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Acids and Bases

Acids and Bases. The basics…. Acids and bases are a group of compounds that share similar chemical properties. There are a few ways that this group can be classified. . Arrhenius Acid and Bases. Brønsted -Lowry Acid and Bases. Lewis Acids and Bases. Arrhenius Acids and Bases.

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Acids and Bases

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  1. Acids and Bases

  2. The basics… • Acids and bases are a group of compounds that share similar chemical properties. • There are a few ways that this group can be classified. Arrhenius Acid and Bases Brønsted-Lowry Acid and Bases Lewis Acids and Bases

  3. Arrhenius Acids and Bases • Arrhenius’ is the most common definition of acidic and basic compounds. • Acid: Releases an H+ (hydronium) ion in solution • HA  H+ + A- • Base: Releases an OH- (hydroxide) ion in solution • BOH  B+ + OH- or H3O+

  4. Common Arrhenius Acids and Bases HCl H+ + Cl- Ca(OH)2 Ca2+ + 2OH-

  5. Regents Question H- H3O+ H+ OH- BOH  B+ + OH-

  6. An Arrhenius Acid will produce which positively charged ion in solution? • Hydronium ion • Hydride ion • Hydroxide ion • Hydrogen

  7. In the following neutralization reaction, which compound is considered an Arrhenius base? • HCl • NaOH • H2O • NaCl HCl + NaOH H2O + NaCl

  8. Brønsted-Lowry Model • While Arrhenius was H+ and OH-, Brønsted-Lowry focused exclusively on the H+. • Brønsted-Lowry Acid: Donates an H+ ion • Brønsted-Lowry Base: Accepts an H+ ion HCl + NH3 NH4+ + Cl- Donates H+ Accepts H+

  9. Who is the Brønsted-Lowry Base?HF + H2O  H3O+ + F- • HF • H2O • H3O+ • F-

  10. Who is the Brønsted-Lowry Acid?H3O+ + Cl- H2O + HCl • HCl • H2O • H3O+ • Cl-

  11. Lewis’ Model: Acids and Bases • Lewis’ Model further expands the definition of acids and bases • Lewis Acid: Electron-Pair Acceptor • Lewis Base: Electron-Pair Donor LewisAcid LewisBase Accepts Electrons DonatesElectrons

  12. Strengths of Acids and Bases • Ionize: To break apart into ions in solution • A strong acid/base will break apart completely • A weak acid/base will produce fewer ions HCl H+ + Cl- CompletelyIonizes HF HF + H+ + F- PartiallyIonizes

  13. pH Scale • We measure the strength of Arrhenius acids using the pH scale. Acid Base Neutral

  14. pH Scale • pH measures the concentration of H+ ions in solution • An increase of 1 pH means a 10 times increase in OH- (or a 10 time decrease in H+) • At a pH of 7 (neutral) there are equal amounts of H+ and OH- in solution. • Acids have more H+ in solution • Bases have less H+ in solution

  15. Which of the following compounds is an Arrhenius Acid? • NaOH • NH3 • CaCl2 • H2SO4

  16. In the following equation, which compound is the Brønsted-Lowry base? HCl + H2O  H3O+ + Cl- • Cl- • H3O+ • H2O • HCl

  17. Measures of Concentration

  18. Concentration • The amount of a solute in a solvent is something that we can quantify (assign a number to). • We measure this in terms of molarity:

  19. Moles •  Remember we can always determine moles from a given mass using the formula:

  20. Calculating Molarity • Consider the following statement: In a 500L solution, 50 moles of NaCl are dissolved.

  21. Calculating Molarity • Consider the following statement: 30 moles of KCl are disssolved in 60 L solution.

  22. Significant Figures http://blog.swivel.com/weblog/2007/02/ode_to_numbers.html

  23. Not All Numbers Were Created Equal When we are measuring an object, we always guess a little http://www.petitemallette.com/iphone/

  24. Guessing 2 . 4 5 Guess Definite Definite

  25. Remember, you can only guess on one number. http://www.doughroller.net/personal-finance/treat-personal-finance-business/

  26. Sig Figs Rules • When adding or subtracting measurements, your answer can have no more decimal places than the measurement with the fewest decimal places. 45.6 54.65 324.93 425.18 425.2 +

  27. Sig Figs Rules • When multiplying or dividing measurements, your answer can have no more numbers than the fewest number of significant (definite) figures. 48.3 2 96.6 100 1 Sig Fig

  28. The Rules of Zero Pacific Left Atlantic Right

  29. The Rules of Zero How many significant figures? Pacific Present Left Atlantic Absent Right Determine if there is a decimal present or absent. 1.0450

  30. The Rules of Zero How many significant figures? Pacific Left Atlantic Right Start counting with the first non-zero number. 1.0450

  31. The Rules of Zero How many significant figures? Pacific Present Left Atlantic Absent Right 1.0450 5 Sig Figs

  32. The Rules of Zero How many significant figures? Pacific Present Left Atlantic Absent Right 98700 3 Sig Figs

  33. The Rules of Zero How many significant figures? Pacific Present Left Atlantic Absent Right 98.70 4 Sig Figs

  34. Acid-Base Titrations Classic Part II Question

  35. What we know… • An Arrhenius acid is one that produces H+ or H3O+ in solution. • When an acid reacts with a base, a neutralization reaction occurs. • A neutralization reaction produces a salt and water each and every time.

  36. Neutralization Reactions • In a neutralization reaction, acidreacts with base to produce salt and water. • Neutralization reactions are a type of double replacement reaction HCl + Ca(OH)2 H2O + CaCl2 Acid Base Water Salt

  37. Titration reaction • Titration reactions are used to determine the concentration of an unknown acid. MAVA = MBVB Moles H+ = Moles OH- • We can calculate the amount needed to neutralize any solution.

  38. Titration • How many milliliters of 3M NaOH are needed to neutralize 400mL of 2M HCl?

  39. How much 4M NaOH is needed to neutralize 50mL of 2M HCl?

  40. How much 6M HCl are needed to neutralize 100mL of 3M NaOH?

  41. Titrating an Unknown Solution • If we combine the information we have about titrations and indicators, we can determine the concentration of an unknown solution. • We will need to use an indicator that has a changing point that is close to the neutral point.

  42. MB Titration Base VB When the indicator changes color, all of the H+ has been neutralized. If we know the VA, the MB and VB of the system we can back calculate the concentration of the acid. VA Acid of Unknown Concentration

  43. Titration • What is the concentration of 50mL of an acid that is titrated to neutrality with 75mL of 3M NaOH?

  44. Titration • What is the concentration of 80mL of a base that is titrated to neutrality with 40mL of 2M HCl?

  45. A student neutralized 16.4 milliliters of HCl by adding 12.7 milliliters of 0.0620 M KOH. What was the molarity of the HCl acid?

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