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Acids and Bases

Acids and Bases. Acids. Definition : latin meaning sour “Acidus” Lots of acids Dangerous Nitric Acid, Sulfuric Acid Essential Ascorbic Acid Dietary Acetic Acid (ethanoic acid) (vinegar), Citric Acid, Carbonic Acid Odd Stearic Acid, Benzoic Acid. info. Turns blue Litmus paper Red

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Acids and Bases

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  1. Acids and Bases

  2. Acids • Definition : latin meaning sour “Acidus” • Lots of acids • Dangerous • Nitric Acid, Sulfuric Acid • Essential • Ascorbic Acid • Dietary • Acetic Acid (ethanoic acid) (vinegar), Citric Acid, Carbonic Acid • Odd • Stearic Acid, Benzoic Acid

  3. info • Turns blue Litmus paper Red • React with metals to produce hydrogen gas H2SO4 + Zn ZnSO4 + H2 • React with Carbonates to produce CO2

  4. Arrhenius Theory • An acid is a substance that dissociates in water to produce H+ ions • Svante Arrhenius (nobel prize 1903)

  5. Add HCl to water and we get H+ ions and Chlorine Nitric and Sulfuric acid behave the same HCl H+ + Cl HNO3 H+ + NO3 H2SO4 2H+ + SO42-

  6. When we add a solution of Hydrogen chloride to water we call it Hydrochloric acid Mono basic: HCl H+ + Cl Di Basic H2SO4 2H+ + SO42- Tri Basic H3PO4 3H+ + PO43- Dependant on the number of hydrogen ions donated

  7. Strong and weak acids Sulfuric and nitric are strong as they dissociate fully in water but acetic acid is weak as it only partially dissociates

  8. Hydronium Ion The H+ ion ....just a proton Cannot exist independently in solution so the Hydronium ion is born The oxygen atom allows an electron to form a dative covalent bond with the hydrogen atom

  9. . H+ . .. H+ + .. .. O . . . . O HX XH HX XH Hydrogen ion reacts with water to form Hydronium Ion H3O+

  10. Hydronium Ion For accuracy we should use HA + H2O H3O + + A- HCl + H2O H3O + + Cl- Many chemists simply say the hydrogen ion

  11. Importance of water If we add pure Hydrogen Chloride or acetic acid into a solvent like benzene (no water) we do not get either H+ or Hydronium ion formation and blue litmus paper stays blue Shows that Hydrogen Chloride or acetic acid is only acid when water is present

  12. Bases • Behave in the opposite manner to acids • Turn Red litmus paper blue • Example: • Sodium Hydroxide (NaOH) • Magnesium Hydroxide ([Mg(OH)2]) • Calcium Hydroxide ([Ca(OH)2])

  13. Info Many bases have a soapy feel Used as degreasers in household detergents Act by converting the oil into soap which washes away more easily

  14. Arrhenius Theory A base is a substance that dissociates in water to produce OH- ions The OH- ion is called the hydroxide ion When added to water it dissociates completely into Sodium ions and hydroxide ions NaOH Na+ + OH-

  15. Arrhenius Theory Similarly for Magnesium Hydroxide and Calcium Hydroxide [Mg(OH)2] Mg2+ + 2OH- [Ca(OH)2] Ca2+ + 2OH-

  16. Strong and Weak bases Strong bases include Sodium Hydroxide because they dissociate almost completely in water but ....Magnesium Hydroxide and Calcium Hydroxide do not and are referred to as weak bases

  17. A number of flaws to the Arrhenius Theory Hydronium ions are present not bare hydrogen ions Arrhenius theory limited to aqueous solutions and not all acid base reactions are water based NH3 + HCl NH4Cl Base acid ammonium chloride

  18. Brønsted -Lowry Update needed to reflect more accurately the reactions that occur 1923 Johannes Bronsted (Danish) & Thomas Lowry (English) – working independently came up with the same theory

  19. Brønsted -Lowry • Definition of an Acid • An acid is a proton donor • Definition of a base • A Base is a proton acceptor

  20. Detail HCl + H2O H3O + + Cl- Acid base Donates accepts a proton a proton Therefore these obey the B/L definition

  21. Ammonia Gas NH3 + H2O NH4 + + OH- base acid accepts Donates a proton a proton Therefore these obey the B/L definition

  22. What to learn Water can act as an acid or a base - amphoteric

  23. Can be applied to non aqueous reactions HCl + NH3 NH4+ + Cl- Acid base Brønsted –Lowry broadens the definition of what can act as an acid or a base

  24. Homework Questions 12.1 in textbook and 12.1 in workbook

  25. Conjugate acid-base pairs Add acetic acid (ethanoic acid) to water CH3COOH + H2O CH3COO- + H3O The reaction works in both directions

  26. Conjugate acid-base pairs Add acetic acid (ethanoic acid) to water CH3COOH + H2O CH3COO- + H3O Donates accepts A proton a proton

  27. Conjugate acid-base pairs Add acetic acid (ethanoic acid) to water CH3COO- + H3O CH3COOH + H2O Accepts Donates A proton a proton The water is behaving like an acid

  28. Conjugate acid-base pairs Add acetic acid (ethanoic acid) to water CH3COOH + H2O CH3COO- + H3O The reaction works in both directions so we call each conjugate pairs CH3COOH is a conjugate acid of CH3COO- CH3COO- is a conjugate base of CH3COOH

  29. An acid changes into a conjugate base when it donates a proton CH3COOH CH3COO- H+ acid Conjugate proton base A base changes into a conjugate acid when it accepts a proton CH3COO- H+ CH3COOH base proton conjugate acid

  30. Every acid has a conjugate base and every base has a conjugate acid... We call this an conjugate acid - base pair A conjugate acid – base pair is any pair consisting of an acid and a base which differs by one proton

  31. Important The definition says that the pair must involve a single proton so...the conjugate pair of H2SO4 HSO4-

  32. Example What is the conjugate acid and the conjugate base of HC2O4- To change into its conjugate the base must accept a proton...so HC2O4- + H+ H2C2O4 base conjugate acid

  33. Example What is the conjugate acid and the conjugate base of HC2O4- To change into its conjugate the acid must donate a proton...so HC2O4- C2O4 2 -+ H+ Acid conjugate base

  34. Tell me Which is the acid and which is the base HNO3 + H2F2 H2NO3 + HF2 Also mark out the pairs

  35. Base Acid Base Acid Conjugate acid-base pair Conjugate acid-base pair HNO3 + H2F2 H2NO3 + HF2

  36. Neutralisation Neutralisation is the reaction between an acid and a base to form salt and water

  37. Neutralisation Acids and base in the correct proportions cancel each other out This means they lose their characterisitics,the acid is no longer behaving like and acid and vice versa The resulting solution has a neutral effect on litmus paper

  38. example HCl + NaOH NaCl + H2O The word salt simply refers to the fact that the hydrogen in the acid is replaced by a metal or ammonium ion

  39. What’s Happening? HCl + NaOH NaCl + H2O In soln: H+ + Cl - + Na + + OH - Na + + Cl - = H2O Lets ignore the spectator ions

  40. H+ + Cl - + Na + + OH - Na + + Cl - = H2O The hydrogen (hydronium) ions from the acid are reacting with the hydroxide ions from the base to form water which results in a neutral solution

  41. Everyday examples • Stomach HCL neutralised by NaHCO3 • In other words...by an antacid (bioSodol) containing sodium hydrogencarbonate HCl + NaHCO3 NaCl + H2O + CO2 Another example (Maalox) 2HCl + Mg(OH)2 MgCl + H2O

  42. Everyday examples • Calcium Oxide (lime) spread on soil to neutralize the acid conditions CaO + H2O Ca(OH)2 Lime + water Calcium Hydroxide Calcium Hydroxide can neutralize acidity as follows Ca(OH)2 + H2SO4 CaSO4 + 2H2O Calcium hydroxide plus Sulfuric Acid becomes Calcium Sulfate and Water

  43. Everyday examples • Limestone added to lake water to neuralise the effects of acid rain CaCO3 + H2SO4 CaSO4 + 2H2O + CO2 Calcium carbonate plus Sulfuric Acid becomes Calcium Sulfate and Water and Carbon Dioxide

  44. Homework Questions 12.2 – 12.6 in textbook and 12.2 – 12.4 in workbook

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