Động hoá học và hoá lý hệ phân tán

ĐỘNG HÓA HỌC VÀ HÓA LÝ HỆ PHÂN TÁN - Tài liệu tham khảo chính: Hóa lý Hóa Keo, Nguyễn Hữu Phú, Nhà Xuất Khoa học Kỹ thuật, 2003 Bài tập Hóa lý sở, Lâm Ngọc Thiềm, Trần Hiệp Hải, Nguyễn Thị Thu, Nhà Xuất Khoa học Kỹ thuật, 2003 Physical Chemistry, Third Edition, Robert G Mortimer, Elsevier Inc., 2008 Phần 1: Động hóa học Physical Chemistry – Understanding our Chemical Word, Paul Monk, John Wiley & Sons, Ltd, 2004 Prepared by NGUYEN Dinh Lam – DUT - UD Một số khái niệm Prepared by NGUYEN Dinh Lam – DUT - UD Một số khái niệm -Tốc độ phản ứng (Reaction rates) - Động hóa học môn học nghiên cứu tốc độ chế trình hóa học - Định luật tác dụng khối lượng (Rate Law) - Bậc phản ứng (Reaction Order) - Phản ứng nguyên tố (Elementary step) - Phân tử số (Molecularity) - Nghiên cứu động học: Năng suất Công nghệ trình - Cơ chế phản ứng (Reaction Mechanism) - Lý thuyết va chạm (The Collision Theory) - Năng lượng hoạt hóa (Activation Energy) -Xúc tác (Catalyst) Prepared by NGUYEN Dinh Lam – DUT - UD Prepared by NGUYEN Dinh Lam – DUT - UD Kinetics At 298K, reaction: H2(g) + 1/2O2(g) = H2O(l) ∆Go298(r) = -254,8 kJ.mol-1 Thermodynamics – does a reaction take place? Kinetics – how fast does a reaction proceed? • Studies the rate at which a chemical process occurs • Besides information about the speed at which reactions occur, kinetics also sheds light on the reaction mechanism (exactly how the reaction occurs) Part 1: Chemical Kinetics Prepared by NGUYEN Dinh Lam – DUT - UD Prepared by NGUYEN Dinh Lam – DUT - UD Chemical Kinetics (Simple Homogenous reaction) Outline: Kinetics Reaction Rates How we measure rates Rate Laws How the rate depends on amounts of reactants Integrated Rate Laws How to calc amount left or time to reach a given amount Half-life How long it takes to react 50% of reactants Arrhenius Equation How rate constant changes with T Mechanisms Link between rate and molecular scale processes Reaction rate is the change in the concentration of a reactant or a product with time (M/s) A ∆[A] ∆t ∆[B] rate = ∆t rate = - B ∆[A] = change in concentration of A over time period ∆t ∆[B] = change in concentration of B over time period ∆t Because [A] decreases with time, ∆[A] is negative Prepared by NGUYEN Dinh Lam – DUT - UD Prepared by NGUYEN Dinh Lam – DUT - UD A Exercise 1: Br2 (aq) + HCOOH (aq) B time time ∆[B] ∆t 393 nm light Prepared by NGUYEN Dinh Lam – DUT - UD Exercise 1: Br2 (aq) + HCOOH (aq) slope of tangent average rate = - 2Br- (aq) + 2H+ (aq) + CO2 (g) slope of tangent slope of tangent ∆[Br2] α ∆Absorption Prepared by NGUYEN Dinh Lam – DUT - UD Exercise 1: Br2 (aq) + HCOOH (aq) 10 2Br- (aq) + 2H+ (aq) + CO2 (g) rate α [Br2] rate = k [Br2] [Br2]final – [Br2]initial ∆[Br2] =∆t tfinal - tinitial rate = rate constant [Br2] = 3.50 x 10-3 s-1 k= instantaneous rate = rate for specific instance in time Prepared by NGUYEN Dinh Lam – DUT - UD Detector 393 nm Br2 (aq) ∆[A] rate = ∆t rate = 2Br- (aq) + 2H+ (aq) + CO2 (g) 11 Prepared by NGUYEN Dinh Lam – DUT - UD 12 Exercise 2: 2H2O2 (aq) Exercise 2: 2H2O2 (aq) 2H2O (l) + O2 (g) 2H2O (l) + O2 (g) PV = nRT P= n RT = [O2]RT V [O2] = P RT rate = ∆[O2] ∆P = RT ∆t ∆t measure ∆P over time Prepared by NGUYEN Dinh Lam – DUT - UD 13 Prepared by NGUYEN Dinh Lam – DUT - UD Reaction Rates and Stoichiometry The “classical” methods for determining the reaction rate The absorbance of radiation at some wavelength at which a given product or reactant absorbs The intensity of the emission spectrum of the system at a wavelength at which a given product or reactant emits The volume of a solution required to titrate an aliquot removed from the system The pressure of the system (for a reaction at constant volume) The volume of the system (for a reaction at constant pressure) The electrical conductance of the system The mass spectrum of the system The ESR or NMR spectrum of the system The dielectric constant or index of refraction of the system 10 The mass loss if a gas is evolved Prepared by NGUYEN Dinh Lam – DUT - UD 15 14 Factors That Affect Reaction Rates • Concentration of Reactants – As the concentration of reactants increases, so does the probability that reactant molecules will collide • Temperature – At higher temperatures, reactant molecules have more kinetic energy, move faster, and collide more often and with greater energy • Catalysts – Speed reaction by changing mechanism Prepared by NGUYEN Dinh Lam – DUT - UD 16 Reaction Rates Reaction Rates C4H9Cl(aq) + H2O(l) → C4H9OH(aq) + HCl(aq) Average Rate, M/s C4H9Cl(aq) + H2O(l) → C4H9OH(aq) + HCl(aq) The average rate of the reaction over each interval is the change in concentration divided by the change in time: average rate = − ∆[C4 H 9Cl ] ∆t average rate = − ∆[C4 H 9Cl ] 0.1000 − 0.0905 M = 50.0 − 0.0 s ∆t Prepared by NGUYEN Dinh Lam – DUT - UD 17 • Note that the average rate decreases as the reaction proceeds • This is because as the reaction goes forward, there are fewer collisions between reactant molecules Prepared by NGUYEN Dinh Lam – DUT - UD Reaction Rates Reaction Rates C4H9Cl(aq) + H2O(l) → C4H9OH(aq) + HCl(aq) C4H9Cl(aq) + H2O(l) → C4H9OH(aq) + HCl(aq) • A plot of concentration vs time for this reaction yields a curve like this • The slope of a line tangent to the curve at any point is the instantaneous rate at that time Prepared by NGUYEN Dinh Lam – DUT - UD 18 • The reaction slows down with time because the concentration of the reactants decreases 19 Prepared by NGUYEN Dinh Lam – DUT - UD 20 Reaction Rates and Stoichiometry Reaction Rates and Stoichiometry C4H9Cl(aq) + H2O(l) → C4H9OH(aq) + HCl(aq) • In this reaction, the ratio of C4H9Cl to C4H9OH is 1:1 • Thus, the rate of disappearance of C4H9Cl is the same as the rate of appearance of C4H9OH Rate = -∆[C4H9Cl] = ∆t • What if the ratio is not 1:1? H2(g) + I2(g) → HI(g) • mol of HI are made for each mol of H2 used ∆[C4H9OH] ∆t Prepared by NGUYEN Dinh Lam – DUT - UD 21 Reaction Rates and Stoichiometry Prepared by NGUYEN Dinh Lam – DUT - UD Write the rate expression for the following reaction: CH4 (g) + 2O2 (g) • To generalize, for the reaction aA + bB Reactants (decrease) Prepared by NGUYEN Dinh Lam – DUT - UD rate = - cC + dD 22 CO2 (g) + 2H2O (g) ∆[CH4] ∆[CO2] ∆[O2] ∆[H2O] = == ∆t ∆t ∆t ∆t Products (increase) 23 Prepared by NGUYEN Dinh Lam – DUT - UD 24 The Rate Law The Rate Law The rate law expresses the relationship of the rate of a reaction to the rate constant and the concentrations of the reactants raised to some powers aA + bB cC + dD Rate = k [A]x[B]y Concentration and Rate Each reaction has its own equation that gives its rate as a function of reactant concentrations ⇒ this is called its Rate Law To determine the rate law we measure the rate at different starting concentrations reaction is xth order in A reaction is yth order in B reaction is (x +y)th order overall Prepared by NGUYEN Dinh Lam – DUT - UD Example: F2 (g) + 2ClO2 (g) 25 2FClO2 (g) • A rate law shows the relationship between the reaction rate and the concentrations of reactants – For gas-phase, reactants use PA instead of [A] Double [F2] with [ClO2] constant x=1 Quadruple [ClO2] with [F2] constant Rate quadruples 26 Rate Laws rate = k [F2]x[ClO2]y Rate doubles Prepared by NGUYEN Dinh Lam – DUT - UD rate = k [F2][ClO2] This equation is called the rate law, and k is the rate constant • k is a constant that has a specific value for each reaction • The value of k is determined experimentally rate = k [F2][ClO2] “Constant” is relative here - k is unique for each reaction, k changes with T y=1 Prepared by NGUYEN Dinh Lam – DUT - UD 27 Prepared by NGUYEN Dinh Lam – DUT - UD 28 Rate Laws Exercise 3: Determine the rate law and calculate the rate constant for the following reaction from the following data: 2SO42- (aq) + I3- (aq) S2O82- (aq) + 3I- (aq) • Rate laws are always determined experimentally • Reaction order is always defined in terms of reactant (not product) concentrations • The order of a reactant is not related to the stoichiometric coefficient of the reactant in the balanced chemical equation F2 (g) + 2ClO2 (g) [S2O82-] [I-] Initial Rate (M/s) 0.08 0.034 2.2 x 10-4 0.08 0.017 1.1 x 10-4 0.16 0.017 2.2 x 10-4 Double [S2O82-], rate doubles (experiment & 3) rate = k [F2][ClO2] k= 29 2.2 x 10-4 M/s rate = = 0.08/M•s [S2O82-][I-] (0.08 M)(0.034 M) Prepared by NGUYEN Dinh Lam – DUT - UD Consider a simple first order reaction: A → B Experiment [S2O82-] [I-] Initial Rate (M/s) 0.08 0.034 2.2 x 10-4 0.08 0.017 1.1 x 10-4 rate = k [S2O82-]x[I-]y y=1 x=1 0.16 0.017 2.2 x 10-4 rate = k [S2O82-][I-] • • 30 Integrated Rate Laws First order reaction Exercise 3: Determine the rate law and calculate the rate constant for the following reaction from the following data: S2O82- (aq) + 3I- (aq) 2SO42- (aq) + I3- (aq) • • rate = k [S2O82-]x[I-]y y=1 x=1 rate = k [S2O82-][I-] Double [I-], rate doubles (experiment & 2) 2FClO2 (g) Prepared by NGUYEN Dinh Lam – DUT - UD Experiment Differential form: How much A is left after time t? Integrate: Exponents tell the order of the reaction with respect to each reactant This reaction is First-order in [S2O82-] First-order in [I-] The overall reaction order can be found by adding the exponents on the reactants in the rate law This reaction is second-order overall Prepared by NGUYEN Dinh Lam – DUT - UD 31 Prepared by NGUYEN Dinh Lam – DUT - UD 32 First-Order Reactions Integrated Rate Laws First order reaction Manipulating this equation produces… The integrated form of first order rate law: Can be rearranged to give: …which is in the form = mx + b y [A]0 is the initial concentration of A (t=0) [A]t is the concentration of A at some time, t, during the course of the reaction Prepared by NGUYEN Dinh Lam – DUT - UD 33 First-Order Reactions Prepared by NGUYEN Dinh Lam – DUT - UD 34 Exercise 4: The reaction 2A B is first order in A -2 -1 with a rate constant of 2.8 x 10 s at 800C How long will it take for A to decrease from 0.88 M to 0.14 M ? [A]0 = 0.88 M ln[A] = ln[A]0 - kt [A] = 0.14 M kt = ln[A]0 – ln[A] t= ln[A]0 – ln[A] = k ln [A]0 [A] k ln = 0.88 M 0.14 M 2.8 x 10-2 s-1 = 66 s If a reaction is first-order, a plot of ln [A]t vs t will yield a straight line with a slope of -k So, use graphs to determine reaction order Prepared by NGUYEN Dinh Lam – DUT - UD 35 Prepared by NGUYEN Dinh Lam – DUT - UD 36 First-Order Reactions Second-Order Reactions The half-life, t½, is the time required for the concentration of a reactant to decrease to half of its initial concentration k= t½ = t when [A] = [A]0/2 ln t½ = [A]0 [A]0/2 k A product What is the half-life of N2O5 if it decomposes with a rate constant of 5.7 x 10-4 s-1? 0.693 t½ = ln2 = = 1200 s = 20 minutes k 5.7 x 10-4 s-1 d[A] dt rate M/s = = 1/M•s M2 [A]2 1 = + kt [A] [A]0 ln2 0.693 = = k k rate = - also in the form y = mx + b - 37 Zero-Order Reactions A k= product rate = M/s [A]0 [A] = [A]0 - kt also in the form y = mx + b rate = - d[A] dt rate = k [A]0 = k - d[A] =k dt [A] is the concentration of A at any time t [A]0 is the concentration of A at time t=0 The half-life, t½ t½ = t when [A] = [A]0/2 k[A]0 The half-life, t½ t½ = t when [A] = [A]0/2 38 Summary of the Kinetics of Zero-Order, First-Order and Second-Order Reactions Concentration-Time Equation Order Rate Law rate = k [A] = [A]0 - kt rate = k [A] ln[A] = ln[A]0 - kt rate = k [A]2 1 = + kt [A]0 [A] [A]0 is the concentration of A at time t=0 t½ = Prepared by NGUYEN Dinh Lam – DUT - UD Prepared by NGUYEN Dinh Lam – DUT - UD d[A] = k [A]2 dt [A] is the concentration of A at any time t t½ = Prepared by NGUYEN Dinh Lam – DUT - UD rate = k [A]2 Half-Life t½ = [A]0 2k t½ = ln2 k t½ = k[A]0 [A]0 2k 39 Prepared by NGUYEN Dinh Lam – DUT - UD 40 Langmuir theory (monolayer adsorption) BET theory (multilayer adsorption) Specific surface area - Determination by using Langmuir theory Derivation of the BET Isotherm BET : Brunauer, Emmet, Teller The specific surface area SL of the adsorbent evaluated from Langmuir theory can be calculated from Vm by : Where : SL = VmσN A mV0 σ: the area of the surface occupied by a single physisorbed gas molecule (σ=16.2Ų for N2) NA : Avogadro constant = 6.02 1023 mol-1 m: Mass of the adsorbent solid sample V0 : Molar volume of the gas (22414 cm3) First theory : Langmuir for monolayer adsorption When the pressure system is increased, the adsorbed species adsorb in multilayer on the surface Second theory : BET for multilayer adsorption Prepared by NGUYEN Dinh Lam – DUT - UD 105 Prepared by NGUYEN Dinh Lam – DUT - UD 106 BET theory (multilayer adsorption) BET theory (multilayer adsorption) Assumptions Isotherm adsorption Equation of BET and Graphical form Vm c Brunauer, Emmet, Teller (BET) theory : V= Generalization of the Langmuir theory to multilayer adsorption, with the following hypotheses : • The evaporation (desorption) rate of adsorbed molecules in a layer is equal to the condensation (adsorption) rate on the layer under it • The adsorption heat in the layers (except the first one) is equal to the liquefaction heat of the gas P P0  P (1 − P0 ) 1 + (c − 1)  P0   Graphical form of the BET isotherm V = f(P) • At saturation the number of layers is considered as infinite Prepared by NGUYEN Dinh Lam – DUT - UD 107 Prepared by NGUYEN Dinh Lam – DUT - UD 108 BET theory (multilayer adsorption) BET theory (multilayer adsorption) Isotherm adsorption Equation of BET and Graphical form Linearization of BET isotherm P Vm c P0 V=  P (1 − P0 ) 1 + (c − 1)  P  0 Vm c V= P P0  P (1 − P0 ) 1 + (c − 1)  P 0  linearized as P (c − 1) P = + V ( P0 − P) Vm c Vm c P0 Intercept = 1/cVm Slope = (c-1)/cVm VM = c= x = P/P0 Prepared by NGUYEN Dinh Lam – DUT - UD 109 Prepared by NGUYEN Dinh Lam – DUT - UD Slope + Intercept Slope + Intercept Slope 110 Other theories proposed BET theory (multilayer adsorption) Specific surface area determination Depending on the hypotheses made (mono or multilayer adsorption, interactions between the adsorbed molecules or not, several theories have been developed Ex : linearised isotherms BET theory is valuable in the range 0.05 < P/P0 < 0.35 At low P : heterogeneous surface At high P : capillary condensation From Vm value obtained using BET linearized isotherm, the specific surface area called SBET is calculated using the same formula as in Langmuir theory : S BET = VmσN A mV0 Prepared by NGUYEN Dinh Lam – DUT - UD Where : σ: Area of the surface occupied by a single physisorbed gas molecule (σ=16.2Ų for N2) NA Avogadro constant = 6.02 1023 mol-1 m the mass of the adsorbent solid sample V0 the molar volume of the gas (22414 cm3) Langmuir and the BET theories are the mostly used 111 Prepared by NGUYEN Dinh Lam – DUT - UD 112 Types of the adsorption - desorption isotherms Typical Adsorbed Species Adsorbed species N2 O2 Ar Kr CO CO2 C6H6 Adsorption Temperature, K 77 90 77 Area of surface occupied σ (n.m2) 0,162 0,141 0,138 90 0,144 77 90 195 90 195 273 0,202 0,15 0,217 0,168 0,207 0,430 Six types of adsorption isotherms following IUPAC classification : Type I : non porous or micro-porous samples (∅ < nm) Types II and III : macroporous samples (∅ > 50 nm) Types IV and V : mesoporous samples (2 nm < ∅ < 50 nm) Type VI : step isotherm (rare) Types III and V correspond to a low enthalpy of adsorption IUPAC: The International Union of Pure and Applied Chemistry Prepared by NGUYEN Dinh Lam – DUT - UD 113 Prepared by NGUYEN Dinh Lam – DUT - UD Apparatus used for adsorption Apparatus used for adsorption Picture Scheme Prepared by NGUYEN Dinh Lam – DUT - UD 114 115 Prepared by NGUYEN Dinh Lam – DUT - UD Once clean, the sample is brought to a constant temperature by means of an external bath Then adsorptive pressure is slowly increased and adsorption takes place 116 Properties of Disperse Systems (Colloids) I Kinetics properties Motion of the particles with respect to the dispersion medium • Thermal motion Properties of Disperse Systems (Colloids) Kinetics properties Brownian movement (1827) Bombardment of the particles by the molecules of the dispersion medium - Brownian movement - Diffusion - Osmosis Einstein and Smoluchowski Equation (1906) • Gravity or centrifugal field - Sedimentation ∆= • Viscous flow ∆x = Prepared by NGUYEN Dinh Lam – DUT - UD 117 Properties of Disperse Systems (Colloids) Kinetics properties Prepared by NGUYEN Dinh Lam – DUT - UD – Diffusion: the colloidal sols will from a region of high concentration to a region of low concentration 118 Properties of Disperse Systems (Colloids) Kinetics properties First Fick’s Law (1855) dm = − D – Colligative properties: colloidal sols show colligative properties ik = dC S dt dx dm dC = −D Sdt dx m = −D dC St dx dC = 1, S = 1, t = dx k T t 3.π µ r D=− Prepared by NGUYEN Dinh Lam – DUT - UD k T t 3.π µ r Diffusion of particles according to a concentration gradient – Stable system: the force of gravity is counteracted by Brownian movement ∆x = R.T 2t = N 6.π η r Diffusion Consequences of Brownian movement R.T 2t = N 6.π η r ∆21 + ∆22 + K + ∆2n n 119 Prepared by NGUYEN Dinh Lam – DUT - UD m dx mol.m m = = m s −1 S t dC m s.mol 120 Properties of Disperse Systems (Colloids) Kinetics properties The radius ( r ) of the colloidal particle is obtained from the Diffusion coefficient (D) D= Properties of Disperse Systems (Colloids) Kinetics properties Diffusion Second Fick’s Law - Instable Diffusion kT 6π η r  d 2C d 2C d 2C  dC = D + +  dt dy dz   dx The molecular weight (M) of colloidal particle is obtained from M = πρ r N D: diffusion coefficient (m2.s-1) η: viscosity of the dispersion medium (kg.s-1.m-1) N: Avogadro’s number r: radius (m) M: molecular weight ρ: specific gravity of dispersed phase (kg.m3) 10 P = kg·m−1·s−1= Pa·s cP = 0.001 Pa·s = mPa·s Prepared by NGUYEN Dinh Lam – DUT - UD 121 Properties of Disperse Systems (Colloids) Kinetics properties Osmosis: Flow of solvent across a semipermeable membrane to equalize concentrations dC = D.∇ C dt Prepared by NGUYEN Dinh Lam – DUT - UD Sedimentation: Stokes’ law for a spherical particle r= π = C.R.T Dilute Colloids: C π= Prepared by NGUYEN Dinh Lam – DUT - UD NA R.T 122 Properties of Disperse Systems (Colloids) Kinetics properties Van’t Hoff equation: γ  d2 d2 d2  ∇ =  + +  dy dz   dx = Where : x: distance to be travelled (m) dx/dt: rate of sedimentation (m.s-1) r: radius of the particle (m) σ: density of the particle (kg.m-3) ρ: density of the medium (kg.m-3) η: viscosity of the medium (kg.m-1.s-1) g: acceleration due to gravity (m.s-2) γ NA or π = γ k B T 123 Prepared by NGUYEN Dinh Lam – DUT - UD 9.η.v 2(σ − ρ o ).g v= H t Mono-dispersion 124 Properties of Disperse Systems (Colloids) Kinetics properties Sedimentation: Properties of Disperse Systems (Colloids) Kinetics properties Sedimentation: r= 9.η.v 2(σ − ρ o ).g For particles less than 0.5 µm, centrifugal force is required with s = Where : Where : w : angular velocity (s-1) x : distance of the particle from the center of rotation (m) Figurowsly’s balance (a) Poly-dispersion (b) Mono-dispersion Prepared by NGUYEN Dinh Lam – DUT - UD 125 Properties of Disperse Systems (Colloids) Kinetics properties Viscosity: 2r (σ − ρ o ) 9η s : sedimentation coeffecient (s) Molecular weight M is given by η: viscosity of the medium (kg.m-1.s-1) Prepared by NGUYEN Dinh Lam – DUT - UD υ: specific volume 126 Properties of Disperse Systems (Colloids) Kinetics properties Viscosity: The Einstein equation for dilute colloidal dispersions: Specific viscosity ηsp (viscosity ratio increment): Where ηο = viscosity of the dispersion medium η = viscosity of the disperse system ϕ = the volume fraction of colloidal particle (volume of the particles relative to the volume of the dispersion) φ is dependent on concentration For dilute solutions: For concentrated solutions: Relative viscosity ηrel (viscosity ratio): ) Prepared by NGUYEN Dinh Lam – DUT - UD 127 Prepared by NGUYEN Dinh Lam – DUT - UD 128 Properties of Disperse Systems (Colloids) Kinetics properties Viscosity: Properties of Disperse Systems (Colloids) Kinetics properties Viscosity: Effect of shape of the particles on the viscosity of the colloidal dispersions Intrinsic viscosity [ η ] : Reduced viscosity Spherocolloids dispersions are of relatively low viscosity Linear particles systems are more viscous due to solvation Morphology (shape, inner structure) Linear relationship between ηsp/c and c For a polymer solution K and a are constants characteristic of the particular polymer solution Prepared by NGUYEN Dinh Lam – DUT - UD 129 Properties of Disperse Systems (Colloids) Optical properties The Faraday-Tyndall Effect: Prepared by NGUYEN Dinh Lam – DUT - UD Prolate (a>b) oblate (a CH3COO- > NCS- > I- > NO3- > Br- > ClMg2+ > Ca2+ > Ba2+ > K+ > Na+ > Li+ Thermodynamically stable systems 2- Effect of solvents The colloid becomes susceptible to small amounts of electrolytes Prepared by NGUYEN Dinh Lam – DUT - UD 153 Stability of lyophilic colloids Prepared by NGUYEN Dinh Lam – DUT - UD 154 Sensitization and protective colloid action Sensitization 3- Coacervation : The separation from a lyophilic sol of a colloid - rich layer upon addition of another substance E.g.: Mixing of oppositely charged lyophilic colloid Prepared by NGUYEN Dinh Lam – DUT - UD 155 Prepared by NGUYEN Dinh Lam – DUT - UD 156 Sensitization and protective colloid action Protective Colloid action Sensitization and protective colloid action Protective Colloid action The protective property of a lyophilic colloid is expressed in terms of the gold number The Gold number : The minimum weight in mg of the protective colloid (dry weight of dispersed phase) required to prevent a color change from red to violet in 10 ml of a gold sol on the addition of ml of a 10% sodium chloride The lower the gold number, the higher is the protective property Prepared by NGUYEN Dinh Lam – DUT - UD 157 Prepared by NGUYEN Dinh Lam – DUT - UD Soap and Surfactants Soap and Surfactants Anionic Surfactants Soap 158 Cationic Surfactants Cetyl trimethyl ammonium bromide Alkyl ether sulphate Distearyl dimethyl ammonium chloride Alkyl aryl sulphonate Prepared by NGUYEN Dinh Lam – DUT - UD Fatty alcohol sulphate 159 Lauryl dimethyl benzyl ammonium chloride Prepared by NGUYEN Dinh Lam – DUT - UD 160 Soap and Surfactants Nonionic Surfactants Glycol and glycerol esters - Glyceryl monostearate Polyoxyethylene esters - Polyoxyethylene stearate Polyoxyethylene ethers Polyoxyethylene-polyoxypropylene copolymers Sorbitan derivatives Sucrose esters Esters of sucrose with fatty acids such as stearic or palmitic acid END Prepared by NGUYEN Dinh Lam – DUT - UD 161