课题：水的电离和溶液的pH 参赛教师：雷安明学校：遵义清华中学时间：2007年10月25日遵义清华中学教·学案课后阅读材料：Water Ionization（水的电离）From:/water/ionis.htmlWater molecules ionize endothermically f due to electric field fluctuations caused by nearby dipole librations [191] resulting from thermal effects, and favorable localized hydrogen bonding [567]; a process that is facilitated by exciting the O-H stretch overtone vibration [393]. Ions may separate by means of the Grotthuss mechanism (see below) but normally recombine within a few femtoseconds. Rarely (about once every eleven hours per molecule at 25°C, or less than once a week at 0°C) the localized hydrogen bonding arrangement breaks before allowing the separated ions to return [191], and the pair of ions (H+, OH-) hydrate independently and continue their separate existence a for about 70 μs (this lifetime also dependent on the extent of hydrogen bonding, being shorter at lower temperatures). They tend to recombine when only separated by one or two water molecules.H2O H+ + OH-K w = [H+][OH-]Although the extent of ionization is tiny ([H+]/[H2O] = 2.8 x 10-9 at 37°C), the ionization and changes in the tiny concentrations of hydrogen ions have absolute importance to living processes. Hydrogen ions are produced already hydrated (that is, as hydronium ions, H3O+; also called oxonium or hydroxonium ions) and have negligible existence as naked protons in liquid or solid water, where they interact extremely strongly with electron clouds. All three hydrogen atoms in the hydronium ion are held by strong covalent bonds and are equivalent (that is, C3v symmetry). The above equations are better written as:2 H2O H3O+ + OH-K w = [H3O+][OH-]Both ions create order and form stronger hydrogen bonds with surrounding water molecules. The concentrations of H3O+ and OH- are taken as the total concentrations of all the small clusters including these species. As other water molecules are required to promote the hydrolysis, the equation below includes the most important.4 H2O H5O2+ + H3O2-The concentration of hydronium and hydroxide ions produced is therefore equal to the square-root of the ionization constant (K w). The hydronium ion concentration (commonly called 'hydrogen ion concentration') is often given in terms of the pH, wherepH = Log10(1/[H3O+]) = -Log10([H3O+]) (that is, [H3O+] = 10-pH) with the concentration in mol l-1.b In a similar manner pK w = Log10(1/K w) = -Log10(K w), also with the concentrations in mol l-1.g OH- does not ionise further (O2- + H2O 2OH-, K > 1022).K w is very temperaturedependent, increasing withpK w = -log10(K w ) [IAPWS ] temperature (that is, from0.001 x 10-14 mol2 l-2 at -35°C(pH 8.5) [112], 0.112 x 10-14mol2 l-2 at 0°C (pH 7.5), to0.991 x 10-14 mol2 l-2 at 25°C(pH 7.0), to 9.311 x 10-14 mol2l-2 at 60°C (pH 6.5) [87]), to10-12 mol2 l-2 at 300°C (pH 6.0,~50 MPa) [456] in agreementwith the high positive standardfree energy.c A theoreticaltreatment of this temperaturedependence is available [763].Ionization depends on thepressure with K w doubling atabout 100 MPa; unsurprising inview of the negative ΔVassociated with the ionization,-18.1 cm3 mol-1.Ionization also varies with solute concentration and ionic strength; for example, K w goes through a maximum of about 2 x 10-14 mol2 l-2 at about 0.25 M ionic strength (using tetramethylammonium chloride, where possibly the change in hydrogen bonding caused by clathrate formation encourages ionization) before dropping to a value of about 1 x 10-16 mol2 l-2at 5 M (higher concentrations disrupting the hydrogen bonding).《水的电离和溶液的pH 》课堂阅读材料 Part I:Hydronium （水合氢离子）/Hydroxide （氢氧根离子） Balance ①There is also an internal relationship between the concentrations of H 3O + and OH -. They are not independent of one another. As one goes up, the other goes down. They cannot both go up because the higher concentrations of H 3O + and OH - would react with one another to make water molecules. That is a consequence of the reversibility of the self-ionization reaction of water. (2H 2OH 3O + + OH -)Let's use the self-ionization of pure water as our starting point.The concentrations of both H 3O + and OH - are 1.0 x 10-7 M. Ifthe concentration of H 3O + is doubled, the concentration of OH - willl be halved. If the concentration of H 3O + is halved, the concentration of OH - willl be doubled 译：让我们以纯水的自身电离作为我们的起点。

H 3O +和OH -浓度均为1.0 x 10-7 M ②。