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Acids and Bases

Acids and Bases. Chapter 15. Acid Nomenclature Review. No Oxygen . w/Oxygen. An easy way to remember which goes with which… “In the cafeteria, you ATE something IC ky”. Acid/Base definitions Definition 1: Arrhenius. Arrhenius acid is a substance that produces H + (H 3 O + ) in water.

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Acids and Bases

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  1. Acids and Bases Chapter 15

  2. Acid Nomenclature Review No Oxygen w/Oxygen An easy way to remember which goes with which… “In the cafeteria, youATEsomethingICky”

  3. Acid/Base definitions Definition 1: Arrhenius Arrhenius acidis a substance that produces H+ (H3O+) in water Arrhenius baseis a substance that produces OH- in water 4.3

  4. Acid/Base Definitions • Definition #2: Brønsted – Lowry Acids – proton donor Bases – proton acceptor A “proton” is really just a hydrogen atom that has lost it’s electron!

  5. A Brønsted-Lowryacidis a proton donor A Brønsted-Lowrybaseis a proton acceptor conjugatebase conjugateacid base acid

  6. ACID-BASE THEORIES The Brønsted definition means NH3 is aBASE in water — and water is itself anACID

  7. Conjugate Pairs

  8. Learning Check! Label the acid, base, conjugate acid, and conjugate base in each reaction: HCl + OH-   Cl- + H2O Acid Base Conj.Base Conj.Acid H2O + H2SO4   HSO4- + H3O+ Conj.Base Conj.Acid Base Acid

  9. Acids & Base Definitions Definition #3 – Lewis Lewis acid - a substance that accepts an electron pair Lewis base - a substance that donates an electron pair

  10. Lewis Acids & Bases Formation ofhydronium ion is also an excellent example. • Electron pair of the new O-H bond originates on the Lewis base.

  11. Lewis Acid/Base Reaction

  12. Some Properties of Acids • Produce H+ (as H3O+) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) • Taste sour • Corrode metals • Electrolytes • React with bases to form a salt and water • pH is less than 7 • Turns blue litmus paper to red “Blue to Red A-CID”

  13. Some Properties of Bases • Produce OH- ions in water • Taste bitter, chalky • Are electrolytes • Feel soapy, slippery • React with acids to form salts and water • pH greater than 7 • Turns red litmus paper to blue “Basic Blue”

  14. The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H+ (or OH-) ion.Under 7 = acid 7 = neutral Over 7 = base

  15. Acid Rain • Consider • Causes • natural • human • Effects • buildings • flora • fauna • health

  16. Increasing acidity pH of Rainwater across United States in 2001 You are here! air masses Why is the eastern US more acidic?

  17. What is acid rain? Dissolved carbon dioxide lowers the pH CO2 (g) + H2O  H2CO3H+ + HCO3- Atmospheric pollutants from combustion NO, NO2 + H2O …  HNO3 both strong acids SO2, SO3 + H2O …  H2SO4 pH < 5.3

  18. Acid Reactions • Acid + Base  Salt + Water • Acid + Metal Salt + Hydrogen • Acid + Carbonate  Salt + Water + Carbon Dioxide • Hydrochloric acids (HCl) form CHLORIDE salts • Nitric acid (HNO3) forms NITRATE salts • Sulfuric acid (H2SO4) forms SULFATE salts

  19. Testing Gases • Hydrogen - POP TEST • Flame Splint explodes with a squeaky pop • Carbon Dioxide – Limewater goes cloudy • Flame Splint is extinguished • Oxygen – Relights a glowing splint

  20. Neutralization Reactions When acid and bases with equal amounts of hydrogen ion H+ and hydroxide ions OH- are mixed, the resulting solution is neutral. NaOH (aq) + HCl(aq) NaCl + H2O base acid salt water Ca(OH)2 + 2 HCl CaCl2 + 2H2O base acid salt water

  21. Neutralization H3O+ and OH- combine to produce water H3O+ + OH- 2 H2O from acidfrom base neutral Net ionic equation: H+ + OH- H2O

  22. Ionic Equations for Neutralization Write strong acids, bases, and salt as ions H+ + Cl- + Na+ + OH- Na+ + Cl- + H2O Cross out matched ions H+ + Cl-+ Na+ + OH-Na+ + Cl- + H2O Write a net ionic reaction H+ + OH-H2O

  23. Balancing Neutralization Equations Write the equation for the neutralization between magnesium hydroxide and nitric acid.1. Write the formulas of the acid and base Mg(OH)2 + HNO3 2. Balance to give equal OH- and H+ Mg(OH)2 + 2 HNO3

  24. 3. Write the products: Mg(OH)2 + 2HNO3 Mg(NO3)2 + H2O salt water (metal and nonmetal) 4. Balance products Mg(OH)2 + 2 HNO3 Mg(NO3)2 + 2 H2O

  25. Solution N2 A. 3HCl + 1Al(OH)31AlCl3 + 3H2O B. 3Ba(OH)2 + 2H3PO41Ba3(PO4)2 + 6H2O

  26. Learning Check N3 Write a balanced equation and calculate the mL of 2.00 M H2SO4 required to neutralize 50.0 mL of 1.00 M KOH? ___H2SO4 + ___KOH ___K2SO4 + H2O a) 12.5 mL b) 50.0 mL c) 200. mL

  27. Solution N3 How many mL of 2.00 M H2SO4 are required to neutralize 50.0 mL of 1.00 M KOH? H2SO4 + 2KOH K2SO4 + 2H2O 0.0500 L x 1.00 mole KOH x 1 mole H2SO4 x 1 L 2 mole KOH 1 L x 1000 mL = 12.5 mL 2 mole H2SO41 L

  28. Learning Check N4 A 25 mL sample of phosphoric acid is neutralized by 40. mL of 1.5 M NaOH. What is the molarity of the phosphoric acid solution? 3NaOH + H3PO4 Na3PO4 + 3H2O a) 0.45 M b) 0.80 M c) 7.2 M

  29. Calculating the pH pH = - log [H+] (Remember that the [ ] mean Molarity) Example: If [H+] = 1 X 10-10pH = - log 1 X 10-10 pH = - (- 10) pH = 10 Example: If [H+] = 1.8 X 10-5pH = - log 1.8 X 10-5 pH = - (- 4.74) pH = 4.74

  30. Try These! Find the pH of these: • A 0.15 M solution of Hydrochloric acid 2) A 3.00 X 10-7 M solution of Nitric acid pH = - log [H+] pH = - log 0.15 pH = - (- 0.82) pH = 0.82 pH = - log 3 X 10-7 pH = - (- 6.52) pH = 6.52

  31. pH calculations – Solving for H+ If the pH of Coke is 3.12, [H+] = ??? Because pH = - log [H+] then - pH = log [H+] Take antilog (10x) of both sides and get 10-pH =[H+] [H+] = 10-3.12 = 7.6 x 10-4 M *** to find antilog on your calculator, look for “Shift” or “2nd function” and then the log button

  32. pOH • Since acids and bases are opposites, pH and pOH are opposites! • pOH does not really exist, but it is useful for changing bases to pH. • pOH looks at the perspective of a base pOH = - log [OH-] Since pH and pOH are on opposite ends, pH + pOH = 14

  33. pH [H+] [OH-] pOH

  34. - H+ + H+ When life goes either way amphoteric (amphiprotic) substances Acting like a base Acting like an acid HCO3- H2CO3 CO3-2 accepts H+ donates H+

  35. - H+ + H+ Show how water can be amphoteric. H2O

  36. More About Water H2O can function as both an ACID and a BASE. In pure water there can beAUTOIONIZATION Equilibrium constant for water = Kw Kw = [H3O+] [OH-] =1.00 x 10-14at 25 oC

  37. More About Water Autoionization Kw = [H3O+] [OH-] = 1.00 x 10-14 at 25 oC In a neutral solution [H3O+] = [OH-] and so [H3O+] = [OH-] = 1.00 x 10-7 M

  38. [H3O+], [OH-] and pH What is the pH of the 0.0010 M NaOH solution? [OH-] = 0.0010 (or 1.0 X 10-3 M) pOH = - log 0.0010 pOH = 3 pH = 14 – 3 = 11 OR Kw = [H3O+] [OH-] [H3O+] = 1.0 x 10-11 M pH = - log (1.0 x 10-11) = 11.00

  39. What is the pH of a 1.8 x 10-2 M Ba(OH)2 solution? HNO3(aq) + H2O (l) H3O+(aq) + NO3-(aq) Ba(OH)2(s) Ba2+(aq) + 2OH-(aq) What is the pH of a 2 x 10-3 M HNO3 solution? HNO3 is a strong acid – 100% dissociation. 0.0 M 0.0 M Start 0.002 M 0.0 M 0.002 M 0.002 M End pH = -log [H+] = -log [H3O+] = -log(0.002) = 2.7 Ba(OH)2 is a strong base – 100% dissociation. 0.0 M 0.0 M Start 0.018 M 0.0 M 0.018 M 0.036 M End pH = 14.00 – pOH = 14.00 + log(0.036) = 12.56 15.4

  40. Does pure water conduct electrical current? Water is a very, very, very weak electrolyte. H2O  H+ + OH- How are (H+) and (OH-) related? (H+)(OH-) = 10-14 For pure water: (H+) = (OH-) = 10-7M This is neutrality and at 25oC is a pH = 7. water

  41. Dilution water (solvent) solute moles of solute remain constant diluted, Mfinal Vfinal molesinitial = molesfinal Vinitial concentrated, Minitial adding water lowers the solute concentration Mfinal x Vfinal = Minitial x Vinitial

  42. Preparing Solutions by Dilution A shortcut Minitial • Vinitial = Mfinal • Vfinal

  43. Calculation How many milliliters of 6.0 M NaOH solution are needed to prepare 1.0 L of a 0.15 M NaOH solution? M1 = 6.0 M M2 = .15 M V1 = ??? V2 = 1.0 L Rearrange the dilution equation for V1

  44. Calculation How many milliliters of 6.0 M NaOH solution are needed to prepare 1.0 L of a 0.15 M NaOH solution? M1 = 6.0 M M2 = .15 M V1 = ??? V2 = 1.0 L Rearrange the dilution equation for V1 V1 = M2V2= 0.15 M x 1.0 L M1 6.0 M = 0.025 L x 1000 mL = 25 mL 1 L

  45. Titration Calculation indicator HCl + NaOH  NaCl + HOH A way to analyze solutions! at equivalence point: moleHCl = moleNaOH moles = M x VL Macid x Vinitial acid = Mbase x Vburet

  46. Let’s examine the behavior of an acid, HA, in aqueous solution. HA What happens to the HA molecules in solution?

  47. 100% dissociation of HA HA H+ Strong Acid A- Would the solution be conductive?

  48. Partial dissociation of HA HA H+ Weak Acid A- Would the solution be conductive?

  49. HA  H+ + A- HA H+ Weak Acid A- At any one time, only a fraction of the molecules are dissociated.

  50. Strong and Weak Acids/Bases The strength of an acid (or base) is determined by the amount of IONIZATION. HNO3, HCl, HBr, HI, H2SO4 and HClO4 are the strong acids.

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