Solutions Chapters 13 and 14

Solutions are homogeneous mixture Homogeneous mixture = same composition and properties throughout Soluble = capable of being dissolved Solvent = dissolving medium Water = ‘universal solvent’ Solute = substance being dissolved

Examples of solute/solvent Sodium chloride and water Solute = sodium chloride Solvent = water Some water is in the air Solute = water Solvent = air 14 karat gold is composed of 58% gold and 42% silver Solute = silver Solvent = gold Solvent is most abundant

Dissociation Separation of ions in an ionic compound Must have polar solvent (like water) and ionic compound Hydration = solution process with water as the solvent – water molecules surround the ions and carry them off

Ionization Ions are formed from solute molecules by the action of the solvent Must have polar solvent (like water) and solute with weak bonds

Solubility - “Like dissolves like” Substances that have similar bonding, polarity, and IMF will dissolve into each other Toluene is nonpolar Water is polar have different characteristics and will NOT mix – Immiscible

More ex. of like dissolves like Toluene and gasoline are nonpolar Grease and oils are nonpolar Therefore, they will mix = Miscible (Ex Fat soluble and water soluble vitamins)

Electrolytes and Nonelectrolytes Electrolyte = conducts electricity due to mobile charges in solution Strong and weak – depends on how much they ionize or dissociate Nonelectrolytes = do not conduct electricity Neutral solute molecules (sugar dissolved in water)

Factors Affecting the Rate of Dissolution To increase the rate, increase Surface area Temperature (except for gases and some solids) Agitation

Solubility There is a limit to how much solute will dissolve in a certain amount of solvent Depends on the nature of the solvent, solute, and temperature Solution Equilibrium – processes of dissolution and recrystallization occur at the same rate

C. Solubility Solubility maximum grams of solute that will dissolve in 100 g of solvent at a given temperature varies with temp based on a saturated soln

Saturated Solution = contains maximum amount of dissolved solute Unsaturated = contains less solute than a saturated solution Supersaturated = solution that contains more dissolved solute than saturated Made by cooling a warm saturated solution, must not be disturbed

When does the solution become saturated? Look at the solubility of the substance = Amount of substance needed to make a saturated solution at a specific temperature

Solubility Curve

C. Solubility Gases are more soluble at... low temperatures & Solids are more soluble at... high temperatures. Gases are more soluble at... low temperatures & high pressures (Henry’s Law). EX: nitrogen narcosis, the “bends,” soda

C. Solubility Solubility Curve shows the dependence of solubility on temperature

Concentration of Solutions Concentration = amount of solute in a given amt of solvent Molarity = moles of solute in one liter of solution M = mol of solute L of solution Molality = moles of solute per kilogram of solvent m = mol of solute kg of solvent

Molarity Examples You have 0.8 L of a 0.5 M HCl solution. How many moles of HCl does this solution have? (answer 0.4 mol HCl) What volume of 3.00 M NaCl is needed for a reaction that requires 146.3 g of NaCl? (answer 0.834 L) 3.5 L of solution contains 90.0 g of NaCl. What is the solution’ s molarity? (0.441 M) How many grams of solute are needed to make 2.50 L of a 1.75 M solution of Ba(NO3)2? (1140 g)

Molality Examples What is the molality of a solution composed of 255 g of acetone, (CH3)2CO, dissolved in 200. g of water? (22 m) How many grams of methanol, CH3OH, are required to prepare a 0.244 solution in 400. g of water? (3.12 g) What is the molality of a solution containing 18.2 g HCl and 250. g of water? (1.99 m)

Dilutions MdiluteVdilute = MconcentratedVconcentrated Example How can 100 mL of 0.04 M K2Cr2O7 be prepared from 0.2 M K2Cr2O7?