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Definitions of Acids & Bases

Definitions of Acids & Bases. Chem -To-Go Lesson 38 Unit 10. 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 of Acids & Bases

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  1. Definitions of Acids & Bases Chem-To-Go Lesson 38 Unit 10

  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. HClH+ + Cl- • 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 during the forward reaction, but the reverse reaction rebuilds the original acid quickly. HC2H3O2 H+ + C2H3O2- The reaction reaches equilibrium, meaning the ions often rebuild the acid. • Only a few acids dissociate completely and remain dissociated. • Halides: HCl, HBr, HI • Ex. HCl + H2O  H++ Cl- • Oxyacids: H2SO4, HClO4, HNO3 • Ex. HNO3 + H2O  H++ 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-

  10. Acid-Base Pairs • Previous Example: NH3(aq) + H2O(l)  NH4+(aq) + OH-(aq) • According to the Bronsted-Lowry 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.

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