week-5 - 1 Demo today ??? 2 Colloids Colloids Hydrophilic...

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Unformatted text preview: 1 Demo today ??? 2 Colloids Colloids Hydrophilic and Hydrophobic Colloids Focus on colloids in water . Water loving colloids: hydrophilic. Water hating colloids: hydrophobic. Molecules arrange themselves so that hydrophobic portions are oriented towards each other. If a large hydrophobic macromolecule (giant molecule) needs to exist in water (e.g. in a biological cell), hydrophobic molecules embed themselves into the macromolecule leaving the hydrophilic ends to interact with water. Hydrophilic and Hydrophobic Colloids.. Typical hydrophilic groups are polar (containing C-O, O-H, N-H bonds) or charged. Hydrophobic colloids need to be stabilized in water. Adsorption: when something sticks to a surface we say that it is adsorbed. If ions are adsorbed onto the surface of a colloid, the colloids appears hydrophilic and is stabilized in water. Consider a small drop of oil in water. Add to the water sodium stearate. Hydrophilic and Hydrophobic Colloids Hydrophilic and Hydrophobic Colloids Sodium stearate has a long hydrophobic tail (CH 3 (CH 2 ) 16-) and a small hydrophobic head (-CO 2- Na + ). The hydrophobic tail can be absorbed into the oil drop, leaving the hydrophilic head on the surface. The hydrophilic heads then interact with the water and the oil drop is stabilized in water. 3 Removal of Colloidal Particles Colloid particles are too small to be separated by physical means (e.g. filtration). Colloid particles may be coagulated (enlarged) until they can be removed by filtration. Methods of coagulation: heating (colloid particles move and are attracted to each other when they collide); adding an electrolyte (neutralize the surface charges on the colloid particles). Dialysis: using a semipermeable membranes separate ions from colloidal particles Chapter 14 Chemical Kinetics 14.1 Factors that Affect Reaction Rates 14.2 Reaction Rates Changes of Rate with Time Reaction Rates and Stoichiometry 14.3 Concentration and Rate Exponents in the Rate Law Units of Rate Constants Using Initial Rates to Determine Rate Laws 14.4 The Change of Concentration with Time First-Order Reactions Second-Order Reactions Half-Life 14.5 Temperature and Rate 14.5 Reaction Mechanisms 14.7 Catalysis Following the Progress of the Reaction A B 4 C 4 H 9 Cl( aq ) + H 2 O ( l ) C 4 H 9 OH ( aq ) + HCl ( aq ) t OH H C t Cl H C Rate + = = ] [ ] [ 9 4 9 4 Note the signs! In fact, the instantaneous rate corresponds to d[A]/dt Consider the reaction 2 HI( g ) H 2 ( g ) + I 2 ( g ) Its convenient to define the rate as t I t H t HI rate + = + = = ] [ ] [ ] [ 2 1 2 2 And, in general for aA + bB cC + dD t D d t C c t B b t A a Rate = = = = ] [ 1 ] [ 1 ] [ 1 ] [ 1 Sample exercise 14.2 The decomposition of N 2 O 5 proceeds according to the equation 2 N 2 O 5 ( g ) 4 NO 2 ( g ) + O 2 ( g ) If the rate of decomposition of of N...
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week-5 - 1 Demo today ??? 2 Colloids Colloids Hydrophilic...

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