2.1 the properties of water
ionic(electrolyte) and polar(-OH,,hydrogen bonding.) substances dissolve in water(hydrophilic)
non polar substance are insoluble in water(hydrophobic)
O—H….O 在一条直线上
有一对lone pair就可以连一个氢键，所以O可以连两个，双键O可以连一个
一个水分子4个氢键，但两两共用，所以1mol水有2mol氢键。
冰中水分子间的距离更小所以氢键能量更大。
the hydrophobic effect is critical for the folding of proteins and the self-assembly of biological membranes.
detergents: amphipathic substances 两性物质 Osmotic Pressure 渗透压
2.2 weak interactions in aqueous systems
4 major non covalent bonds(forces) in biomolecules:
a. electrostatic interactions: charge-charge interactions, hydrogen bonds, van der waals forces.
b. hydrophobic interactions.
偶极矩的单位为D( Debye德拜), 方向用+->表示，从正到负，指向电子云密度高的一方。
而电子对转移箭头则是从带负电的nucleophile（Nu-）一端到正电。
2.3 ionization of water, weak acids and weak bases
1g/cm^3 = 1000/18 = 55.5 mol/L
water: k_eq = [H][OH]/55.5M = 1.810^-16 \therefore k_w = [H][OH] = 110^-14 M^2
weak acids(a.a.) and weak bases(purines, pyrimidines):
k_a = [H][A]/[HA] , k_b = [HA][OH]/[A]
0.01, 0, 0 —> 0.01-X , X, X [X]^2/[0.01-X] ~= [X]^2/0.01 (原弱酸浓度基本不变)
Henderson-Hasselbach Equation: pH = pKa + log([A]/[HA])
the titration curve (将碱加入为[HA]的一半，这样生成的[A]和剩下的[HA]就一样多了)
2.4 buffers and buffered solutions resist changes in pH
buffer: a weak conjugate acid-base pair
working pH range: pH = pKa +/- 1
blood 7.4: H2CO3— HCO3-
cytoplasm of all cells: HPO_4^2- — H_2PO_4^-
buffer preparation: 给出pKa, 配一定pH的buffer, 可以先用hhe求出[A^-][HA]碱酸浓度比，再根据题中所给的两物质各自的浓度和总体积，求出各物质的体积。
