C HAPTER 8 A CIDS AND B ASES 8.1 Acids and Bases 1

A CIDS Arrhenius acids produce H + ions in water. H 2 O H Cl( g ) H + ( aq ) + Cl - ( aq ) are electrolytes. have a sour taste. turn litmus red. neutralize bases. 2

N AMES OF A CIDS Acids with H and a nonmetal are named with the prefix hydro and end with ic acid. HCl hydro chlor ic acid Acids with H and a polyatomic ion are named by changing the end of the name of the polyatomic ion from ate to ic acid or ite to ous acid. ClO 3 − chlor ate HClO 3 chlor ic acid ClO 2 − chlor ite HClO 2 chlor ous acid 3

N AMES OF S OME C OMMON A CIDS 4 Copyright © 2009 by Pearson Education, Inc.

L EARNING C HECK Select the correct name for each of the following acids. A. HBr 1. bromic acid 2. bromous acid 3. hydrobromic acid B. H 2 CO 3 1. carbonic acid 2. hydrocarbonic acid 3. carbonous acid C. HBrO 2 1. bromic acid 2. hydrobromous acid 3. bromous acid 5

B ASES Arrhenius bases produce OH − ions in water. taste bitter or chalky. are electrolytes. feel soapy and slippery. neutralize acids. 6

S OME C OMMON B ASES Bases with OH − ions are named as the hydroxide of the metal in the formula. NaOHSodium hydroxide KOHPotassium hydroxide Ba(OH) 2 Barium hydroxide Al(OH) 3 Aluminum hydroxide Fe(OH) 3 Iron(III) hydroxide 7

L EARNING C HECK Match the formulas with the names. A. ___HNO 2 1) Iodic acid B. ___Ca(OH) 2 2) Sulfuric acid C. ___H 2 SO 4 3) Sodium hydroxide D. ___HIO 3 4) Nitrous acid E. ___NaOH5) Calcium hydroxide 8

C OMPARING A CIDS AND B ASES 9 Copyright © 2009 by Pearson Education, Inc.

L EARNING C HECK Identify each as a characteristic of an A) acid or B) base. ____1. has a sour taste ____2. produces OH − in aqueous solutions ____3. has a chalky taste ____4. is an electrolyte ____5. produces H + in aqueous solutions 10

B R Ø NSTED -L OWRY A CIDS AND B ASES According to the Br Ø nsted-Lowry theory, acids donate a proton (H + ). bases accept a proton (H + ). 11

NH 3, A B R Ø NSTED -L OWRY B ASE In the reaction of ammonia and water, NH 3 is the base that accepts H +. H 2 O is the acid that donates H +. 12

C ONJUGATE A CID -B ASE P AIRS In any acid-base reaction, there are two conjugate acid-base pairs. Each pair is related by the loss and gain of H +. One pair occurs in the forward direction. One pair occurs in the reverse direction. conjugate acid-base pair 1 HA + B A − + BH + conjugate acid-base pair 2 13

C ONJUGATE A CIDS AND B ASES In this acid-base reaction, an acid, HF, donates H + to form its conjugate base, F −. a base, H 2 O, accepts H + to form its conjugate acid, H 3 O+. there are two conjugate acid-base pairs. 14

C ONJUGATE A CID -B ASE P AIRS In the reaction of HF and H 2 O, one conjugate acid-base pair is HF/F −. the other conjugate acid-base pair is H 2 O/H 3 O +. each pair is related by a loss and gain of H +. 15

C ONJUGATE A CID -B ASE P AIRS In the reaction of NH 3 and H 2 O, one conjugate acid-base pair is NH 3 /NH 4 + the other conjugate acid-base is H 2 O/H 3 O +. 16

L EARNING C HECK A. Write the conjugate base of each of the following: 1. HBr 2. H 2 S 3. H 2 CO 3 B. Write the conjugate acid of each of the following: 1. NO 2 − 2. NH 3 3. OH − 17

L EARNING C HECK Identify the sets that contain acid-base conjugate pairs. 1. HNO 2, NO 2 − 2. H 2 CO 3, CO 3 2− 3. HCl, ClO 4 − 4. HS −, H 2 S 5. NH 3, NH

L EARNING C HECK A. The conjugate base of HCO 3 − is 1. CO 3 2− 2. HCO 3 − 3. H 2 CO 3 B. The conjugate acid of HCO 3 − is 1. CO 3 2− 2. HCO 3 − 3. H 2 CO 3 C. The conjugate base of H 2 O is 1. OH − 2. H 2 O 3. H 3 O + D. The conjugate acid of H 2 O is 1. OH − 2. H 2 O 3. H 3 O + 19

C HAPTER 8 A CIDS AND B ASES 8.2 Strengths of Acids and Bases 20

S TRENGTHS OF A CIDS A strong acid completely ionizes (100%) in aqueous solutions. HCl( g ) + H 2 O( l ) H 3 O + ( aq ) + Cl − ( aq ) A weak acid dissociates only slightly in water to form a few ions in aqueous solutions. H 2 CO 3 ( aq ) + H 2 O( l ) H 3 O + ( aq ) + HCO 3 − ( aq ) 21

S TRONG A CIDS In water, the dissolved molecules of a strong acid dissociate into ions. give large concentrations of H 3 O + and the anion (A − ). 22

W EAK A CIDS In weak acids, only a few molecules dissociate. most of the weak acid remains as the undissociated (molecular) form of the acid. the concentrations of the H 3 O + and the anion (A − ) are small. 23 HA( aq ) + H 2 O( l ) H 3 O( aq ) + A − ( aq )

S TRONG AND W EAK A CIDS In an HCl solution, the strong acid HCl dissociates 100%. A solution of the weak acid HC 2 H 3 O 2 contains mostly molecules and a few ions. 24

S TRONG A CIDS Strong acids make up six of all the acids. have weak conjugate bases. 25 Copyright © 2009 by Pearson Education, Inc.

W EAK A CIDS Weak acids make up most of the acids. have strong conjugate bases. 26

S TRONG B ASES Strong bases are formed from metals of Groups 1A (1) and 2A (2). include LiOH, NaOH, KOH, and Ca(OH) 2. dissociate completely in water. KOH( s ) K + ( aq ) + OH − ( aq ) 27

W EAK B ASES Weak bases are most other bases. dissociate only slightly in water. form only a few ions in water. NH 3 ( g ) + H 2 O( l ) NH 4 + ( aq ) + OH − ( aq ) 28

L EARNING C HECK Identify each of the following as a strong or weak acid or base. A. HBr B. HNO 2 C. NaOH D. H 2 SO 4 E. Cu(OH) 2 29

L EARNING C HECK Identify the stronger acid in each pair. 1. HNO 2 or H 2 S 2. HCO 3 − or HBr 3. H 3 PO 4 or H 3 O + 30

C HAPTER 8 A CIDS AND B ASES 8.3 Ionization of Water 31

I ONIZATION OF W ATER In water, H + is transferred from one H 2 O molecule to another. one water molecule acts as an acid, while another acts as a base. H 2 O + H 2 O H 3 O + + OH − : O : H + H: O : H : O :H + + : O : H − H H H water water hydronium hydroxide ion (+) ion (-) 32

P URE W ATER IS N EUTRAL In pure water, the ionization of water molecules produces small, but equal quantities of H 3 O + and OH − ions. molar concentrations are indicated in brackets as [H 3 O + ] and [OH − ]. [H 3 O + ] = 1.0 x 10 − 7 M [OH − ] = 1.0 x 10 − 7 M 33

A CIDIC S OLUTIONS Adding an acid to pure water increases the [H 3 O + ]. causes the [H 3 O + ] to exceed 1.0 x M. decreases the [OH − ]. 34

B ASIC S OLUTIONS Adding a base to pure water increases the [OH − ]. causes the [OH − ] to exceed 1.0 x 10 − 7 M. decreases the [H 3 O + ]. 35

C OMPARISON OF [H 3 O + ] AND [OH − ] 36 Copyright © 2009 by Pearson Education, Inc.

I ON P RODUCT OF W ATER, K W The ion product constant, K w, for water is the product of the concentrations of the hydronium and hydroxide ions. K w = [ H 3 O + ] [ OH − ] can be obtained from the concentrations in pure water. K w = [ H 3 O + ] [ OH − ] K w = [1.0 x 10 − 7 M] x [ 1.0 x 10 − 7 M] = 1.0 x 10 − 14 37

[H 3 O + ] AND [OH − ] IN S OLUTIONS 38 In neutral, acidic, or basic solutions, the K w is always 1.0 x 10 −14. [ OH - ]

C ALCULATING [H 3 O + ] What is the [H 3 O + ] of a solution if [OH − ] is 5.0 x M? STEP 1: Write the K w for water. K w = [H 3 O + ][OH − ] = 1.0 x 10 −14 STEP 2: Rearrange the K w expression. [H 3 O + ] = STEP 3: Substitute [OH − ]. [H 3 O + ] = 39

L EARNING C HECK If lemon juice has [H 3 O + ] of 2 x 10 −3 M, what is the [OH − ] of the solution? 1) 2 x 10 −11 M 2) 5 x 10 −11 M 3) 5 x 10 −12 M 40

L EARNING C HECK The [OH − ] of an ammonia solution is 4.0 x 10 −2 M. What is the [H 3 O + ] of the solution? 1) 2.5 x 10 − 11 M 2) 2.5 x 10 −12 M 3) 2.5 x 10 −13 M 41