Chapter 14

1. Chapter 14 Acids and Bases

2. Lemons contain citric acid, • Citric acid produces H+ ions in your mouth • H+ ions react with protein molecules on your tongue • The protein molecule changes shape – sending an electrical signal to your brain “Sour!”

3. Acids • How do I identify an acid? • HCl, H2SO4, HNO3 • First atom is hydrogen • Produces H+ ions in water • HCl(aq)  H+(aq) + Cl-(aq) • HCl + H2O  H3O+(aq) + Cl-(aq) • H2SO4(aq)  • HNO3(aq) 

4. ACIDS Taste sour Dissolve many metals Turn litmus paper red BASES Taste bitter Feel slippery Turn litmus paper blue Sodium borate Carbonic acid, phosphoric acid Sodium carbonate “washing soda” Tartaric acid Citric acid Acids and Bases Sodium hydroxide or “lye”

5. Arrhenius Theory • Acids ionize in water to H+ ions and anions • HCl(aq)  • Bases ionize in water to OH- ions and cations • NaOH(aq)  • Neutralization reaction net ionic equation:

6. Brønsted-Lowery Theory • Acid is H+ donor • HCl(aq)  H+(aq) + Cl-(aq) • Base is H+ acceptor • NH3(aq) + H+(aq) ↔ NH4+(aq) • H2O(l) + H+(aq) ↔ H3O+(aq) • What else do NH3 and H2O has in common? • In the reaction, a H+ from the acid molecule is transferred to the base molecule

7. Conjugate Acids and Bases Acid Conjugate Base • NH3(aq) + H2O(l) ↔ NH4+(aq) + OH-(aq) • H2SO4(aq) + H2O(l)  HSO4-(aq) + H3O+(aq) • C5H5N(aq) + H2O(l) ↔ C5H5NH+(aq) + OH-(aq) Base Conjugate Acid

8. Strong versus Weak Acids • Strong acids completely dissociate into ions • Major species: ions • Minor species: un-ionized acid • Weak acids slightly dissociate into ions. • Major species: un-ionized acid • Minor species: ions

9. Strong versus Weak Acids

10. Strong versus Weak Acids • Which solution contains the strong acid?

11. Strong versus Weak Acids

12. Which Hydrogen atoms are acidic?

13. Strong versus Weak Bases • Strong bases completely dissociate into ions • Major species: ions • Minor species: un-ionized acid • NaOH(aq)  Na+(aq) + OH-(aq) • Weak bases slightly dissociate, producing hydroxide ions. • Major species: un-ionized acid • Minor species: ions • NH3(aq) + H2O(aq) ↔ NH4+(aq) +OH-(aq)

14. Strong versus Weak Bases

15. Relative Strength of Conjugate Acids and Bases Acid Conjugate Base • H2SO4(aq) + H2O(l)  HSO4-(aq) + H3O+(aq) • A strong acid has a weak conjugate base • A strong base has a weak conjugate acid • A weak base has a strong conjugate acid • A weak acid has a strong conjugate base Conjugate Acid Base

16. Recognizing Acids and Bases • Bases need a lone pair of electrons to accept a proton • Acids leave behind stable anions

17. Reactions of Acids and Bases • Neutralization Reactions • H2SO4(aq) + Ca(OH)2(aq) → • Single Replacement Redox • 3 H2SO4(aq) + 2 Al(s) → • Acids react with metal oxides… • 3 H2SO4 + Al2O3 →

18. Water • NH3(aq) + H2O(l)  NH4+(aq) + OH-(aq) • H2SO4(aq) + H2O(l)  HSO4-(aq) + H3O+(aq) • Can act as an acid or base - amphoteric

19. Water • Auto-ionization • H2O(l) + H2O(l) ↔ H3O+(aq) + OH-(aq) • At equilibrium, the [H3O+] and [OH-] are constant and equal. • KW = [H3O+][OH-]=1x10-14 at 25°C • What is the concentration of [H3O+] at equilibrium?

20. Acidic versus Basic Solutions H2O • Every aqueous solution contains water molecules, hydronium ions (H30+ or H+) and hydroxide ions (OH-) • A neutral solution: • [H+] ~ [OH-] • An acidic solution: • [H+] > [OH-] • A basic solution: • [OH-] > [H+] H2O H+ OH- H2O H2O H2O H+ H2O H+ OH- H2O H+ H2O H2O OH- H2O H+ OH- H2O OH- H2O

21. pH scale • Neutral: pH ~ 7 • Acidic: pH < 7 • Basic: pH > 7 • pH = - log [H3O+] • Significant figures: • [H3O+] = 1.0 x 10-3 • pH = 3.00

23. 1 2 3 4 5 6 7 8 9 10 11 12 Measuring pH pH meter Universal Indicators 4

24. pH and pOH • pOH = - log [OH-] • KW = [H3O+][OH-] = 1 x 10-14 • pH + pOH = 14 • Calculate the pH of a solution with: • [H3O+] = 1.0 x 10-8 M • pOH = 8.00 • [OH-] = 1.0 x 10-8 M • Calculate the [H3O+] of a solution with: • pH = 4.00 • pOH = 6.00 • [OH-] = 1.0 x 10-4 M • Calculate the pH of 0.10 M HNO3 solution.

25. pH and pOH • pOH = - log [OH-] • KW = [H3O+][OH-] = 1 x 10-14 • pH + pOH = 14 • Calculate the pH of a solution with: • [H3O+] = 9.5 x 10-9 M • pOH = 4.80 • [OH-] = 1.3 x 10-2 M • Calculate the [H3O+] of a solution with: • pH = 4.80 • pOH = 5.67 • [OH-] = 7.2 x 10-11 M • Calculate the pH of 0.10 M H2SO4 solution. • Calculate the pH of 0.10 M Ba(OH)2 solution.

26. Titrations Add NaOH (with indicator) Basic solution Oxalic acid solution • To a colorless acidic solution, we will add base. • When the solution is basic, it will be red. • We are looking for the equivalence point where the • moles of H+ = moles of OH- • We will determination of molarity of NaOH solution

27. Calculations H2C2O4 + NaOH H2O + Na2C2O4 24.7 mL ? M 0.628 g Concentration of NaOH solution (M) Mass of H2C2O4 (g) Volume of Added NaOH Moles H2C2O4 Moles NaOH

28. Buffers resist changes in pH • Buffers contain large amount of an weak acid and its conjugate base • HCl(aq) + NaC2H3O2(aq)  • NaOH(aq) + HC2H3O2(aq)  • Which of the following would constitute a buffer solution? (a) H2SO4 & H2SO3(aq) (b) HF(aq) & NaF(aq) (c) HCl & NaCl (d) NaCl & NaOH