Acids and Bases. Properties of Acids. Properties of Bases. Slide 1 / 174. Slide 2 / 174. Slide 3 / 174

Transcription

1 Slide 1 / 174 Acids and Bases PSI Chemistry covers the material approximately up to slide 75. Properties of Acids Slide 2 / 174 Acids release hydrogen ion(s) into (aqueous) solution Acids neutralize bases in a neutralization reaction. Acids corrode active metals. Acids turn blue litmus to red. Acids taste sour. Properties of Bases Slide 3 / 174 Bases release a hydroxide ion(s) into a water solution. Bases neutralize acids in a neutralization reaction. Bases denature protein. Bases turn red litmus to blue. Bases taste bitter.

2 Arrhenius Acids and Bases Slide 4 / 174 A definition of acids and bases from the 1800's Considered obsolete now since it only relates to reactions in water, aqueous solutions. He defined acids and bases this way: An acid is a substance that, when dissolved in water, increases the concentration of hydrogen ions. A base is a substance that, when dissolved in water, increases the concentration of hydroxide ions. BrønstedLowry Acids and Bases Slide 5 / 174 A more modern definition: formulated in the early 1900's More general since it works for all reactions; not just in water An acid is a proton, H +, donor. A base is a proton, H +, acceptor. BrønstedLowry Acids and Bases Slide 6 / 174 A BrønstedLowry acid: must have a removable (acidic) proton or must transfer a proton to another substance A BrønstedLowry base: must have a pair of nonbonding electrons or must accept a proton

3 1 A BronstedLowry base is defined as a substance that. Slide 7 / 174 A B C D E increases [H+] when placed in H2O decreases [H+] when placed in H2O increases [OH] when placed in H2O acts as a proton acceptor acts as a proton donor 2 A BronstedLowry acid is defined as a substance that. Slide 8 / 174 A B C D E increases Ka when placed in H2O decreases [H + ] when placed in H2O increases [OH ] when placed in H2O acts as a proton acceptor acts as a proton donor BrønstedLowry Acids and Bases HCl + H 2 O # Cl + H 3 O + Slide 9 / HCl donates the proton and acts as a BrønstedLowry acid _ + H 2 O accepts the proton and acts as a BrønstedLowry base H 3 O + is called a hydrated proton or a hydronium ion. It is also written as H +

4 Lewis Acids Slide 10 / 174 BrønstedLowry acids replaced Arrhenius acids because the former were more general: Arrhenius acids could only be defined in aqueous (water) solutions. BrønstedLowry acids don't have that limitation. Similarly, BrønstedLowry acids are limited to substances that gain or lose hydrogen. But there are acids and bases that don't. The most general approach is that of Lewis acids; which don't require an aqueous environment or an exchange of hydrogen. Lewis Acids Slide 11 / 174 Lewis acids are defined as electronpair acceptors. Atoms with an empty valence orbital can be Lewis acids. Lewis Bases Slide 12 / 174 Lewis bases are defined as electronpair donors. Anything that could be a BrønstedLowry base is a Lewis base. Lewis bases can interact with things other than protons, however. Therefore, this definition is the broadest of the three.

5 3 Which of the following compounds could never act as an acid? Slide 13 / A SO 4 B HSO 4 C H 2 SO 4 D NH 3 E CH 3 COOH 4 According to the following reaction model, which reactant is acting like an acid? H 2 O + H 2 SO 4 H 3 O + + HSO 4 Slide 14 / 174 A H 2 SO 4 B H 2 O C H 3 O + D HSO 4 E None of the above 5 According to the following reaction, which reactant is acting as a base? Slide 15 / 174 H 3 O + + HSO 4 H 2 O + H 2 SO 4 A H 2 SO 4 B H 2 O C H 3 O + D HSO 4 E None of the above

6 6 For the following reaction, identify whether the compound in bold is behaving as an acid or a base. H 3 PO 4 + H 2 O H 2 PO 4 + H 3 O + A B C D E Acid Base Neither Both None of the above Slide 16 / For the following reaction, identify whether the compound in bold is behaving as an acid or a base. Slide 17 / 174 H 3 PO 4 + H 2 O H 2 PO 4 + H 3 O + A B C D E Acid Base Both Neither None of the above 8 For the following reaction, identify whether the compound in bold is behaving as an acid or a base. Slide 18 / 174 H 3 PO 4 + H 2 O H 2 PO 4 + H 3 O + A B C D E Acid Base Both Neither None of the above

7 Acids in Water Slide 19 / 174 What Happens When an Acid Dissolves in Water? + Which is the acid? _ + Which is the base? Water acts as a BrønstedLowry base and takes a proton (H+) from the acid. As a result, the conjugate base of the acid and a hydronium ion are formed. Conjugate Acids and Bases Slide 20 / 174 The term conjugate comes from the Latin word conjugare, meaning to join together. Reactions between acids and bases always yield their conjugate bases and acids. remove H + HNO 2(aq) + H 2O(l) NO 2 (aq) + H 3O (aq) Acid Base Conjugate conjugate base acid add H+ Conjugate Acids and Bases remove H + Slide 21 / 174 HNO 2(aq) + H 2O(l) NO 2 (aq) + H 3O (aq) Acid Base Conjugate conjugate base acid add H+ After the acid donates a proton, the result is called its conjugate base. After the base accepts a proton, the result is called its conjugate acid.

8 Amphoteric Substances If a substance can act both as an acid and base, it is known as amphoteric. For example, water can act as a base or acid depending on the situation. HCl + H 2 O Cl + H 3 O + Above, water accepts a proton, thus acting as a base. NH 3 +H 2 O NH OH Above, water donates a proton, thus acting as an acid. Slide 22 / A substance that is capable of acting as both an acid and as a base is. Slide 23 / 174 A B C D E autosomal conjugated amphoteric saturated miscible Amphoteric Substances Slide 24 / 174 Another term for amphoteric is amphiprotic. For each of the following substances, write two equations, one showing it as a BronstedLowry acid and another showing it as a BronstedLowry base. HCO 3 HSO 4 H 2 O

9 10 What is the conjugate acid of NH 3? Slide 25 / 174 A B C D E NH 3 + NH 2 + NH 3 + NH 4 NH 4OH 11 What are the conjugate bases of HClO 4, H 2 S, PH 4 +, HCO 3? Slide 26 / 174 A B C ClO 4 +, HS, PH 3, CO 3 ClO 4, HS, PH 3, CO 3 2 ClO 4 2, HS 2, PH 3 3, CO 3 2 Acid and Base Strength Slide 27 / % ionized in H2O Acid strength increases Acid Base HCl Cl H2SO4 HSO4 HNO3 NO3 H3O + H2O HSO4 SO4 2 H3PO4 H2PO4 HF F HC2H3O2 C2H3O2 H2CO3 HCO3 H2S HS H2PO4 HPO4 2 NH4 + NH3 HCO3 CO3 2 HPO4 2 PO4 3 H2O OH OH O 2 Strong Weak N Strong Weak Negligible H2 H CH4 CH3 Base strength increases 100% protonated in H2O Strong acids are completely dissociated in water. Their conjugate bases are quite weak.

10 Acid and Base Strength Slide 28 / % ionized in H2O Acid strength increases Acid Base HCl Cl H2SO4 HSO4 HNO3 NO3 H3O + H2O 2 HSO4 SO4 H3PO4 H2PO4 HF F HC2H3O2 C2H3O2 H2CO3 HCO3 H2S HS 2 H2PO4 HPO4 + NH4 NH3 HCO3 CO HPO4 PO4 H2O OH OH O 2 Strong Weak N Strong Weak Negligible H2 H CH4 CH3 Base strength increases 100% protonated in H2O Weak acids only dissociate partially in water. Their conjugate bases are weak bases. Acid and Base Strength Slide 29 / % ionized in H2O Acid strength increases Acid Base HCl Cl H2SO4 HSO4 HNO3 NO3 H3O + H2O HSO4 SO4 2 H3PO4 H2PO4 HF F HC2H3O2 C2H3O2 H2CO3 HCO3 H2S HS H2PO4 HPO4 2 NH4 + NH3 HCO3 CO3 2 HPO4 2 PO4 3 H2O OH OH O 2 Strong Weak Negligible Strong Weak H2 H CH4 CH3 Base strength increases 100% protonated in H2O Substances with negligible acidity do not dissociate in water. They will not readily give up protons. Their conjugate bases are exceedingly strong. Strong Acids Slide 30 / 174 The seven strong acids are: HCl hydrochloric acid HBr hydrobromic acid HI hydroiodic acid HNO 3 nitric acid H 2 SO 4 sulfuric acid HClO 3 chloric acid HClO 4 perchloric acid Memorize this list.

11 Strong Acids Slide 31 / 174 The seven strong acids are strong electrolytes because they are 100% ionized. In other words, these compounds exist totally as ions in aqueous solution. For the monoprotic strong acids (acids that donates only one proton per molecule of the acid), the hydronium ion concentration equals the acid concentration. [acid] = [H 3 O + ] So, if you have a solution of 0.5 M HCl, then [H 3 O + ] = 0.5 M Strong Bases All strong bases are group of compounds called "metal hydroxides." Slide 32 / 174 All alkali metals in Group I form hydroxides that are strong bases: LiOH, NaOH, KOH, etc. Only the heavier alkaline earth metals in Group II form strong bases: Ca(OH) 2, Sr(OH) 2, and Ba(OH) 2. Again, these substances dissociate completely in aqueous solution. In other words, NaOH exists entirely as Na + ions and OH ions in water. 12 What is the hydroxide ion concentration of a 0.22 M calcium hydroxide solution? Slide 33 / 174 A 0.11 B 0.22 C 0.44 D 0.88 E Not enough information.

12 13 What is the concentration of a 25ml solution of 0.05M HCl when diluted to final volume of 100ml? Slide 34 / What is the concentration of a 50 ml solution of 0.025M H 2 SO 4 diluted with 150 ml of water? Slide 35 / What is the [H + ] ion concentration of a 50 ml solution of 0.025M H 2 SO 4, when diluted with 150 ml of water? Slide 36 / 174

13 16 A solution of 25 ml of 0.1M HCl and 50 ml of 0.5M HNO 3 are mixed together. What is the [H+] ion concentration of the resulting solution? Slide 37 / A solution of 25 ml of 0.1M HCl and 50 ml of 0.5M HNO 3 are mixed together. What is the molarity of the resulting solution? Slide 38 / 174 Acid and Base Strength Slide 39 / 174 In any acidbase reaction, equilibrium will favor the reaction in which the proton moves toward the stronger base. In other words, a stronger base will "hold onto" its proton whereas a strong acid easily releases its proton(s). 100% ionized in H2O An alternative way to consider equilibrium is that it will favor the reaction AWAY from the stronger acid. Acid Base HCl Cl H2SO4 HSO4 HNO3 H3O + HSO4 NO3 H2O 2 SO4 H2PO4 H3PO4 HF F HC2H3O2 C2H3O2 H2CO3 HCO3 H2S HS Weak Negligible Strong Weak Negligible HCl (aq) + H 2 O (l) H 3 O + (aq) + Cl (aq) acid base conj. acid conj. base Acid strength increases H2PO4 HPO4 2 + NH4 NH3 2 HCO3 CO3 2 3 HPO4 PO4 H2O OH OH O 2 H2 H CH4 CH3 Base strength increases 100% protonated in H2O

14 Acid and Base Strength HCl (aq) + H 2 O (l) H 3 O + (aq) + Cl (aq) acid base conj. acid conj. base Slide 40 / 174 Acid Base 100% ionized in H2O Acid strength increases HCl Cl H2SO4 HSO4 HNO3 NO3 H3O + H2O HSO4 SO4 2 H3PO4 H2PO4 HF F HC2H3O2 C2H3O2 H2CO3 HCO3 H2S HS Strong Weak Negligible Strong Weak Negligible H2PO4 HPO4 2 NH4 + NH3 HCO3 CO3 2 HPO4 2 PO4 3 H2O OH OH O 2 Base strength increases 100% H2 H CH4 CH3 protonated in H2O In this example, H 2 O is a much stronger base than Cl, so the proton moves from HCl to H 2 O Conversely, HCl is a much stronger acid than the hydronium ion, so equilibrium lies very far to the right K >>1 Acid and Base Strength Consider this equilibrium between acetic acid and acetate ion: Slide 41 / 174 CH 3 COOH (aq) + H 2 O (l) H 3 O + (aq) + CH 3 COO (aq) Does equilibrium lie to the left (K<1) or to the right (K>1)? If you look for the stronger acid: If you look for the stronger base: Equilib lies away from the stronger acid. Equilib favors this base accepting a proton. Acid and Base Strength Slide 42 / 174 CH 3 COOH (aq) + H 2 O (l) H 3 O + (aq) + CH 3 COO (aq) 100% ionized in H2O Acid strength increases Acid Base HCl Cl H2SO4 HSO4 HNO3 NO3 H3O + H2O HSO4 SO4 2 H3PO4 H2PO4 HF F HC2H3O2 C2H3O2 H2CO3 HCO3 H2S HS H2PO4 + HPO4 2 NH4 NH3 HCO3 CO3 2 HPO4 2 PO4 3 H2O OH OH O 2 Strong Weak Neglig Base strength increases Strong Weak Negligible H2 H 100% CH4 CH3 protonated in H2O Since the hydronium ion is a stronger acid than acetic acid, equilibrium lies to the left (K<1).

15 Acid and Base Strength Slide 43 / 174 Acetic acid is a weak acid. This means that only a small percent of the acid will dissociate. The double headed arrow is used only in weak acid or weak base dissociation equations. CH 3 CO 2 H (aq) + H 2 O(l) H 3 O + (aq) + CH 3 CO 2 (aq) A single arrow is used for strong acid or strong bases which dissociate completely. NaOH Na + (aq) + OH (aq) 18 Strong acids have conjugate bases. Slide 44 / 174 A B C D strong weak neutral negative 19 HBr, hydrobromic acid is a strong acid. This means that. Slide 45 / 174 A B C D aqueous solutions of HBr contain equal concentrations of H + and OH does not dissociate at all when it is dissolved in water cannot be neutralized by a base dissociates completely to H + and Br when it dissolves in water

16 Autoionization of Water Slide 46 / 174 As we have seen, water is amphoteric, meaning that it can act as either an acid or a base. In pure water, a few molecules act as bases and a few act as acids, in a process referred to as autoionization. H O + H O H O H + O H H H H The double headed arrow indicates that both the forward and reverse reactions occur simultaneously. H 2 O (l) + H 2 O (l) H 3 O + (aq) + OH (aq) Autoionization of Water H 2 O (l) + H 2 O (l) H 3 O + (aq) + OH (aq) Slide 47 / 174 When there is an equilibrium state, the ratio of products to reactants yields a constant. This value is known as the equilibrium constant, K and will be discussed in more depth later in this unit. All concentrations are in M, molarity, as designated by brackets, [ ]. K = [H 3O + ] x [OH ] [H 2O] x [H 2O] IonProduct Constant Slide 48 / 174 In most dilute acid and base solutions, the concentration of undissociated water, remains more or less a constant. We can thus disregard the denominator in the equilibrium expression. So, K = [H3O+ ] x [OH ] [H 2O] x [H 2O] becomes K w = [H 3O + ] x [OH ]

17 IonProduct Constant Slide 49 / 174 K w = [H 3 O + ] x [OH ] This special equilibrium constant, K w is referred to as the ionproduct constant for water. At 25 C, K w = 1.0 x Since this is such a small number, we conclude that pure water contains relatively very few ions. 20 The magnitude of K w indicates that Slide 50 / 174 A B C D water ionizes to a very small extent the autoionization of water is exothermic water ionizes very quickly water ionizes very slowly 21 The ionproduct constant for water, K w is represented by Slide 51 / 174 A [H2O] 2 B [H 3 O + ] x [OH ] C [H 3 O + ] + [OH ] D [H 3O + ] [OH ]

18 ph Slide 52 / 174 It is a measure of hydrogen ion concentration, [H + ] in a solution, where the concentration is measured in moles H + per liter, or molarity. The ph scale ranges from 014. ph is defined as the negative base10 logarithm of the concentration of hydronium ion. ph = log [H 3 O + ] ph Slide 53 / 174 ph is defined as the negative base10 logarithm of the concentration of hydronium ion. ph = log [H 3O + ] Hydrogen ion concentration, [H+] in moles/liter ph 1.0 x x x Is the relationship between [H + ] and ph a direct or an inverse one? ph Slide 54 / 174 Because of the base10 logarithm, each 1.0point value on the ph scale differs by a value of ten. A solution with ph = 9 has a hydrogen ion concentration, [H + ], that is ten times more than a ph = 10 solution. A solution with ph = 8 has a hydrogen ion concentration, [H + ], that is 10 2 or 100 times more than a ph = 10 solution. A solution with ph = 7 has a hydrogen ion concentration, [H + ], that is 10 3 or 1000 times more than a ph = 10 solution.

19 ph Slide 55 / 174 Recall that in pure water, the ionproduct is K w = In pure water, the hydronium ion concentration and hydroxide ion concentrations are equal: [H 3 O + ] = [OH ] Therefore, in pure water, [H 3 O + ] = = 1.0 x 10 7 M and [OH ] = = 1.0 x 10 7 M 22 The molar concentration of hydronium ion, [H 3 O + ], in pure water at 25 C is. Slide 56 / 174 A 0 B 1 C 7 D 10 7 E A solution with ph = 3 has a hydrogen ion concentration that is than a solution with ph = 5. Slide 57 / 174 A B C D 2x more 2x less 100x more 100x less

20 24 A solution with ph = 14 has a hydrogen ion concentration that is than a solution with ph = 11. Slide 58 / 174 A B C D 3x more 3x less 1000x more 1000x less ph Slide 59 / 174 Therefore, in pure water, ph = log [H 3 O + ] = 7.00 ph = log ( ) = 7.00 An acid has a higher [H 3 O + ] than pure water, so its ph is <7. A base has a lower [H 3 O + ] than pure water, so its ph is >7. Solution type [H +](M) [OH] (M) ph value Acidic > 1.0x10 7 <1.0x10 7 <7.00 Neutral =1.0x10 7 =1.0x10 7 =7.00 Basic <1.0x10 7 > 1.0x10 7 >7.00 ph Slide 60 / 174 ACID [H+] > [OH] There are excess hydrogen ions in solution. BASE [H+] < [OH] There are excess hydroxide ions in solution. Solution type [H +](M) [OH] (M) ph value Acidic > 1.0x10 7 <1.0x10 7 <7.00 Neutral =1.0x10 7 =1.0x10 7 =7.00 Basic <1.0x10 7 > 1.0x10 7 >7.00

21 25 For a basic solution, the hydrogen ion concentration is than the hydroxide ion concentration. Slide 61 / 174 A B C D greater than less than equal to Not enough information. 26 For an acidic solution, the hydroxide ion concentration is than the hydrogen ion concentration. Slide 62 / 174 A B C D greater than less than equal to Not enough information. 27 Which solution below has the highest concentration of hydroxide ions? Slide 63 / 174 A ph = 3.21 B ph = 7.00 C ph = 8.93 D ph = 12.6

22 28 Which solution below has the lowest concentration of hydrogen ions? Slide 64 / 174 A ph = 11.4 B ph = 8.53 C ph = 5.91 D ph =1.98 ph These are the ph values for several common substances. More acidic Battery acid lemon juice gastric fluid carbonated beverages vinegar orange juice Slide 65 / 174 pure rain or water beer coffee egg yolks milk distilled water sea water baking soda blood milk of magnesia household ammonia More basic household bleach household lye 29 For a 1.0M solution of a weak base, a reasonable ph would be. Slide 66 / 174 A 2 B 6 C 7 D 9 E 13

23 30 For a 1.0M solution of a strong acid, a reasonable ph would be. Slide 67 / 174 A 2 B 6 C 7 D 9 E A solution with the ph of 5.0 Slide 68 / 174 A is basic B has a hydrogen ion concentration of 5.0M C is neutral D has a hydroxideion concentration of 1x The ph of a solution with a concentration of 0.01M hydrochloric acid is Slide 69 / 174 A 10 2 B 12 C 2 D 10 12

24 How Do We Measure ph? Slide 70 / 174 For less accurate measurements, one can use Litmus paper Red litmus paper turns blue above ~ph = 8 Blue litmus paper turns red below ~ph = 5 Or an indicator (usually an organic dye) such as one of the following: ph range for color change Methyl violet Thymol blue Methyl orange Methyl red Bromothymol blue Phenolphthalein Alizarin yellow R How Do We Measure ph? Slide 71 / 174 For more accurate measurements, one uses a ph meter, which measures the voltage in the solution. How Do We Calculate ph? Slide 72 / 174 Recall that ph is defined as the negative base10 logarithm of the concentration of hydronium ion (or hydrogen ion). ph = log [H 3 O + ] or ph = log [H + ]

25 How Do We Calculate ph? Slide 73 / 174 What is the ph of the solution with hydrogen ion concentration of 5.67 x 10 8 M (molar)? ph = log [H + ] First, take the log of 5.67 x 10 8 = Now, change the sign from to + Answer: ph = If you take the log of 5.67 x 10 8, you will end up with an incorrect answer. The order of operations: 1. Take the log 2. Switch the sign 33 What is the ph of a solution with a hydrogen ion concentration of 1 x 10 5 M? Slide 74 / 174 A 1 x 10 5 B 5 C 5 D 9 34 What is the ph of a solution with a hydrogen ion concentration of 1 x M? Slide 75 / 174 A 1 x B 12 C 2 D 12

26 35 What is the ph of an aqueous solution at 25.0 C in which [H + ] is M? A B C D E Slide 76 / What is the ph of an aqueous solution at 25.0 C in which [H + ] is M? Slide 77 / 174 A B C D E Additional ph calculations If you are given the ph and asked to find the [H + ] (or [H 3 O + ]) in a solution, use the inverse log. Slide 78 / 174 Since ph = log [H + ], then [H + ] = 10 ph What is the hydrogen ion concentration (M) in a solution of Milk of Magnesia whose ph = 9.8? [H + ] = [H + ] = 1.58 x M or mol/liter

27 37 What is the ph of a solution whose hydronium ion concentration is 7.14 x 10 3 M? Slide 79 / What is the ph of a solution whose hydronium ion concentration is 1.92 x 10 9 M? Slide 80 / What is the hydronium ion concentration in a solution whose ph = 4.29? Slide 81 / 174

28 40 What is the hydroxide ion concentration in a solution whose ph = 4.29? Slide 82 / The ph of an aqueous solution is What is the molarity of the hydrogen ion, H +? Slide 83 / Answer x M Other p Scales Slide 84 / 174 The p in ph tells us to take the negative base10 logarithm of the quantity (in this case, hydronium ions). Some similar examples are poh = log [OH] pk w = log K w pk a = log K a

29 Relationship between ph and poh Slide 85 / 174 Because [H 3 O + ] [OH ] = Kw = 1.0 x 10 14, we know that log [H 3 O + ] + log [OH ] = log K w = or, in other words, ph + poh = pk w = An aqueous solution of an acid has a hydrogen ion concentration of 2.5x10 4. What is the OH ion concentration of this solution? Slide 86 / 174 A 4.0x10 11 B 5.0x10 11 C 4.5x10 8 D 7.5x10 11 E 4.0x An aqueous solution has a hydrogen ion concentration of 1.5x What is the ph of this solution? Slide 87 / 174 Report your answer to 3 significant figures.

30 Acid Dissociation Constants Slide 88 / 174 HA (aq) + H 2 O (l) A (aq) + H 3 O + (aq) For a generalized acid dissociation, the equilibrium expression would be K c, AKA K a = [H 3 O + ][A ] [HA] This equilibrium constant is called the aciddissociation constant, Ka. K a = [H 3O + ][A ] [HA] Acid Dissociation Constants Slide 89 / 174 The greater the value of K a, the stronger is the acid. 44 The acid dissociation constant (K a ) of HF is 6.7 x Which of the following is true of a 0.1M solution of HF? Slide 90 / 174 A [HF] is greater than [H + ][F ] B [HF] is less than [H + ][F ] C [HF] is equal to [H + ][F ] D [HF] is equal to [H ][F + ] K a = [H 3O + ][A ] [HA]

31 Calculating K a from the ph Slide 91 / 174 The ph of a 0.10 M solution of formic acid, HCOOH, at 25 C is Calculate K a for formic acid at this temperature. The dissociation equation for formic acid may be written as a reaction with water HCOOH + H 2 O HCOO + H 3 O + or, without water HCOOH HCOO + H + Calculating K a from the ph Slide 92 / 174 HCOOH + H 2 O HCOO + H 3 O + From this dissociation equation, we can obtain the K a expression: K a = [H 3 O + ][HCOO ] [HCOOH] Weak Acids: Calculating K a from the ph Slide 93 / 174 The ph of a 0.10 M solution of formic acid, HCOOH, at 25 C is Calculate K a for formic acid at this temperature. To calculate K a, we need the equilibrium concentrations of all three things. We can find [H 3 O + ], which is the same as [HCOO ], from the ph.

32 Weak Acids: Calculating K a from the ph Slide 94 / 174 ph = log [H 3 O + ] 2.38 = log [H 3 O + ] 2.38 = log [H 3 O + ] = 10 log [H3O+] = [H 3 O + ] 4.2 x 10 3 M = [H 3 O + ] = [HCOO ] Note that this is a monoprotic acid, so [acid] = [conjugate base] Weak Acids: Calculating K a from the ph Slide 95 / 174 Now, we substitute values into the Ka expression and solve: K a = K a = [H 3 O + ][HCOO ] [HCOOH] [ ] [ ] [0.10] K a = Calculating Percent Ionization Slide 96 / 174 One way to compare the strength of two acids is by the extent to which each one ionizes. This is done by calculating percent ionization, or the ratio of [H + ] ions that are produced, compared to the original acid concentration. [H 3 O + ] eq Percent Ionization = 100 [HA] initial

33 Calculating Percent Ionization Slide 97 / 174 [H 3 O + ] eq Percent Ionization = 100 [HA] initial In this example [H 3 O + ] eq = M [HCOOH] initial = 0.10 M 4.2 x 10 3 Percent Ionization = = 4.2 % Calculating Percent Ionization Slide 98 / 174 What would be the analogous formula to calculate percent ionization for a base? [OH ] eq Percent Ionization = 100 [Base] initial Slide 99 / 174 Calculating ph from K a Calculate the ph of a 0.30 M solution of acetic acid, HC 2 H 3 O 2, at 25 C. K a for acetic acid at 25 C is 1.8 x First, we write the dissociation equation for acetic acid HC 2 H 3 O 2 (aq) + H 2 O (l) H 3 O + (aq) + C 2 H 3 O 2 (aq)

34 Calculating ph from K a Slide 100 / 174 Calculate the ph of a 0.30 M solution of acetic acid, HC 2H 3O 2, at 25 C. K a for acetic acid at 25 C is 1.8 x From the dissociation equation, we obtain the equilibrium constant expression: K a = [H 3O + ][C 2 H 3 O 2 ] [HC 2 H 3 O 2 ] Calculating ph from K a Slide 101 / 174 Calculate the ph of a 0.30 M solution of acetic acid, HC 2H 3O 2, at 25 C. K a for acetic acid at 25 C is 1.8 x We next set up an ICE chart... [HC 2H 3O 2], M [H 3O + ], M [C2H3O2], M Initial 0.30 M 0 0 Change x + x + x Equilibrium about 0.30 M x x We are assuming that x will be very small compared to 0.30 and can, therefore, be ignored. Calculating ph from K a Slide 102 / 174 Calculate the ph of a 0.30 M solution of acetic acid, HC 2 H 3 O 2, at 25 C. K a for acetic acid at 25 C is 1.8 x Now, substituting values from the ICE chart into the K a expression yields = (x) 2 (0.30) ( ) (0.30) = x x 10 6 = x x 10 3 = x Remember what your "x" is! In this case, it's [H 3O + ], but other times it's [OH ].

35 Calculating ph from K a Slide 103 / 174 Calculate the ph of a 0.30 M solution of acetic acid, HC 2 H 3 O 2, at 25 C. K a for acetic acid at 25 C is 1.8 x ph = log [H 3 O + ] ph = log (2.3 x 10 3 ) ph = 2.64 Significant figure rules for ph on the AP exam: The calculated ph value should have as many DECIMAL places as the [H + ] has sig figs. So if the [H + ] has 2 sig figs, report the ph to the 0.01 place value. If the [H + ] has 3 sig figs, report the ph to the place value. 45 What is the hydrogen ion concentration if the acid dissociation constant is 1 x 10 6 and the acid concentration is 0.01M? Slide 104 / 174 A 10 6 B 10 5 C 10 4 D 10 3 K a = [H 3O + ][A ] [HA] 46 What is the concentration of the acid if the ph is 4 and the K a is 1 x 10 7? Slide 105 / 174 A 10 7 B 10 5 C 10 3 D 10 1 K a = [H 3O + ][A ] [HA]

36 Polyprotic Acids Slide 106 / 174 Polyprotic acids are characterized by having more than one acidic proton. Here are some examples: Sulfuric acid H 2SO 4 Phosphoric acid H 3PO 4 Carbonic acid H 2CO 3 Oxalic acid H 2C 2O 4 Polyprotic Acids Slide 107 / 174 Polyprotic acids have a K a value for each proton that can be removed. For example, consider carbonic acid, H 2 CO 3. The first ionization equation for carbonic acid is H 2 CO 3 + H 2 O < > HCO 3 + H 3 O + Write the Ka expression for this equation. This is referred to as K a1. Polyprotic Acids Slide 108 / 174 The second ionization equation for carbonic acid is HCO 3 + H 2 O < > CO H 3 O + Write the Ka expression for this equation. This is referred to as K a2.

37 Polyprotic Acids Slide 109 / 174 Now, we examine both dissociation constants. H 2 CO 3 + H 2 O < > HCO 3 + H 3 O + HCO 3 + H 2 O < > CO H 3 O + K a1 = [HCO 3 ][H 3 O + ] [H 2 CO 3 ] [CO 2 3 ][H 3 O + ] K a2 = [HCO 3 ] Polyprotic Acids Slide 110 / 174 Notice that the bicarbonate ion, HCO 3, appears in each expression; in the numerator for K a1 and in the denominator for K a2. [HCO 3 ][H 3 O + ][CO 2 3 ][H 3 O + ] K a1 x K a2 = [H 2 CO 3 ] [HCO 3 ] [HCO 3 ][H 3 O + ][CO 2 3 ][H 3 O + ] K a1 x K a2 = [H 2 CO 3 ] [HCO 3 ] Polyprotic Acids Slide 111 / 174 The equation for the complete ionization of carbonic acid is H 2 CO 3 + H 2 O < > CO H 3 O + and the K a expression for this reaction is K = [CO 3 2 ][H 3 O + ] 2 [H 2 CO 3 ] [HCO 3 ][H 3 O + ][CO 2 3 ][H 3 O + ] K a1 x K a2 = [H 2 CO 3 ] [HCO 3 ] K a1 x K a2 = overall K So, the product of K a1 x K a2 for a diprotic acid yields the overall K for complete dissociation.

38 Polyprotic Acids Slide 112 / 174 Generally, the ph of polyprotic acids depends only on the removal of the first proton. This holds true when the difference between the K a1 and K a2 values is at least The Ka of carbonic acid is 4.3 x 10 7 H 2 CO 3 <> H + + HCO 3 Slide 113 / 174 This means that H 2 CO 3 is a. A B C D good hydrogenion acceptor good hydrogenion donor poor hydrogenion acceptor poor hydrogenion donor 48 A diprotic acid, H 2 X, has the following dissdiprotic ociation constants: K a1 = 2.0 x 10 4 K a2 = 3.0 x 10 6 Slide 114 / 174 What is the overall K value for this acid? A 5.0 X B 6.0 X C 5.0 X D 6.0 x E 6.0 x 10 24

39 Weak Bases Slide 115 / 174 Bases react with water to produce hydroxide ion. Even though NH 3 does not have the hydroxide ion, OH, in its formula, note that it is a base according to both the Arrenhius and BronstedLowry definitions. Weak Bases Slide 116 / 174 B + H 2 O HB + OH The equilibrium constant expression for this reaction is K b = [HB][OH ] [B ] where K b is the basedissociation constant. Just as for K a, the stronger a base is, it will have a higher K b value. In fact, since the strong bases dissociate 100%, their K b values are referred to as "very large". Weak Bases Slide 117 / 174 K b can be used to find [OH ] and, ultimately, ph.

40 49 Which base has the smallest base dissociation constant, K b? Slide 118 / 174 A B C D potassium hydroxide sodium hydroxide calcium hydroxide ammonia 50 A base has a dissociation constant, K b = 2.5 x Which of the following statements is true? Slide 119 / 174 A B C D This is a concentrated base. This base ionizes slightly in aqueous solution. This is a strong base. An aqueous solution of this would be acidic. 51 A substance with a K a of 1x10 5 would be classified as a. Slide 120 / 174 A strong acid B weak acid C strong base D weak base

41 Weak Bases Slide 121 / 174 Most problems involving weak bases require you to calculate either ph or the basedissociation constant, K b. ph of Basic Solutions Slide 122 / 174 What is the ph of a 0.15 M solution of NH 3? NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH (aq) As with weak acids, first write the equilibrium expression for the dissociation equation. Obtain the K b value from an earlier page. K b = [NH 4 + ][OH ] [NH 3 ] =1.8 x 10 5 ph of Basic Solutions Slide 123 / 174 What is the ph of a 0.15 M solution of NH 3? Tabulate the data [NH 3 ], M [NH 4 + ], M [OH ], M Initially Change x +x +x At Equilibrium NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH (aq) 015 x 0.15 x x

42 ph of Basic Solutions Slide 124 / = (x) 2 (0.15) ( ) (0.15) = x x 10 6 = x x 10 3 = x Again, remember what your "x" is! ph of Basic Solutions Slide 125 / 174 In this case, "x" is [OH ]. Therefore, [OH ] = 1.6 x 10 3 M poh = log (1.6 x 10 3 ) poh = 2.80 So, now solving for ph: ph = ph = K a and K b Slide 126 / 174 For a conjugate acidbase pair, K a and K b are related in a special way. Write the ionization equations for the following: 1) reaction of ammonia (NH 3 ) and water 2) reaction of ammonium ion (NH 4 + ) and water

43 K a and K b Slide 127 / 174 NH 3 + H 2 O NH OH NH H 2 O NH 3 + H 3 O + Write the corresponding equilibrium constant expression for each of these equations. Which of these expressions is referred to as "K a"? Which is referred to as "K b"? K a and K b Slide 128 / 174 NH 3 + H 2 O NH OH K b = [NH 4 + ][OH ] [NH 3 ] NH H 2 O NH 3 + H 3 O + K a = [NH 3][H 3 O + ] [NH 4 + ] What do these expressions have in common? K a and K b Slide 129 / 174 K b x K a = K b x K a = [NH + 4 ][OH ] [NH 3 ][H 3 O + ] [NH 3 ] [NH + 4 ] [NH + 4 ][OH ] [NH 3 ][H 3 O + ] [NH 3 ] [NH 4 + ] K b x K a = [OH ][H 3 O + ] = K w So, the product of K a x K b for any conjugate acidbase pair yields the ionproduct constant, K w.

44 K a and K b Slide 130 / 174 For a specific conjugate acidbase pair, K a and K b are related in this way: K a x K b = K w Therefore, if you know the value of one of them, you can calculate the other. 52 For the acid HCN, what is the equation on which the K a expression is based? Slide 131 / 174 A HCN <> OH + HCN B HCN <> OH + CN C HCN + H 2 O <> CN H 3 O + D HCN + H 2 O <> OH + CN 53 The K a for an acid, HX, is 2.0 x What is the K b for its conjugate base, X? No calculator. Slide 132 / 174 A 5 X B 2 X C 5 X D 8 x E 2 x 10 4 K a x K b = K w

45 54 The K a for HCN is 4.0 x What is the K b for the cyanide ion, CN? No calculator. Slide 133 / 174 A 2.5 X 10 3 B 2.5 X 10 4 C 2.5 X 10 5 D 4 x 10 4 E 4 x 10 4 K a x K b = K w 55 The K b for a base, B, is 5.0 x What is the K a for its conjugate acid, HB +? No calculator. Slide 134 / 174 A 5.0 X 10 8 B 5.0 X 10 6 C 2.0 X 10 5 D 2.0 X 10 6 E 2.0 X 10 7 K a x K b = K w 56 Which of the substances below is the strongest acid? Slide 135 / 174 A HClO B HCO 3 C H 2S D NH 3CH 3 + E H 2S and HClO

46 Neutralization Reactions Slide 136 / 174 Neutralization reactions are a special class of doublereplacement reactions that occur between an acid and a base. Recall from last year that the general formula for a doublereplacement reaction is: AB + CD > AD + CB Doublereplacement reactions are also known as ionexchange or precipitation reactions. Slide 137 / 174 Neutralization Reactions The general formula for any acidbase neutralization reaction is: acid + base > salt + water Note that the term "salt" refers to any ionic compound that does not include H + or OH. Slide 138 / 174 AcidBase Properties of Salt Solutions acid + base > salt + water When an acid and base react together, the resulting solution is not always neutral. The ph of the resulting mixture depends on the relative strengths of the acid and of the base. The ph of a salt solution depends on the ability of the salt's ions to hydrolyze. (Hydrolyze means to interact with water molecule and dissociate.)

47 AcidBase Properties of Salt Solutions Slide 139 / 174 The ph of a salt solution depends on the ability of the salt's ions to hydrolyze. Consider the anion, X, which may be formed as the conjugate base of an acid. This anion may undergo hydrolysis as shown below: X + H 2 O <> Predict the products. Do you think the resulting solution will be acidic, basic or neutral? Justify your response. AcidBase Properties of Salt Solutions Slide 140 / 174 The ph of a salt solution depends on the ability of the salt's ions to hydrolyze. Consider the anions chloride ion, Cl and cyanide ion, CN. Which one has the ability to hydrolyze? Cl + H 2O <> HCl + OH <> H + + Cl + OH Because HCl is a strong acid, it will dissociate completely in solution. Therefore, since the products are H + + Cl + OH, there is no effect on ph. We conclude that Cl DOES NOT HYDROLYZE. CN + H 2O <> HCN + OH Because HCN is a weak acid, it will not dissociate completely in solution. As a result, the excess hydroxide ions cause the solution to become. AcidBase Properties of Salt Solutions Slide 141 / 174 The ph of a salt solution depends on the ability of the salt's ions to hydrolyze. As we have seen, the conjugate base (Cl ) of a strong acid (HCl) will not hydrolyze. In fact, none of the anions from the strong seven acids will hydrolyze. In other words, these anions will not affect ph. List here the conjugate bases of the strong seven acids. Again, none of these anions will undergo hydrolysis to affect ph.

48 AcidBase Properties of Salt Solutions Slide 142 / 174 The ph of a salt solution depends on the ability of the salt's ions to hydrolyze. Metal cations can also hydrolyze to affect ph. Consider the ability of the aluminum and potassium cations Al 3+ and K + to hydrolyze: Al 3+ + H 2O <> Al(OH) 3 + H + Because Al(OH) 3 is a weak base, it will not dissociate completely in solution. The excess hydrogen ions the ph. K + + H 2O <> KOH + H + <> K + + OH + H + Because KOH is a strong base it will dissociate completely into K + and OH. There is no effect on ph due to the balance of the hydroxide ions and hydrogen ions. AcidBase Properties of Salt Solutions The ph of a salt solution depends on the ability of the salt's ions to hydrolyze. Slide 143 / 174 As we have seen, the metal cation (K + ) of a strong base (KOH) will not hydrolyze. In fact, none of the cations from the strong bases will hydrolyze. In other words, these metal cations in solution will not affect ph. List here the metal cations from Groups 1 and 2 that form strong bases. Again, none of these cations will undergo hydrolysis to affect ph. AcidBase Properties of Salt Solutions Slide 144 / 174 Summary: Anions from weak acids will raise ph by creating excess OH ions. Cations from weak bases will lower ph by creating excess H + ions. Anions from strong acids will have NO effect on ph. Cations from strong bases will have NO effect on ph.

49 AcidBase Properties of Salt Solutions Slide 145 / 174 We have observed that metal cations (hydrated in solution) lower the ph of a solution. Lone pairs on oxygen are attracted to the cation. The shift of electron density in water makes the OH bond more polar. Hydrogen atoms become more acidic, and thus more likely to become H + ions in solution. Shift in electron density away from hydrogen atoms. AcidBase Properties of Salt Solutions Slide 146 / 174 We have observed that metal cations (hydrated in solution) lower the ph of a solution. Compare the following: attraction between a 1+ cation and H 2O molecule. attraction between a 3+ cation and H 2O molecule. The cation with the greater charge will make the solution more acidic. Summary of AcidBase Properties of Salts When a salt is formed between Example Salt anion comes from this acid Salt cation comes from this base (Brown, LeMay & Slide 147 / 174 Bursten Section 16.9) the ph of the resulting solution is Strong acid Strong base NaCl Strong acid Weak base Al(NO 3) 3 HNO 3 Weak acid Strong base HC 2H 3O 2 Ba(OH) 2 Weak acid Weak base NH 4CN HCN NH 3 Basic if K b>k a Acidic if K a>k b

50 Hydrolysis I Salts from strong acid and strong base Slide 148 / 174 Neither cation nor anion will undergo hydrolysis ph will not change Anions from strong acids: Cl, Br, I ClO 3, ClO 4, NO 3, SO 4 2 Cations from strong bases: K +, Li +, Na +, K +, Rb +, Cs +, Ca 2+, Ba 2+. Sr 2+ Hydrolysis II Salts from strong acid and weak base Slide 149 / 174 Examples: NH 4 Cl, NH 4 NO 3, MgCl 2, Mg(NO 3 ) 2 The anions will have no effect on ph. Only the cation will undergo hydrolysis: Mg 2+ + H 2 O < > Mg(OH) 2 + H + Since Mg(OH) 2 is a weak base, it will not dissociate completely. So the ph will decrease due to excess H + ions. Similarly with ammonium ion: NH H 2 O < > NH 3 + H 3 O + Hydrolysis III Salts from weak acid and strong base Slide 150 / 174 Examples: LiF, Ba(C 2 H 3 O 2 ) 2, NaOCl, NaC 2 H 3 O 2, NaF The cations will have no effect on ph. Only the anion will undergo hydrolysis: F + H 2 O < > HF +OH Since HF is a weak acid, it will not dissociate completely. So the ph will increase due to excess OH ions. Similarly with the hypochlorite ion: OCl + H 2 O < > HOCl +OH

51 Hydrolysis IV Salts from weak acid and weak base Slide 151 / 174 Example: NH 4 CN Consider the ions that make up the salt and write hydrolysis equations for each: NH H 2 O < > NH 3 + H 3 O + CN + H 2 O < > HCN +OH You must compare the K a of the cation, NH 4 + with the K b of the anion, CN. However, you will not normally find these values in common tables. Instead, you will find the K b of NH 3 and the K a of HCN. Use the formula K a x K b = K w to obtain the values you need. If the K a > K b, then the solution is acidic. If the K a < K b, then the solution is basic. Hydrolysis IV Salts from weak acid and weak base Will an aqueous solution of NH 4 CN be acidic or basic? What is the K a of the cation, NH 4 +? Slide 152 / 174 Look up the K b value for NH 3. Use the formula K a = K w / K b What is the K b of the anion, CN? Look up the K a value for HCN. Use the formula K b = K w / K a If the K a > K b, then the solution is acidic. If the K a < K b, then the solution is basic. AcidBase Properties of Salt Solutions Revised Summary: Slide 153 / 174 Salts from STRONG ACID + STRONG BASE = ph of 7 Salts from STRONG ACID + WEAK BASE = ph below 7 Salts from WEAK ACID + STRONG BASE = ph above 7 If both cation and anion come from a weak base and weak acid, then the solution will be basic if K b > K a the solution will be acidic if K a > K b

52 57 A 0.1M aqueous solution of will have a ph of 7.0 at 25 o C. Slide 154 / 174 A B C NaOCl KCl NH 4 Cl D Ca(C 2 H 3 O 2 ) 2 E none of these 58 A 0.1M aqueous solution of has a ph of 7.0 Slide 155 / 174 A B Na 2 S KF C NaNO 3 D E NH 4 Cl NaF 59 An aqueous solution of will produce a basic solution. Slide 156 / 174 A NH 4 ClO 4 B C KBr NaCl D MgCO 3 E NaHCO 3

53 60 An aqueous solution of will produce an acidic solution. Slide 157 / 174 A NH 4 ClO 4 B C KBr NaCl D SrCO 3 E NaHCO 3 61 An aqueous solution of will produce a neutral solution. Slide 158 / 174 A NH 4 ClO 4 B AlBr 3 C FeCl 3 D SrCO 3 E BaCl 2 62 Of the following substances, an aqueous solution of will form basic solutions. Slide 159 / 174 NH 4 Cl, Cu(NO 3 ) 2, K 2 CO 3, NaF A NH 4 Cl and Cu(NO 3 ) 2 B NH 4 Cl and K 2 CO 3 C D E K 2 CO 3 and NaF NaF only NH 4 Cl only

54 Factors Affecting Acid Strength Slide 160 / 174 The more polar the HX bond and/or the weaker the HX bond, the more acidic the compound. So acidity increases from left to right across a row and from top to bottom down a group. Factors Affecting Acid Strength In oxyacids, in which an OH is bonded to another atom, Y, the more electronegative Y is, the more acidic the acid. Slide 161 / 174 K a = 3.0x10 8 K a = 2.3x10 11 In HOCl, the electron density will be shifted to the more electronegative Cl atom weakening the OH bond. The strength of the acid will be in the order HOCl > HOBr > HOI Factors Affecting Acid Strength Slide 162 / 174 Among oxyacids, the more oxygen atoms in the molecule, the stronger the acid would be. The electron density will be more towards the oxygen atoms and the oxidation number increases, the strength of the acid increases.

55 Factors Affecting Acid Strength Slide 163 / 174 For a series of oxyacids, acidity increases with the number of oxygen atoms. Factors Affecting Acid Strength Slide 164 / 174 Resonance in the conjugate bases of carboxylic acids stabilizes the base and makes the conjugate acid more acidic. Lewis Acids Slide 165 / 174 BrønstedLowry acids replaced Arrhenius acids because they were more general: Arrhenius acids could only be defined in aqueous (water) solutions. BrønstedLowry acids don't have that limitation. Similarly, BrønstedLowry acids are limited to substances that gain or lose hydrogen. But there are acids and bases that don't. The most general approach is that of Lewis acids; which don't require an aqueous environment or an exchange of hydrogen.

56 Lewis Acids Slide 166 / 174 Lewis acids are defined as electronpair acceptors. Atoms with an empty valence orbital can be Lewis acids. Lewis Bases Slide 167 / 174 Lewis bases are defined as electronpair donors. Anything that could be a BrønstedLowry base is a Lewis base. Lewis bases can interact with things other than protons, however. 63 Which of the following cannot act as a Lewis base? Slide 168 / 174 A Cl B NH 3 C BF 3 D CN E H 2 O

57 64 In the reaction BF 3 + F <> BF 4 Slide 169 / 174 BF 3 acts as a/an acid. A B C D E Arrhenius BronstedLowry Lewis Arrhenius, BronstedLowry, and Lewis Arrhenius and BronstedLowry Slide 170 / 174 END Also print slide 164 as a full page Summary of AcidBase Properties of Salts (Section 16.9) Slide 171 / 174 When a salt is formed between Example Salt anion comes from this acid Salt cation comes from this base the ph of the resulting solution is Strong acid Strong base NaCl Strong acid Weak base Al(NO 3) 3 HNO 3 Weak acid Strong base HC 2H 3O 2 Ba(OH) 2 Weak acid Weak base NH 4CN HCN NH 3 Basic if K b>k a Acidic if K a>k b

58 Summary of AcidBase Properties of Salts (Section 16.9) When a salt is formed between Example Salt anion comes from this acid Salt cation comes from this base the ph of the resulting solution is Slide 172 / 174 Strong acid Strong base NaCl HCl NaOH ph=7, neutral Strong acid Weak base Al(NO3)3 HNO3 Al(OH)3 ph below 7, acidic Weak acid Strong base Ba(C2H3O2)2 HC2H3O2 Ba(OH)2 ph above 7, basic Weak acid Weak base NH4CN HCN NH3 Basic if Kb>Ka Acidic if Ka>Kb Show the hydrolysis reactions for CN and for NH4 +. Show how to use Ka of HCN to get the Kb for CN = 2.0 x 10 5 Show how to use the Kb of NH3 to get the Ka for NH4 + = 5.6 x salts and hydrolysis Slide 173 / 174 Salt Acid Base Hydrolysis ph NaCl HCl NaOH None neutral, 7 KNO3 HNO3 KOH None neutral, 7 NH4Cl HCl NH3 NH4 + +H2O > NH3 + H3O + acidic KCN HCN KOH CN + H2O > HCN + OH basic KF HF KOH F + H2O > HF + OH basic NH4CH3COO CH3COOH NH3 NH4+ + H2O > NH3 + H3O+ acidic? CH3COO+ H2O > CH3COOH + OH basic? compare ka of CH3COOH and Kb of NH3 whichever larger will have the effect on the solution CH3NH3Cl HCl CH3NH2 CH3NH3 + + H2O > CH3NH2 + H3O acidic NH4F HF NH3 F + H2O > HF + OH basic? NH4 + + H2O > NH3 + H3O+ acidic? Ka HF = Kb NH3 = it is acidic! NH4CN HCN NH3 CN + H2O > HCN + OH basic NH4+ + H2O > NH3 + H3O+ acidic? Mg(CO3) H2CO3 Mg(OH)2 CO3 2 + H2O > HCO3 1 + OH basic NaOCl HOCl NaOH OCl + H2O > HOCL + OH basic KBr HBr KOH none neutral,7 Any weak acid/base combination of salt origin, the Ka or Kb values are needed to predict the outcome of the solution. Slide 174 / 174