Predicting Unit_Book Notes.docx

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University of Minnesota Twin Cities
CHEM 1061
Hyunjoo Im

Predicting Unit Book Notes 4.2) Reactions of Acids and Bases  Strong acids: strong electrolytes; completely ionized  Weak acids: weak electrolytes; partially ionized; reversible reaction, keeps going back and forth from neutral to ionic  Separate reactions to pull of all Hs if there’s more than 1 o Sulfuric acid = strong in first ionization, but weak in second o Phosphoric acid = weak in all ionizations  Acid? Strong or weak? o Molecular formula written with ionizable H first o Structural and condensed formulas show where H is found, location helps identify if ionizable or not  Strong bases: strong electrolytes; completely ionize or react with water to form OH -  Weak bases: remain partially nonionized at equilibrium; most molecular bases = weak  Amines: molecular compounds in which one or more H in NH is replaced by 3 hydrocarbon group  Base? Strong or weak? - o Strong are written w/ metal ion + OH ion o Most common weak bases are ammonia and amines o Need to use chem equation to see how it ionizes  Neutralization: reaction btwn sol’ns of acid and base, their characteristics cancel out; one product = a salt + - o Indicator: color’s affected by relative amounts of H or OH ions o Remove spectator ions – appear same form on two sides of equation o Net ionic equation – simplest form 4.3) Reactions that Form Precipitates  Precipitate: insoluble ionic compound; cations and anions from diff sources mix, precipitates from sol’n to bottom  Predicting: reactants = in sol’n so write out its separate ions, swap cations of reactants, see who’s soluble, one that’s not = precipitate o Net Ionic Equation: if soluble (aqueous (aq)) on both sides, cancel (= spectator ions), everything that remains = part of reaction  Applications: easy to prepare chemical substances, high percentage yield o Chemical analysis: qualitative: what it contains o Quantitative analysis: how much it contains 4.4) Reactions Involving Oxidation and Reduction (Redox)  Oxidation number: either actual charge on a monotomic ion or a hypothetical charge o Pretty much actual charge for ionics b/c electrons actually gained/lost o Molecular: arbitrarily assign #s; RULES!! By priority  1) For atoms in neutral species (isolated atom, molecule, formula) sum of all oxidation #s = 0; each atom in diatomics like C2 and S8is also 0  2) For atoms in an ion, sum of oxidation #s = charge on ion  3) In compounds, group 1A metals have oxidation # +1 and 2A metals have +2  4) In compounds, Flourine’s oxidation # = –1  5) In compounds, hydrogen has oxidation # of +1 EXCEPT when bonded to a metal -1  In most compounds, Oxygen has oxidation # -2 EXCEPT when O atoms bonded to one another like peroxides -1, and when in superoxides - 1/2  In binary compounds with metals, group 7A elements have oxidation # of -1, group 6A has -2, and group 5A has -3  Identifying redox reactions o *thermite reactions – produce liquid iron for welding large iron objects o Assign oxidation #s to all elements of a reaction o Oxidation: # increases o Reduction: # decreases o Oxidation and reduction must happen together; 2 half reactions occur simultaneously, one process, electrons lost, other, gained  Redox equations o Write reactants and products o Balance O with water and H with H+ o Balance electrical charges w/ coefficients o Balance equation by inspection???  Oxidizing and Reducing Agents o Reducing agent: what’s oxidized; causes other substance to be reduced o Oxidizing agent: what’s reduced o Compounds = agents even if atoms = oxidized/reduced  Oxidization #s of nonmetals o Maximum oxidation # = atom’s group # in periodic table (+5 for 5A, +6 for 6a, +7 for 7A) o Minimum oxidation # = group # - 8 o Species in which nonmetal has max ox # = ox agents b/c # can only decrease o Vice versa for min o Species w/ nonmetal w/ intermediate ox # can do either, but tend to do one over the other o Disproportionation reaction: redox reaction where same substance is both ox and red agent (like decomposition of hydrogen peroxide)  Metals as Reducing Agents o Metallic compounds: metals have positive oxidation #  = red agents o In elemental metals, # = 0 o Activity series of metals: metal will displace from sol’n ions of any metal that’s below it in the series o *any metal above H can react w/ acid to produce H ; 2nes below cannot, but there = few exceptions that still react 4.5) Applications of Oxidation and Reduction (go back to this section, not all notes done, see examples)  Everyday Life: hydrogen peroxide for cleaning cuts/antiseptic; benzoyl peroxide treats acne, but if exposed to sun, promotes skin cancer; chlorine cleans pools  Foods and Nutrition: antioxidants = red agents  Organic Chemistry o Aldehyde: if OH group is on terminal carbon atom and product is distilled off as formed o Ketone: OH bonded to interior carbon 4.6) Titrations  Titration: one reactant is carefully added to another until both have combined in exact stoichiometric proportions both reactants fully consumed at end of titration o Purpose: to find # moles/grams/concentration/percentage of analyte (substance we’re looking for) o Titrant: solution that’s added; we know it’s info o Get vol & concentration of titrant used stoichiometry moles of a
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