Chapter 16. Acids and Bases. Copyright Cengage Learning. All rights reserved 1

Section 16.1 Acids and Bases Models of Acids and Bases Arrhenius: Acids produce H + ions in solution, bases produce OH ions. Brønsted Lowry: Acids are proton (H + ) donors, bases are proton acceptors. HCl + H 2 O Cl + H 3 O + acid base Copyright Cengage Learning. All rights reserved 2

Section 16.1 Acids and Bases Acid in Water HA(aq) + H 2 O(l) H 3 O + (aq) + A (aq) acid base conjugate conjugate acid base Conjugate base is everything that remains of the acid molecule after a proton is lost. Conjugate acid is formed when the proton is transferred to the base. Copyright Cengage Learning. All rights reserved 3

Section 16.1 Acids and Bases Concept Check Which of the following represent conjugate acid base pairs? a) HCl, HNO 3 b) H 3 O +, OH c) H 2 SO 4, SO 4 2 d) HCN, CN Copyright Cengage Learning. All rights reserved 5

Section 16.2 Acid Strength Common Strong Acids Sulfuric acid, H 2 SO 4 Hydrochloric acid, HCl Nitric acid, HNO 3 Perchloric acid, HClO 4 And HI and HBr Copyright Cengage Learning. All rights reserved 11

Section 16.2 Acid Strength Oxyacid acidic proton is attached to an oxygen atom Organic acids have a carbon atom backbone and commonly contain the carboxyl group: Typically a weak acid Copyright Cengage Learning. All rights reserved 12

Section 16.2 Acid Strength Concept Check Consider a 1.0 M solution of HCl. Order the following from strongest to weakest base and explain: H 2 O(l) A (aq) (from weak acid HA) Cl (aq) Copyright Cengage Learning. All rights reserved 13

Section 16.2 Acid Strength Let s Think About It How good is Cl (aq) as a base? Is A (aq) a good base? The bases from strongest to weakest are: A, H 2 O, Cl Copyright Cengage Learning. All rights reserved 14

Section 16.2 Acid Strength Concept Check Acetic acid (HC 2 H 3 O 2 ) and HCN are both weak acids. Acetic acid is a stronger acid than HCN. Arrange these bases from weakest to strongest and explain your answer: H 2 O Cl CN C 2 H 3 O 2 Copyright Cengage Learning. All rights reserved 15

Section 16.2 Acid Strength Let s Think About It H 2 O(l) + H 2 O(l) H 3 O + (aq) + OH (aq) acid base conjugate conjugate acid base At 25 C, K w = 1.0 x 10 14 The bases from weakest to strongest are: Cl, H 2 O, C 2 H 3 O 2, CN Copyright Cengage Learning. All rights reserved 16

Section 16.3 Water as an Acid and a Base Water as an Acid and a Base Water is amphoteric: Behaves either as an acid or as a base. At 25 C: K w = [H + ][OH ] = 1.0 10 14 No matter what the solution contains, the product of [H + ] and [OH ] must always equal 1.0 10 14 at 25 C. Copyright Cengage Learning. All rights reserved 17

Section 16.3 Water as an Acid and a Base Three Possible Situations [H + ] = [OH ]; neutral solution [H + ] > [OH ]; acidic solution [H + ] < [OH ]; basic solution In each case, however, K w = [H + ][OH ] = 1.0 10 14. Copyright Cengage Learning. All rights reserved 18

Section 16.3 Water as an Acid and a Base Concept Check In an acidic aqueous solution, which statement below is correct? a) [H + ] < 1.0 10 7 M b) [H + ] > 1.0 10 7 M c) [OH ] > 1.0 10 7 M d) [H + ] < [OH ] Copyright Cengage Learning. All rights reserved 19

Section 16.3 Water as an Acid and a Base Exercise In an aqueous solution in which [OH ] = 2.0 x 10 10 M, the [H + ] = M, and the solution is. a) 2.0 10 10 M ; basic b) 1.0 10 14 M ; acidic c) 5.0 10 5 M ; acidic d) 5.0 10 5 M ; basic [H + ] = K w /[OH ] = 1.0 10 14 /2.0 10 10 = 5.0 10 5 M. Since [H + ] is greater than [OH ], the solution is acidic. Copyright Cengage Learning. All rights reserved 20

Section 16.4 The ph Scale ph = log[h + ] A compact way to represent solution acidity. ph decreases as [H + ] increases. Significant figures: poh = -log[oh - ] The number of decimal places in the log is equal to the number of significant figures in the original number. Copyright Cengage Learning. All rights reserved 21

Section 16.4 The ph Scale Exercise Calculate the ph for each of the following solutions. a) 1.0 10 4 M H + ph = log[h + ] = log(1.0 10 4 M) = 4.00 b) 0.040 M OH K w = [H + ][OH ] = 1.00 10 14 = [H + ](0.040 M) = 2.5 10 13 M H + ph = log[h + ] = log(2.5 10 13 M) = 12.60 Copyright Cengage Learning. All rights reserved 24

Section 16.4 The ph Scale Exercise The ph of a solution is 5.85. What is the [H + ] for this solution? [H + ] = 1.4 10 6 M [H + ] = 10^ 5.85 = 1.4 10 6 M Copyright Cengage Learning. All rights reserved 25

Section 16.4 The ph Scale Exercise Calculate the poh for each of the following solutions. a) 1.0 10 4 M H + ph = log[h + ] = log(1.0 10 4 M) = 4.00; So, 14.00 = 4.00 + poh; poh = 10.00 b) 0.040 M OH poh = log[oh ] = log(0.040 M) = 1.40 Copyright Cengage Learning. All rights reserved 27

Section 16.4 The ph Scale Exercise The ph of a solution is 5.85. What is the [OH ] for this solution? [OH ] = 7.1 10 9 M 14.00 = 5.85 + poh; poh = 8.15 [OH ] = 10^ 8.15 = 7.1 10 9 M Copyright Cengage Learning. All rights reserved 28

Section 16.5 Calculating the ph of Strong Acid Solutions Concept Check Consider an aqueous solution of 2.0 10 3 M HCl. What is the ph? ph = 2.70 2.0 10 3 M HCl 2.0 10 3 M H + and 2.0 10 3 M Cl ph = log[h + ] ph = log(2.0 10 3 M) ph = 2.70 Copyright Cengage Learning. All rights reserved 30

Section 16.5 Calculating the ph of Strong Acid Solutions Concept Check Calculate the ph of a 1.5 10 2 M solution of HNO 3. ph = 1.82 ph = log[h + ] ph = log(1.5 10 2 M) ph = 1.82 Copyright Cengage Learning. All rights reserved 32

Section 16.6 Buffered Solutions You are NOT responsible for Buffers Buffered solution resists a change in its ph when either an acid or a base has been added. Presence of a weak acid and its conjugate base buffers the solution. Copyright Cengage Learning. All rights reserved 33

Section 16.6 Buffered Solutions The Characteristics of a Buffer 1. The solution contains a weak acid HA and its conjugate base A. 2. The buffer resists changes in ph by reacting with any added H + or OH so that these ions do not accumulate. 3. Any added H + reacts with the base A. H + (aq) + A (aq) HA(aq) 4. Any added OH reacts with the weak acid HA. OH (aq) + HA(aq) H 2 O(l) + A (aq) Copyright Cengage Learning. All rights reserved 34

Section 16.6 Buffered Solutions Concept Check If a solution is buffered with NH 3 to which has been added NH 4 Cl, what reaction will occur if a strong base such as NaOH is added? a) NaOH + NH 3 NaNH 4 O b) NaOH + NH 4+ Na + + NH 3 + H 2 O c) NaOH + Cl NaCl + OH d) NaOH + H 2 O NaH 3 O 2 Copyright Cengage Learning. All rights reserved 35