Chap18 Acid-Base (2) - Chapter 18 Acid-Base Equilibria 18-1...

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Chapter 18 Acid-Base Equilibria 18-1
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Acid-Base Equilibria 18.1 Acids and Bases in Water 18.2 Autoionization of Water and the pH Scale 18.3 Proton Transfer and the Brønsted-Lowry Acid-Base Definition 8 4 Solving Problems Involving Weak cid quilibria 18.4 Solving Problems Involving Weak-Acid Equilibria 18.5 Weak Bases and Their Relation to Weak Acids 18.6 Molecular Properties and Acid Strength 18.7 Acid-Base Properties of Salt Solutions 18.8 Generalizing the Brønsted-Lowry Concept: The Leveling Effect 18.9 Electron-Pair Donation and the Lewis Acid-Base Definition 18-2
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et Direction of Reaction Net Direction of Reaction The net direction of an acid-base reaction depends on the relative strength of the acids and bases involved. A reaction will favor the formation of the weaker acid and base. H 2 S + NH 3 HS - + NH 4 + tronger base weaker base stronger acid eaker acid stronger base weaker acid This reaction favors the formation of the products . 18-3
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Strengths of conjugate acid-base pairs. The stronger the acid is, the eaker its conj gate base weaker its conjugate base. When an acid reacts with a base that is farther down the list, the reaction proceeds to the right ( K c > 1). 18-4
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Sample Problem 18.5 Predicting the Net Direction of an Acid- ase Reaction Base Reaction PROBLEM: Predict the net direction and whether K c is greater or less than 1 for each of the following reactions (assume equal initial concentrations of all species): (a) H 2 PO 4 - ( aq ) + NH 3 ( aq ) HPO 4 2- ( aq ) + NH 4 + ( aq ) (b) H O( l ) + HS - ( aq ) OH - ( aq ) + H S( aq ) PLAN: We identify the conjugate acid-base pairs and consult figure 18.8 to see which acid and base are stronger. The reaction vors the formation of the weaker acid and base 2 2 SOLUTION: favors the formation of the weaker acid and base. ) O - q + N H q H P O 2- q + N H + q stronger acid weaker acid stronger base weaker base (a) H 2 PO 4 ( aq ) + NH 3 ( aq ) HPO 4 ( aq ) + NH 4 ( aq ) The net direction for this reaction is to the right, so K > 1. 18-5 c
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Sample Problem 18.5 (b) H 2 O( l ) + HS - ( aq ) OH - ( aq ) + H 2 S( aq ) stronger acid weaker acid stronger base weaker base The net direction for this reaction is to the left, so K c < 1. 18-6
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Sample Problem 18.6 Using Molecular Scenes to Predict the Net irection of an Acid ase Reaction Direction of an Acid-Base Reaction PROBLEM: Given that 0.10 M of HX ( blue and green ) has a pH of 2.88, and 0.10 M HY ( blue and orange ) has a pH 3.52, which bt t t h f ili t f t i l scene best represents the final mixture after equimolar solutions of HX and Y - are mixed? PLAN: A stronger acid and base yield a weaker acid and base, so we have to determine the relative acid strengths of HX and HY to choose the correct molecular scene. The concentrations of the acid solutions are equal, so we can recognize the stronger acid y comparing the pH values of the two solutions 18-7 by comparing the pH values of the two solutions.
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Sample Problem 18.6 SOLUTION: he HX solution has a lower pH than the HY solution so HX is the The HX solution has a lower pH than the HY solution, so HX is the stronger acid and Y - is the stronger base. The reaction of HX and Y - has a K c
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Chap18 Acid-Base (2) - Chapter 18 Acid-Base Equilibria 18-1...

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