6.01 Solutions. The Chemistry of Matter in Water. Dr. Fred Omega Garces. Chemistry 111, Miramar College. 1 Solutions. January 10

Transcription

1 6.01 Solutions The Chemistry of Matter in Water Dr. Fred Omega Garces Chemistry 111, Miramar College 1 Solutions

2 6.01 Solutions ow water Dissolves Salts 2 Solutions

3 Components of Solution omogeneous systems : Solutions Solution - omogeneous mixture of two or more substances Components of solution Solute - Substance being dissolve Solvent - Substance in which solute is dissolved in. If solvent is water, then solution is considered Aqueous. 3 Solutions

4 9 Types of Solution (derived from 3 phases) Solute Solvent Solution Gas in a gas Air Gas in a liquid carbonated water Gas in a solid whipped cream, foam Liquid in a gas fog Liquid in a liquid wine. Solid in a solid 14 karat gold Solid in a liquid salt water. 4 Solutions

5 Properties of Solution Characteristics: Distribution of particles is uniform Components in solution do not separate upon standing Components cannot be separated by filtration. Solute / Solvent mixes in ratios - up to the solubility limit. Solution is almost always transparent. Compounds of solution may be separated by other methods i.e., distillation or chromatography. 5 Solutions

6 Properties of Solution Characteristics: Distribution of particles is uniform Components in solution do not separate upon standing Components cannot be separated by filtration. Solute / Solvent mixes in ratios - up to the solubility limit. Solution is almost always transparent. Compounds of solution may be separated by other methods i.e., distillation or chromatography. 6 Solutions

7 Suspended in Solution: Dissolution Solubility - The process in which substances dissolves at the molecular level. Solubility - The maximum amount of that solute that dissolves in a given amount of solvent in a given temperature. Unsaturated Saturated SuperSaturated A solution that has the capacity to dissolve solute A solution that contains all solute it can dissolve (There are no residue) A solution that contains more solute (in dissolved form) than normal Miscible When two liquids are soluble in each other Immiscible When two liquids are not soluble in each other. 7 Solutions

8 Suspended in Solution: Dissolution Supersaturated Solution. SuperSaturated A solution that contains more solute (in dissolved form) than normal 8 Solutions

9 Nature of Solute and Solvent Dissolving Process: Why does water not mix with oil? Yet water mixes with alcohol. An oil layer floating on water. For a Solubility Factor: Solute and Solvent characteristic: In aqueous solution, water as the solvent will dissolve only other polar molecules Oil is a nonpolar substance which will only dissolve other nonpolar substances such as organic solvents. The result is the immisciblity of the two liquid. Like Dissolves Like substance to dissolve, the water-water hydrogen bonds must be broken to make a hole for each solute particle. owever, the water-water interactions will break only if they are replaced by similar strong interactions with the solute. 9 Solutions

10 Nature of Solute and Solvent Dissolving Process: Why does water not mix with oil? Yet water mixes with alcohol. An oil layer floating on water. For a Solubility Factor: Solute and Solvent characteristic: In aqueous solution, water as the solvent will dissolve only other polar molecules Oil is a nonpolar substance which will only dissolve other nonpolar substances such as organic solvents. The result is the immisciblity of the two liquid. Like Dissolves Like substance to dissolve, the water-water hydrogen bonds must be broken to make a hole for each solute particle. owever, the water-water interactions will break only if they are replaced by similar strong interactions with the solute Solutions

11 Dissolution of Solid Solute What is the driving force which cause solutes to dissolve to form solutions? Ionic versus covalent solute 1. Ion solutes dissolve by dissociation into their ions. 2. Covalent solutes dissolve by -bonding to water or by LDF Picture of NaCl and Ethanol dissolving 11 Solutions

12 Dissolving at the molecular Level Ionic substances NaCl, MgCl 2, AgCl The salt; NaCl and ionic compound (3D lattice) O O - δ+ δ+ δ δ+ δ+ + δ δ δ δ+ δ+ δ+ δ+ The Na+ and Cl- are arranged in 3 D alternating lattice The positive Cl- attracts the (δ+) of hydrogen in 2 O while the negative Na+ attracts the (δ -) of oxygen in 2 O. This occurs because opposite attracts. The solvent ( 2 O) interaction to the ion is called ydration. 2 O literally pulls the lattice arrangement of the solid salt apart because of the attraction of the d+ or d- of water for the - or + ions. Competing factors are: 1) M + & X - (i.e., Na + and Cl - ) 2) M + for δ - oxygen of 2 O & X - for δ + hydrogen of 2 O. If (1) is favorable (lattice energy) then solute does not dissolve (insoluble) AgCl if (2) is favorable then hydration, solute does dissolve (soluble). NaCl 12 Solutions

13 Equilibrium: Dissolution = Crystallization Observe: After some time, no change in amount of solid precipitate at the bottom of the beaker. Concentration of the solution is maintained At the molecular level: Amount of salt dissolving into solution equals to amount of salt recrystallize out of solution. [Solute] D [Solute] Solid Solution 13 Solutions

14 Dynamic Equilibrium Equilibrium Situation in which changes occur at equal rates so no net change is apparent. LeChatelier Principle A change (stress) on a system at equilibrium will cause the system to self adjust to reduce the stress until a new equilibrium is reestablish. Example: Traffic at a toll bridge Vapor Pressure Sugar dissolving 14 Solutions

15 Ionic Vs Covalent Compounds: Electrolyte Vs. Nonelectrolyte Substance when dissolve can break-up to ions (NaCl) or stay intact (sugar). Type: % ionization: Solubility Electrolyte: conducts electricity. Strong electrolyte 100 % ionization very soluble weak electrolyte less 100% ionization slightly soluble zero ionization insoluble ionic or covalent. Nonelectrolyte: no conduction 15 Solutions

16 Factors Affecting Solubility Nature of Solute / Solvent. - Like dissolves like (IMF) Temperature Factor - i) Solids/Liquids- Solubility increases with Temperature Increase K.E. increases motion and collision between solute / solvent. ii) gas - Solubility decreases with Temperature Increase K.E. result in gas escaping to atmosphere. Pressure Factor - i) Solids/Liquids - Very little effect Solids and Liquids are already close together, extra pressure will not increase solubility. ii) gas - Solubility increases with Pressure. Increase pressure squeezes gas solute into solvent. 16 Solutions

17 Principles of Solubility omogeneous systems: Solutions Solution - omogeneous mixture of two or more substances Components of solution Solute - Substance being dissolve Solvent - Substance in which solute is dissolved in. If solvent is water, then solution is considered aqueous. 17 Solutions

18 Solution Composition omogeneous systems: Solutions Solution - omogeneous mixture of two or more substances Components of solution Solute- Substance being dissolve Solvent-Substance which dissolves solute. If solvent is water, then solution is considered aqueous. 18 Solutions

19 Solution concentration Concentration- Amount of solute in given amount of solvent. Most common type: Molarity Molarity - moles solute / Liter solution ow many moles in 16.0 g CuSO 4 (MW = g/mol)? If this amount of CuSO 4 is dissolved in 0.100L of water what is the Molarity of the solution (mol / L)? To make a 1.00-M solution ofcuso 4, 16.0 g, or mol, of CuSO 4 (the blue crystalline solid) is placed in a 100-mL volumetric flask. Exactly 100 ml of water is measured out and slowly added to the volumetric flask. When enough water had been added so that the solution volume is exactly 100 ml. The emphasizes here is that molar concentrations is defined as moles per liter of solution and not per liter of water or other solvent. 19 Solutions

20 Solution and Concentration 5 ways of expressing concentration- Molarity(M) - moles solute / Liter solution Mass percent (% m)- (grams solute/total grams of solution)*100 Molality * (m) - moles solute / Kg solvent Normality(N) - Number of equivalent / Liter solution mole fraction( χ A) - moles solute / Total moles solution But learn the main two * Note that molality is the only concentration unit in which denominator contains only solvent information rather than solution. 20 Solutions

21 Solution at a Glance Solutions can be describe by the following: Solvent The component of a solution present in the greatest quantity Solute The component of solution present in the lesser quantity Solution A homogeneous mixture of two or more substances in which each substance retains its chemical identity Concentration of a Solution The amount of solute in a specific amount of solution. Molarity (M) moles of solute Liters of solution 21 Solutions