Solutions Ch. 11

Solution: Dissolved: Concentration: A solute dissolved in a solvent A homogeneous mixture Dissolved: Broken apart into base particles (ions or molecules) Concentration: The density of dissolved solute in the solvent

Simulation / Animation

Dissociation Reactions communicate the process using symbols NaCl  Na + Cl CaCl2  Ca + 2 Cl CuSO4  Cu + SO4 NH3  NH3 CO2  CO2 Cu(NO3)2  Cu + 2 NO3

Like Dissolves Like Most solutions we discuss and encounter are aqueous (water solvent) Water is polar so it dissolves polar or ionic substances (dipole-dipole or ion-dipole forces in the solution) Oil is nonpolar so it dissolves nonpolar substances (dispersion forces) Dipole-dipole forces will not be broken in order to be replaced by dipole-induced dipole forces or dispersion forces Dispersion forces can not break dipole-dipole forces

Like Dissolves Like Hydrophilic Hydrophobic Hydro = water Philia = love Hydrophilic = love for water Hydrophobic Phobia = fear Hydrophobic = fear of water Molecules with both a hydrophobic and hydrophilic end Soap Cell membranes

Energy Lattice Energy: Enthalpy of Hydration: Enthalpy of Solution: Formula:

Energy: Review Calorimetry System vs surroundings

Electrolytes Conduct electricity when dissolved in water Electricity is due to mobile charges Dissolved ionic compounds contain mobile charges and are therefore electrolytes Higher concentration of ions = stronger electrolyte

Concentration: density of solute in solvent or solution Molarity = moles solute / Liters solution Molality = moles solute / kg solvent Mole fraction = moles solute / moles solution % by mass = grams solute / grams solution G solute / 100 g H2O (self explanatory) ppm = ? Grams solute / 1,000,000 g solution (parts per million) ppb = ? Grams solute / 1,000,000,000 g solution (parts per billion)

Concentration of ions in solution: CaCl2(s)  Ca2+(aq) + 2 Cl-(aq) If you have a 1.0 M solution of CaCl2, Then you have a 1.0 M solution of Ca2+ ions And you have a 2.0 M solution of Cl- ions And you have a 3.0 M solution of total ions.

Concentration of ions: CaCl2 is a stronger electrolyte than NaCl Because it produces more ions Therefore, if you have equal concentrations of CaCl2 and NaCl, CaCl2 solution will have greater conductivity than NaCl. However, 0.05 M CaCl2 will have less conductivity than 2.0 M NaCl. Why?

Dilutions Dilution: If solute isn’t changed molesi = molesf Since moles = (molarity)(Liters) MolarityiLitersi = MolarityfLitersf

Types of solutions Typical solutions: solid dissolved in liquid But all phases can be solute or solvent.

Solubility Solubility = maximum possible concentration of dissolved particles Saturated Solution: Concentration = solubility Unsaturated Solution: Concentration < solubility Supersaturated Solution: Concentration > solubility How does this occur?

Solubility Solubility = maximum possible concentration of dissolved particles Solubility of a solid-liquid solution is typically increased with increased temperature. Why? Solubility of a gas-liquid solution is typically decreased with increase temperature. Why? Solubility of a gas-liquid solution is typically increased with increased pressure. Why?

Density is based on concentration. Density is also based on temperature. Hotter liquids spread out and therefore have greater volume with equal mass (lower density) D = m / v Concentration could also change with temperature: Any conc calculated using volume is temperature dependent. Any conc calculated using only masses / # particles is not temperature dependent.

Colligative Properties Anything that depends on the number of dissolved particles.

Colligative Properties Solution’s boiling point increases with greater concentration of particles. Solution’s melting point decreases with greater concentration of particles. Solutions remain liquid through a greater range of temperatures with greater concentration of particles.

Colligative Properties

Colligative Properties: Melting Point

Colligative Properties: Melting Point & Boiling Point

Colligative Properties: Melting Point & Boiling Point

Colligative Properties

Colligative Properties: Vapor Pressure A nonvolitile Liquid lowers the vapor pressure of a solvent. Vapor Pressure: pressure over a liquid at gas-liquid phase equilibrium More solute  less vapor pressure  less solvent will turn to gas Psolution = Xsolvent Psolvent

Colligative Properties: Vapor Pressure

Colligative Properties: Vapor Pressure

Colligative Properties: Vapor Pressure

Side Note: Surface area of liquid is directly proportional to the evaporation rate: Water in a wider beaker will evaporate faster than water in a narrow, tall beaker

Osmosis Osmosis: the flow of solvent through a semipermiable membrane from lower concentration to higher concentration Net Flow of solvent continues until concentration on both sides are equal Similar to heat transfer between 2 substances of different temperatures

Osmotic Pressure Excess pressure on a solution with greater volume of solvent (see Figure 11.18) By applying more pressure than the osmotic pressure to a container, you can create “reverse osmosis” Desalinization !!!