Solutions Chm 3.2

Solutions Solute – substance dissolving Solute – substance dissolving Solvent – substance solute is dissolved in Solvent – substance solute is dissolved in –(substance you have in greatest amount) Solution – solvent + solute Solution – solvent + solute

Types of Solutions Solids – alloys (metal mixtures) Solids – alloys (metal mixtures) Liquids – sugar or salt in water Liquids – sugar or salt in water Gases – air Gases – air Suspensions – solute particles so large they settle out (muddy water) Suspensions – solute particles so large they settle out (muddy water) Colloids – solute particles are sized in-between solution and suspension Colloids – solute particles are sized in-between solution and suspension Homogeneous - solutions Homogeneous - solutions Heterogeneous – colloids, suspensions Heterogeneous – colloids, suspensions

Electrolyte vs Non-electrolyte Electrolyte – substance that dissolves to form a solution that conducts electricity Electrolyte – substance that dissolves to form a solution that conducts electricity Non-electrolyte – substance that dissolves to form a solution that DOES NOT conduct electricity Non-electrolyte – substance that dissolves to form a solution that DOES NOT conduct electricity

Factors affecting Rate of Dissociation Rate depends on Solute/Solvent Interactions or Attraction Rate depends on Solute/Solvent Interactions or Attraction –Increasing Surface Area –Agitating a Solution –Heating (more KE = more collisions)

Solubility Solubility has a limit Solubility has a limit Solution equilibrium – opposing processes of dissolution and crystallization occuring at equal rates Solution equilibrium – opposing processes of dissolution and crystallization occuring at equal rates Saturated Solution – contains the max amount of solute Saturated Solution – contains the max amount of solute Unsaturated Solution – contains less solute than a saturated solution Unsaturated Solution – contains less solute than a saturated solution Supersaturated Solution – more dissolved solute than a saturated solution under the same conditions Supersaturated Solution – more dissolved solute than a saturated solution under the same conditions

Measuring Solubility The amount of substance required to form a saturated solution with a specific amount of solvent at a specific temperature The amount of substance required to form a saturated solution with a specific amount of solvent at a specific temperature Solubility varies with temperature Solubility varies with temperature Rate of a solid dissolving is not related to solubility Rate of a solid dissolving is not related to solubility

Dissolving Ionic Compounds in Water (Hydration) Polar water attracts + and – ions Polar water attracts + and – ions Water molecules surround ions Water molecules surround ions Ions are drawn away from surface of the crystal Ions are drawn away from surface of the crystal Hydrates Hydrates –Some ionic compounds will re-crystallize with water molecules attached CuSO 4 · 5H 2 O

Like Dissolves Like Polar dissolves in polar Polar dissolves in polar Non-polar DOES NOT dissolve in polar Non-polar DOES NOT dissolve in polar Immiscible – Immiscible – –Liquid solvents and solute that are not soluble Miscible – Miscible – –Liquids that dissolve freely in eachother

Gas Solubility Pressure Pressure –Increasing pressure = stress on EQ –More molecules collide with surface of liquid –EQ shifts so fewer molecules are in gas phase –Increases solubility –Henry’s Law – solubility of gas is directly proportional to pressure of the gas on surface of liquid

Temperature and Solubility Gas Solubility in Liquids Gas Solubility in Liquids –Increase temperature = less gas dissolved Solid Solubility in Liquids Solid Solubility in Liquids –Increasing temperature increases solubility in SOME cases

Concentration of Solutions Molarity Molarity moles of solute per liter of solution moles of solute per liter of solution n L M =

Molarity Examples 1. You have 3.50L of solution that contains 90.0g of sodium chloride. What is the molarity of the solution? 2. You have 0.8 L of a 0.5 M HCl solution. How many moles of HCl does this solution contain? 3. What volume of a 6.0M potassium chromate solution is needed to ensure that 23.4g of potassium chromate are in the solution?

Dilution Diluting Diluting –Taking a solution of one concentration and adding solvent to lower the concentration M 1 V 1 = M 2 V 2 M 1 V 1 = M 2 V 2 The concentration x volume of initial solution is equal to the concentration x volume of the final solution.

Dilution water (solvent)solute concentrated, M initial diluted, M final adding water lowers the solute concentration moles of solute remain constant V initial V final moles initial = moles final M final x V final = M initial x V initial

Dilution Examples 1. What volume of a 5.0 M stock HCl solution is needed to produce 1.5L of a 2.5M HCl solution? 2. What will the new concentration be when a 0.3 M solution of NaOH is diluted from 1.0 L to 2.5 L?

Colligative Properties Properties of solutions that depend on the concentration of solute particles dissolved Properties of solutions that depend on the concentration of solute particles dissolved 1. Vapor Pressure Lowering 2. Freezing Point Depression 3. Boiling Point Elevation 4. Osmotic Pressure