CHM152Chapter 14 - 6

Chemistry (MasteringChemistry Series)

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1 Chapter 14 - Aqueous Equilibria: Acids & Bases Acid-Base Concepts Acids and bases are all around us. They make up one of the most important (and practical) aspects of chemistry. What are some examples of each? What do you know about acids and bases? Acid-Base Concepts CHM 151 taught Arrhenius theory ± Acids produce hydrogen ions in water ² HA (aq) ' H + (aq) + A - (aq) ± Bases produce hydroxide ions in water ² MOH (aq) ' M + (aq) + OH - (aq) Now Brønsted-Lowry theory ± Acid: Substance that can donate H + ± Base: Substance that can accept H + Acid-Base Pairs Which substance donates H + ? Which substance accepts H + ? Conjugate acid-base pairs. Remember that reactions proceed in both directions. Acid-Base Pairs Write an equation for the dissociation of HCN in water. Identify the acid, the base, the conjugate acid, and the conjugate base. Acid-Base Pairs Identify acid-base pairs in the reaction of HS - with HF.
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2 Strengths of Acids/Bases Competition for protons (H + ) HS - (aq) + HF(aq) ' H 2 S(aq) + F - (aq) Which acid is stronger? Which acid is stronger? ± HF Which base is stronger? ± HS - The proton is always transferred to the stronger base ! Strength of Acids Strong acids almost completely dissociate in water. ± HClO 4 , HCl, HBr, HI, HNO 3 , H 2 SO 4 ± These have weak conjugate bases. Equilibrium lies very far to the right. Weak acids (HF, CH 3 COOH, HNO 2 ) have strong conjugate bases. Equilibrium lies to the left (most stay bonded, few dissociate). Strength of Acids HCl, H 2 SO 4 HNO 2 , HF H 2 O Strength of Bases 8 Strong bases: NaOH, KOH, LiOH, RbOH, CsOH, Ca(OH) 2 , Sr(OH) 2 , Ba(OH) 2 ± Don’t react with water, just dissociate in it ± NH 3 compounds DO react with water ± NH 3 + H 2 O ' NH 4 + + OH - Example 14.3, Problem 14.4, Key Concept 14.4 Draw the following in water: HNO 3 , HF, NaOH, Ca(OH) 2 , Fe(OH) 3 Strength of Acids/Bases Hydronium Ions HA (aq) ' H + (aq) + A - (aq) H + is very reactive and will bond with O in H 2 O to form H 3 O + H + and H 3 O + mean the same thing but H 3 O + is more accurate
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3 Dissociation of Water H 2 O (l) + H 2 O (l) ' H 3 O + (aq) + OH - (aq) Identify the acid-base pairs This is the dissociation of water an This is the dissociation of water, an amphoteric substance. Write an equilibrium expression for this eqn. K w is ion-product constant for water. Calculate K w if [H 3 O + ] = 1.0 x 10 -7 (experimentally determined for pure H 2 O) Dissociation of Water We can compare [H 3 O + ] and [OH - ] for solutions. They’re equal in neutral solutions. Which one is greater in acidic solutions? Basic solutions? [H 3 O + ] = 5.6 x 10 -4 M. What is [OH - ]? Acidic, Basic, Neutral Solns pH Scale Logarithmic scale (like Richter scale for earthquakes).
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CHM152Chapter 14 - 6 - Acid-Base Pairs Chapter 14 - Aqueous...

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