UNIT 9 CHEMISTRY OF SOLUTIONS

Transcription

1 UNIT 9 CHEMISTRY OF SOLUTIONS Acids and Bases 2013 Pearson Education, Inc. Chapter 10, Section 1 1 1

2 Arrhenius Acids Arrhenius acids produce H + ions in water. H 2 O have a sour taste. turn blue litmus paper red. corrode some metals. Turn cabbage indicator pink Turn universal indicator red Citrus fruits are sour because of the presence of acids Pearson Education, Inc. Chapter 10, Section 1 2

3 Bases Arrhenius bases produce OH ions in water. taste bitter or chalky. feel soapy and slippery. turn red litmus paper blue. turn purple cabbage indicator green Turn universal indicator blue/purple Pearson Education, Inc. Chapter 10, Section 1 3

4 Some Common Bases Bases with OH ions are named as the hydroxide of the metal in the formula. NaOH KOH Ba(OH) 2 Al(OH) 3 Fe(OH) 3 sodium hydroxide potassium hydroxide barium hydroxide aluminum hydroxide iron (III) hydroxide 2013 Pearson Education, Inc. Chapter 10, Section 1 4

5 Base Ca(OH) 2 Slaked Lime Calcium hydroxide, Ca(OH) 2, also called slaked lime, is used to produce beverages, neutralize acids, and in dentistry as a filler for root canals Pearson Education, Inc. Chapter 10, Section 1 5

6 Comparing Acids and Bases 2013 Pearson Education, Inc. Chapter 10, Section 1 6

7 Brønsted Lowry Acids According to the Brønsted Lowry theory, acids donate a proton (H + ). In the reaction of hydrochloric acid and water, HCl is the acid that donates H +, and H 2 O is the base that accepts H Pearson Education, Inc. Chapter 10, Section 1 7

8 Brønsted Lowry Bases According to the Brønsted Lowry theory, bases accept a proton (H + ). In the reaction of ammonia and water, NH 3 is the base that accepts H +, and H 2 O is the acid that donates H Pearson Education, Inc. Chapter 10, Section 1 8

9 Conjugate Acid Base Pairs In any acid base reaction, there are two conjugate acid base pairs. Each is related by the loss and gain of H +. One occurs in the forward direction. One occurs in the reverse direction. conjugate acid base pair 1 HA conjugate acid base pair Pearson Education, Inc. Chapter 10, Section 1 9

10 Conjugate Acids and Bases, HF The first conjugate acid base pair is HF/F. HF loses one H + to form its conjugate base F. The other conjugate acid base pair is H 2 O/H 3 O +. H 2 O acts as a base accepting one H + to form its conjugate acid H 3 O Pearson Education, Inc. Chapter 10, Section 1 10

11 Conjugate Acids and Bases, NH 3 The first conjugate acid base pair is NH 3 /NH 4+. NH 3, acts as a base by gaining H + to form its conjugate acid NH 4+. The other conjugate acid base pair is H 2 O/OH. H 2 O acts as an acid by donating one H + to form its conjugate base OH Pearson Education, Inc. Chapter 10, Section 1 11

12 Learning Check 1. Write the conjugate base of the following. A. HBr B. H 2 S C. H 2CO 3 2. Write the conjugate acid of the following. A. NO 2 B. NH 3 C. OH 2013 Pearson Education, Inc. Chapter 10, Section 1 12

13 Learning Check Identify the sets that contain acid base conjugate pairs. A. HNO 2, NO 2 B. H 2 CO 3, CO 3 2 C. HCl, ClO 4 D. HS, H 2 S E. NH 3, NH Pearson Education, Inc. Chapter 10, Section 1 13

14 Learning Check 1. The conjugate base of HCO 3 is A. CO 3 2. B. HCO 3. C. H 2 CO The conjugate acid of HCO 3 is A. CO 2 3. B. HCO 3. C. H 2CO The conjugate base of H 2 O is A. OH. B. H 2 O. C. H 3 O The conjugate acid of H 2 O is A. OH. B. H 2 O. C. H 3 O Pearson Education, Inc. Chapter 10, Section 1 14

15 Learning Check Identify the acid base conjugate pairs Pearson Education, Inc. Chapter 10, Section 1 15

16 Strengths of Acids Strong acids completely ionize (100%) in aqueous solutions. We use a single arrow in the chemical equation. HCl(g) + H 2 O(l) H 3 O + (aq) + Cl (aq) Weak acids dissociate only slightly in water to form a solution of mostly molecules and a few ions. H 2 CO 3 (aq) + H 2 O(l) H 3 O + (aq) + HCO 3 (aq) 2013 Pearson Education, Inc. Chapter 10, Section 1 16

17 Strong and Weak Acids There are six strong acids in solution. HCl, a strong acid, dissociates 100%. Acetic acid (CH 3 COOH), a weak acid, is mostly molecules and only a few ions Pearson Education, Inc. Chapter 10, Section 1 17

18 Stronger Acid, Weaker Conjugate Base Weaker acids have a varying degree of strength. The stronger the acid, the weaker the conjugate base Pearson Education, Inc. Chapter 10, Section 1 18

19 Stronger Acid, Weaker Conjugate Base Weak acids make up most of the acids and have strong conjugate bases. Increasing Acid Strength Increasing Base Strength 2013 Pearson Education, Inc. Chapter 10, Section 1 19

20 H 2 CO 3, Weak Acid H 2 CO 3 is a diprotic acid. It partially dissociates in water, giving up one H + at a time. H 2 CO 3 (aq) + H 2 O(l) H 3 O + (aq) + HCO 3 (aq) Because HCO 3 is also a weak acid, a second dissociation can take place to produce another hydronium ion and the carbonate ion. HCO 3 (aq) + H 2 O(l) H 3 O + (aq) + CO 3 2 (aq) 2013 Pearson Education, Inc. Chapter 10, Section 1 20

21 H 2 SO 4, Strong Acid H 2 SO 4 is also a diprotic acid. It completely dissociates in water. H 2 SO 4 (aq) + H 2 O(l) H 3 O + (aq) + HSO 4 (aq) Because HSO 4 is a weak acid, a second dissociation takes place to produce another hydronium ion and the sulfate ion. HSO 4 (aq) + H 2 O(l) H 3 O + (aq) + SO 4 2 (aq) 2013 Pearson Education, Inc. Chapter 10, Section 1 21

22 Strong Bases 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) 2013 Pearson Education, Inc. Chapter 10, Section 1 22

23 Weak Bases 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) 2013 Pearson Education, Inc. Chapter 10, Section 1 23

24 Common Household Bases Bases in Household Products are used to clean, remove grease, and to open drains Pearson Education, Inc. Chapter 10, Section 1 24

25 Learning Check 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) Pearson Education, Inc. Chapter 10, Section 1 25

26 Learning Check Identify the stronger acid in each pair. A. HNO 2 or H 2 S B. HCO 3 or HBr C. H 3 PO 4 or H 3 O Pearson Education, Inc. Chapter 10, Section 1 26

27 Auto-Ionization of Water In the auto-ionization of 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(l) + H 2 O(l) H 3 O + (aq) + OH (aq) 2013 Pearson Education, Inc. Chapter 10, Section 1 27

28 Ion Product of Water, K w The ion product constant, K w, for water at 25 C is the product of the concentrations of the hydronium and hydroxide ions. K w = [ H 3 O + ][ OH ] is obtained from the concentrations in pure water. K w = [ H 3 O + ][ OH ] K w = [1.0 x 10 7 M][1.0 x = 1.0 x Pearson Education, Inc. Chapter 10, Section 1 28

29 Pure Water is Neutral In pure water, the ionization of water molecules produces small but equal quantities of H 3 O + and OH ions Pearson Education, Inc. Chapter 10, Section 1 29

30 Acidic Solutions Adding an acid to pure water increases the [H 3 O + ], decreases the [OH ], and causes the [H 3O + ] to exceed 1.0 x 10 7 M Pearson Education, Inc. Chapter 10, Section 1 30

31 Basic Solutions Adding a base to pure water, increases the [OH ], decreases the [H 3 O + ], and causes the [OH ] to exceed 1.0 x 10 7 M Pearson Education, Inc. Chapter 10 Section 3 31

32 Comparison of [H 3 O + ] and [OH ] 2013 Pearson Education, Inc. Chapter 10, Section 1 32

33 [H 3 O + ] and [OH ] in Solutions In neutral, acidic, or basic solutions, the K w at 25 C is always 1.0 x Pearson Education, Inc. Chapter 10, Section 1 33

34 Guide to Calculating [H 3 O + ] and [OH ] 2013 Pearson Education, Inc. Chapter 10, Section 1 34

35 Calculating [H 3 O + ] What is the [H 3 O + ] of a solution if [OH ] is 5.0 x 10 8 M? Step 1 Write the K w for water. K w = [H 3 O + ][OH ] Step 2 Solve the K + w for the unknown [H 3 O ]. [H 3 O + ] = 1.0 x [OH ] Step 3 Substitute the known [OH ] into the equation and calculate. [H 3 O + ] = 1.0 x Pearson Education, Inc. Chapter 10, Section 1 35

36 Learning Check If lemon juice has [H 3 O + ] of 2 x 10 3 M, what is the [OH ] of the solution? A. 2 x M B. 5 x M C. 5 x M 2013 Pearson Education, Inc. Chapter 10, Section 1 36

37 Solution If lemon juice has [H 3 O + ] of 2 x 10 3 M, what is the [OH ] of the solution? Step 1 Write the K w for water. K w = [H 3 O + ][OH ] = 1.0 x Step 2 Solve the K w for the unknown [OH ]. [OH ] = 1.0 x [H 3 O + ] Step 3 Substitute the known [H 3 O + ] into the equation and calculate. [2 x 10 3 ] Answer is C Pearson Education, Inc. Chapter 10, Section 1 37

38 ph Scale The ph of a solution is used to indicate the acidity of a solution. has values that range from 0 to 14 representing the H 3 O + concentration of a solution. is acidic when the values are less than 7. is neutral with a ph of 7. is basic when the values are greater than Pearson Education, Inc. Chapter 10, Section 1 38

39 ph of Everyday Substances 2013 Pearson Education, Inc. Chapter 10, Section 1 39

40 ph: Acidic, Neutral, or Basic Acidic solution ph < 7.0 [H 3 O + ] > 1.0 x 10-7 M Neutral solution ph = 7.0 [H 3 O + ] = 1.0 x 10-7 M Basic solution ph > 7.0 [H 3 O + ] < 1.0 x 10-7 M 2013 Pearson Education, Inc. Chapter 10, Section 1 40

41 ph: Acidic, Neutral, or Basic Acidic solution ph < 7.0 [H 3 O + ] > 1.0 x 10-7 M Neutral solution ph = 7.0 [H 3 O + ] = 1.0 x 10-7 M Basic solution ph > 7.0 [H 3 O + ] < 1.0 x 10-7 M 2013 Pearson Education, Inc. Chapter 10, Section 1 41

42 Measuring ph ph can be measured using a ph meter. ph papers that turn specific colors when placed in solutions of different ph values. test papers and a color comparison chart. indicators that change color with changes in ph Pearson Education, Inc. Chapter 10, Section 1 42

43 Learning Check Identify each solution as acidic, basic, or neutral. A. HCl with a ph = 1.5 B. pancreatic fluid [H 3 O + ] = 1 x 10 8 M C. Sprite soft drink, ph = 3.0 D. ph = 7.0 E. [OH ] = 3 x M F. [H 3 O + ] = 5 x M 2013 Pearson Education, Inc. Chapter 10, Section 1 43

44 Calculating ph ph is the negative logarithm (base 10) of the [H 3 O + ]. For a solution with [H 3 O + ] = 1 x 10 4 M: 2013 Pearson Education, Inc. Chapter 10, Section 1 44

45 Significant Figures in ph When expressing log values, the number of decimal places in the ph is equal to the number of significant figures in the coefficient of [H 3 O + ]. coefficient decimal places 2013 Pearson Education, Inc. Chapter 10, Section 1 45

46 Guide to Calculating ph 2013 Pearson Education, Inc. Chapter 10, Section 1 46

47 Calculate ph from [H 3 O + ] Find the ph of a solution with a [H 3 O + ] of 1.7 x 10 3 M. Step 1 Enter the [H 3 O + ]. Enter 1.7, then press EE or EXP. Enter 3, and then /+ to change the sign or or 1.7E 03 Calculator Display Step 2 Press log key and change the sign. log / Pearson Education, Inc. Chapter 10, Section 1 47

48 Calculate ph from [H 3 O + ] Find the ph of a solution with a [H 3 O + ] of 1.7 x 10 3 M. Step 3 Adjust the number of SFs on the right of the decimal point to equal the SFs in the coefficient. 2 SF 2013 Pearson Education, Inc. Chapter 10, Section 1 48

49 Learning Check What is the ph of coffee if the [H 3 O + ] is 1 x 10 5 M? A. ph = 9.0 B. ph = 7.0 C. ph = Pearson Education, Inc. Chapter 10, Section 1 49

50 Solution What is the ph of coffee if the [H 3 O + ] is 1 x 10 5 M? Step 3 Adjust the number of SFs on the right of the decimal point to equal the SFs in the coefficient. Answer is C. 1 SF 2013 Pearson Education, Inc. Chapter 10, Section 1 50

51 Learning Check The [H 3 O + ] of tomato juice is 2 x 10 4 M. What is the ph of the solution? A. 4.0 B. 3.7 C Pearson Education, Inc. Chapter 10, Section 1 51

52 Learning Check The [OH ] of a solution is 1.0 x 10 3 M. What is the ph? A B C Pearson Education, Inc. Chapter 10, Section 1 52

53 [H 3 O + ], [OH - ], and ph Values 2013 Pearson Education, Inc. Chapter 10, Section 1 53

54 Guide to Calculating [H 3 O + ] from ph 2013 Pearson Education, Inc. Chapter 10, Section 1 54

55 Calculating [H 3 O + ] from ph Calculate the [H 3 O + ] for a ph value of Step 1 Enter the ph value and change the sign. Enter 8.25 / Calculator display Step 2 Convert ph to concentration. Press the 2nd function key and then the 10 x key. 2 nd 10 x or or E 09 Or, press the inverse key and then the log key. inv log Calculator display 2013 Pearson Education, Inc. Chapter 10, Section 1 55

56 Calculating [H 3 O + ] from ph Calculate the [H 3 O + ] for a ph value of Step 3 Adjust the SFs in the coefficient. 2 SF 2013 Pearson Education, Inc. Chapter 10, Section 1 56

57 Learning Check What is the [H 3 O + ] of a solution with a ph of 11.2? A. 6 x M B x M C x M 2013 Pearson Education, Inc. Chapter 10, Section 1 57