Presentation is loading. Please wait.

Presentation is loading. Please wait.

Acid-Base Equilibria: Acids and Bases What makes an Acid an Acid? An acid possess a sour taste An acid dissolves active metals magnesium An acid causes.

Similar presentations


Presentation on theme: "Acid-Base Equilibria: Acids and Bases What makes an Acid an Acid? An acid possess a sour taste An acid dissolves active metals magnesium An acid causes."— Presentation transcript:

1 Acid-Base Equilibria: Acids and Bases What makes an Acid an Acid? An acid possess a sour taste An acid dissolves active metals magnesium An acid causes certain vegetable dyes to turncharacteristic colors What makes a Base a Base? A bases possess a bitter taste A base feels slippery to the touch A base causes certain vegetable dues to turn a characteristic color

2

3 7 strong acids and 8 strong bases Acids - HI, HBr, HCl, HClO 3, HClO 4, H 2 SO 4, HNO 3 Bases – LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH) 2, Sr(OH) 2, Ba(OH) 2

4 The Arrhenius Definition of an Acid and a Base acid An acid is a substance that produces H+ ions in water solutions HCl H + + Cl - base A base is a substance that produces OH- ions in a water solution NaOH Na + + OH -

5 acid dissociation equations HC 6 H 5 O 3 C 6 H 5 O H + Fe(H 2 O) 6 3+ Fe(H 2 O) 5 (OH) 2+ + H + CH 3 CH 2 NH 3 1+ CH 3 CH 2 NH 2 + H +

6 The Proton in Water When HCl dissolves in water we write: HCl(g) H+(aq) + Cl-(aq)

7 Reality for the Hydronium ion H5O2+H5O2+ H9O4+H9O4+

8 Acidic solutions are formed by a chemical reaction in which and acid transfers a proton (H + ) to water, so we can write them either way. HCl (aq) + H 2 O (aq) H 3 O + (aq) + Cl - (aq) or HCl (aq) H + (aq) + Cl - (aq)

9 protonated Nitrogen compounds are Bronsted acids when they are protonated. NH 4 Cl NH 4 + NH 3 + H + CH 3 ) 2 NH 2 + (CH 3 ) 2 NH + H +

10 The Bronsted-Lowry definition for Acids and Bases Acids may be defined as a substance that is capable of donating protons Bases may be defined as substance that accepts protons. HCl + NH 3 NH Cl - acid base conjugate conjugate acid base

11 Is Water an Acid? NH 3(aq) +H 2 O (aq) NH 4 + (aq) + OH - (aq)

12 Is Water a Base? HC 2 H 3 O 2(aq) + H 2 O (aq) H 3 O + (aq) +C 2 H 3 O 2 1- (aq)

13 The auto ionization of water The reaction occurs to a very small extent; about 1 in 10 8 molecules is ionized at any given moment H H O : : H H O : : + H H O : H + + H O :..

14 Dissociation of Water, pH Scale H 2 O (l) H + (aq) + OH - (aq) K =[H + ] [OH - ] [H 2 O] since water is a liquid and its concentration is therefore constant, this expression may be written as: K w = [H + ] [OH - ] = 1.0 x [H + ] = [OH - ] = 1.0 x M

15 Sample exercise: Indicate whether each of the following solutions is neutral, acidic, or basic: a)[H+] = 2 x M b)[OH-] = M c)[OH-] = 1.0 x M

16 Calculate the concentration of H + (aq) in (a)a solution in which the [OH - ] is 0.020M (b)a solution in which the [OH - ] = 2.5 x M. Indicate whether the solution is acidic or basic

17

18 The pH Scale pH = -log [H + ] If [H + ] = 2. 5 x 10 5 the pH is? pH = -log [2. 5 x ] = 4.6 If pH is 3.8 the H + concentration is Antilog -3.8= 1.58 x M

19 In a sample of lemon juice, [H + ] = 3.8 x M. What is the pH? A commonly available window cleaner has a [H + ] = 5.3 x M. What is the pH? In a sample of freshly pressed apple juice has a pH of Calculate the [H + ]

20 What if we took the –log of the K w expression K w = [H + ] [OH - ] = 1.0 x pK w = pH + pOH = 14

21 What is the pH, [H + ], [OH - ], of a solution with a pOH of 2.5? Is the solution acidic or basic?

22 Major species HCl (aq) + H 2 O (aq) H 3 O + (aq) + Cl - (aq) or HCl (aq) H + (aq) + Cl - (aq) HC 2 H 3 O 2(aq) + H 2 O (aq) H 3 O + (aq) +C 2 H 3 O 2 1- (aq) Pb(NO 3 ) 2 + NaCl NaNO 3 + PbCl 2

23 Indicators

24

25 What is the pH of M solution of HCl? strong If it ionizes completely which is what strong means then take the negative log of the concentration. HCl (aq) H + (aq) + Cl - (aq). 01M.01M.01M pH = 2

26 What is the pH of a solution made from 20mL of 2.0M HCl and 35mL of 3.2M HNO 3 ?

27 What about H 2 SO 4 H 2 SO 4 H + + HSO 4 1- (Strong) HSO 4 1- H + + SO 4 2- (Weak)

28 What about weak acids HX (aq) H + (aq) + X - (aq), then Ka = [H + ][X - ] [HX] The smaller the value of the acid dissociation constant Ka, the weaker the acid

29 What is the Ka of a 0.10 M solution of formic acid (HCHO 2 ) which has a pH = 2.38? HCHO 2 H + + CHO 2 1- I C E K a = (.00417) 2 = 1.8 x

30 What is the concentration of H + ions in a 0.10 M solution of HC 2 H 3 O 2 (K a = 1.8 x )? pH? % ionization? HC 2 H 3 O 2 H + + C 2 H 3 O 2 1- I C -X+X+X E.10 – X X X 1.8 x = X 2 X = 1.3 x – X pH = 2.87

31 percent dissociation 1.3 X x 100 = 1.3%.10

32 What is the pH and percent ionization of a 0.20 M solution of HCN? K a = 4.9 x

33 Acid-Base Equilibria: Strong Bases The most common soluble strong Bases are the hydroxides of group IA and Ca, Ba and Sr What is the pH of a M solution of Ba(OH) 2 ?

34 Amines Anions of Weak Acids

35 NH 3 + H 2 O NH OH - I C E Dealing with Weak Bases Weak base + H 2 O conjugate acid + OH - NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) K b = [NH 4 + ] [OH - ] [NH 3 ] The base dissociation constant K b refers to the equilibrium in which a base reacts with H 2 O to form the conjugate acid and OH - Calculate the [OH - ] in a 0.15 M solution of NH 3.

36

37 Polyprotic Acids H 2 SO 3(aq) H + (aq) + HSO 3 - (aq) K a1 = 1.7 x HSO 3 - (aq) H + (aq) + SO 3 2- (aq) K a2 = 6.4 x Calculate the pH of a.1M solution

38 Anions of Weak Acids HC 2 H 3 O 2(aq) + H 2 O (aq) H 3 O + (aq) + C 2 H 3 O 2 - (aq) Bronsted base Bronsted acid Conjugate acid Conjugate base A second class of weak base is composed of the anions of weak acids Anions of weak acids can be incorporated into salts. NaC 2 H 3 O 2 Na + (aq) + C 2 H 3 O 2 - (aq) C 2 H 3 O H 2 O HC 2 H 3 O 2 + OH - K b = 5.6 x 10 10

39 NaOH (aq) +HC 2 H 3 O 2(aq H 2 O+NaC 2 H 3 O 2 NaC 2 H 3 O 2 Na + (aq) + C 2 H 3 O 2 - (aq) Na + (aq) + H 2 O NaOH (aq) + H + (aq) C 2 H 3 O 2 - (aq) +H 2 O HC 2 H 3 O 2 (aq) +OH - (aq)

40 NH 4 Cl NH Cl - NH 4 + NH 3 + H +

41 NH 4 Cl NaC 2 H 3 O 2 NH 4 C 2 H 3 O 2

42 ClO - + H 2 O HClO + OH - I C E Calculate the pH of a 0.01 M solution of sodium hypochlorite (NaClO) Anions of Weak Acids

43 Now its you turn: the K b for BrO - is 5.0 x Calculate the pH of a M solution of NaBrO

44 K a and K b NH 4 + (aq) NH 3(aq) + H + (aq) NH 3(aq) + H 2 O NH 4 + (aq) + OH - (aq) Ka =Ka =Ka =Ka = [H + ][NH 3 ] [NH 4 + ] Kb =Kb =Kb =Kb = [NH 4 ][OH - ] [NH 3 ] NH 4 + (aq) NH 3 (aq) + H + (aq) NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH - (aq) H 2 O H + (aq) + OH - (aq) When two reactions are added to give a third reaction, the equilibrium constant for the third reaction reaction is given by the product of the equilibrium constants for the two added reactions K a x K b = K w pK a + pK b = pK w

45 Calculate the (a) base-dissociation constant, K b, for the fluoride ion, is the pK a of HF = 3.17 pK a = -log K a 3.17 = -log K a Antilog = 6.76 x SinceK a x K b = K w (6.76 x )x K b = 1.0 x K b = 1.0 x / 6.76 x = 1.5 x

46 Now its your turn Calculate the pK b for carbonic acid (K a = 4.3 x )

47 Acid-Base Properties of Salt Solutions Anions of weak acids, HX, are basic and will react with H 2 O to produce OH - X - (aq) + H 2 O (l) HX(aq) + OH - (aq) Anions of strong acids, such as NO 3 -, exhibit no basicitiy, these ions do not react with water and consequently do not influence the pH Anions of polyprotic acids, such as HCO 3 -, that still have ionizable protonsare capable of acting as either proton donors or acceptors depending upon the magnitudes of the K a or K b

48 Predict whether the salt Na 2 HPO 4 will form an acidic or basic solution on dissolvingin water. Na 2 HPO 4 2Na + (aq) + HPO 4 - HPO 4 - (aq) + H 2 O H 3 O + + PO 4 3- (aq) HPO 4 - (aq) + H 2 O H 2 PO 4 2- (aq) + OH - (aq) K 3 = 4.2 x HPO 4 - acting like an acid HPO 4 - acting like an base So HPO - is the conjugate base of H 2 PO 4 -. Since the K 2 of H 2 PO 4 - = 6.2 x then: K b = KaKa = KwKw 1.0 x x = 1.6 x Since K b is larger than K a, HPO 4 - will act like a base

49 Salt derived from a strong base and a strong acid will have a pH of 7 Salt derived from a strong base and a weak acid will have a pH above 7 Salt derived from a weak acid and a weak base depends upon whether the dissolved ion acts as an acid or a base as determined by the size of the K a or K b

50 Acid-Base Character and Chemical Structure HF > HCl > HBr > HI (most polar least) Based on electronegativity difference HF is the most polar but a weak acid because the bond is so strong two things to consider polarity difference and strength of the bond

51

52 Acid strength of oxyacids The more oxygen's the stronger the acid because of the oxygen pulling the electrons towards themselves. HClO 4 > HClO 3 > HClO 2 > HOCl


Download ppt "Acid-Base Equilibria: Acids and Bases What makes an Acid an Acid? An acid possess a sour taste An acid dissolves active metals magnesium An acid causes."

Similar presentations


Ads by Google