Solutions Are Homogeneous Mixtures

Chpt 14 Notes:

Solutions

•Solutions are homogeneous mixtures

•Solute is the dissolved substance

–Seems to “disappear” or “Takes on the state” of the solvent

•Solvent is the substance the solute dissolves in

–Does not appear to change state

–When both solute and solvent have the same state, the solvent is the component present in the highest percentage

•Solutions in which the solvent is water are called aqueous solutions

–Water is often called the universal solvent

•Solutions that contain metal solutes and solvent are called alloys

The Solution Process - Ionic Compounds

•When ionic compounds dissolve in water they dissociate into ions

–ions become surrounded by water molecules - hydrated

•When solute particles are surrounded by solvent molecules we say they are solvated

The Solution Process- Covalent Molecules

•Covalent molecules that are small and have “polar” groups tend to be soluble in water

•The ability to H-bond with water enhances solubility

Solubility

•When one substance (solute) dissolves in another (solvent) it is said to be soluble

–Salt is soluble in Water,

–Bromine is soluble in methylene chloride

•When one substance does not dissolve in another they are said to be insoluble

–Oil is insoluble in Water

•There is usually a limit to the solubility of one substance in another

–Gases are always soluble in each other

–Some liquids are always mutually soluble

Solutions & Solubility

•Molecules that are similar in structure tend to form solutions

–Like dissolves like

•The solubility of the solute in the solvent depends on the temperature

–Higher Temp = Larger solubility of solid in liquid

–Lower Temp =Larger solubility of gas in liquid

•The solubility of gases depends on the pressure

–Higher pressure = Larger solubility

Describing Solutions - Qualitatively

•A concentrated solution has a high proportion of solute to solution

•A dilute solution has a low proportion of solute to solution

•A saturated solution has the maximum amount of solute that will dissolve in the solvent

–Depends on temp

•An unsaturated solution has less than the saturation limit

•A supersaturated solution has more than the saturation limit

–Unstable

Describing Solutions Quantitatively

•Solutions have variable composition

•To describe a solution accurately, you need to describe the components and their relative amounts

•Concentration = amount of solute in a given amount of solution

–Occasionally amount of solvent

Solution Concentration-Percentage

•Parts Per Hundred

•% = grams of solute per 100 g of solution

–Mass Percent or Percent by Mass

–5.0% NaCl has 5.0 g of NaCl in every 100 g of solution

•Mass of Solution = Mass of Solute + Mass of Solvent

•Divide the mass of solute by the mass of solution and multiply by 100%

Solution Concentration-Molarity

•moles of solute per 1 liter of solution

•used because it describes how many molecules of solute in each liter of solution

•If a sugar solution concentration is 2.0 M , 1 liter of solution contains 2.0 moles of sugar, 2 liters = 4.0 moles sugar, 0.5 liters = 1.0 mole sugar, etc.

•Molarity = Moles of Solute/ Liters of Solution

Molarity & Dissociation

•the molarity of the ionic compound allows you to determine the molarity of the dissolved ions

•CaCl2(aq) = Ca+2(aq) + 2 Cl-1(aq)

•A 1.0 M CaCl2(aq) solution contains 1.0 moles of CaCl2 in each liter of solution

–1 L = 1.0 moles CaCl2, 2 L = 2.0 moles CaCl2, 0.5 L = 0.5 moles CaCl2

•Because each CaCl2 dissociates to one Ca+2, 1.0 M CaCl2 = 1.0 M Ca+2

–1 L = 1.0 moles Ca+2, 2 L = 2.0 moles Ca+2, 0.5 L = 0.5 moles Ca+2

•Because each CaCl2 dissociates to 2 Cl-1, 1.0 M CaCl2 = 2.0 M Cl-1

–1 L = 2.0 moles Cl-1, 2 L = 4.0 moles Cl-1, 0.5 L = 1.0 moles Cl-1

Dilution

•Dilution is adding solvent to decrease the concentration of a solution

•The amount of solute stays the same, but the concentration decreases

•Dilution Formula

M1 x V1 = M2x V2

•Concentrations and Volumes can be most units as long as consistent

Solution Stoichiometry

•Many reactions occur in solution, therefore you need to be able to predict amounts of reactants and products in terms of concentrations and volumes as well as masses

•Basic strategy is the same

¬Balance the Equation

¬Change Given Amounts to Moles

¬Determine Limiting Reactant

¬Calculate Moles of Required Substance

¬Convert Moles of the Required Substance into the Desired Unit

Molarity problems