Solutions Solutions are homogeneous mixtures of two or more pure - PDF document

Slide 1 / 101 Slide 2 / 101 Solutions · Solutions are homogeneous mixtures of two or more pure substances. · In a solution, the solute is dispersed uniformly throughout the solvent. Properties of Solutions State of Solution State of Solvent State of Solute Example Gas Gas Gas Air Liquid Liquid Gas Oxygen in water Liquid Liquid Liquid Alcohol in water Liquid Liquid Solid Salt in water Solid Solid Gas H2 in Palladium Solid Solid Liquid Hg in Silver Slide 3 / 101 Slide 4 / 101 How Does a Solution Form? Solutions As a solution forms, the solvent pulls solute particles apart and surrounds, or solvates, them. The intermolecular forces between solute and solvent - + particles must be strong solute enough to compete with - + those between solute + particles and those between solvent solvent particles. The solute is added to the solvent The negative ions are pulled away by the positive pole of the solvent molecule The positive ions are pulled away by the negative pole of the solvent molecule Slide 5 / 101 Slide 6 / 101 How Does a Solution Form? 1 The process of solute particles being surrounded by solvent particles is known as _____. A salutation If an ionic salt is soluble in water, it is because the ion- B agglomeration dipole interactions are strong C solvation enough to overcome the lattice D agglutination energy of the salt crystal. E dehydration

Slide 7 / 101 Slide 8 / 101 Energy Changes in Solution Energy Changes in Solution Three processes affect the energetics of solution: D H1- Separation of solute molecules The enthalpy change of · separation of solute the overall process particles, depends on ΔH for each of these steps. · separation of solvent D H 2 - Separation of solvent molecules particles, · new interactions between solute and + solvent. D H 3 - Formation of solute-solvent interactions Slide 9 / 101 Slide 10 / 101 Solution Formation Energy Changes in Solution Chemical reactions, as well as solution formation, will occur spontaneously as long as the change in Gibbs Free Energy is negative. Just because a substance disappears when it comes When an overall process is in contact with a solvent, it doesn’t mean the endothermic, the increase substance dissolved. in enthalpy is offset by an increase in entropy. Dissolution is a physical change — you can get back the original solute by evaporating the solvent. If you can’t recover the original solute, then the substance didn’t dissolve; it reacted. Slide 11 / 101 Slide 12 / 101 Unsaturated Solutions Saturated Solutions An unsaturated solution contains less than the maximum amount of solute that can be dissolved in In a saturated solution, the the solvent (at a given temperature). solvent holds as much solute as is possible at that temperature. Dissolved solute is in dynamic equilibrium with solid solute particles. Solid solute is not in dynamic equilibrium with dissolved solute.

Slide 13 / 101 Slide 14 / 101 Supersaturated Solutions Rapid Crystallization (Supersaturated Solution Demo) - Video In supersaturated solutions, the solvent holds more solute than is normally possible at that temperature. These solutions are unstable; crystallization can usually be stimulated by adding a “seed crystal” or scratching the side of the flask. Slide 15 / 101 Slide 16 / 101 2 A saturated solution ________. 3 An unsaturated solution is one that ______. A contains as much solvent as it can hold A has no double bonds B contains no double bonds contains the maximum concentration B of solute possible, and is in contains dissolved solute in C equilibrium with undissolved solute equilibrium with undissolved solute has a concentration lower than the will rapidly precipitate if a seed crystal C D solubility is added contains more dissolved solute than E cannot be attained D the solubility allows E contains no solute Slide 17 / 101 Slide 18 / 101 4 A solution with a 5 A supersaturated concentration higher than the solution _________. solubility is _____. A is one with more than one solute A is not possible B is one that has been heated B is unsaturated is one with a higher concentration C C is supercritical than the solubility D is saturated must be in contact with undissolved D solid E is supersaturated exists only in theory and cannot E actually be prepared

Slide 19 / 101 Slide 20 / 101 Factors Affecting Solubility Factors Affecting Solubility Chemists use the axiom “like dissolves like." Temperature and Solubility · Polar ionic substances and tend to dissolve in polar solvents. · Nonpolar substances tend to dissolve in nonpolar solvents. Alcohol Solubity Solubility Generally, the solubility in water in hexane of solid solutes in liquid CH3OH ∞ 0.12 methanol solvents increases with CH3CH2OH ∞ ∞ increasing temperature. ethanol CH3CH2CH2OH ∞ ∞ propanol CH3CH2CH2CH2OH 0.11 ∞ butanol CH3CH2CH2CH2CH2OH 0.030 ∞ pentanol CH3CH2CH2CH2CH2CH2OH 0.0058 ∞ hexanol Slide 21 / 101 Slide 22 / 101 Factors Affecting Solubility Factors Affecting Solubility The more similar the intermolecular attractions, the more likely one substance is to be soluble in another. Vitamin A has a large non-polar portion consisting of C-C and C-H bonds. Because of this long hydrophobic "tail", Glucose (which has hydrogen bonding) is very soluble in water, Vitamin A is soluble in nonpolar compounds (like fats). while cyclobutane (which only has dispersion forces) is not. Hydrogen Vitamin A bonding sites In contrast, Vitamin C is Cyclobutane-has soluble in water due to its Glucose- has no polar OH groups ability to form several hydrogen hydroxyl groups and is essentially bonds. and is highly insoluble in water soluble in water Vitamin C Slide 23 / 101 Slide 24 / 101 6 The phrase "like dissolves 7 Which one of the following like" refers to the fact that is most soluble in water? _________. A CH 3 OH A gases can only dissolve other gases B CH 3 CH 2 CH 2 OH polar solvents dissolve polar solutes; B nonpolar solvents dissolve nonpolar C CH 3 CH 2 OH solutes D CH 3 CH 2 CH 2 CH 2 OH solvents can only dissolve solutes of C similar molar mass E CH 3 CH 2 CH 2 CH 2 CH 2 OH condensed phases can only dissolve D other condensed phases polar solvents dissolve nonpolar E solutes and vice versa

Slide 25 / 101 Slide 26 / 101 8 Which one of the following 9 Which of the following is most soluble in hexane substances is more likely (C 6 H 14 )? to dissolve in CH 3 OH? A CH 3 OH A CCl 4 B CH 3 CH 2 CH 2 OH B Kr C CH 3 CH 2 OH C N 2 D CH 3 CH 2 CH 2 CH 2 OH D CH 3 CH 2 OH E CH 3 CH 2 CH 2 CH 2 CH 2 OH E H 2 Slide 27 / 101 Slide 28 / 101 Which one of the following 11 10 Which of the following substances is more likely substances is more likely to dissolve in CCl 4 ? to dissolve in water? A CBr 4 A HOCH 2 CH 2 OH HBr B B CHCl 3 C HCl C CH 3 (CH 2 ) 9 HC O D CH 3 CH 2 OH D CH 3 (CH 2 ) 8 CH 2 OH E NaCl E CCl 4 Slide 29 / 101 Slide 30 / 101 Temperature Temperature The opposite is true of gases: as the solvent temperature Generally, the solubility increases, gases are usually of solid solutes in liquid LESS soluble. solvents increases with increasing temperature. · Carbonated soft drinks are more “bubbly” if stored in the refrigerator. · Warm lakes have less O 2 dissolved in them than cool lakes.

Slide 31 / 101 Slide 32 / 101 Gases in Solution Gases in Solution · In general, the solubility · The solubility of liquids and of gases in water solids does not change increases with increasing appreciably with pressure. mass. · The solubility of a gas in a · Larger molecules have liquid is directly proportional stronger dispersion forces. to its pressure. Slide 33 / 101 Slide 34 / 101 Henry’s Law HenrysLawMovie.MOV S g = kP g where · S g is the solubility of the gas, · k is the Henry’s Law constant for that gas in that solvent, and · P g is the partial pressure of the gas above the liquid. Slide 35 / 101 Slide 36 / 101 13 Increasing the pressure on 12 Increasing the temperature a liquid _____ the solubility _____ the solubility of of solids and ______ the solids and ______ the solubility of gases in a solubility of gases in a liquid. liquid. A decreases, increases A decreases, increases B doesn't effect, increases B doesn't effect, increases C increases, decreases C increases, decreases D increases, increases D increases, increases E solids and liquids E solids and liquids