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4.8 Acid-Base Reactions

4.8 Acid-Base Reactions. Definitions. Arrhenius: Acid- produces H + when dissolved in water Base- produces OH - when dissolved in water Bronsted -Lowry : Acid - H + /proton donor Base - H + /proton acceptor

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4.8 Acid-Base Reactions

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  1. 4.8 Acid-Base Reactions

  2. Definitions • Arrhenius: • Acid- produces H+ when dissolved in water • Base- produces OH- when dissolved in water • Bronsted-Lowry: • Acid- H+/proton donor • Base- H+/proton acceptor • Since H2O is a non-electrolyte, large amounts of OH- and H+ cannot exist in solution without combining

  3. Lewis Model • even more general than Bronsted-Lowry • acid • electron pair acceptor • has empty atomic orbitals • base • electron pair donor • has lone pair

  4. ArrheniusAcid H2O HA ----> H3O+ + A-

  5. Lewis Base

  6. Monoprotic acid: HCl HCl(aq) + NaOH(aq) ---> H2O(l) + NaCl(aq) H+ + Cl- + Na+ + OH- ---> H2O + Na+ + Cl- H+ + OH- ---> H2O

  7. Diprotic acid: H2SO4 Polyprotic acid: H3PO4

  8. Strong Acids • Know these!!! • HCl – hydrochloric acid • HBr – hydrobromic acid • HI – hydroiodic acid • H2SO4 – sulfuric acid • HNO3 – nitric acid • HClO4 – perchloric acid

  9. Strong Bases • All are metal hydroxides – especially group I and II • Dissociate completely in water • List

  10. Neutralization Reactions • Metathesis reaction  AKA Double replacement or displacement  • Typically involves ion transfer (not redox) • Involves reaction of H+ (or H3O+) and OH- to form water molecules

  11. Arrhenius acid/base reactionNeutralization acid + base ---> H2O + a salt HA + MOH ---> H2O + MA Salt = ionic compound formed from the anion of an acid and the cation from a base

  12. NeutralizationExample 4.13 p. 160 28.0 mL of 0.250 M HNO3 is added to 53.0 mL of 0.320 M KOH. Calculate the grams of water formed. What is the concentration of H+ and OH- ions after reaction is complete?

  13. Example 1 • Write balanced net ionic equation. Molecular: HNO3(aq) + KOH(aq)  H2O(l) + KNO3(aq) Complete Ionic: H+(aq) + NO3-(aq) + K+(aq) + OH-(aq)  H2O(l) + K+(aq) + NO3-(aq) Net Ionic: H+(aq) + OH-(aq)  H2O(l)

  14. Example 1 • Find number of moles of each reactant H+: OH-:

  15. Example 1 • Find limiting reactant Since we have extra OH- left, H+ is the LR. • Find the grams of product made.

  16. Example 1 • Find the concentrations of H+ and OH- • Since H+ was the limiting reactant, there should be none left. • We already calculated how much OH- will be used, so to find the amount left, we can subtract. • To find the molarity, divide the moles by total volume:

  17. Titrations • volumetric analysis- technique used to find amount of certain substance by doing a titration • titration- when you add a certain volume of a solution with a known concentration (titrant) to a certain amount of solution being analyzed (analyte)

  18. Titrations • equivalence point- when there are equal moles of each reactant present • indicator- substance that changes color near equivalence point • end point- when indicator changes color

  19. Titrations • For a good titration: • reaction between titrant and analyte must be known • equivalence point must be marked accurately • volume of titrant needed for equivalence must be known • phenolphthalein- • common indicator used • clear until acid is consumed and one drop of excess base is added; turns pink

  20. Neutralization Titration - Example 4.14 p. 162 - 163 • To standardize a sodium hydroxide solution, a student plans to titrate the solution with a monoprotic acid, KHP (KHC8H4O4, potassium hydrogen phthalate). She dissolves 1.3009 g of KHP in water, adds phenolphthalein, and titrates to the endpoint. It took 41.20 mL of sodium hydroxide to titrate the KHP solution. Calculate the concentration of NaOH.

  21. Example 2 • Write the balanced net ionic equation: NaOH(aq) + KHP(aq)  NaKP(aq) + H2O(l) Na+(aq) + OH-(aq) + KHP(aq)  Na+(aq) + KP-(aq) + H2O(l) OH-(aq) + KHP(aq)  H2O(l) + KP-(aq)

  22. Example 2 • Find the moles of H+ in the KHP: • Find the moles of NaOH used: • Find molarity of NaOH used:

  23. Neutralization Analysis Example 4.15 p. 163 – 164 A 0.3518 g mixture of CCl4 and HC7H5O2 was mixed with water and titrated by 10.59 mL of 0.1546 M NaOH. Find the percent by mass of HC7H5O2 in the original sample.

  24. Example 3 • Write the net ionic equation HC7H5O2(aq) + OH-(aq)  H2O(l) + C7H5O2-(aq) • Find moles of OH- used:

  25. Example 3 • Find moles of HC7H5O2 used: • Find the grams of HC7H5O2: • Find percent by mass:

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