Presentation on theme: "Chapter 4 Solutions and Chemical Reactions"— Presentation transcript:
1 Chapter 4 Solutions and Chemical Reactions WaterImportanceLife (as we know it) depends on waterHuman civilization requires water for many purposesMany important chemical reactions occur in Aqueous Solutions, where other compounds are dissolved in waterThe nature of waterBent shape and unequal sharing of electrons makes water polarThis aids water in dissolving ionic compounds (cations and anions)Water hydrates the ions by interacting with its oppositely charged ends
2 NaCl(s) -----> Na+(aq) + Cl-(aq) The ionic substance breaks up into independent cations and anionsNonionic compounds can also dissolve in water if they are polarNonpolar substances generally don’t dissolve in water: grease, oils, skinElectrolytesSolutionsA solution is a homogeneous mixture the same throughoutWe can vary the composition by adding more or less of the componentsSolvent = usually a liquid; the most abundant component of a solutionSolute = the lesser abundant component(s) of a solutionEthanolNaCl(s) -----> Na+(aq) + Cl-(aq)
3 that the more ions present, the better the conductivity B. Solutions and Electrical ConductanceA substance allowing current to flow through it is electrically conductivePure water does not conduct electricityDifferent solutes dissolved in water help it to be conductiveStrong electrolyte = completely ionized; strongly conductive solutionWeak electrolyte = partially ionized; somewhat conductive solutionNonelectrolyte = not ionized; nonconductive solutionArrhenius ( ) foundthat the more ions present, thebetter the conductivity
4 C. Strong ElectrolytesCompletely ionized when dissolved in waterMany salts (ionic compounds) are strong electrolytesStrong Acids are strong electrolytesAcid = substance that produces H+ when dissolved in waterStrong Acids completely ionize in solutionHydrochloric Acid HCl(g) > H+(aq) Cl-(aq)Nitric Acid HNO3(g) > H+(aq) NO3-(aq)Sulfuric Acid H2SO4(l) > H+(aq) HSO4-(aq)Strong Bases are strong electrolytesBase = substance that produces OH- when dissolved in waterStrong bases completely ionize in solutionNaOH(s) > Na+(aq) + OH-(aq) KOH(s) > K+(aq) + OH-(aq)
5 D. Weak ElectrolytesOnly partially ionized when dissolved in waterWeak Acids are weak electrolytesWeak acid only produces a few H+ ionsAcetic acid is a weak acidHC2H3O2(aq) > H+(aq) C2H3O2(aq)Only 1 molecule in a 100 dissociatesWeak Bases are weak electrolytesWeak base produces only a few OH- ionsAmmonia is a weak baseNH3(aq) + H2O(l) > NH4+(aq) + OH-(aq)Only 1 molecule in 100 reactsNonelectrolytesDoes not ionize when dissolve in waterSugar is a nonelectrolyteC12H22O11(s) > C12H22O11(aq)
6 III. Solution Concentration The Stoichiometry of Chemical ReactionsWe must know what the reactants and products areWe must know the amounts of the reactants and productsHow do we describe the amounts in a solution?MolarityUnit for the concentration of a solute in a solutionM = moles solute/liters of solution1.0 M NaCl = 1 mole of NaCl dissolved in 1 L of solutionAny volume having the same concentration is also 1.0 M NaCl500 ml (0.500 L) of 1.0 M NaCl would contain 0.5 mol NaClExample: Calculate M of 11.5 g NaOH in 1.5 L of total solution.
7 5. Example: M = ? for 1.56 g HCl in a total of 26.8 ml of solution? 6. Molarity descriptions of a solution reflect composition before dissolution1.0 M NaCl actually contains no NaCl1.0 M NaCl is 1.0 M in Na+ and 1.0 M in Cl-1.0 M CaCl2 is 1.0 M in Ca2+ and 2.0 M in Cl-CaCl2(s) > Ca2+(aq) Cl-(aq)7. Example: Give the concentration of each ion0.5 M Co(NO3)2 = 0.5M in Co2+ and 1.0 M in NO3-Co(NO3)2 (s) > Co2+(aq) NO3-(aq)1M Fe(ClO4)3 = 1M Fe3+ and 3M ClO4-8. Example: ??? moles of Cl- in 1.75L of M ZnCl2
8 9. Example: What volume of 0.14 M NaCl contains 1.0mg NaCl? 10. Standard Solution = concentration is accurately knownAccurate masses come from an analytical balance (0.4563g)Accurate volumes are obtained using a Volumetric FlaskExample: How much K2Cr2O7 needed for 1.00 L of M?
9 DilutionChemicals are often purchased or prepared as concentrated stock solutionsDilution = adding water to stock solution to make a less concentrated oneM1V1 = M2V2 is a useful equation to calculate dilutionsExample: ??? volume of 16 M H2SO4 is needed for 1.5 L 0.10M H2SO4
10 IV. Precipitation Reactions DefinitionsWhen two solutions are mixed and a solid formsPrecipitate = solid that forms from a precipitation reactionK2CrO4(aq) + Ba(NO3)2(aq) = 2K+(aq) + CrO42-(aq) + Ba2+(aq) +2NO3-(aq)K2CrO4 and Ba(NO3)2 are both soluble (all dissolve in water)A yellow precipitate forms when these solutions are mixedK2CrO4(aq) + Ba(NO3)2(aq) > BaCrO4(s) + 2KNO3(aq)AgNO3(aq) + KCl(aq) > AgCl(s) + KNO3(aq)+=Precipitate Spectator Ions
11 B. Solubility RulesExample: predict what will happen when you mix:KNO3(aq) + BaCl2(aq) >Na2SO4(aq) + Pb(NO3)2(aq) >3KOH(aq) + Fe(NO3)2(aq) >
12 Describing Reactions in Solution Molecular Equation shows what compounds the ions came fromDoes not give clear picture of what happens in solutionK2CrO4(aq) + Ba(NO3)2(aq) > BaCrO4(s) + 2KNO3(aq)Complete Ionic Equation represents the form of the ions in solutionAll strong electrolytes are represented as their ions2K+(aq) + CrO42-(aq) + Ba2+(aq) +2NO3-(aq) ----> BaCrO4(s) + 2K+(aq) + 2NO3-(aq)Net Ionic Equation shows only the ions participating in the reactionThe K+ and NO3- ions occur on both sides of the complete ionic eqn.These spectator ions can be cancelled out of each side (algebra)Ba2+(aq) CrO42-(aq) > BaCrO4(s)Example3KOH(aq) + Fe(NO3)3(aq) > Fe(OH)3(s) + 3KNO3(aq)b. 3K+(aq) + 3OH-(aq) + Fe3+(aq) + 3NO3-(aq) ----> Fe(OH)3(s) + 3K+(aq) + 3NO3-(aq)c. Fe3+(aq) + 3OH-(aq) > Fe(OH)3(s)