Understanding Acids and Bases: Properties and Reactions

1. Acids and Bases

2. Properties of Acids (in aq solution) • Sour taste • Low pH • Turn litmus paper red • Conduct electrical current

3. Properties of Bases (in aq solution) • Bitter taste • Slippery • High pH • Turn litmus paper blue • Conduct electrical current

4. Arrhenius Definition Acid = substance that releases H+ ions in aq solution HCl  H+ + Cl- Base = substance that releases OH-ions in aq solution NaOH  Na+ + OH-

5. Acid-Base Reactions • Known as a neutralization reaction. Acids and bases will react with each other to form salt and water. HCl + NaOH  NaCl + H2O

6. Bronsted-Lowry Definition As more and more substances were determined to have acidic or basic properties, even some without obvious H+ or OH-, a new definition was needed. • Acid = proton donor • Base = proton acceptor

7. Bronsted-Lowry Definition • Acid = proton donor H2O + HCl  H3O+ + Cl-

8. Bronsted-Lowry Definition • Base = proton acceptor NH3 + H2O  NH4+ + OH–

9. Lewis Acid – something that accepts an electron pair to form a covalent bond • Lewis Base – something that donates an electron pair to form a covalent bond A + :B → A—B

10. Acids & Bases Review • Acid • substance that releases H+ ions in aq solution • Proton donor • Electron pair acceptor • Base • substance that releases OH-ions in aq solution • Proton acceptor • Electron pair donator

11. Conjugate Acid-Base Pairs • In an acid-base reaction, and acid plus a base reacts to form a conjugate base plus a conjugate acid Acid + Base  Conjugate Base + Conjugate Acid • The conjugate acid of a base is formed when the base gains a proton. A conjugate base is formed when an acid loses a proton.

12. NH3 + H20  NH4+ + OH- Additional Proton means it is now a Proton Donor = Conjugate Acid Loss of proton means it is now a Proton Acceptor = Conjugate Base Proton Acceptor = Base Proton Donor = Acid • Note: • The conjugate name only refers to acids and bases in the PRODUCTS • Conjugate pairs differ only by a proton • NH3 and NH4+ are a conjugate acid-base pair • H20 and OH-are a conjugate acid-base pair • A strong acid becomes a weak conj. base (and vice versa)

13. Acid & Base Naming • Bases are named exactly the same • Ex. Ca(OH)2 is Calcium hydroxide

14. Acid Naming Overview Binary Start with hydro- Element End with –ic acid Tertiary (Oxyacids) “I ate something, and now I am sick” If anion ends in –ate then the acid ends in –ic If the anion ends in –ite then the acid ends in -ous

15. Naming WS

16. Acid Strength A stronger acid will transfer MORE protons (H+) than a weak acid. It will create more hydronium ions (H3O+) in water. Hydrochloric acid HCl + H2O  H3O+ + Cl- Acetic Acid CH3COOH + H2O H3O+ + CH3COO- More dissociation! Less dissociation!

17. How do we compare the strength of an acid or a base? We measure the amount of hydronium ions they create (acids) or the amount of hydroxide ions they create (bases)….using concentration.

18. When water gains a proton it is called HYDRONIUM!! H3O+

19. When water loses a proton it is called HYDROXIDE!! OH-

20. What is concentration? • Using molarity, it is a measure of moles of solute in liters of solution. • Concentration is measured in WATER!

21. H2O is both an acid and a base Water is simultaneously donating and accepting protons!

22. What are the ion concentrations in water? • The concentrations of H3O+ and OH- in pure water are each 1.0×10-7 mol/L at 25ºC. • Putting a symbol in brackets is used to signify the concentration. • [H30+] = 1.0×10-7 M • [OH-] = 1.0×10-7 M

23. Ionization Constant of water, KW • KW = [H30+] [OH-] • KW = (1.0×10-7)(1.0×10-7) = 1.0×10-14

24. With an increase in [H30+], some of the H30+ ions will react with the OH- ions, reducing [OH-] . [H30+][OH-] will still = 1.0x10-14 • Acids increase the [H30+] Whenever [H30+] is greater than [OH-], the solution is acidic. • Bases increase the [OH-] Whenever [OH-] is greater than [H30+], the solution is basic.

25. Concentration values tend to be small…so we use a more convenient scale. pH!

27. pH + pOH = 14 • pH – A measure of the acidity of a solution. • It is the negative logarithm of the hydronium ion [H30+] concentration. pH = -log [H30+]

28. pH + pOH = 14 • pOH – A measure of how basic a solution is. • It is the negative logarithm of the hydroxide [OH-] concentration. pOH = -log [OH-]

29. The logarithm scale is created to make numbers over a large range more manageable.

30. The logarithm base 10 of a number x is the power to which 10 must be raised in order to equal x. • Log 10 x = ? Log 100 = ? • 10? = x 10 ? = 100

31. Remember, our concentrations are SMALL. So we are going to be dealing with decimals… • Log 10 x = ? Log .001 = ? • 10? = x 10 ? = .001

32. [H+] = 1×10-3 = 0.001 pH = -log [H+] pH = -log (1×10-3) pH = 3 To determine pH from a concentration where 1 is the only digit, write the concentration in scientific notation. The absolute power of the exponent will be the pH.

33. For a base, you do the same thing except remember that you are solving for pOH first…

34. Ionization Constant of water, KW • KW = [H30+] [OH-] • KW = (1.0×10-7)(1.0×10-7) = 1.0×10-14

35. 11 3.0 1.0×10-3M 1.0×10-11M 2.0 12 1.0×10-2M 1.0×10-12M 8 6 1×10-8M 1×10-6M 10.8 3.22 6.00×10-4M 1.67×10-11M 13 .70 2.0×10-1M 5.0×10-14M 2.22 11.8 6.00×10-3M 1.67×10-12M

36. Equations to Know!! • [H30+] [OH-] = 1.0×10-14 M • pH + pOH = 14 • pH = -log [H30+] • pOH = -log [OH-] • [H30+] = 10-pH • [OH-] = 10-pOH

38. Green Workbook • Pg. 262 #2 • Pg. 264 #1 • Pg. 267 #3 • Pg. 269 #1 & #2 • Pg. 270 #7