CH 1020 Exam #3 Study Guide For reference see Chemistry: An Atoms-focused Approach by Gilbert, Kirss, and Foster

Transcription

1 CH 1020 Exam #3 Study Guide For reference see Chemistry: An Atoms-focused Approach by Gilbert, Kirss, and Foster *In addition to reviewing this study guide, you should i) consult the Chapter Objectives posted on Blackboard and ii) PRACTICE PROBLEMS (Old exams, mock exams, end of chapter problems, etc.) Chapter 15: Aqueous Equilibria Important Terms to know: o Brønsted-Lowry Acid: a substance that can transfer H + o Brønsted-Lowry Base: a substance that can accept H + o Strong Acid: an acid that dissociates completely in water to give H + ions o Strong Base: a base that dissociates completely in water to give OH ions o Weak Acid: an acid that dissociates incompletely in water o Weak Base: a base that dissociates incompletely in water o Conjugate Acid: the species HA formed by addition of H + to a base A o Conjugate Base: the species A formed by loss of H + from an acid HA o Common Ion Effect: the shift in the position of an equilibrium on addition of a substance that provides an ion in common with one of the ions already involved in the equilibrium o Buffer solution: a solution of a weak acid and its conjugate base that resists drastic changes in ph o Buffer Capacity: a measure of the amount of acid or base that a buffer can absorb without a significant change in ph o The greater the # of moles of acid & conjugate base buffer, the higher the buffer capacity o Equivalence point: the point in a titration at which stoichiometrically equivalent quantities of reactants have been mixed together Be familiar with acids & bases on the following table (you don t need to necessarily memorize these, but take a look through them) 1 of 6

2 General Chemistry: Atom s First, McMurry & Fay Factors that affect acid strength o Bond Strength For binary acids (H A) of elements in the same group of the periodic table, as H A bond strength increases, acid strength decreases In order of increasing acidity: HF << HCl < HBr < HI o Electronegativity For binary acids (H A) of elements in the same row of the periodic table, as the electronegativity of A increases, acid strength increases In order of increasing acidity: CH4 < NH3 < H2O < HF For oxoacids that contain the same # of OH groups & the same # of O atoms (ex: H O Y), acid strength increases as electronegativity of Y increases In order of increasing acidity: H O I < H O Br < H O Cl For oxoacids that contain the same atom Y but different numbers of O atoms, acid strength increases as the # of O atoms increases In order of increasing acidity: HClO < HClO2 < HClO3 < HClO4 Acid-Base Properties of Salts o Strong Acid + Strong Base = neutral solution Ex: HCl + NaOH Na + + Cl + H2O o Strong Acid + Weak Base = Acidic solution Ex: HCl + NH3 NH4 + + Cl o Weak Acid + Strong Base = Basic Solution Ex: HCN + NaOH Na + + CN + H2O 2 of 6

3 o Cations from strong bases are inert Alkali metal cations of group 1A Alkaline-earth cations of groups 2A (except Be 2+ ) o Anions from strong monoprotic acids are inert Cl, Br, I, NO3, ClO4 There are 4 types of neutralization Rxns: o Strong Acid-Strong Base = neutral soln, ph = 7 o Weak Acid-Strong Base = basic solution, ph > 7 o Strong Acid-Weak Base = acidic solution, ph < 7 o Weak Acid-Weak Base, ph depends on the strength of each Be able to write neutralization equations for each of the above (what are the products formed?) Be able to predict the ph of the solution that results from each of the above neutralization rxns Be able to calculate the ph of a buffer solution o Know how to construct and use an ICE table Be able to calculate the change in ph upon addition of a strong base or strong acid to a buffer solution o Know how to construct and use an ICE table Be able to use the Henderson-Hasselbalch equation: ph = pka + log ([base]/[acid]) o We can use this equation to calculate percent dissociation o It also helps to pick an appropriate buffer Select a buffer with a pka close to the desired ph Be able to interpret ph Titration curves and identify/predict the equivalence point o Be able to calculate ph at different points along the curve o Consider what principal rxn is occurring at various points in the titration Important equations to know: o ph = log [H3O + ] ph < 7, acidic solution ph > 7, basic solution ph = 7, neutral solution Be able to calculate the ph of a strong acid or strong base solution Be able to calculate the ph of a weak acid or weak base solution Know how to use the ICE table o [H3O + ] = 10 ph o Acid Dissociation Constant: Ka = {[H3O + ][A ]}/[HA] o Base Dissociation Constant: Kb = {[BH + ][OH ]}/[B] o Kw = [H3O + ][OH ] o Ka Kb = Kw o {[HA]dissociated/[HA]initial} 100% o ph = pka + log ([base]/[acid]) Chapter 17: Electrochemistry Important Terms to know o Galvanic Cell: a spontaneous chemical rxn generates an electric current o Electrolytic Cell: an electric current drives a nonspontaneous rxn o Electrode: a conductor through which electrical current enters or leaves a cell 3 of 6

4 o Oxidation: the loss of one or more electrons by a substance o Reduction: the gain of one or more electrons by a substance o Oxidizing Agent: a substance that causes an oxidation by accepting an electron o Reducing Agent: a substance that causes a reduction by donating an electron o Half-Reaction: the oxidation or reduction part of a redox reaction o Cell Potential (E ): the electrical potential that pushes electrons away from the anode and pulls them toward the cathode (a.k.a. electromotive force, emf) o Oxidation Number: a value that measures whether an atom in a compound is neutral, electron-rich, or electron-poor compared to an isolated atom o Salt Bridge: a tube that contains a gel permeated with a solution of an inert electrolyte connecting the 2 sides of an electrochemical cell o Cathode: the electrode at which reduction takes place o Anode: the electrode at which oxidation takes place Oxidation Numbers o An atom in its elemental state has an oxidation # of 0 o An atom in a monatomic ion has an oxidation # identical to its charge o An atom in a polyatomic ion or in a molecular compound usually has the same oxidation # it would have if it were a monatomic ion H = +1 when bonded to a nonmetal H = 1 when bonded to a metal O = 2, except in peroxides (ex. H-O-O-H) Halogens = 1 o The sum of the oxidation # s is 0 for a neutral compound & is equal to the net charge for a polyatomic ion Be able to identify and balance redox rxns 1) Identify which atoms get oxidized & which get reduced 2) Write the unbalanced half-reactions 3) Balance each half-reaction individually for all atoms except for O & H 4) Balance each half-reaction for O by adding H2O to the side with less O and balance for H by adding H + to the side with less H 5) Balance each half-reaction for charge by adding e to the side with greater (+) charge 6) Multiply each entire half-reaction by a factor to make the e count the same in both halfreactions 7) Add the 2 balanced half-reactions together & cancel an e and species that appear on both sides of the equation Be able to draw a galvanic cell given a redox reaction Be able to interpret drawings of a galvanic cells Be able to interpret shorthand notation for galvanic cells Given a balanced redox rxn, be able to write the shorthand notation 4 of 6

5 A Pt electrode is a commonly used inert electrode Be able to calculate E cell for a given redox rxn: E cell = E ox + E red o Use the standard reduction potentials table to find E red In the table the half-reactions are written as reductions In a cell in which this half-reaction occurs in the opposite direction (oxidation rather than reduction), the corresponding half-cell potential has the same magnitude but opposite sign The half-reactions are listed in order of decreasing standard reduction potential E = (+), greater tendency to become reduced (stronger oxidizing agent) E = ( ), greater tendency to become oxidized (stronger reducing agent) Be able to calculate G using the equation: G = nfe o n = number of moles of electrons transferred in the rxn o F = Faraday s constant (96,500 C/mol e ) o E = cell potential Chapter 23: Organic Chemistry The study of carbon compounds Functional Group: an atom or group of atoms within a molecule that has a characteristic chemical behavior & that undergoes the same kinds of rxns in every molecule where it occurs Be able to visually identify the following functional groups: o Alkanes A hydrocarbon in which each carbon atom is bonded to four other atoms o Alkenes Hydrocarbon containing one or more carbon-carbon double bonds o Alkynes Hydrocarbon containing one or more carbon-carbon triple bonds o Arenes (aromatic compounds) Aromatic compounds are a class of compounds that can be represented as having a 6-membered ring with alternating single & double bonds o Alcohols An organic compound whose molecular structure includes a hydroxyl group ( OH) bonded to a carbon atom that is not bonded to any other functional group(s) o Ethers Organic compound with the general formula R-O-R, where R and R are any alkyl group or aromatic ring; the R and R groups may be the same o Amines Organic compound that contains a group with general formula RNH2, R2NH, or R3N where R is any organic subgroup o Carboxylic acids A compound containing the COOH functional group Carboxylic acids are carbonyl compounds Carbonyl group: contains a carbon-oxygen double bond Acidic 5 of 6

6 Isomers: compounds that have the same formula but a different bonding arrangement of their constituent atoms o Be able to recognize structural isomers and cis/trans isomers Structure isomers: molecules with the same molecular formula have bonded together in different orders Cis/trans isomers Cis isomer: molecule with two like groups on the same side of the molecule Trans isomer: molecule with two like groups on opposite sides of the molecule o Given a chemical formula, be able to determine the number of isomers Be able to recognize/interpret: o Structural formulas o Condensed formulas (shorthand method for drawing organic structures in which C-H & C- C single bonds are understood rather than shown) o Line structures (where the end of a line represents a carbon & the hydrogen atoms are not drawn but rater assumed) o Ball & stick models o Space-filling models Be able to predict some physical properties of simple organic compounds based on their structure, polarity, and intermolecular forces: o Water solubility o Boiling point o Melting point o Vapor pressure 6 of 6