山东大学：《物理化学》课程教学资源（讲义资料）8.9 coagulation and flocculation-for students

日一句 王蒙:书好比是前人走过的脚印。读书有 个最大的问题,就是通过书本去发现生活, 去解释生活,去推动生活,而不是就书论书

王蒙：书好比是前人走过的脚印。读书有一 个最大的问题，就是通过书本去发现生活， 去解释生活，去推动生活，而不是就书论书。 一日一句

8.8.2 Dynamic properties of colloids (4)ultracentrifuge b) Differential Centrifugation Density Gradient Centrifugation Time(min) Time( min) Speed (RPM) Speed (RPM bvIrus A eel Virus B Virus A irus B

(4) ultracentrifuge: 8.8.2 Dynamic properties of colloids

8.8.2 Dynamic properties of colloids (4)ultracentrifuge: For sedimentation at equilibrium Centrifuge acceleration: a=0 x dc( mr F=oxM (1-vpo)dx RT Fi=oxO=MvPoox 2RTIn M F=M1(1-vP0)2x (1-v0)2(x2-x v specific volume Relative centrifugal force. RcF rTdc rt dc dhl dxl c a8=0xlg

(4) ultracentrifuge: Centrifuge acceleration: a x 2 = r 2 Fc = xM F xM M v x b 2 0 r 0 2 = =   For sedimentation at equilibrium v dx RT M x c dc (1 )0 2 r   = − 8.8.2 Dynamic properties of colloids d = d d RTdc RT c f cdhL xL c = v specific volume 2 c r 0 F M v x = − (1 )   (1 ) ( ) 2 ln 2 1 2 2 2 0 1 2 r v x x c c RT M − − =   2 a g x g / / = Relative centrifugal force, RCF

8.9 Stability and coagulation of colloids After Before

8.9 Stability and coagulation of colloids

8.9.1 Stability of colloids Why the colloidal system is quite stable? (1)Dynamic stabilization: Brownian motion and diffusion prevent colloidal particles from sedimentation. The less, the more stable. (2) Electric stabilization: All the colloid particles possessing the same charge tends to repulse each other and keep the colloid from coagulation (3)Solvation shell: The interaction between particle and solvent also helps to prevent aggregation of colloidal particles on collision How can we destroy the stability of a colloid?[Group discussion and share What is the role of stabilizing agent in preparation of colloids? Ag-Na, co Chinese ink--gelatin

Why the colloidal system is quite stable? (1) Dynamic stabilization: Brownian motion and diffusion prevent colloidal particles from sedimentation. The less, the more stable. (2) Electric stabilization: All the colloid particles possessing the same charge tends to repulse each other and keep the colloid from coagulation. (3) Solvation shell: The interaction between particle and solvent also helps to prevent aggregation of colloidal particles on collision. 8.9.1 Stability of colloids How can we destroy the stability of a colloid? [Group discussion and share] What is the role of stabilizing agent in preparation of colloids? Ag-Na2CO3 ; Chinese ink—gelatin

8.9.2 Precipitation of colloids by electrolytes Precipitating value: The lowest concentration of electrolyte( in mmol. dm)at which precipitation of colloid can be easily observed (precipitating efficiency/power) Al(OH)3(+) Electrolytes Precipitating value Electrolytes Precipitating value LICI 58 Nacl 43.5 KCI KCI 49.5 KNO3 60 0.65 K2SO4 0.30 Mgcl 0.72 K.Cro 0.63 MgSO4 0.81 (KOOC)2 0.69 AlCI 0.093 K,[Fe(CN)]0.08 Al(NO3)3 0.095 What can we learn from the results

As2S3 (−) Al(OH)3 (+) Electrolytes Precipitating value Electrolytes Precipitating value LiCl 58 NaCl 43.5 NaCl 51 KCl 46 KCl 49.5 KNO3 60 CaCl2 0.65 K2SO4 0.30 MgCl2 0.72 K2Cr2O7 0.63 MgSO4 0.81 (KOOC)2 0.69 AlCl3 0.093 K3 [Fe(CN)6 ] 0.08 Al(NO3 )3 0.095 Precipitating value: The lowest concentration of electrolyte ( in mmol dm-3 ) at which precipitation of colloid can be easily observed. (precipitating efficiency/power) 8.9.2 Precipitation of colloids by electrolytes What can we learn from the results?

8.9.2 Precipitation of colloids by electrolytes (1)Which ion is effective in causing precipitation of a sol? As2S3(-) The one whose charge is opposite to that Electrolytes Precipitating value of the colloidal particles, i.e. counterions LiCl NaCl KCI 5

(1) Which ion is effective in causing precipitation of a sol? 8.9.2 Precipitation of colloids by electrolytes As2S3 (−) Electrolytes Precipitating value LiCl 58 NaCl 51 KCl 49.5 The one whose charge is opposite to that of the colloidal particles, i.e., counterions

8.9.2 Precipitation of colloids by electrolytes (2) Valence the higher the valence, the lower the Electrolytes Precipitating value precipitating value LiCI Nacl M:M:M=100:16:0.14= KCI 49.5 CaCl 0.65 d ardy Schulze rules Mgcl 0.72 MgSOA 0.81 AlCI 0.093 is only valid without specific adsorption Al(NO3)3 0.095 The precipitating efficiency of morphia D) chloride is larger than Mg (ii) and ca (r)

As2S3 (−) Electrolytes Precipitating value LiCl 58 NaCl 51 KCl 49.5 CaCl2 0.65 MgCl2 0.72 MgSO4 0.81 AlCl3 0.093 Al(NO3 )3 0.095 the higher the valence, the lower the precipitating value. is only valid without specific adsorption. The precipitating efficiency of morphia (I) chloride is larger than Mg (II) and Ca (II) 6 6 6 I II III 1 1 1 M : M : M 100 :1.6 : 0.14 : : 1 2 3       = =             Hardy-Schulze rules. 8.9.2 Precipitation of colloids by electrolytes (2) Valence

8.9.2 Precipitation of colloids by electrolytes (3)Radius As2S3(-) Electrolytes Precipitating value H+> Cst> rbt>nh+>kt>Nat> Lit LiCl F->Cl> Br>No,>I 51 KCI 49.5 Hofmeister /lyotropic series AI(OH)3(+) Can you give explanation to these facts? Electrolytes Precipitating value KCI 46 KNO 60

(3) Radius Hofmeister / lyotropic series H+ > Cs+ > Rb+ > NH4 + > K+ > Na+ > Li+ F- > Cl- > Br- > NO3 - > I- 8.9.2 Precipitation of colloids by electrolytes As2S3 (−) Electrolytes Precipitating value LiCl 58 NaCl 51 KCl 49.5 Al(OH)3 (+) Electrolytes Precipitating value KCl 46 KNO3 60 Can you give explanation to these facts?

8.9.2 Precipitation of colloids by electrolytes cO-Ions Precipitating values for As,s, colloids As2S3(-) Electrolytes KNO Electrolytes Precipitating value K,SO4 Mgcl 0.72 Precipitating values 50 32.7 MgSO 0.81 When counterion is the same, the higher the valence of the co-ions the higher the precipitating value

(4) co-ions When counterion is the same, the higher the valence of the co-ions, the higher the precipitating value. Electrolytes KNO3 K2SO4 Precipitating values 50 32.7 Precipitating values for As2S3 colloids As2S3 (−) Electrolytes Precipitating value MgCl2 0.72 MgSO4 0.81 8.9.2 Precipitation of colloids by electrolytes