Strong and Weak. Acids and Bases

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1 Strong and Weak Acids and Bases

2 Strength of Acids H2SO4 HSO4 - + H + HNO3 NO3 - + H + Strong Acids HCl Cl - + H + H3PO4 H2PO4 - + H + Phosphoric acid Moderate Acid CH3COOH CH3COO - + H + Acetic acid HF F - + H + Weak Acids H2CO3 HCO H + HCN CN - + H +

3 HCl is a Strong Acid HF is a Weak Acid

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5 Strong Bases NaOH Na + + OH - KOH K + + OH - LiOH Li + + OH - Ba(OH)2 Ba OH - sparingly soluble in water

6 Weak Bases: ammonia NH3 + H2O NH4 + + OH - acetate CH3COO - + H2O CH3COOH + OH - carbonate CO H2O HCO3 - + OH -

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9 Acidity and Basicity of Aqueous Solutions

10 Water is Amphoteric HCl + H2O > Cl - + [H3O] NH3 + H2O > NH4 + + [HO] - + -

11 Water can act as an acid or base. (It s amphoteric ) H2O (l) + H2O (l) [H3O]+ (aq) + [HO]- (aq) proton acceptor proton donor + [ ] + + [ ] - In pure water this reaction takes place to a very small extent. Concentration of hydronium ions = Concentration of hydroxide ions [ H3O + ] = 1 x 10-7 = [ OH - ] = 1 x 10-7 M

12 A neutral solution is defined as a solution in which [ H3O + ] = 1 x 10-7 M & [ OH - ] = 1 x 10-7 M

13 1. What is the hydrogen ion concentration in a 1.0 M hydrochloric acid solution? A) 0.5 M B) 1.0 M C) 1.5 M D) 2.0 M E) 4.0 M HCl H + (aq) + Cl - (aq) 2. What is the hydronium ion concentration in a 1.0 M sulfuric acid solution? A) 0.5 M B) 1.0 M C) 1.5 M D) 2.0 M E) 4.0 M H2SO4 2 H + (aq) + SO4 - (aq)

14 3. What is the hydroxide ion concentration in a 1.0 M potassium hydroxide solution? A) 0.5 M B) 1.0 M C) 1.5 M D) 2.0 M E) 4.0 M KOH K + (aq) + OH - (aq) 4. What is the hydroxide ion concentration in a 1.0 M calcium hydroxide solution? A) 0.5 M B) 1.0 M C) 1.5 M D) 2.0 M E) 4.0 M Ca(OH)2 Ca 2+ (aq) + 2 OH - (aq)

15 Acidic Solution Basic Solution [H+] H+ H+ H+ H+ H+ [] [H+] vs []

16 Ion Product of Water = Kw =[H3O+][]=1.0 x [H+] H+ H+ H+ H+ H+ [] [H+] vs []

17 5. If the [H3O+] of a solution is 3.6 x10-8, what is the []? Kw =[H3O+][]=1.0 x (3.6 x10-8 )[]=1.0 x []=(1.0 x )/(3.6 x10-8 ) []=2.8 x10-7

18 6. If the [] of a solution is 4.6 x10-4, what is the [H3O+]? Kw =[H3O+][]=1.0 x [H3O+](4.6 x10-4 )=1.0 x [H3O+]=(1.0 x )/(4.6 x10-4 ) [H3O+] =2.2 x10-11

19 A neutral solution is defined as a solution in which [ H3O + ] = 1 x 10-7 M & [ OH - ] = 1 x 10-7 M An acidic solution is defined as a solution in which [ H3O + ] > 1 x 10-7 M & [ OH - ] < 1 x 10-7 M A basic solution is defined as a solution in which [ H3O + ] < 1 x 10-7 M & [ OH - ] > 1 x 10-7 M

20 [H+] vs [] [H+] H+ H+ H+ H+ H+ [] ACIDIC BASIC

21 7. A solution with H3O + concentration of 2 x 10 4 M can be described as A) basic. B) acidic. C) neutral. 8. A solution with H3O + concentration of 2.8 x 10 7 M can be described as A) basic. B) acidic. C) neutral. 9. A solution with H3O + concentration of 2.2 x M can be described as A) basic. B) acidic. C) neutral.

22 Because of the wide range of values for hydronium ion concentrations (from M to 100 M) a logarithmic scale (the ph scale) is usually used. The Log Function

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24 ph vs poh ph [H+] H+ H+ H+ H+ H+ [] poh ph + poh =14

25 1 10-1

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27 10. How many times more acidic is a solution with a ph of 1 (stomach acid) than a solution with a ph of 7 (blood)? A) 6 B) 7 C) 7000 D) 1,000, How many times more basic is a solution with a ph of 12 (household ammonia) than a solution with a ph of 5 (coffee)? A) 2.4 B) 7 C) 700 D) 10,000,000

28 12. What is the ph of 1.0 x 10-3 M HCl? ph = -log [H3O + ] ph = -log (1.0 x 10-3 ) ph = -(-3.00) = What is the ph of a solution if [H3O + ] =2.6 x 10-10? ph = -log [H3O + ] ph = -log (2.6 x ) ph = -(-9.58) = 9.58

29 14. What is [H3O + ] of a solution with a ph of 8.00? [H3O + ] = 10 -ph [H3O + ] = 10 -(8.00) [H3O + ] = 1.0 x 10-8 M 15. What is [H3O + ] of a solution with a ph of 6.22? [H3O + ] = 10 -ph [H3O + ] = 10 -(6.22) [H3O + ] = 6.0 x 10-7 M

30 16. What is [OH ] in an aqueous solution with a ph of 10.34? A) 4.6 x M B) 2.2 x 10 4 M C) 4.6 x 10 3 M D) 2.2 x M E) 1.0 x M [H3O + ] = 10 -ph [H3O + ] = 10 -( 10.34) [H3O + ] = 4.6 x M Kw =[H3O+][]=1.0 x (4.6 x10-11 )[]=1.0 x []=(1.0 x )/(4.6 x10-11 ) []=2.2 x10-4

31 ACIDIC BASIC ph [H+] H+ H+ H+ H+ H+ [] poh Ion Product of Water = Kw =[H3O+][]=1.0 x ph + poh =14

32 Buffers Buffer System - A solution which resists a change in ph when small amounts of acid or base are added Components of a Buffer System A weak acid, and A salt of that weak acid or A weak base, and A salt of that weak base

33 17. Which of the following pairs of components would create a buffer solution? HCl and NaOH NaOH and NaCl KCl and NaCl H2CO3 and NaHCO3 HF and KF CH3COOH and CH3COO - Na +

34 How Does the Acetate Buffer System Work? 1) An acetate buffer system contains CH3COOH and CH3COO - (acetic acid) (acetate anion) 2) The acetate anion reacts with excess acid (H + ) CH3COO - + H + CH3COOH 3) The acetic acid component reacts with excess base (OH - ) CH3COOH + OH - CH3COO -

35 Buffer systems A buffer contains significant amounts of a weak acid and its conjugate base. The acid consumes any added base, and the base consumes any added acid. In this way, a buffer resists ph change. How Does the Acetate Buffer System Work?

36 ph changes in pure water and a buffer solution A comparison of the change in ph when mol of acid and mol of base are added to 1.0 L of pure water and to 1.0 L of 0.10 M acetic acid-0.10 M acetate ion buffer.

37 Two Important Physiological Buffer Systems H2CO3(aq) H + (aq) + HCO3 - (aq) The bicarbonate buffer system operates in the bloodstream. H2PO4 - (aq) H + (aq) + HPO4 2- (aq) The dihydrogen phosphate buffer system operates within cells.