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Chemistry 20

Chemistry 20. Chapter 6 – Acids and Bases PowerPoint Presentation by R. Schultz robert.schultz@ei.educ.ab.ca. 6.1 Theories of Acids and Bases. Acids and Bases at home:. chart page 208. 6.1 Theories of Acids and Bases. Nomenclature Bases have no special nomenclature Acid nomenclature:

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Chemistry 20

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  1. Chemistry 20 Chapter 6 – Acids and Bases PowerPoint Presentation by R. Schultz robert.schultz@ei.educ.ab.ca

  2. 6.1 Theories of Acids and Bases • Acids and Bases at home: chart page 208

  3. 6.1 Theories of Acids and Bases • Nomenclature • Bases have no special nomenclature • Acid nomenclature: New IUPAC nomenclature – name the compound as if it was ionic adding the word “aqueous” in front • examples: • HCl(aq) • H2SO4(aq) aqueous hydrogen chloride aqueous hydrogen sulfate this method is relatively new and still not commonly used by chemists

  4. 6.1 Theories of Acids and Bases • Classical acid nomenclature • Start by naming the compound as it was ionic • Look at ending and apply following rules __________ide  hydro_______ic acid __________ate  __________ic acid __________ite  __________ous acid

  5. 6.1 Theories of Acids and Bases • Example: Consider the following group of acids: Formula Name (if it was ionic) Classical Acid Name rule 1 HC ( aq ) l hydrogen chloride hydrochloric acid rule 2 HC O ( aq ) l hydrogen perchlorate perchloric acid 4 rule 2 HC O ( aq ) l hydrogen chlorate chloric acid 3 rule 3 HC O ( aq ) l hydrogen chlorite chlorous acid 2 rule 3 HC O ( aq ) l hydrogen hypochlorite hypochlorous acid put the word “aqueous” in front and you’ve got the IUPAC name

  6. 6.1 Theories of Acids and Bases • 2 elements to be careful about: S and P • both keep the middle syllable in classical acid nomenclatureH2SO4(aq) “sulfuric acid”, not “sulfic acid”H3PO4(aq) “phosphoric acid”, not “phosphic acid” • Quiz next day – same format as practice quiz you’ll do now • After quiz you won’t need to know classical acid nomenclature by memory as the names and formulae of many acids are in your Data Booklet, pages 8 and 9

  7. 6.1 Theories of Acids and Bases • acids and bases can be defined empirically (in terms of properties) or theoretically (in terms of theories that explain their properties) chart page 210

  8. 6.1 Theories of Acids and Bases • Explaining (theories) • Arrhenius acid: ionizes in water to produce H+(aq)base: dissociates in water to produce OHˉ(aq) • according to Arrhenius’ theory, acid formulas must contain H and base formulas must contain OH • do Investigation 6.B to test this out

  9. 6.1 Theories of Acids and Bases • problems from lab: NH3(aq) was basic, NaHCO3(aq) was basic, others?? • Arrhenius’ theory worked well for many, but not all acids and bases • Slight modifications provide great improvement

  10. 6.1 Theories of Acids and Bases • revised or modified Arrhenius theory: • acid: reacts with water to produce hydronium ion, H3O+(aq) before: HCl(aq) H+(aq) + Clˉ(aq) now:HCl(aq) + H2O(l) H3O+(aq) + Clˉ(aq) • base: dissociates or reacts with water to produce OHˉ(aq) before: NaOH(s) Na+(aq) + OHˉ(aq) now: exactly the same

  11. 6.1 Theories of Acids and Bases • Here’s where the benefit comes: • NH3(aq): before: NH3(aq) ??????? now: NH3(aq) + H2O(l) NH4+(aq) + OHˉ(aq) now NH3’s basic behaviour is explained • NaHCO3(aq): • NaHCO3(s) Na+(aq) + HCO3ˉ(aq), then,HCO3ˉ(aq) + H2O(l) H2CO3(aq) + OHˉ(aq) now NaHCO3’s basic behaviour is explained

  12. 6.1 Theories of Acids and Bases • Try a weird acid like CO2(aq) (soda water) • standard Arrhenius theory doesn`t explain • Revised: CO2(g) + H2O(l) H2CO3(aq), then, H2CO3(aq) + H2O(l) HCO3ˉ(aq) + H3O+(aq) oxides will always be 2 steps – metal oxides to produce bases; non-metal oxides to produce acids Worksheet BLM 6.1.0

  13. 6.2 Strong and Weak Acids and Bases • terms: “strong acid” and “weak acid” have technical meaning – they are based on identity, not acidic behaviour • note that at both 1.0 mol/L and 0.10 mol/L HCl(aq) is more reactive than CH3COOH(aq) fig 6.7 page 218

  14. 6.2 Strong and Weak Acids and Bases • Strong acid: reacts 100% with water or 100% ionized in water HCl(aq) + H2O(l) H3O+(aq) + Clˉ(aq) strong acids are the 1st 6 acids listed in your chart, page 8-9 of the Data Booklet fig 6.8, page 219

  15. 6.2 Strong and Weak Acids and Bases • Weak Acid: reacts only partially (usually very weakly) with water or ionizes only partially CH3COOH(aq) + H2O(l)  H3O+(aq) + CH3COOˉ(aq) weak acids are all the others fig 6.9 page 220 do worksheet BLM 6.2.4

  16. 6.2 Strong and Weak Acids and Bases • Is it possible for a strong acid to be less acidic in behaviour than a weak acid? • strong bases and weak bases: aqueous ionic hydroxides and ionic oxides are strong bases all other bases (from Data Booklet page 8-9 “Conjugate Base” column) are weak yes, if its concentration is very low and the weak acid’s concentration is very high read about “weak acids and bases” page 221 bottom and page 223 bottom discuss questions 5-7, page 222

  17. 6.2 Strong and Weak Acids and Bases • Mono and polyprotic acids • monoprotic acids: have only 1 hydrogen atom that reacts to produce H3O+(aq), e.g. HCl(aq), HBr(aq), HNO3(aq) • polyprotic acids: have 2 or more hydrogen atoms that react to produce H3O+(aq), e.g. H2SO4(aq) (diprotic), H3PO4(aq)  (triprotic)

  18. 6.2 Strong and Weak Acids and Bases • in a series of acids, one with most H’s is strongest • e.g. H3PO4(aq) • H3PO4(aq) + H2O(l)  H3O+(aq) + H2PO4ˉ(aq) H2PO4ˉ(aq) + H2O(l)  H3O+(aq) + HPO42ˉ(aq) HPO42ˉ(aq) + H2O(l)  H3O+(aq) + PO43ˉ(aq) H3PO4(aq) > H2PO4ˉ(aq) > HPO42ˉ(aq) strongest weakest

  19. 6.2 Strong and Weak Acids and Bases • mono and polyprotic bases • monoprotic base: reacts with water or ionizes to produce 1 OHˉ(aq)e.g. NaOH(aq), NH3(aq) • polyprotic base: reacts with water or ionizes to produce 2 or more OHˉ(aq) e.g. CO32ˉ(aq), HPO42ˉ(aq) • in a series of bases, one with the least H’s is most basic: PO43ˉ(aq) > HPO42ˉ(aq) > H2PO4ˉ(aq) strongest weakest

  20. 6.2 Strong and Weak Acids and Bases • Read pages 224-225 • neutralization reaction: acid + base water + a salt neutral ionic compound e.g. NaOH(aq) + HNO3(aq) H2O(l) + NaNO3(aq) net ionic equation for all strong acid/strong base neutralizations: H3O+(aq) + OHˉ(aq) 2 H2O(l)

  21. 6.3 Acids, Bases and pH • all aqueous solutions contain both H3O+(aq) and OHˉ(aq) ionsIf [H3O+] is high, [OHˉ] is low • following slide illustrates their relationship in aqueous solutions • note: to fit this comfortably on 1 page, I have used H+(aq) instead of H3O+(aq), recognizing that they both represent same chemical entity

  22. 6.3 Acids, Bases and pH example [H+]: 10-5 mol/L 10-1 mol/L 10-3 mol/L 10-7 mol/L 10-9 mol/L 10-13 mol/L 10-11 mol/L acidic basic pH= 1 3 5 9 11 13 7 corresponding [OHˉ]: 10-13 mol/L 10-11 mol/L 10-9 mol/L 10-5 mol/L 10-3 mol/L 10-1 mol/L 10-7 mol/L

  23. 6.3 Acids, Bases and pH fig 6.17, page 230

  24. 6.3 Acids, Bases and pH • H2O(l) + H2O(l)  H3O+(aq) + OHˉ(aq) • water is an extremely weak acid;[H3O+]=[OHˉ]=1.0 x 10-7 mol/L • also, [H3O+]=[OHˉ]=1.0 x 10-7 mol/L in any neutral solution • In previous slide if [H3O+] = 10ˉ9 mol/L, pH equaled 9 • formula: pH = -log [H3O+] orpH = -log [H+]

  25. 6.3 Acids, Bases and pH • log is a function on your calculator • log of a # is the power of 10 you’d need to get the # • based on this, what is log 100 (no calculator)? • log 1000? • log 0.1? 2 3 -1

  26. 6.3 Acids, Bases and pH • log (10ˉ7 mol/L)=-7 (try it on your calculator) • Why do you think pH = - log [H3O+]? • Discuss should look like this or you could enter like this

  27. 6.3 Acids, Bases and pH • Try the following exercise (write your answers): • -log (1.89x10ˉ9) (enter as 1.89E-9) • -log(1.89x10ˉ8) • -log(1.89x10ˉ7) • -log(1.89x10ˉ6) 8.723538 this part is related to the 1.89 7.723538 6.723538 this part is related to the power of 10 5.723538 significant digits not significant if [H3O+] = 1.89 x 10-6 mol/L, pH = 5.724 !

  28. 6.3 Acids, Bases and pH • General rule: when finding pH from concentration, number of significant digits in concentration is same as the number of decimal places in pH! (this is rule 4 on significant digits handout!) • When finding concentration from pH, number of decimal places in pH is same as significant digits in concentration

  29. 6.3 Acids, Bases and pH • What is meaning of pH increase by 2 units? • Examples: Practice Problems 1a, 1c page 230 • 1a) • 1c) • Do worksheet BLM 6.3.4 questions 1, 2, 5, 6, 9, 10a [H3O+] has decreased by 100 times

  30. 6.3 Acids, Bases and pH • Measuring pH – indicators and pH meters • Indicators: substances whose colour changes with pH page 10, Data Booklet: shorthand formulas here’s a few; fig 6.18, page 231 4.8-6.0 HMr(aq)/Mrˉ(aq) 6.0-7.6 HBb(aq)/Bbˉ(aq) 11.4-13.0 HIc(aq)/Icˉ(aq)

  31. 6.3 Acids, Bases and pH • Examples: following indicators are added to fresh samples of a solution. Results given. Estimate pH. pH > 1.6 pH > 4.4 pH < 4.8 pH < 8.2 conclusion: pH 4.4 – 4.8

  32. 6.3 Acids, Bases and pH • Try this one: pH < 11.4 pH < 6.6 pH < 3.8 pH 3.2 – 4.4 conclusion: pH 3.2 – 3.8 do worksheet BLM 6.3.6 Investigation 6.D, page 232

  33. 6.3 Acids, Bases and pH • Demonstration: Investigation 6.E, page 234

  34. 6.3 Acids, Bases and pH • pH after dilution – note can’t raise pH of an acid to > 7 by dilution (since water already has [H3O+] = 10ˉ7 mol/L) • can’t lower pH of a base to < 7 by dilution (since water already has [OHˉ] = 10ˉ7 mol/L)

  35. 6.3 Acids, Bases and pH • Example: A 35.0 mL sample of 0.489 mol/L HCl(aq) is diluted to 300 mL • What is pH of the concentrated solution? • What is concentration of diluted solution? • pH of diluted solution? do worksheet BLM 6.3.8 #2, 3, 4

  36. 6.3 Acids, Bases and pH • pOH = -log [OHˉ] (like pH, but for OHˉ) • you haven’t heard of pOH because it’s never measured or reported – it’s calculated and used as a calculation tool because ……….. • pOH is opposite to pH – it’s low for bases and high for acids (see table 6.8, page 237) • pH + pOH = 14.00

  37. 6.3 Acids, Bases and pH • Further formulas: • [H3O+] = 10ˉpH [OHˉ] = 10ˉpOH • Examples: • Practice Problem 13a, page 241 • 2 ways to enter: 1 significant digit a) type “10^-3.9” b) Do “2nd log” then enter -3.9

  38. 6.3 Acids, Bases and pH • Practice Problem 13d, page 241 • What is the pOH of a 5.467 mol/L solution of barium hydroxide, Ba(OH)2? Ba(OH)2(s) Ba(OH)2(aq) Ba2+(aq) + 2 OHˉ(aq)

  39. 6.3 Acids, Bases and pH • What is the concentration of sodium hydroxide, NaOH(aq), that gives a solution with a pH of 10.32? • since it’s a base start by finding pOH • Since NaOH dissociates as • NaOH(s) Na+(aq) + OHˉ(aq), • [NaOH]=2.1x10-4 mol/L

  40. 6.3 Acids, Bases and pH • Example: What mass of rubidium hydroxide, RbOH(s), needs to be dissolved in 1.50 L of water to create a solution with a pH of 9.35? • Do worksheet BLM 6.3.12 questions 1a, 2a, 3, 4, 6, 7, 8 RbOH(s) → RbOH(aq) → Rb+(aq) + OH‾(aq)

  41. 6.3 Acids, Bases and pH • Putting it all together: • Worksheet BLM 6.3.13 question 1, 3, 4, 6, 7

  42. 6.3 Acids, Bases and pH Chapter Review: Worksheet BLM 6.3.14

  43. 6.3 Acids, Bases and pH

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