notes_Chapter_7 - Chapter 7 Chapter 7 Acids and Bases Acids...

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Unformatted text preview: Chapter 7 Chapter 7 Acids and Bases Acids and Bases Chapter 7 Acids and Bases 7.1 The Nature of Acids and Bases 7.2 Acid Strength 7.3 The pH Scale 7.4 Calculating the pH of Strong Acid Solutions 7.5 Calculating the pH of weak Acid Solutions 7.6 Bases 7.7 Polyprotic Acids 7.8 Acid-Base Properties of Salts 7.9 Acid Solutions in Which Water Contributes to the H+ Concentration 7.10 Strong Acid Solutions in Which Water Contributes to the H+ Concentration 7.11 Strategy for solving Acid-Base Problems: A Summary A circle of shiny pennies is created by the reaction between the citric acid of the lemon and the tarnish on the surface of the copper. Source: Fundamental Photos Arrhenius (or Classical) Acid-Base Definition An acid is a substance that contains hydrogen and dissociates in water to yield a hydronium ion : H 3 O + A base is a substance that contains the hydroxyl group and dissociates in water to yield : OH- Neutralization is the reaction of an H + (H 3 O + ) ion from the acid and the OH- ion from the base to form water, H 2 O. The neutralization reaction is exothermic and releases approximately 56 kJ per mole of acid and base. H + (aq) + OH- (aq) H 2 O (l) H rxn = -55.9 kJ Brnsted-Lowry Acid-Base Definition An acid is a proton donor , any species that donates an H + ion. An acid must contain H in its formula; HNO 3 and H 2 PO 4- are two examples, all Arrhenius acids are Brnsted-Lowry acids. A base is a proton acceptor , any species that accepts an H + ion. A base must contain a lone pair of electrons to bind the H + ion; a few examples are NH 3 , CO 3 2- , F- , as well as OH- . Brnsted-Lowry bases are not Arrhenius bases, but all Arrhenius bases contain the Brnsted-Lowry base OH- . Therefore in the Brnsted-Lowry perspective, one species donates a proton and another species accepts it: an acid-base reaction is a proton transfer process. Acids donate a proton to water Bases accept a proton from water Molecular model: Two water molecules react to form H 3 O+ and OH- Autoionization of Water H 2 O (l) + H 2 O (l) H 3 O + + OH- K c = [H 3 O + ][OH- ] [H 2 O] 2 The ion-product for water, K w : K c [H 2 O] 2 = K w = [H 3 O + ][OH- ] = (at 25C) For pure water the concentration of hydroxyl and hydronium ions must be equal: [H 3 O + ] = [OH- ] = 1.0 x 10-14 = 1.0 x 10-7 M (at 25C) The molarity of pure water is: = M 1000g/L 18.02 g/mol Molecular model: The reaction of an acid HA with water to form H 3 O+ and a conjugate base. Acid Base Conjugate Conjugate acid base The Acid-Dissociation Constant ( K a ) Strong acids dissociate completely into ions in water: HA (g or l) + H 2 O (l) H 3 O + (aq) + A- (aq) In a dilute solution of a strong acid, almost no HA molecules exist: [H 3 O + ] = [HA] init or [HA] eq = 0 Q c = [H 3 O + ][A- ] [HA][H 2 O] at equilibrium, Q c = K c >> 1 Nitric acid is an example: HNO 3 (l) + H 2 O (l) H 3 O + (aq) + NO 3- (aq) Weak acids dissociate very slightly into ions in water: HA (aq) + H 2 O (aq) H 3 O + (aq) + A- (aq) In a dilute solution of a weak acid, the great majority of HA...
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notes_Chapter_7 - Chapter 7 Chapter 7 Acids and Bases Acids...

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