chem ch 15

chem ch 15 - Arrhenius Acid and base defns Ch 15: Acids and...

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Ch 15: Acids and Bases Equilibrium problems of another kind Arrhenius Acid and base defns • Acid increases H + conc (hydrogen ion, proton) when dissolved in water. • HCl (aq Cl - (aq) • Acid has to have __ to be acid. • Base increases OH- (hydroxide ion) conc when dissolved in water • NaOH Na + (aq) + OH - (aq) • Base has to have ___ • Arrhenius acid-base neutralization rxn yields salt + water. • HCl(aq) + NaOH(aq) NaCl (aq) + HOH(l) • acid + base salt + water • Arrhenius definition limited to aqueous solutions. But NH 3 is a base? Bronsted defn • A Bronsted acid donates a proton (H + ) to a base. An acid is a • A Bronsted base accepts a proton from the acid . Base is a
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Identify acids and bases in • HPO 4 2- + H 2 SO 4 HSO 4 - + H 2 PO 4 - • Note that the products of the rxn are acids and bases themselves. Conjugate acid-base pairs are species (on opposite sides of rxn) that differ by ___ proton only. • H 3 PO 4 + H 2 O H 3 O + + H 2 PO 4 - • H 3 O + : hydronium ion • HCO 3 - + H 2 O H 2 CO 3 + OH - • Note that H 2 O can act as a base in some cases and as an acid in other cases. Species that can act as both an acid and a base, depending on the environment, said to be amphoteric (amphiprotic). • Conjugate acid-base pairs are species on opposite sides of the rxn that differ by ___ proton only. • Are these conjugate acid/base pairs? • H 2 O/OH- • HNO 3 /NO 3 - • H 2 SO 4 / HSO 3 - • OH - /H 3 O + • H 3 O + / H 2 O Given base, to get conjugate acid: • What is the conjugate acid of: F - NH 3 HSO 3 - • Given acid to get conjugate base: • What is the conjugate base of: • HS - • NH 3 • HPO 4 2- • S 2- 15.2: Autoionization (acid- base properties) of water • H 2 O(l) + H 2 O(l) H 3 O + + OH- • Acid1 base2 acid2 base1 • Or H 2 O(l) H + (aq) + OH - (aq) • K = [H 3 O + ][OH - ] [H 2 O] 2 • or K w = [H 3 O + ][OH - ] = [H + ][OH - ] • K w is the ion-product constant
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• Find from experiment that for pure water at 25 o C that [H + ] = [OH-] = • K w = [H 3 O + ][OH - ] • So K w = • This holds for all solutions not just pure H 2 O. • K w = [H + ][OH-] = 1 x10 -14 • as [H + ] i • If [H + ] = 2.9 x10 -3 M, [OH-] =? • as [OH - ] i If [OH-] = 6.25 x 10 -4 M, [H + ]=? • 15.11:Ion-product constant for water is 1 x10 -14 at 25 o C and 3.8 x 10 -14 at 40 o C. Is the forward process H 2 O(l) H + (aq) + OH-(aq) • exo or endo thermic? 15.3:pH--a Measure of Acidity • define pH = -log 10 [H + ] • define pOH = -log[OH-] • define pK = -logK • K w = [H + ][OH-] = 1 x10 -14 • Neutral sol’n: [H + ] =[OH-] = 1 x10 -7 M pH=_ • Acidic sol’n; [H + ]>[OH-] ; [H + ] > 1x10 -7 M pH__ • Basic sol’n: [OH-]>[H + ]; [OH-]>1x10 -7 M pH __ [H + ]M pH pOH [OH-]M 10 -1 15 1x10 -15 1 0 14 1x10 -14 0. 1 1 13 1x10 -13 • 0.001 3 11 1x10 -11 • 1x10 -7 7 7 1x10 -7 • 1x10 -10 10 4 1x10 -4 • 1x10 -14 14 0 1 • 1x10 -15 15 -1 10 • As pH [H + ]
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• What’s pH, pOH, [OH-] for a sol’n
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chem ch 15 - Arrhenius Acid and base defns Ch 15: Acids and...

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