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Physical Chemistry. Dónal Leech Ext 3563 Room C205, Physical Chemistry. Notes for downloading (powerpoint and word) Chemistry. Physical Sciences Sub-atomic Atoms Materials Atmosphere Stellar. - PowerPoint PPT Presentation


  • Physical ChemistryDnal Leechdonal.leech@nuigalway.ieExt 3563Room C205, Physical ChemistryNotes for downloading (powerpoint and word)

  • ChemistryBiological SciencesOrganismsOrgansTissuesCellsDNAPhysical SciencesSub-atomicAtomsMaterialsAtmosphereStellarChemistryMolecular SciencesMoleculesBondsForces

  • Physical ChemistryEstablishes and develops the principles that are used to explain and interpret the observations made in chemistry Bulk Individual RatesEquilibrium Structure Change

    Thermodynamics Chemical reactionsQuantum mechanics & spectroscopyENERGY

  • TextbookBrown, LeMay, BurstenChemistry: The Central Science, 9th or 10th Edition

    Companion Web-site

  • Aqueous ReactionsChapter 4

  • Reactions in SolutionThe most important substance on earth is water. In chemistry, water is necessary for many reactions to take place. Table salt (NaCl) when put into water dissolves into its ions, Na+ and Cl-. Water is the solvent and NaCl, is the solute.The mixture is an aqueous solution. The Water Molecule allows many substances to be dissolved in them. One side of the water molecule is negatively charged, and the other side is positively charged. Water is a polar molecule.

  • Electricity and SolutionsA useful characteristic of solutions is the ability to conduct electricity. To determine if a solution has the ability to conduct electricity, an electrical conductivity apparatus is used. An electrical conductivity apparatus is basically a battery and light bulb setup which lights up when electricity is conducted through the solution. Electrolytes are substances that produce ions upon dissolving. There are two ways to provide these mobile ions for conducting purposes. Dissociation of Ionic CompoundsIonisation of Polar Covalent Molecular Substances

  • Common Ions

  • Electrolytes1.Dissociation of Ionic Compounds:Ionic compounds are made of cations (+) and anions (-). (Note see tables 2.4 and 2.5 for formulas and charges of common ions)These ions are locked into position in their crystal structure and are not able to move around. In water, the water molecules, are attracted to the ions. The ions are said to be dissociated, and able to carry electrical particles to conduct current. K3PO4 + H2O 3K+ (aq) + PO4-3 (aq)Such substances are said to be electrolytes. Salts that are completely soluble in water are strong electrolytes. Salts that are slightly soluble are weak electrolytes at best. The strength of an electrolyte is measured by its ability to conduct electrical current. See permanganate and NaCl dissolution

  • NaCl Dissolution

  • Electrolytes 2.Ionisation of Polar Covalent Molecular SubstancesPolar molecular substances are substances whose atoms are covalently bonded. Each molecule has a net molecular dipole moment and thus a positive and a negative end. Polar water molecules can line up around polar molecule. If this dipole-dipole interaction can overcome the dissociation energy of a bond the molecule will fragment with bonding electrons going with the most electronegative atom in the broken bond, creating ions. (Electronegativity is the electron attracting ability of an atom)Such polar molecular compounds are called electrolytes. An example of a strong electrolyte is any of the strong acids, such as HBr. H-Br + H2O H3O+ (aq) + Br- (aq)

  • ElectrolytesCH3COOH + H2O H3O++CH3COO-

    Some polar molecular substances have such strong covalent bonding that water is only able to overcome these stronger dissociation energies in a portion of the molecules.

    For example,a weak acid such as ethanoic acid, CH3-COO-H, dissolves in water with only a small percentage of the molecules being ionized.Non-electrolytes are substances that do not produce ions when they dissolve. Sugar-sucroseThis results when polar molecular substances are large enough and their covalent bonding is strong enough so that water is not able to break any of the covalent bonds during the solvation process. As a result, the neutral molecules are solvated (separated by solvent water molecules) without any ionization occurring.

  • Precipitation reactionsOccur when pairs of oppositely charged ions attract each other so strongly that they form an insoluble solid (precipitate) that drops out of solution, removing material, and therefore driving the reaction along.To predict whether a reaction will occur we must know the solubilities of the potential products in a reaction.Solubility definition: Amount of substance that can be dissolved in a given quantity of solvent.AgNO3 (aq.)+ NaCl(aq.) AgCl (s.)+ NaNO3 (aq.)

  • Solubility Guidelines

    Table 4.1Guidelines:Compounds containing the group 1 (Li, Na, K etc) or NH4+ cations are most likely soluble.Compounds containing the Halide anions, Cl-, Br- and I- (except Ag+, Hg22+ and Pb2+ compounds), the nitrate (NO3-), acetate (ethanoate) or sulphate anions (except Sr2+, Ba2+, Hg22+ and Pb2+ sulphates) are most likely soluble.Compounds containing sulfide (except NH4+, group 1 and heavy group 2), carbonate (except NH4+ and group 1), phosphate (except NH4+ and group 1) and hydroxyl (except NH4+, group 1 and heavy group 2) anions are most likely insoluble.Periodic Table:

  • Table 4.1

  • PredictionsGive the chemical formula for the following, and then classify as soluble or insoluble:Sodium carbonateLead sulfateAmmonium phosphate

    Na2CO3 solublePbSO4 insoluble(NH4)3PO4 soluble

  • Metathesis (transposition)Reactions involving exchange of partnersAX + BY AY + BXAgNO3(aq.) + KCl(aq.) AgCl(s) + KNO3(aq.)

    STEPSDetermine ions present as reactantsCombine cation of one reactant with anoin of the otherBalance equationTry:barium chloride mixed with potassium sulfate

  • Molecular and ionic equationsSometimes convenient to identify whether dissolved substances are present as ionsMolecular equationAgNO3(aq.) + KCl(aq.) AgCl(s) + KNO3(aq.)Ionic equationAg+(aq.) + NO3(aq.) + K+(aq.) + Cl(aq.) AgCl(s) + K+(aq.) + NO3(aq.)

    NOTE K+, NO3are SPECTATOR ionsNet ionic equationAg+(aq.) + Cl(aq.) AgCl(s)

  • Acids and BasesThe properties of acids include the following: Taste sour (but don't taste them!!) Their water solutions conduct electrical current (electrolytes) They react with bases to form salts and water Turns Blue Litmus Paper to Red The properties of bases include the following: Have a slippery feel between the fingers Have a bitter taste (but don't taste them!!) React with acids to form salts and water Turns Red Litmus Blue Their water solutions conduct electrical current (electrolytes)

  • Acids and BasesArrhenius in 1884 discovered that acids give off H+ ions and allow for a good flow of electricity through a solution. Arrhenius also discovered that bases give off OH- ions and OH- ions also allow for a good flow of electricity through the solution. Traditionally Svante Arrhenius defined:Acid released Hydrogen ion (as Hydronium ions, H3O+) in water solution.Base produced Hydroxide ion in water solution. The limitations on these definitions were: 1. The need for water2. The need for a protic acid 3. The need for Hydroxide bases

  • Bronsted/Lowry acids and basesBronsted and Lowry defined these two terms the following: Acid-Proton donor Base-Proton acceptor These definitions are not as restrictive as Arrhenius definitions. No need for water although it can be present, it need not be. Bases do not have to be Hydroxide compounds. Ammonia as a base!However, one restriction still remaining is the need for a protic acid. (see Lewis theory later) Each Bronsted acid is coupled to a conjugate base to constitute a CONJUGATE ACID-BASE PAIRCH3COOH + H2O H3O++CH3COO-

    See student activities

  • Strong acids (memorise) dissociate completely in waterHClO4, HClO3, HCl, HBr, HI, HNO3 and H2SO4Acid and Base StrengthStrong bases are the metal hydroxides of Group 1 and heavy Group 2E.g.LiOH, NaOH, KOH, Ba(OH)2 etc Weak acids and bases are not completely ionised in solutionCH3COOH + H2O H3O++CH3COO-

  • Acid-Base Reactions

    Acid/Base reactions are reactions that involve the neutralisation of an acid through the use of a base. HCl + NaOH NaCl + H2OIn this reaction, the Na+ and the Cl- are called spectator ions because they play no role in the overall outcome of the reaction. The only thing that reacts is the H+ (from the HCl) and the OH- (from the NaOH). So the reaction that actually takes place is: H+ + OH- H2OIf in the end, the OH- was the limiting reagent and there are H+'s still left in the solution then the solution is acidic, but if the H+ was the limiting reagent and OH-'s were left in the solution then the solution is basic.

    Example application: antacids (milk of magnesia invented by an Irishman, James Murray)

  • Oxidation-Reduction (REDOX) reactionsOriginally oxidation was assigned to the combination of an element with oxygen to give an oxide and reduction was the reverse.Today, a much broader definition is given: loss of electron(s) for oxidation gain of electron(s) for reductionThus redox reactions are electron transfer reactions.2Na 2Na+ + 2e-Cl2 + 2e- 2Cl-2Na + Cl2 2Na+ + 2Cl-In more complex reactions a bookkeeping system, oxidation numbers, is used to keep track of electron transfers.A redox reaction is therefore a reaction in which changes in oxidation numbers occur.See student activities

  • Oxidation NumbersRules for assigning oxidation numbers:An atom in its elemental state, 0.An atom in a simple monoatomic ion, charge on the ion. Group 1, +1 etc.Non-metals usually have negative