Chapter 18 - Solutions

Chapter 4, Part II: Solution ChemistryProperties of SolutionsSolventThis is the liquid that is doing the dissolvingSoluteThis is what is being dissolvedForm a homogenous mixture

Saturated vs. Unsaturated Solutions

Solubility Two liquids that dissolve in each other are said to be miscible

Immiscible liquids are insoluble in each other

Think of some examples!Immiscible vs. Miscible Solutions

Factors Affecting SolubilitySolubility increases with the increase in temperature (Easier to dissolve something when the temperature is increased) Few exceptions that occur in the reverseConcentrations of SolutionsMolarity is the concentration of moles per litersMolarity (M) = moles of solute / liters of solutionDilute solution contains a low concentration of soluteConcentrated solution contains a high concentration of solutePractice Problems: Calculate the molarity of a solution which contains 0.40 mol of C6H12O6 dissolved in 1.6 L of a solution.

What is the molarity of a solution containing 325 g of NaCl dissolved in 750. mL of solution?(1000 ml = 1L)

Making DilutionsFormula for making a dilutionC1 V1 = C2 V2(Volume must be in units of L)Stock solution is the same as the original solution.

ExampleA stock solution of HCl has a concentration of 12M. How much of the stock solution would be required to make 325 mL of a 6M solution?

stoichiometrySolutionsStoichiometry overviewRecall that in stoichiometry the mole ratio provides a necessary conversion factor:

grams (x) moles (x) moles (y) grams (y)molar mass of xmolar mass of y mole ratio from balanced equation We can do something similar with solutions:

volume (x) moles (x) moles (y) volume (y)mol/L of xmol/L of y mole ratio from balanced equation 1. If I combined 15.0 grams of calcium hydroxide with 0.075 L of 0.500 M HCl, how many grams of calcium chloride would be formed?

2. If 257.8 ml of a 0.0468 M solution of lead(II) acetate is added to 156.00 mL of a 0.095 M solution of sodium sulfide, what mass of solid lead sulfide will be formed?Practice Problems 14What Happens When a Solute Dissolves?there are attractive forces between the solute particles holding them together; likewise for the solventUpon mixing the solute with the solvent, there are attractive forces between the solute particles and the solvent moleculesif the attractions between solute and solvent are strong enough, the solute will dissolve

14Tro, Chemistry: A Molecular Approach15Table Salt Dissolving in WaterEach ion is attracted to the surrounding water molecules and pulled off and away from the crystalWhen it enters the solution, the ion is surrounded by water molecules, insulating it from other ions The result is a solution with free moving charged particles able to conduct electricity

15Tro, Chemistry: A Molecular Approach16

Electrolytes and Nonelectrolytesmaterials that dissolve in water to form a solution that will conduct electricity are called electrolytesmaterials that dissolve in water to form a solution that will not conduct electricity are called nonelectrolytes16Tro, Chemistry: A Molecular Approach17Molecular View of Electrolytes and Nonelectrolytesin order to conduct electricity, a material must have charged particles that are able to flowelectrolyte solutions all contain ions dissolved in the waterionic compounds are electrolytes because they all dissociate into their ions when they dissolvenonelectrolyte solutions contain whole molecules dissolved in the watergenerally, molecular compounds do not ionize when they dissolve in water the notable exception being molecular acids17Tro, Chemistry: A Molecular Approach18Salt vs. Sugar Dissolved in Water

ionic compounds dissociate into ions when they dissolve

molecular compounds do not dissociate when they dissolve18Tro, Chemistry: A Molecular Approach19Acidsacids are molecular compounds that ionize when they dissolve in waterthe molecules are pulled apart by their attraction for the waterwhen acids ionize, they form H+ cations and anionsthe percentage of molecules that ionize varies from one acid to anotheracids that ionize virtually 100% are called strong acidsHCl(aq) H+(aq) + Cl-(aq)acids that only ionize a small percentage are called weak acidsHF(aq) H+(aq) + F-(aq)19Tro, Chemistry: A Molecular Approach20Strong and Weak Electrolytesstrong electrolytes are materials that dissolve completely as ionsionic compounds and strong acidstheir solutions conduct electricity wellweak electrolytes are materials that dissolve mostly as molecules, but partially as ionsweak acidstheir solutions conduct electricity, but not wellwhen compounds containing a polyatomic ion dissolve, the polyatomic ion stays togetherNa2SO4(aq) 2 Na+(aq) + SO42-(aq)HC2H3O2(aq) H+(aq) + C2H3O2-(aq)

20Tro, Chemistry: A Molecular Approach21Classes of Dissolved Materials

21Tro, Chemistry: A Molecular Approach22Acid-Base Reactionsalso called neutralization reactions because the acid and base neutralize each others properties2 HNO3(aq) + Ca(OH)2(aq) Ca(NO3)2(aq) + 2 H2O(l)the net ionic equation for an acid-base reaction isH+(aq) + OH(aq) H2O(l)as long as the salt that forms is soluble in water22Tro, Chemistry: A Molecular Approach23Acids and Bases in Solutionacids ionize in water to form H+ ionsmore precisely, the H from the acid molecule is donated to a water molecule to form hydronium ion, H3O+most chemists use H+ and H3O+ interchangeablybases dissociate in water to form OH ionsbases, like NH3, that do not contain OH ions, produce OH by pulling H off water moleculesin the reaction of an acid with a base, the H+ from the acid combines with the OH from the base to make waterthe cation from the base combines with the anion from the acid to make the saltacid + base salt + water23PracticeWrite the balanced molecular and net ionic equations for the reaction between:

1. Hydrobromic Acid and Potassium Hydroxide

2. Nitric Acid and Calcium Hydroxide

****Hint: Remember what an acid-base reaction always produces!Electrolytes

Strong Acids and Strong Bases= Strong Electrolytes

Weak Acids and Weak Bases = Weak Electrolytes Tro, Chemistry: A Molecular Approach26Red-ox Reactionsother kinds of reactions involve transferring electrons from one atom to another these are called oxidation-reduction reactionsalso known as redox reactionsmany involve the reaction of a substance with O2(g)4 Fe(s) + 3 O2(g) 2 Fe2O3(s)26Tro, Chemistry: A Molecular Approach27Oxidation and Reductionatoms that lose electrons are being oxidized, atoms that gain electrons are being reduced2 Na(s) + Cl2(g) 2 Na+Cl(s)2Na 2Na+ + 2e oxidationCl2 + 2 e 2 ClreductionLeo

Ger27Tro, Chemistry: A Molecular Approach28Electron Bookkeepingfor reactions that are not metal + nonmetal, or do not involve O2, we need a method for determining how the electrons are transferredchemists assign a number to each element in a reaction called an oxidation state that allows them to determine the electron flow in the reactioneven though they look like them, oxidation states are not ion charges!oxidation states are imaginary charges assigned based on a set of rules ion charges are real, measurable charges28Tro, Chemistry: A Molecular Approach29Rules for Assigning Oxidation Statesrules are in order of priorityfree elements have an oxidation state = 0Na = 0 and Cl2 = 0 in 2 Na(s) + Cl2(g)monatomic ions have an oxidation state equal to their chargeNa = +1 and Cl = -1 in NaCl (a) the sum of the oxidation states of all the atoms in a compound is 0Na = +1 and Cl = -1 in NaCl, (+1) + (-1) = 029Tro, Chemistry: A Molecular Approach30Rules for Assigning Oxidation States(b) the sum of the oxidation states of all the atoms in a polyatomic ion equals the charge on the ionN = +5 and O = -2 in NO3, (+5) + 3(-2) = -1(a) Group I metals have an oxidation state of +1 in all their compoundsNa = +1 in NaCl

(b) Group II metals have an oxidation state of +2 in all their compoundsMg = +2 in MgCl2

30Tro, Chemistry: A Molecular Approach31Rules for Assigning Oxidation Statesin their compounds, nonmetals have oxidation states according to the table belownonmetals higher on the table take priority

NonmetalOxidation StateExampleF-1CF4H+1CH4O-2CO2Group 7A-1CCl4Group 6A-2CS2Group 5A-3NH331Tro, Chemistry: A Molecular Approach32Practice Assign an Oxidation State to Each Element in the followingBr2K+LiFCO2SO42-Na2O232Tro, Chemistry: A Molecular Approach33Practice Assign an Oxidation State to Each Element in the followingBr2 Br = 0, (Rule 1)K+K = +1, (Rule 2)LiFLi = +1, (Rule 4a) & F = -1, (Rule 5)CO2O = -2, (Rule 5) & C = +4, (Rule 3a)SO42- O = -2, (Rule 5) & S = +6, (Rule 3b)Na2O2 Na = +1, (Rule 4a) & O = -1, (Rule 3a)33Tro, Chemistry: A Molecular Approach34Oxidation and ReductionAnother Definitionoxidation occurs when an atoms oxidation state increases during a reactionreduction occurs when an atoms oxidation state decreases during a reactionCH4 + 2 O2 CO2 + 2 H2O-4 +1 0 +4 2 +1 -2oxidationreduction34Tro, Chemistry: A Molecular Approach35OxidationReductionoxidation and reduction must occur simultaneously if an atom loses electrons another atom must take them the reactant that reduces an element in another reactant is called the reducing agentthe reducing agent contains the element that is oxidizedthe reactant that oxidizes an element in another reactant is called the oxidizing agentthe oxidizing agent contains the element that is reduced

2 Na(s) + Cl2(g) 2 Na+Cl(s)Na is oxidized, Cl is reducedNa is the reducing agent, Cl2 is the oxidizing agent35Tro, Chemistry: A Molecular Approach36Identify the Oxidizing and Reducing Agents in Each of the Following3 H2S + 2 NO3 + 2 H+ 3 S + 2 NO + 4 H2OMnO2 + 4 HBr MnBr2 + Br2 + 2 H2O36