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Reactions in Aqueous Solution I: Acids, Bases, and Salts

Reactions in Aqueous Solution I: Acids, Bases, and Salts. Chapter 10. Properties of Acidic Solutions. They have a sour taste Vinegar is 5% acetic acid (tastes sour) Change the colors of indicators Blue litmus turns red React with active metals to produce hydrogen

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Reactions in Aqueous Solution I: Acids, Bases, and Salts

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  1. Reactions in Aqueous Solution I: Acids, Bases, and Salts Chapter 10

  2. Properties of Acidic Solutions • They have a sour taste • Vinegar is 5% acetic acid (tastes sour) • Change the colors of indicators • Blue litmus turns red • React with active metals to produce hydrogen • Mg(s) + H2SO4(aq)  MgSO4(aq) + H2(g) • React with metal oxides and hydroxides to form salts and water • HCl(aq) + LiOH(aq)  LiCl(aq) + H2O(l) • Aqueous solutions conduct electric current

  3. Properties of Basic Solutions • They taste bitter and feel slippery • Change color of indicators • Red litmus turns blue • React with acids to form salts and water • HCl(aq) + LiOH(aq)  LiCl(aq) + H2O(l) • Aqueous solutions conduct electricity

  4. Arrhenius Theory for Acids and Bases • An acid is a substance that contains _____ and produces ____ in aqueous solutions • A base is a substance that contains _____ and produces ____ in aqueous solutions • Neutralization is defined as the combination of H+ ions with OH- ions to form H2O molecules • This is a common acid/base reaction • HBr(aq) + NaOH(aq) What is the net ionic equation?

  5. The Hydronium Ion • H+(aq) does not exist in aqueous solutions. The ion exists as H+(H2O)n • n is some small integer • The hydrated ion is commonly represented as H3O+ • n=1 • Recall that we used H+(aq) as an abbreviated form for H3O+(aq). They indicate the same hydrated ion in aqueous solutions.

  6. Brønsted-Lowry Theory • An acid is defined as a proton _____ (H+), and a base is defined as a proton _____. • Any hydrogen-containing molecule or ion that can release a proton is a acid, while any molecule or ion that can accept a proton is a base. • HBr(aq) + H2O(l)  Br-(aq) + H3O+(aq) • NH3(aq) + H2O(l)  NH4+(aq) + OH-(aq) Are these reversible reactions? Indicate the arrows.

  7. Brønsted-Lowry Theory • An acid-base reaction is simply the transfer of a proton from an ____ to a _____ • Indicate the transfer on the previous reactions • Notice that there is a newly created acid and base on the product side of the equation • HBr(aq) + H2O(l) Br-(aq) + H3O+(aq) acid1 base2 base1 acid2 • NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) • Identify the newly-created acid and base on the product side

  8. Brønsted-Lowry Theory • Notice that an acid creates a _____ upon losing a proton. Additionally, the base creates an ____ upon gaining the proton • Illustrate with previous reactions • Designated with the same subscript • These are called conjugate acid-base pairs • The two species differ by only a _____ HF(aq) + H2O(l) ????

  9. Brønsted-Lowry Theory • The stronger the acid, the _______ is its conjugate base. The weaker the acid, the ____ is its conjugate base. • This also holds for strong and weak bases • This will indicate how to draw the arrows and the predominant species present • The direction of the reaction depends on the strength of the acid (covered later) • Water can act as an acid or a base depending on the other species with which it reacts

  10. The Autoionization of Water • Pure water ionizes slightly to produce hydrated hydrogen ions and hydroxide ions • Illustrate • H2O(l) + H2O(l)  H3O+(aq) + OH-(aq) or 2H2O(l)  H3O+(aq) + OH-(aq) • Concentration of OH- and H3O+ in water is 1.0  10-7 M • Identify the conjugate acid-base pairs and the relative lengths of the arrows • Water undergoes an acid/base reaction and autoionizes

  11. Amphoterism • Amphiprotic – proton transfer reactions in which a substance can act as either an acid or a base • Water is amphiprotic since it can behave as an acid or base • Amphoteric (optional) -

  12. Strengths of Binary Acids • Acid strength increases with ______ bond strength. The proton is easier to remove • Bond strength HF>>HCl>HBr>HI • Acid strength HF<<HCl<HBr<HI • HI is a very strong acid • Group VIA hydrides, Bond strength H2O >> H2S > H2Se > H2Te • Place these acids in order of increasing bond strength

  13. Strengths of Binary Acids • Acid leveling (leveling effect of water) • It is very difficult to differentiate the strengths of HCl, HBr, and HI in dilute aqueous solutions. This is because H3O+ is the strongest acid that can exist in aqueous solution. All acids stronger than H3O+(aq) react almost completely (i.e. ionize completely) with water to produce H3O+(aq). • All strong acids have nearly the same strength in water • HI, HBr, HCl • Acid strengths can be distinguished, however, in nonaqueous solutions • Likewise, any base stronger than OH- reacts almost completely with H2O to produce OH-(aq) • Not many bases are stronger than OH- (NH2-)

  14. Ternary Acids • Ternary acids are hydroxyl compounds of nonmetals that produce H3O+ in water • HNO3 and H3PO4 (write structures and illustrate the OH’s) • The electronegative nonmetal and oxygen combination pulls electron density away from the hydrogens • Hydrogen atom leaves as H+ (combines with H2O) • On the contrary, hydroxyl compounds of metals commonly produce hydroxide ions in water and are bases (Don’t confuse the acids from the bases)

  15. Ternary Acids • Many ternary acids possess more than one proton to donate to a base (e.g. H2O). These are termed as _______ acids. • Each ionization step can be represented separately • Each successive proton, H+, is more difficult to remove. This is reflected in the extent of ionization • H2SO4(aq) + H2O(l) HSO4-(aq) + H3O+(aq) • HSO4-(aq) + H2O(l) SO42-(aq) + H3O+(aq) • H2SO4 is a much stronger acid than HSO4-

  16. Ternary Acids • The strength of a ternary acid also increases with decreasing O-H bond strength • The strength of a ternary acid containing the same central element increases with increasing oxidation state of the central atom • Increasing oxidation state scales with the number of _____ atoms • H2SO4 and H2SO3 • HClO, HClO2, HClO3, and HClO4 What can you say about O-H bond strengths in these acids?

  17. Ternary Acids • For most ternary acids containing different elements in the same oxidation state from the same group in the periodic table, acid strengths increase with increasing electronegativity of the central atom • Acid strength would decrease going down the periodic table • H2SeO4 and H2SO4 • HClO4, HBrO4, and HIO4

  18. Acid Strengths There is another table in your books (Table 10-2)

  19. Acid Strengths • An acid will react almost completely with the conjugate base of any acid below it in these tables • The direction of the arrows can be determined from this information • HCN(aq) + H2O(l) ???? • H3O+(aq) + F-(aq) ???? • H2PO4-(aq) + SO42-(aq) ???? The stronger acid wins!!!

  20. Reaction of Acids and Bases • Strong acids and bases • H2SO4(aq) + LiOH(aq) • Write the formula unit, total ionic, and net ionic equations • Formation of water and salt in the formula unit equation • Salt – anion of the acid and cation of the base • Net ionic equation from the reaction of strong acids and bases that form soluble salts • H+(aq) + OH-(aq)  H2O(l)

  21. Reactions of Acids and Bases • H2SO4(aq) + Ba(OH)2(aq) Write the formula unit, total ionic, and net ionic equation This is the only reaction of this type (formation of an insoluble salt) Demo: Extra practice • Write the formula unit equation for an acid and base that will form Ca(ClO3)2 • MgSO4 formation

  22. Reactions of Acids and Bases • Reactions of weak acids and weak bases • These mostly produce soluble salts • CH3COOH(aq) + NH3(aq) • HClO2(aq) + NH3(aq) Name the salts that are formed

  23. Reactions of Acids and Bases • Reactions of weak acids with strong bases (soluble) • These produce water and a soluble salt • Nitrous acid + sodium hydroxide • Write the formula unit, total ionic, and net ionic equations • Practice • Acetic acid + calcium hydroxide

  24. Reactions of Acids and Bases • Reactions of strong acids with weak bases • These form soluble salts • Nitric acid + ammonia • Write the three equations for this reaction

  25. Acidic and Basic Salts • When stoichiometric amounts of an acid and base are mixed a ______ salt is formed • H2SO4(aq) + 2NaOH(aq)  Na2SO4(aq) + 2H2O(l) • Na2SO4 is a _____ salt • No protons remaining for reacting further with a base • When less than stoichiometric amounts of a base reacts with a polyprotic acid an _____ salt is formed • H2SO4(aq) + NaOH(aq)  NaHSO4(aq) + H2O(l) • Name the acid salt

  26. Acidic and Basic Salts • H2SO4(aq) + NaOH(aq)  NaHSO4(aq) + H2O(l) • The acid salt, NaHSO4, is still capable of neutralizing bases since it has a proton to donate • The acidic salt is weak, but it still can react with strong bases • NaHSO4-(aq) + NaOH(aq)  Na2SO4(aq) + H2O(l)

  27. Acidic and Basic Salts • When less than stoichiometric amounts of an acid are mixed with a polyhydroxy base an _____ salt is formed • Ba(OH)2(aq) + HCl(aq)  Ba(OH)Cl(aq) + H2O(l) • Ba(OH)Cl is a basic salt since it can react (and neutralize) a strong acid • Ba(OH)Cl(aq) + HCl(aq)  BaCl2(aq) + H2O(l) • What is BaCl2(aq)? • Another: Al(OH)3

  28. Lewis Theory • An acid is any species that ______ a pair of electrons. A base is any species that _____ a pair of electrons • _______ is defined a coordinate covalent bond formation • The electron pair does not move. It originally resides on one of the atoms on the base. The electron pair will be shared between the acid and base

  29. Lewis Theory • NH3(aq) + H2O(l)  NH4+(aq) + OH-(aq) • Show detail of electron pair on NH3 bonding with H+ from water • Almost any species with an ____ ____ of electrons can act as a base • These reactions are common for acids containing only six electrons in the highest energy shell (open sextet) • AlCl3(s) + Cl-(aq)  AlCl4-(aq) • AlCl3(s) possessed on open sextet

  30. Lewis Theory • NaF(aq) + BF3(g)  • Could this be an Arrhenius or Bronsted-Lowry acid/base reaction? • How about the previous reactions? How would they be classified? • Many organic and biological reactions are acid/base reactions that can only be explained by the Lewis theory. Problem-solving tip on page 390 Classify the reaction NH3(aq) + HBr  NH4+(aq) + Br-(aq)

  31. Preparation of Acids • Binary Acids • React elements with hydrogen (Cl2 + hydrogen) • Volatile Acids • React appropriate salt with a nonvolatile acid • NaCl(s) + H2SO4(l)  HCl(g) + NaHSO4(s) • Also used for HF • NaI(s) + H3PO4(l)  HI(g) + NaH2PO4(s) • Also used for HBr • Name the salts that are formed H2SO4 cannot be used to form HBr and HI

  32. Preparation of Acids • Ternary acids • Nonmetal oxides (acid anhydrides) and water • No change in oxidation numbers • N2O5(l) + H2O(l)  2HNO3(aq) • 2CrO3(s) + H2O(l)  H2Cr2O7(aq) DEMO:

  33. Preparation of Acids • Reaction of halides and oxyhalides of some nonmetals react with water to produce a binary and ternary acid • PCl5(s) + 4H2O(l)  H3PO4(aq) + 5HCl(aq) • POCl3(s) + H2O(l)  DEMO:

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