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Acids and bases


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Acids and bases

  1. 1. Acids and Bases Properties Nomenclature Arrhenius’ Theory pH scaleAcid-base Indicators Neutralization Applications
  2. 2. Everyday AcidsLemon juice: citric acidVinegar: acetic acidStomach acid: hydrochloric acidAspirin: acetylsalicylic acidWine: acids in grapes
  3. 3. Omega 3 Fatty Acids• An essential fatty acid (needed by humans but can’t be made by our own bodies and must be ingested)• Found naturally in oily fish, flaxseed, canola oil
  4. 4. Trans Fatty Acids• created when oils are hydrogenated• prevents oil from becoming rancid and keeps them solid at room temperature
  5. 5. CaffeineBaking sodaAntacidsSoapChalkBleach Everyday BasesCleaners
  6. 6. Rotting FishA 56-foot, 60-ton whaledied on a beach inTaiwan in January,2004. The carcass wason its way to a researchcenter when the gasesfrom its decompositioncaused it to explode.
  7. 7. Physical Properties Properties Acids Bases Taste Texture pH SolubilityConductivity Hazards
  8. 8. Physical Properties Properties Acids Bases Taste Sour Bitter Texture NA Feels slippery pH Less than 7 Greater than 7 SolubilityConductivity Hazards
  9. 9. Physical Properties
  10. 10. Physical Properties Properties Acids Bases Taste Sour Bitter Texture NA Feels slippery pH Less than 7 Greater than 7 Solubility Soluble in waterConductivity Conducts electricity Hazards Corrosive, burns skin
  11. 11. Chemical Properties Properties Acids Bases CorrosionReaction with metalLitmus paper reaction
  12. 12. Chemical Properties Properties Acids Bases Corrosion Corrodes metals NAReaction with Produce H2(g) NA metalLitmus paper Turns red Turns blue reaction
  13. 13. Chemical PropertiesMagnesium + hydrochloric acid  magnesium chloride + hydrogen gas Mg(s) + 2HCl(aq)  MgCl2(s) + H2(g)
  14. 14. DefinitionsDissociation: Separation of ions when anionic compound dissolves in water.Ionization: A compound that is convertedinto an ion.Thus, dissociation is a form of ionization.
  15. 15. Arrhenius TheoryAn acid is a substance that dissociatesin water to produce these ions:• hydrogen ions (H+) or• hydronium ions (H3O+)
  16. 16. Arrhenius TheoryExamples of acid ionizing:• HBr(aq) H+ (aq) + Br- (aq)• H2SO4(aq) 2 H+ (aq) + SO42- (aq)• CH3COOH(aq) CH3COO- (aq) + H+ (aq)Note: not all hydrogens in a molecule are ionized
  17. 17. Arrhenius TheoryExamples of acid dissociating in water:• HBr(aq) + H20(l) H30+ + Br-• H2SO4(aq) + H20(l) 2 H30+ + SO42-• CH3COOH(aq) + H20(l) CH3COO- + H30+Note: not all hydrogens in a molecule are dissociated
  18. 18. Recall: Types of AcidsBinary or Simple acids• Consist of hydrogen and a nonmetal• Example: HClOxyacids• Consists of hydrogen and a polyatomic• Example: H2SO4, CH3COOH
  19. 19. Recall: Acid NomenclatureBinary or Simple acids• ‘hydro’ + nonmetal ‘ic’ + ‘acid’Oxyacids• Identify the polyatomic and look for the oxyacid name on the reference chart and add ‘acid’
  20. 20. Arrhenius TheoryAn base is a substance thatdissociates in water to producehydroxide ions (OH-).
  21. 21. Arrhenius TheoryExamples of base dissociating in water:• LiOH(aq) Li+ + OH-• Ba(OH)2(aq) Ba2+ + 2 OH-
  22. 22. Recognizing Bases• All bases have a chemical formula that either: • Ends with an OH (hydroxide) • Ends with an HCO3 (bicarbonate)• Example: • KOH, NaHCO3
  23. 23. Naming Bases• All bases are ionic compounds containing a polyatomic ion• Naming follows the same rules as any ionic compound: metal + polyatomic• Examples: • KOH = Potassium hydroxide • NaHCO3 = Sodium bicarbonate
  24. 24. Strength of Acids and Bases• Determined by the ability to ionize• Strong acids and bases ionize almost completely in water (100%): HCl(aq)  H+ + Cl- NaOH(aq)  Na+ + OH- Notice the single direction of the arrow
  25. 25. Strength of Acids and Bases• Weak acids and bases partially ionize in water.• Some of the molecules remain in its neutral compound form: CH3COOH(aq) CH3COO- + H+ NH4OH(aq) NH4+ + OH- Notice the double arrow indicating that the reaction can be reversed which assumes that not all the substance is in the ion form.
  26. 26. pH = power of hydrogen• A measure of the concentration of hydrogen (H+) or hydronium (H3O+) ions• A measure of how acidic or basic a solution is• Can only be determined if the substance is in an aqueous solution (dissolved in water)
  27. 27. pH Formula• Given the concentration of hydrogen, the pH is calculated by this formula: • pH = -log[H+] • Where concentration is measured in mol/L• Example: What is the pH if the hydrogen concentration is 10-3 mol/L? pH = -log(10 –3) = 3
  28. 28. pH Scale examples [H+] in mol/L pH = -log[H+] 1 x 100 = 1 0 Acid 1 x 10-1 = 0.1 1 Acid 1 x 10-2 = 0.01 2 Acid1 x 10-3 = 0.001 3 Acid 1 x 10-7 7 Neutral 1 x 10-10 10 Base 1 x 10-14 14 Base
  29. 29. pH scaleNumerical scale ranging from 0-14 used to compare the acidity of solutions
  30. 30. pH scale• Pure water has a pH of 7• Substances near pH 7 are neutral Neutral substances are neither acid nor base
  31. 31. pH scaleAcids have a pH below 7 when it is in anaqueous solution.The more acidic the substance, the lower the pH
  32. 32. pH scaleBases have a pH greater than 7 when it isin an aqueous solution.The more basic a substance, the higher the pH
  33. 33. pH scale• One unit of change on the pH scale is a change by a factor of 10• E.g. There are 100x (not 2x) more hydrogens at pH 4 than pH 6.
  34. 34. pH ApplicationWould most edible substances beclassified as mostly acidic or basic?
  35. 35. pH ApplicationAre soaps and toothpastes slightlyacidic or basic? Give a reason.
  36. 36. pH ApplicationExperiments show that teeth begin tolose minerals at pH 5.5 or less. Howcould you adjust your diet to minimizemineral loss?
  37. 37. pH ApplicationExplain why personal hygiene products(e.g. soap, toothpaste) are closer to aneutral pH rather than extremely acidicor basic.
  38. 38. pH ApplicationSome skin creams claim that they are“pH balanced” and yet do not have apH of 7. What do the manufacturersmean when they say “pH balanced”?
  39. 39. Acid-Base Indicators• An acid-base indicator is any substance that changes colour in the presence of an acid or a base
  40. 40. Acid-Base Indicators• The most widely known acid-base indicator is litmus• Litmus is a plant extract that can be blue or red (pink)
  41. 41. Acid-Base Indicators• The colour of hydrangea flowers is dependent upon the pH of the soil
  42. 42. Acid-Base IndicatorsLitmus paper• turns red/pink in an acidic solution• turns blue in a basic solution
  43. 43. Acid-Base Indicators• It would be impossible to determine the pH of all solutions using just one indicator, such as litmus• Several other acid-base indicators exist, each producing a colour change at a specific pH level
  44. 44. Acid-Base Indicators• A universal indicator is a mixture of chemicals that changes colour through a wide range of pH values
  45. 45. An even more preciseway of determining pHis to use a pH meter
  46. 46. Acid-Base Indicators• Indicators can be classified into 2 types depending on where they originated from a. Chemical indicators b. Natural indicators
  47. 47. Acid-Base Indicators• Chemical Indicators are made from chemicals• Most chemical indicators only have 2-3 colour changes that describes a specific pH range• Universal indicators have many colour changes across the whole pH spectrum and thus can provide a specific pH value
  48. 48. Acid-Base Indicator• Natural indicators are made from plants • Leaves: red cabbage • Fruits: strawberry, blueberry • Roots: beets • Bulbs: red onions • Flower: roses
  49. 49. Acid-Base Indicator• Red cabbage indicator colour range
  50. 50. Neutralization Reactions• Neutralization is a chemical reaction between an acid and a base that produces water (H2O) and a salt• acid + base  salt + water
  51. 51. Neutralization Reactions• Neutralization reactions with hydroxide bases are generally double displacement reactions. HCl + NaOH  NaCl + HOH HCl + NaOH  NaCl + H2O acid + base  salt + water
  52. 52. Neutralization Reactions• Sample question: Name the salt in the neutralization reaction between potassium hydroxide and carbonic acid.• Step 1: Write the chemical formula of the reactants• Step 2: Predict the products in the double displacement neutralization reaction• Step 3: Identify the water molecule in the products. The other product will be the salt.
  53. 53. Neutralization ReactionsSample question: Name the salt in theneutralization reaction betweenpotassium hydroxide and carbonic acid. KOH + H2CO3  K2CO3 + HOH KOH + H2CO3  K2CO3 + H2O salt water
  54. 54. Neutralization Reactions • The salts formed may be soluble in water or can be insoluble • If the salt is insoluble, a precipitate will form • Recall: a precipitate is a suspension of small, solid particles formed during a chemical reaction
  55. 55. Neutralization ReactionsNeutralization with a bicarbonate base is adouble displacement action with an extra stepthat produces salt, water and carbon dioxide. HCl + NaHCO3  NaCl + H2CO3 HCl + NaHCO3  NaCl + H2O + CO2acid + base  salt + water + carbon dioxide
  56. 56. Neutralization ApplicationsQuestion 1• In a neutralization reaction with a bicarbonate base, which of the 3 products produced is useful in baking?• Recall: acid + base  salt + water + carbon dioxideQuestion 2• Explain why recipe instructions often say to mix the dry ingredients together before adding the wet ones.• Hint: Dry ingredients usually include a bicarbonate base. Wet ingredients usually include an acid.
  57. 57. Neutralization ApplicationsQuestion 3• A soda-acid fire extinguisher contains both sulfuric acid and sodium bicarbonate.• Write the chemical equation for this reaction.• Which of the products is the main ingredient for smothering flames?• Hint: a fire only survives if it has oxygen gas
  58. 58. Neutralization ApplicationsQuestion 4• Calcium Oxide (CaO) also known as lime has been very useful in managing soil pH and dealing with acid spills. Explain how.• Hint: CaO + H2O  Ca(OH)2
  59. 59. Neutralization ApplicationsQuestion 5• Acid precipitation is mostly due to the formation of sulfuric acid (H2SO4) from sulfur oxides (SOx) produced from burning coal.• Soils have some buffering capacity to resist changes in acidity from acid precipitation.• Calcium Carbonate (CaCO3) also known as limestone plays an important role in buffering• Write the chemical reaction between limestone and acid precipitation. Hint: carbonates act similarly to bicarbonates in a neutralization reaction.
  60. 60. Neutralization ApplicationsQuestion 6• Household hot water pipes can become blocked by deposits of solid calcium carbonate.• What would you suggest to a plumber to use for removing the calcium carbonate?• Write the chemical equation for your reaction between calcium carbonate and your suggested product.
  61. 61. Neutralization ApplicationsQuestion 7• A third type of base that we haven’t studied are amines.• Oils in fish contain amines that give it a distinctive odour.• Why do you think people often squeeze lemon juice on their fish?