A man is rich in proportion to the number of things he can let alone.

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1 Chemistry 132 NT A man is rich in proportion to the number of things he can let alone. enry David Thoreau 1 2 Chem 132 NT Acids and Module 1 AcidBase Concepts Arrhenius Concept of Acids and BronstedLowry Concept of Lewis Concept of Acids and Acid indicator dye. 3 1

2 Acid Base Concepts Acids and s were first recognized by simple properties, such as taste. Acids taste sour. taste bitter Acids and s change the color of certain dyes called indicators. According to Arrhenius, s increase the concentration of in a solution while s increase the concentration of O. 4 Acid Base Concepts In the first part of this chapter we will look at several concepts of theory including The Arrhenius concept The Bronsted Lowry concept The Lewis concept This chapter expands on what you learned in 1 st semester chemistry about s and s. 5 Acid Base Concepts Antoine Lavoisier was one of the first chemists to try to explain what makes a substance ic. In 1777 he proposed that oxygen was an essential element in s. The actual cause of ity and basicity was ultimately explained in terms of the effect these compounds have on water by Svante Arrhenius in

3 Arrhenius Concept of Acids and According to the Arrhenius concept of s and s, an is a substance that, when dissolved in water, increases the concentration of hydronium ion ( 3 O ). Chemists often use the notation (aq) for the 3 O (aq) ion, and call it the hydrogen ion. Remember, however, that the aqueous hydrogen ion is actually chemically bonded to water, that is, 3 O. 7 Arrhenius Concept of Acids and According to the Arrhenius concept of s and s, an is a substance that, when dissolved in water, increases the concentration of hydronium ion ( 3 O ). The 3 O is shown here hydrogen bonded to three water molecules. 8 Arrhenius Concept of Acids and A, in the Arrhenius concept, is a substance that when dissolved in water increases the concentration of hydroxide ion, O (aq). The special role of the hydronium ion (or hydrogen ion) and the hydroxide ion in aqueous solutions arises from the following equilibrium. 2 O(l) 2 O(l) 3 O (aq) O (aq) 9 3

4 Arrhenius Concept of Acids and In the Arrhenius concept, a strong is a substance that ionizes completely in aqueous solution to give 3 O (aq) and an anion. An example is perchloric, ClO 4. ClO4(aq) 2O(l) fi 3O (aq) ClO4 Other strong s include Cl, Br, I, NO 3 and 2 SO 4. (aq) 10 Arrhenius Concept of Acids and In the Arrhenius concept, a strong is a substance that ionizes completely in aqueous solution to give O (aq) and a cation. An example is sodium hydroxide, NaO. NaO(s) 2 O fina (aq) O (aq) Other strong s include LiO, KO, Ca(O) 2, Sr(O) 2, and Ba(O) Common Strong Strong Acids Cl Br I Strong LiO NaO KO 2 SO4 Ca(O) 2 NO 3 Sr(O) 2 ClO 4 Ba(O) 2 RbO CsO 12 4

5 Arrhenius Concept of Acids and Most other s and s that you encounter are weak. They are not completely ionized and exist in reversible reaction with the corresponding ions. An example is acetic, C 2 3 O 2. C 2 3O2(aq) 2O(l) Ammonium hydroxide, N 4 O, is a weak. N4O(aq) N4 3O (aq) C23O2 (aq) (aq) O (aq) 13 Arrhenius Concept of Acids and The Arrhenius concept is limited in that it looks at s and s in aqueous solutions only. In addition, it singles out the O ion as the source of character, when other species can play a similar role. Broader definitions of s and s are discussed in the next sections. 14 BrønstedLowry Concept of According to the BrønstedLowry concept, an is the species donating the proton in a protontransfer reaction. A is the species accepting the proton in a protontransfer reaction. In any reversible reaction, both forward and reverse reactions involve proton transfer. 15 5

6 BrønstedLowry Concept of Consider the reaction of N 3 and 2 O. N3(aq) 2O(l) N4 (aq) O (aq) 16 BrønstedLowry Concept of Consider the reaction of N 3 and 2 O. N3(aq) 2O(l) N4 (aq) O (aq) In the forward reaction, N 3 accepts a proton from 2 O. Thus, N 3 is a and 2 O is an. 17 BrønstedLowry Concept of Consider the reaction of N 3 and 2 O. N3(aq) 2O(l) N4 (aq) O (aq) In the reverse reaction, N 4 donates a proton to O. The N 4 ion is the and O is the. 18 6

7 BrønstedLowry Concept of Consider the reaction of N 3 and 2 O. N3(aq) 2O(l) N4 (aq) O (aq) The species N 4 and N 3 are a conjugate pair. A conjugate pair consists of two species in an reaction, one and one, that differ by the loss or gain of a proton. 19 BrønstedLowry Concept of Consider the reaction of N 3 and 2 O. N3(aq) 2O(l) N4 (aq) O (aq) ere N 4 is the conjugate of N 3 and N 3 is the conjugate of N 4. The BrønstedLowry concept defines a species as an or a according to its function in the proton transfer reaction. 20 BrønstedLowry Concept of Consider the reaction of N 3 and 2 O. N3(aq) 2O(l) N4 (aq) O (aq) We can also view 2 O as the conjugate of O and O as the conjugate of 2 O. They differ by one proton with 2 O as the proton donor () in the forward reaction and O as the proton acceptor ()in the reverse reaction. 21 7

8 BrønstedLowry Concept of Some species can act as an or a. An amphotericspecies is a species that can act either as an or a (it can gain or lose a proton). For example, CO 3 acts as a proton donor (an ) in the presence of O 2 CO 3 (aq) O (aq) CO3 (aq) 2O(l) 22 BrønstedLowry Concept of Some species can act as an or a. An amphotericspecies is a species that can act either as an or a (it can gain or lose a proton). Or it can act as a proton acceptor (a ) in the presence of F. CO 3 (aq) F(aq) 2CO3(aq) F (aq) 23 BrønstedLowry Concept of The amphoteric characteristic of water is important in the properties of aqueous solutions. Water reacts as an with the N 3. N3(aq) 2O(l) N4 (aq) O (aq) 24 8

9 BrønstedLowry Concept of The amphoteric characteristic of water is important in the properties of aqueous solutions. Water can also react as a with the F. F(aq) 2O(l) fi F (aq) 3O (aq) 25 BrønstedLowry Concept of In the BrønstedLowry concept 1. A is a species that accepts protons; O is only one example of a. 2. Acids and s can be ions as well as molecular substances. 3. Acid reactions are not restricted to aqueous solution. 4. Some species can act as either s or s depending on what the other reactant is. 26 In the following equation, label each species as an or a. Show the conjugate pairs. CO 3 (aq) O (aq) CO 3 2 (aq) 2 O(l) 27 9

10 In the following equation, label each species as an or a. Show the conjugate pairs. CO 3 (aq) O (aq) CO 3 2 (aq) 2 O(l) On the left, CO 3 is the proton donor, making it an. 28 In the following equation, label each species as an or a. Show the conjugate pairs. CO 3 (aq) O (aq) CO 3 2 (aq) 2 O(l) On the right, 2 O is the proton donor, making it an. 29 In the following equation, label each species as an or a. Show the conjugate pairs. CO 3 (aq) O (aq) CO 3 2 (aq) 2 O(l) The proton acceptors are O and CO 3 2 making them s

11 In the following equation, label each species as an or a. Show the conjugate pairs. CO 3 (aq) O (aq) CO 3 2 (aq) 2 O(l) Conjugate pair ere, CO 3 and CO 3 2 are a conjugate pair. 31 In the following equation, label each species as an or a. Show the conjugate pairs. CO 3 (aq) O (aq) CO 3 2 (aq) 2 O(l) Conjugate pair 2 O and O are also a conjugate pair. 32 Lewis Concept of Acids and The Lewis concept defines an as an electron pair acceptor and a as an electron pair donor. This concept broadened the scope of theory to include reactions that did not involve. The Lewis concept embraces many reactions that we might not think of as reactions

12 Lewis Concept of Acids and The reaction of boron trifluoride with ammonia is an example. F F B F N F F B F Boron trifluoride accepts the electron pair, so is a Lewis. Ammonia donates the electron pair and so is the Lewis. N 34 In the following reaction, identify the Lewis and the Lewis. B(O) 3 2 O B(O) 4 35 In the following reaction, identify the Lewis and the Lewis. B(O) 3 2 O B(O) 4 We must write the equation using Lewis structures. O O B O O O O B O O 36 12

13 In the following reaction, identify the Lewis and the Lewis. B(O) 3 2 O B(O) 4 Notice the new bond formed between the boron and the oxygen. O O O O O B O O O B 37 In the following reaction, identify the Lewis and the Lewis. B(O) 3 2 O B(O) 4 The electron pair was donated by the oxygen making water the Lewis. O O O O O B O O Lewis O B 38 In the following reaction, identify the Lewis and the Lewis. B(O) 3 2 O B(O) 4 The electron pair was accepted by the boron making B(O) 3 the Lewis. O O O O O B O O O Lewis B 39 13

14 In the following reaction, identify the Lewis and the Lewis. B(O) 3 2 O B(O) 4 The electron pair was accepted by the boron making B(O) 3 the Lewis. O O O O O B O O O B 40 Summary According to the Arrhenius concept of s and s, an is a (proton) donor. According to the Arrhenius concept of s and s, an is a O (hydroxide) donor. 41 Summary According to the BronstedLowry concept of s and s, an is a (proton) donor. According to the BronstedLowry concept of s and s, a is a (proton) acceptor

15 Summary The Lewis concept defines an as an electron pair acceptor and a as an electron pair donor. 43 Operational Skills Identifying and species Identifying Lewis and species Time for a few review questions