 12)
b) Methio
Tyrosine, two glycine, phenylalanine, and methionine residues, all linked by peptide bonds.
1.12 Components of Complex Bimolecules. Figure 1-10 shows the major components of complex biomolecules. For each of the three important biomolecules below (shown in their ionized forms at physiological pH), identify the constituents. (See pg 12)
c) Phosph
Choline esterified to a phosphoric acid group, which is esterified to glycerol, which is esterified to two fatty acids, oleic acid and palmitic acid.
2.8 Physical meaning of pKa. Which of the following aqueous solutions has the lowest pH: 0.1 M HCl; 0.1 M acetic acid (pKa =4.86); 0.1 M formic acid (pKa = 3.75)?
0.1 M HCl has the lowest pH because HCl is a strong acid and dissociates completely to H+ and Cl-, yielding the highest [H+].
2.10 Identifying the Conjugate Base. Which is the conjugate base in each of the pairs below? (a) RCOOH, RCOO-, (b) RNH2, RNH3+, (c) H2PO4-, H2PO4, (d) H2CO3, HCO3-
2.11 Calculation of the pH of a Mixture of a Weak Acid and Its Conjugate Base. Calculate the pH of a dilute solution that contains a molar ratio of potassium acetate to acetic acid (pKa = 4.76) of (a) 2:1, (b) 1:3, (c) 5:1, (d) 1:1, (e) 1:10
2.12 Effect of pH on Solubility. The strongly polar, hydrogen bonding properties of water make it an excellent solvent for ionic (charged) species. By contrast, nonionized, nonpolar organic molecules, such as benzene, are relatively insoluble in water. In
2.13 Treatment of Poison Ivy Rash. The components of poison ivy and poison oak that produce the characteristic itchy rash are catechols substituted with long-chain alkyl groups. (see image on pg. 68). If you were exposed to poison ivy, which of the treatm
2.14 pH and Drug Absorption. Aspirin is a weak acid with a pKa of 3.5 (see image on pg 68). It is absorbed in to the blood through the cells lining the stomach and the small intestine. Absorption requires passage through the plasma membrane, the rate of w
Stomach; the neutral form of aspirin present at the lower pH is less polar and passes through the membrane more easily.
Entropy
(S). The extent of randomness or disorder in a system.
Enthalpy
(H). The heat content of a system.
Endothermic reaction
A chemical reaction that takes up heat, that is, for which delta H is positive.