山东大学：《物理化学》课程教学资源（讲义资料）8.4 Surface adsorption of solution

88.4 Surface adsorption of solution Out-class reading Levine, p 390-397 13.3 thermodynamics of surface 13. 4 surface films on liquids

§8.4 Surface adsorption of solution Out-class reading: Levine, p. 390-397 13.3 thermodynamics of surface 13.4 surface films on liquids

88.4 Surface adsorption of solution 8.4.1 The surface phenomena of solution: Questing Is solution homogeneous? ④③|④(B )(B) B difference in intermolecular interaction Solvent solute Positive/negative adsorption (1)surface adsorption of solution

8.4.1 The surface phenomena of solution: Is solution homogeneous? (1) surface adsorption of solution A A A B A B Solvent A Solute B difference in intermolecular interaction Positive / negative adsorption §8.4 Surface adsorption of solution Questing

单选题1分 设置 Which description is correct? Positive adsorption, higher surface tension Positive adsorption lower surface tension Negative adsorption, higher surface tension 提交

Which description is correct? Positive adsorption, higher surface tension Positive adsorption, lower surface tension. Negative adsorption, higher surface tension. A B C 提交 单选题 1分

88.4 Surface adsorption of solution 8.4.1 The surface phenomena of solution interaction A-B>A-AA-B<A-A Surface concentration Surface tension adsorptio c(mmolL) surface adsorption: the concentration difference between surface and bulk solution The excess surface concentration(1) the concentration difference of solute per unit area in surface layer and in the bulk solution(mol m-2)

interaction A-B > A-A A-B < A-A Surface concentration Surface tension adsorption surface adsorption: the concentration difference between surface and bulk solution. The excess surface concentration (): the concentration difference of solute per unit area in surface layer and in the bulk solution. (mol m-2 ) 8.4.1 The surface phenomena of solution: §8.4 Surface adsorption of solution

88.4 Surface adsorption of solution 8.4.2 Gibbs adsorption isotherm n:+n?+n b B nterface Interphase Interfacial region

interface Interphase Interfacial region   S S’ a a’ b b’ 8.4.2 Gibbs adsorption isotherm    ni = ni + ni + ni    ni = ni − ni − ni i n A   = §8.4 Surface adsorption of solution

88.4 Surface adsorption of solution 8.4.2 Gibbs adsorption isotherm d=-S++al+∑om Ad+∑ndA=0 Let n, be the excess amount of the solute(2) At constant T and p in the surface layer compared to that in a solution of uniform composition. Then the dgo=odA+>u dn lowering of free energy due to the adsorption of solute at the interface is n, du, Integration gives This lowering of free energy in the surface G=a4+∑n is equivalent to -Ado, hence do Further differentiation Ado au2 dG=ad4+Aa+∑om+∑

i i i dG SdT Vdp dA dn   = − + + +    At constant T and p = + i dG dA i dni     = +   G A i ni i i i i dG dA Ad dn n d    = + + +       Integration gives 0 Ad n di i    + =  Let n2 be the excess amount of the solute (2) in the surface layer compared to that in a solution of uniform composition. Then the lowering of free energy due to the adsorption of solute at the interface is n2 d2 . 8.4.2 Gibbs adsorption isotherm Further differentiation n2 d2 = −Ad This lowering of free energy in the surface is equivalent to - Ad, hence: 2 2 T       = −    §8.4 Surface adsorption of solution

88.4 Surface adsorption of solution 8.4.2 Gibbs adsorption isotherm and the surface excess of solute per unit area Is O 00 rr\T Gibbs adsorption isotherm u2=u2+tINc The sign of T2 is determined by(ao/ac), RT while the value of l is determined by both(ao/ac)and c

and the surface excess of solute per unit area is: 2 2 2   = + RT c ln 2 2 2 RT d dc c  = 2 2 2 T c RT c      = −     Gibbs adsorption isotherm The sign of 2 is determined by (/c), while the value of 2 is determined by both (/c) and c. 8.4.2 Gibbs adsorption isotherm 2 2 T       = −    §8.4 Surface adsorption of solution

88.4 Surface adsorption of solution 8.4.3 The types of surface adsorption Three tv f surface adsorption Type I: salts, non-volatile acids and bases, 70 sucrose etc 30 10 C Spring water contains solvable salts

8.4.3 The types of surface adsorption Three types of surface adsorption. Type I: salts, non-volatile acids and bases, sucrose, etc. Spring water contains solvable salts. 10 30 50 70 I II III c  §8.4 Surface adsorption of solution

88.4 Surface adsorption of solution 8.4.3 The types of surface adsorption KCI NaCl NaNo % /mN·m u/%a/mN·m-1w/%a/mN·m-1 0.74 72.99 0.58 72.92 0.85 72.87 3.60 73.45 2.84 73.75 4.08 73.75 6.93 74.15 5.43 74.39 7.84 73.95 13.88 75.55 10.46 76.05 14.53 75.15 18.77 76.95 14.92 77.65 29.82 78.35 22.97 78.25 22.62 80.95 37.30 80.25 24.70 78.75 5.92 5 82.55 47.06 87.05

8.4.3 The types of surface adsorption §8.4 Surface adsorption of solution

88.4 Surface adsorption of solution 8.4.3 The types of surface adsorption Type II: For nonionic solvable organic molecule with low molecular weight (short chains) and containing polar groups such as hydroxyl, amine groups, etc 65 HCOOH The phenomenon that surface tension of solvent CHCOoH O 0 decreases upon addition of 50 CHs COOH solute is called surface activity CaHCOOH 35 CyHoCOOH Traube empirical law for fatty acid 0.18 0.36 0.54c The surface tension of solution decreases by 3.2 times for the increase of per Ch group in the chain of fatty acid

Type II: For nonionic solvable organic molecule with low molecular weight (short chains) and containing polar groups such as hydroxyl, amine groups, etc. The surface tension of solution decreases by 3.2 times for the increase of per CH2 group in the chain of fatty acid. Traube empirical law for fatty acid: The phenomenon that surface tension of solvent decreases upon addition of solute is called surface activity. 8.4.3 The types of surface adsorption 0 c          §8.4 Surface adsorption of solution