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Unit VI Acids, Bases & Salts

Unit VI Acids, Bases & Salts. Textbo ok Chapter 15. Image taken on 8/13/09. Unit Outline. Image taken from http://www.mhhe.com/physsci/chemistry/chang7/esp/ folder_structure/cr/m3/s3/assets/images/crm3s3_1.jpg on 8/14/09. Electrolytes.

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Unit VI Acids, Bases & Salts

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  1. Unit VI Acids, Bases & Salts TextbookChapter 15 Image taken on 8/13/09. Unit Outline Image taken from http://www.mhhe.com/physsci/chemistry/chang7/esp/ folder_structure/cr/m3/s3/assets/images/crm3s3_1.jpg on 8/14/09.

  2. Electrolytes • Dissolve in water, solution formed will conduct electricity. Why conduct? • Conductivity due to presence of free ions. How free ions? • Free ions can be created from processes of dissociation or ionization. • Acids, Bases & Salts are examples of electrolytes. Electrolytes Poem Image taken from http://universe-review.ca/I12-20-electrolyte.jpg on 8/14/09.

  3. Cations are positive. Anions are negative. Dissociation • Occurs when ions of an ionic solid are separatedfrom the crystal lattice structure. • Polar water molecules pull ions from lattice, surround ions and form hydrated ions. • Examples: all ionic compounds (salts) such as NaCl(aq), CuSO4(aq), MgBr2(aq) Image taken from http://media-2.web.britannica.com/eb-media/47/7347-004-68187776.gif on 8/14/09.

  4. Ionization Image taken from http://wwwchem.csustan.edu/chem3070/images/acetic.gif on 8/14/09. • Occurs when a molecular solid is dissolved and creates ions in solution. • Unlike dissociation, ions were not present originally. • Common examples: Acids • HC2H3O2H2O> H+(aq) + C2H3O2-(aq)

  5. Weak or Strong Electrolyte? • Depends on amount of ionization. • Reference Tables K & L list strong electrolytes closer to the top (stronger acids and bases) • Keqvalues such as Ka or Kb can indicate amount of ionization. (Remember Keq’sΔonly w/ temp.) • Large Ka strong electrolyte (acid); many free ions • Small Ka weak electrolyte (acid); few free ions • Complete ionization of HCl animation • Incomplete ionization of weak acid animation • Comparing HCl ionization to HF ionization animation • Conductivity of HCl vs. Acetic Acid video Image taken from http://science.csustan.edu/stone/CHEM3070/HCL.GIF on 8/14/09.

  6. Nonelectrolytes AB(s)  AB(aq) {no free ions} • Do not conduct electricity when in solution. • Examples: All organic compounds except organic acids. • Examples: C12H22O11(aq), C2H5OH(aq) Image taken from http://www.coolschool.ca/lor/CH11/unit6/U06L03/CHEM11_A3_568.jpg on 8/14/09.

  7. How do you define something? • Operational Definition-list properties or behaviors. Include observations from experiments. • Conceptual Definition-tries to answer “Why?” and “How?”. Based on interpretations or conclusions from observed facts. Image taken from http://forpd.ucf.edu/strategies/QUESTION.jpg on 8/14/09.

  8. What is an Acid?6 Operational Definitions of an Acid Bases

  9. Acids: Op Def #1 • Aqueous solutions of acids conduct electricity • Weak acidsweakelectrolytefewionsslight ionization • Strong acidsstrongelectrolyteManyionsAlmost complete ionization Chinese for strong electrolyte (strong acid) ??? Image taken from http://www.cal001.com.cn/en/images/IMG/image309.jpg on 8/14/09.

  10. Acids: Op Def #2 • Acids will react with certain active metals to liberate hydrogen gas. • Think Rocket Lab! • 2HCl(aq) + Zn(s)  ZnCl2(s) + H2(g) • Use Ref Table J. Where are metals found on table that will undergo this reaction? Image taken from http://www.gcsescience.com/Strong-Acid-Weak-Acid.gif on 8/14/09.

  11. Acids: Op Def #3 • Acids cause color changes for acid-base indicators. See Ref Table M. • Note from Table M that all indicators have their own pH range. Depends on the concentration of H+ in solution. Indicators do not change right at pH of 7. Image taken from http://www.elmhurst.edu/~chm/vchembook/182bases.html on 8/14/09.

  12. Acids: Op Def #4 • Acids react with hydroxides (bases) to form water and a salt. Called neutralization. • Example: HNO3(aq) + NaOH(aq)  H2O + NaNO3(aq) • Remember from Lab activity to make salt!!! • Neutralization simplified: H+(aq) + OH-(aq)  H2O • Try another example on next slide! Image taken from http://boomeria.org/chemtextbook/cch24.html on 8/31/09. What is a salt?

  13. Acids react with carbonates to release carbon dioxide. • HCl(aq) + Li2CO3(s)  complete this rxn • 2HCl(aq) + Li2CO3(s)  LiCl(aq) + H2CO3 • Unstable and decomposes • 2HCl(aq) + Li2CO3(s)  LiCl(aq) + H2O(l) + CO2(g)

  14. Acids: Op Def #5 • Dilute aqueous solutions of acids have a sour taste. • Examples: vinegar (acetic acid) in pickles, citric acid in lemonheads/sour candy or citrus fruits (lemons, limes, oranges, etc.) Image taken from http://interiordec.about.com/library/ graphics/ctpcs/ctpc10-011a.jpg on 8/14/09.

  15. Acids: Op Def #6 • Acids react with metallic oxides to form salts and water. • Example: 2HCl + K2O  2KCl +H2O Potassium Oxide Image taken from http://wb4.itrademarket.com/pdimage/05/860605_kaolin325mesh.jpg on 8/31/09.

  16. What is a Base?5 Operational Definitions of a Base Conceptual Definitions

  17. Bases: Op Def #1 • Aqueous solutions of bases conduct electricity • Weak basesweakelectrolytesfewionsslight dissociation • Strong basesstrongelectrolytesManyionsAlmost complete dissociation Image taken from http://universe-review.ca/I12-20-base.jpg on 8/14/09.

  18. Bases: Op Def #2 • Bases cause color changes in acid-base indicators. See Ref Table M. Image taken from http://www.elmhurst.edu/~chm/demos/images/magicpitcher.GIF on 8/14/09.

  19. Bases: Op Def #3 • Bases react with acids to form water and a salt. Called neutralization. • Example: HC2H3O2(aq) + NaOH(aq)  H2O + NaC2H3O2(aq) • Neutralization simplified: H+(aq) + OH-(aq)  H2O Image taken from http://img.sparknotes.com/figures/3/3a5994498f 24d59f5d5d762b40844a2a/titsetup.gif on 8/14/09. What is a salt?

  20. Bases: Op Def #4 • Aqueous solutions of bases feel slippery and taste bitter. • Examples: soaps, cleaners Armor All is great on tires and the dusty dashboard. Why never on the steering wheel? Image taken from http://www.carpages.co.uk/news/tyre-cleaner-14-07-05.asp on 8/14/09.

  21. Bases: Op Def #5 Burn from conc. NaOH • Strong bases have a caustic action on the skin, corrosive to skin and poisonous. • Examples: really strong cleaners, concentrated solutions of KOH or NaOH can cause blindness if in eyes Image taken from http://wpcontent.answers.com/wikipedia/commons /thumb/0/09/Sodium_hydroxide_burn.png/180px-Sodium_hydroxide_burn.png on 8/14/09.

  22. 2 Conceptual Definitions of Acids and Bases • Remember conceptual definitions add reasons to observations. Answer Why? • Arrhenius Theory • Brönsted-Lowry Theory (AKA an alternate acid/base theory according to NYSED) Image taken from http://www.yanswersblogth.com/b4/wp-content/uploads/2009/06/why.jpg on 8/31/09.

  23. Arrhenius’ Theory of an Acid (1887) Examples: HNO3H2O H+(aq) + NO3-(aq) H2SO4H2O 2H+(aq) + SO42- (aq) • A substance that yields hydrogen ions (H+) in aqueous solutions. • Arrhenius said properties of acids in aqueous solutions due to an excess of H+ or H3O+ (hydrogen or hydronium ions) • Good definition but limited to only (aq). Svante Arrhenius, The Nobel Prize in Chemistry 1903 Image taken from http://nobelprize.org/nobel_prizes/chemistry/laureates/1903/arrhenius.jpg on 8/14/09.

  24. Arrhenius’ Theory of a Base (1887) • A substance that yields hydroxide ions (OH-) as the only negative ions in aqueous solutions. Examples: KOH H2O K+(aq) + OH-(aq) Ba(OH)2H2O Ba+2(aq) + 2OH-(aq) Image taken from http://lem.ch.unito.it/didattica/infochimica/Liquidi%20Ionici/LiquidiIonici_File/webquest.jpg on 8/14/09.

  25. Brönsted-Lowry Theory of an Acid (1923) • Any species (molecule or ion) that can donate a proton to another species. • AKA: “a proton donor” • Brönsted-Lowry does not replace Arrhenius’ theory, it just extends it. Includes Arrhenius examples of acids but adds other examples. Johannes Nicolaus Brønsted Image taken from http://kimia.upi.edu/utama/bahanajar/kuliah_web/2008/ Daris%20Qodarisman%20N_0605524/Gambar/Bronsted.gif on 8/14/09. Thomas Martin Lowry Image taken from http://people.clarkson.edu /~ekatz/scientists/lowry1.JPGon 8/14/09.

  26. Brönsted-Lowry Theory of a Base (1923) • Any species(molecule or ion) that can accept a proton. • AKA: “a proton acceptor” • Again Brönsted-Lowry does not replace Arrhenius’ theory, it just extends it. More species can accept a proton than just an OH-. • Ex: H2O + HCl⇆ H3O+ + Cl- • Water is base in forward rxn, accepts H+ to become H3O+ • In reverse rxn, Cl- accepts proton and acts as base to form HCl I luv accepting protons. Image taken from http://www.blobs.org /science/chemistry/base.gif on 8/31/09.

  27. B-L Conjugate Acid-Base Pairs • Bronsted-Lowry acid-base rxn, • Transfer of proton (H+) from acid to base • To accept proton, must have pair of unshared electrons. • An acid give a proton to form a conjugate base. • A base gains a proton to form a conjugate acid. • Ex: HSO4- + H2O  H3O+ + SO42- • Label reacting acid and base and conjugates formed. • Do Examples! Image taken from http://www.lakelandschools.us/lh/lburris/images/donor.gif on 8/14/09.

  28. Lewis A&B Theorydefined in terms of electron pair • Lewis acids- electron-pair acceptor • Lewis bases- electron pair donor. Remember coordinate covalent bonds? Images taken from library.thinkquest.org and education.com on 7/28/11.

  29. Amphoteric(Amphiprotic) Substances Wafflers Unite! • Can act as either an acid or a base. • Pick out the amphoteric substances in the following: • NH3 + H2O ⇆ NH4+ + OH- • H2O + HCl⇆ H3O+ + Cl- • NH3 + OH-⇆ NH2- + H2O Image taken from http://www.smugmug.com/photos/581119447_dpAVF-550x500.jpg on 8/31/09.

  30. Naming Acids • Binary acids (2 elements) use hydro……ic acid • ex: HCl hydrochloric acid • Ternary acids (3 elements) use polyatomic ion name and change ending • ate ic • ite  ous • Ex: H2SO4 • (sulfate) Sulfuric acid • Ex: H2SO3 • (sulfite) Sulfurous acid Image taken from http://boomeria.org/chemtextbook/cch24.html on 8/31/09.

  31. Naming Salts • Binary salts • Change ending to ide • Use Roman numeral if necessary. • Ex: CuCl2 • Copper (II) chloride • Ternary salts • Use polyatomic ion name • Use Roman numeral if necessary. • Ex: Ca3(PO4)2 • Calcium phosphate Image taken from http://www.chem4kids.com/files/atom_naming.html on 8/31/09. What is a salt?

  32. Naming Bases • What is the ion Arrhenius said all bases have? • Use it to name bases. Use Roman numeral if necessary. • Ex: Ba(OH)2 • Barium hydroxide • Ex: Fe(OH)2 • Iron (II) hydroxide Image taken from http://lem.ch.unito.it/didattica/infochimica/Liquidi%20Ionici/LiquidiIonici_File/webquest.jpg on 8/14/09.

  33. Neutralization • A + B  water + salt • Complete and balance the following neutralization rxn: HNO3 + Ca(OH)2  • 2HNO3 + Ca(OH)2  2H2O + Ca(NO3)2 • Name all compounds in this rxn. Image taken from http://www.brooklyn.cuny.edu/bc/ahp/AVC/MacroInv/Protein/graphics/acidBase.gif on 8/31/09.

  34. Hydrolysis • The reverse of neutralization. • Some salts in aqueous solutions react with water and form solutions that are acidic or basic. • Salt + H2O  Acid + Base Image taken from http://www.elmhurst.edu/~chm/vchembook/182bases.html on 8/14/09.

  35. Examples of Hydrolysis • Salt made from strong acid and weak base give aq solutions that are acidic. • Ex: NH4Cl + H2O  HCl + NH4OH • Salts from weak acids and strong bases give aq solutions that are basic. • Ex: NaC2H3O2 + H2O  HC2H3O2 + NaOH • Salts from strong acid and strong base usually do not hydrolyze. If they do, form neutral pH of 7. • Ex: NaOH and HCl Image taken from http://www.docbrown.info/misc/DrMM/DrMM/salthydrolysis1.jpg on 8/31/09.

  36. Acid-Base Titration:a very precise neutralization • The molarity (strength) of an acid (or base) of unknown concentration can be determined by slowly combining it with a base (or acid) of known molarity (standard solution). • A titration is finished when the equivalence or end point is reached, this indicates neutralization and is determined from color changes of indicators. Buret Image taken from http://usm.maine.edu/chy/ manuals/114/images/ABTitr01.gif on 8/14/09.

  37. Titration FormulaRef Table T MAVA = MBVB • Show derivation of formula on overhead. • Before using titration formula, determine mole ratio of acid:base from balanced equation. • Practice Examples! Image taken from http://www.mpcfaculty.net/mark_bishop/titration.gif on 8/14/09. Image taken from ibchem.com on 7/28/11.

  38. Ionization Constants • Remember Keq from last unit? • In this unit we deal mainly with ionization of acids (Ka) and bases (Kb) • Ka & Kb provide method for comparing relative strength of acids or bases. • Example below: CH3COOH H20> H+(aq) + CH3COO-(aq) Size of Ka value tells strength of acid NYS Chem Reference Table pre-2002

  39. Ionization Constant for Water (Kw) • H2O H+ + OH- or 2H20  H3O+ + OH- Since concentration of H2O is relatively constant, Keq expression can be simplified to …. At STP only 1.0 X 10-7 moles/L of H2O will ionize into equal amts of H+ & OH- so therefore…. Image taken from http://www.elmhurst.edu/~chm/vchembook/images2/184waterequi.gif on 8/31/09.

  40. Kw = [H+][OH-] Kw = [1.0X10-7][1.0X10-7]** Kw = 1.0X10-14** ** This is why water is neutral. Because acidity (H+) and basicity (OH-) are in equal concentrations. Kw = 1.0X10-14 @ 25oC w/standard pressure. Image taken from http://www.playgroundteetertotters.com/graphics/playgroundteetertotters_springseesaw_2_blue.jpg on 8/31/09.

  41. Sample Problem What happens to [H+] if [OH-] concentration jumps to 1.0X10-5 @ STP? Kw = [H+][OH-] 1.0X10-14 = [H+][1.0X10-5] [1.0X10-14]/ [1.0X10-5] = [H+] [H+] = [1.0X10-9] [OH-] got bigger, [H+] got smaller

  42. What do you know about the pH scale? • 0-14 • 7 is neutral • Acids below 7, Bases above 7. • Stronger the acid or base the further away from neutral. Image taken from http://www.phschool.com/atschool/science_activity_library/images/acids_and_bases_phscale.jpg on 8/31/09.

  43. pH • pH is the logarithm of the reciprocal of the H+ concentration • pH of a solution tells the concentration of H+ (how acidic it is) • Ex: [H+]=1.0 X 10-9 • pH = 9 • pH is absolute value of exponent for [H+] Image taken from http://tuberose.com/Graphics/AcidBaseScale.JPG on 8/31/09.

  44. pH scale Powers of 10 video Scale of Universe (powers of 10) Image taken from http://www.stormcenter.com/envirocast/2003-04-01/images/article4-1_sm.gif on 8/31/09. • What does a logarithmic scale mean? • Each Δ in pH # by 1 = Δin [H+] or [H3O+] by 10

  45. Remember water at 25oC! [H+]= 1.0 X 10-7 same as [OH-], balanced pH= 7, neutral Image taken from http://packerpedia.wiki.packer.edu/file/view/pH_Scale.jpg on 8/31/09.

  46. pH sample problemsWhat is the pH in each of the following examples? • [H+]=1.0 X 10-3 • pH = 3 • [OH-]=1.0 X 10-11 • Kw=[H+][OH-] • 1.0X10-14 = [H+][1.0X10-11] • 1.0X10-14/1.0X10-11 = [H+] • [H+] = 1.0X10-3 • pH=3

  47. pH sample problemsWhat is the pH in each of the following examples? • 0.001M HCl solution • 0.001M  1.0X10-3 =[H+] • pH=3 • 0.01M NaOH solution • 0.01M  1.0X10-2 = [OH-] • Kw = [H+][OH-] • 1.0X10-14 = [H+][1.0X10-2] • 1.0X10-14/1.0X10-2 = [H+] • [H+] = 1.0X10-12 • pH=12  basic

  48. pOH • pOH = -log [OH-] • pH + pOH = 14.0 Taken from sciencegeek.net on 7/29/11.

  49. Buffers • Solutions used to minimize ( not prevent) a change in pH when an additional acid or base is introduced into solution. • Buffers consist of a conjugate pair of a weak acid and weak base in an equilibrium system. Taken from boughen.com.au on 7/28/11.

  50. Calculating the pH of Buffers • The Henderson-Hasselbalch equation:

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