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Acids, Bases

Acids, Bases. & Salts. Naming Acids. Binary acids hydro (element) ic acid HF Ternary acids replace the anion suffix -ate with -ic H 2 SO 4 replace the anion suffix -ite with -ous H 2 SO 3. Arrhenius Acids Ionize to form H + in water

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Acids, Bases

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  1. Acids, Bases & Salts

  2. Naming Acids • Binary acids • hydro (element) ic acid • HF • Ternary acids • replace the anion suffix -ate with -ic • H2SO4 • replace the anion suffix -ite with -ous • H2SO3

  3. Arrhenius Acids • Ionize to form H+ in water • HCl H+ (aq) + Cl- (aq) H2O Definitions of Acids 1 H+ = Monoprotic 2 H+ = Diprotic 3 H+ = Triprotic • Brønsted-Lowry Acids • Proton donor • HCl + H2O H3O+(aq) + Cl- (aq)

  4. ? water hydrogen ion “proton” hydronium ion

  5. H2SO4 + H2O H3PO4 + H2O CH3COOH + H2O Ionization of Acids H3O+(aq)+ CH3COO-(aq) 2 2H3O+(aq)+ SO4-2(aq) 3 3H3O+(aq)+ PO4-3(aq)

  6. Acid? Yes or No An Acid must ionize with H+ as the only positive ion in soln • H3PO4 • KH • CH3COOH • CH3OH • KI

  7. Acids are electrolytes • …because they ionize in water • The more ions, the stronger the electrolyte • Strong acids completely ionize • Form lots of ions • Weaker acids do not

  8. Ka • Acid dissociation (ionization) constant • Stronger acids • larger Ka

  9. Acids react with “active” metals to produce H2 (g) active =those listed above H2 Table J

  10. Mg + 2HCl H2 + MgCl2 Mg + HCl Zn + 2HNO3 H2 + Zn(NO3)2 Zn + HNO3 Al + HBr 2Al + 6HBr 3H2 + 2AlBr3 Write the balanced equation for the reaction that occurs between

  11. What type of Reaction? Single Replacement Reactions

  12. . . . Other Acid Characteristics • Acids change the colors of indicators • blue litmus changes to red • pH < 7 can be neutralized by bases • Dilute acids taste sour • citrus fruits (citric acid) • vinegar (acetic acid)

  13. Characteristics of Bases • Arrhenius Base • Defined as a substance that provides OH- ions to solution • BrØnsted-Lowry • proton acceptor • Ex: NH3 + H2O NH4+ + OH-

  14. Naming Bases • Name the cation (+) • all bases end in hydroxide • KOH • Mg(OH)2 • NH4OH Exception?

  15. NaOH NaOH Na+ + OH - Metal ion NH4OH NH4OH NH4+ + OH - Polyatomic Ion Base ionization

  16. Bases form electrolytic solutions • strong bases ionize completely • Group 1 hydroxides are strong bases • weak bases have low levels of ionization • all other bases are generally weak

  17. Base? Yes or No A base must ionize with the hydroxide ion as the only negative ion • NaOH • CH3OH • C2H5OH • KOH • Mg(OH)2 • NH4OH

  18. Feel Slippery ex. soap • Taste bitter ex. soap • Change the colors of indicators • Phenolphthalein • Red litmus turns blue • pH > 7 can be neutralized by acids

  19. Neutralization Reactions Despite heavy fire, McAllister’s aim was true, and his carefully measured hydrochloric acid found its mark in the enemy’s reservoir of sodium hydroxide McAllister grinned, one of the enemy’s strongest bases had finally been neutralized

  20. Hydrochloric acid + sodium hydroxide ? ACID + BASE SALT + WATER HCl + NaOH NaCl + HOH Neutralization: An Acid Base Rxn Hydroxide ion Complete neutralization occurs when The acid H+ and the base OH- are 1:1

  21. What kind of reaction? Double Replacement Reaction

  22. Magnesium hydroxide + nitric acid Neutralization Reactions Phosphoric acid + ammonium hydroxide

  23. Net ionic equation: H+ + OH- HOH Complete neutralization . . . • Occurs when H+ and OH- are added together in a 1:1 molar ratio • MaVa = MbVb • BE CAREFUL • If the acid or base has a subscript you have to account for it in the formula. • (H+)MaVa =(OH-)MbVb • Ex. If you have 1L of 1M HCl, what M is necessary to neutralize 1L of Mg(OH)2?

  24. Titrations • Lab procedure used to determine a concentration (M) of a solution. • Titrations use an indicator to signal when the “endpoint” is reached • Endpoint is when the solution is neutralized • Indicator changes color

  25. Titration / Neutralization practice • 55mL of an 8M HCl solution is completely neutralized by 26mL of Ca(OH)2 • Write the balanced neutralization reaction. • What is the concentration of base that was used? • What is the net ionic equation? • What are the spectator ions?

  26. [H+] [OH-] pH scale • The pH scale is used to measure the [H+] and [OH-] in solution. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

  27. Water is neutral • Water ionizes (only slightly) into equal concentrations of H+ and OH- ions. • In 1.0L of water there are [H+] = 1.0x10-7 M and [H+] = 1.0x10-7 M • When multiplied together they give you the ion product constant for water!

  28. Molarity is concentration

  29. Practice problem #1 • 2 moles NaOH is dissolved in water to make a solution of 1000.0ml. What is the molar concentration of OH-and H+ions in this solution? • Step 1: do any conversions and determine given ion concentration • Step 2: [OH-] x [H+] = 1.0 x 10-14

  30. Practice problem #2 • A 4.0g mass of KOH is dissolved in water to make a solution of 500ml. What is the molar concentration of H+ions in this solution? • Step 1: do any conversions and determine given ion concentration • Step 2: [OH-] x [H+] = 1.0 x 10-14

  31. pH numbers? • SØren SØrenson decided that expressing [H+] in scientific notation is tooooooo looooooooooooong • It’s more convenient to express [H+] in terms of pH (0-14) pH = -log [H+]

  32. If [H+] is given, find the absolute value of the log That’s your pH If pH is given, find the antilog (10x)of the negative number That’s your [H+] LOGS What if [OH-] is given?

  33. Find the pH for solutions having the following [H+] 1 x 10-4 M 1 x 10-11 M Find [H+] given these pH 2 8 pH are not always whole numbers The pH of an unknown solution is 6.35, what is the [H+] & [OH-]? pH practice

  34. [H+] [OH-] • pH values greater than 7 have low [H+] and are basic (8, 9, 10 . . .) • pH values less than 7 have high [H+] and are acidic (6, 5, 4 . . .) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

  35. AND…. • Because pH numbers represent log values based on the power of 10 pH 5 is 10 timesmore acidic than pH 6 pH 4 is 100 timesmore acidic than pH 6

  36. [H+] [OH-] 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

  37. methyl orange 3.2 - 4.4 Red to Yellow bromthymol blue 6.0 - 7.6 Yellow to Blue phenolphthalein 8.2 - 10 Colorless to pink litmus 5.5 - 8.2 Red to blue bromcresol green 3.8 - 5.4 Yellow to blue thymol blue 8.0 - 9.6 Yellow to blue pH & indicators Table M Approximate range of pH color change

  38. Methyl orange Bromthymol blue phenolphthalein litmus Bromcresol green Thymol blue 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

  39. Conjugate Acid - Base Pairs • 2 substances related by the loss or gain of a proton according to Bronsted-Lowry NH3 + H2O NH4+ + OH- base conjugate acid acid conjugate base HCl + H2O H3O+ + Cl- acid conjugate acid base conjugate base

  40. Amphoteric / Amphiprotic substance • Acts either as an acid or a base • Water, NH3 & others…… • Sometimes accepts an H+ • Sometimes donates an H+

  41. Identify the conjugate pairs • CH3COOH + H2O H3O+ + CH3COO- • NH4+ + OH- NH3 + H2O • CO3 2- + H2O HCO3- + OH- • HPO4-2 + H2O PO4-3 +H3O+

  42. HOH NH3 HCO3- HOH NH3 HCO3- What is the conjugatebase? acid?

  43. Salt Hydrolysis Reaction of a salt with water • Salts are ionic compounds derived from acids and bases • So when dissolved in water some salts produce either: • A neutral solution • A basic solution • An acidic solution

  44. Cation of NaOH Anion of CH3COOH Salts that hydrolize water & produce alkaline solns • Consists of a cation of a strong base and a anion of a weak acid NaCH3COO

  45. NaCH3COO Na+ + CH3COO- • When this salt dissolves in water dissociation occurs. • Water also ionizes H2O H+ + OH-

  46. Acetic acid CH3COOH is formed • BUT it has a low Ka value and doesn’t ionize completely • Most of the H+ stays bonded • NaOH can form BUT it stays completely ionized as Na+ and OH- • Because it is a strong base • If there are more OH- than H+ in solution the solution is considered BASIC!!!!!!!!!

  47. Weak base bonds Strong acid stays ionized Some salts hydrolyze water & produce acidic solns • The salt of a strong acid and a weak base NH4Cl dissolved in water produces: NH4+ Cl- H+ and OH-

  48. Salts of a weak base and a weak acid may hydrolyze water, but pH needs to be tested. • Salts of strong bases and strong acids do not hydrolyzewater and form neutral solutions • NaCl

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