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Definitions , Theories, & Properties o f Acids & Bases

Definitions , Theories, & Properties o f Acids & Bases. Chapter 16. Properties. Both acids and bases ionize or dissociate in water Acids : taste sour, conduct electricity, cause certain indicators to change color,turn blue litmus paper red, and react with metals to form H 2 gas

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Definitions , Theories, & Properties o f Acids & Bases

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  1. Definitions, Theories, & Properties of Acids & Bases Chapter 16

  2. Properties • Both acids and bases ionize or dissociate in water • Acids: taste sour, conduct electricity, cause certain indicators to change color,turn blue litmus paper red, and react with metals to form H2 gas • Bases: taste bitter, feel slippery, conduct electricity, and cause certain indicators to change color, turn red litmus paper blue

  3. Property: Dissociation in Water • Acids and bases dissociate in water. • Dissociation reactions show this phenomenon in a chemical equation. • EX. HClH+ + Cl- • EX. Ca(OH)2 2OH- + Ca2+ • Notice the arrow. Acid/base dissociations are reversible reactions. • Some reactions are MORE reversible than others.

  4. Strong and Weak • Strong and weak do not mean the same as concentrated and dilute. • Strong = completely dissociate when dissolving in water; the forward dissociation reaction is favored • Weak= partially dissociate when dissolving in water; the dissociation reaction reaches equilibrium (the forward and reverse reactions are equally likely to occur)

  5. Strong Acids vs. Weak AcidsNote: Same ideas apply to strong vs. weak bases. Strong Acids Weak acids Most acids dissociate in water forming ions during the forward reaction, but the reverse reaction rebuilds the original acid quickly. HC2H3O2 H+ + C2H3O2- The reaction reaches equilibrium, which means that the ions often rebuild the acid. In AP, you’ll learn to calculate the amount of the H+ ion compared to the amount of HC2H3O2. • Only a few acids dissociate completely and remain dissociated. • Halides: HCl, HBr, HI • Ex. HCl + H2O  H3O+ + Cl- • Oxyacids: H2SO4, HClO4, HNO3 • Ex. HNO3 + H2O  H3O+ + NO3- • We’ll use strong acids later during our unit in calculations .

  6. First Acid Definition • Arrhenius definition for acid: compound that produces hydrogen ions (H+) when dissolved in water. • Let’s write the dissociation reaction for the HCl example. HCl + H2O  H+ + Cl- Or HCl + H2O  H3O++ Cl- H3O+ = Hydronium ion

  7. First Base Definition • Arrhenius definition of base: a compound that produces hydroxide ions (OH-) when dissolved in water. • Let’s write the dissociation reaction for the NaOH example. NaOH + H2O  Na+ + OH-

  8. Arrhenius Acids & Bases • Acids are hydrogen-containing compounds that ionize to yield hydrogen ions in aqueous solution... • Bases are compounds that ionize to yield hydroxide ions in aqueous solution... • BUT, NH3is a base! Arrhenius’ theory doesn’t hold up in every case, so...

  9. Bronsted-Lowry Acids and Bases • An acid is a hydrogen-ion donor, and a base is a hydrogen-ion acceptor. • Example: NH3(aq) + H2O(l)  NH4+(aq) + OH-(aq) • Analyze the compounds as they react. What happens during the reaction? • NH3 accepts an H+ to become NH4+ • H2O donates an H+ to become OH- BASE ACID

  10. Acid-Base Pairs • According to this theory: • An acid has a conjugate base. • Likewise, a base has a conjugate acid. • We refer to them as conjugate acid-base pairs. The pair differs only by a SINGLE hydrogen. • Example: NH3 and NH4+, H2O and OH-

  11. Application of the Bronsted-Lowry Theory • H2SO4 + H2O  H3O+ + HSO4- • Label the acid, base, conjugate acid, and conjugate base. • Write conjugate acid-base pairs.

  12. Individual Practice of Application of Bronsted-Lowry Theory • Find the “Bronsted-Lowry Acids and Bases Practice Problems” worksheet in your practice packet. • Answer Part I, and we’ll go over them together in five minutes..

  13. Individual Practice of Application of Bronsted-Lowry Theory • Identifying acid-base pairs in dissociation reactions can be a bit confusing at first. • Remember, the acid and base will be found in the reactants. The conjugate acid and base will be found in the products. • The acid will donate an H+ to become the conjugate base. The two substances will differ by ONLY one H+. Therefore, the acid will have one additional H+. • The base will accept an H+ to become the conjugate acid. The two will differ by ONLY one H+. Therefore, the conjugate acid will have one additional H+. • Complete Parts II and III of the “Bronsted-Lowry Acids and Bases Practice Problems” now.

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