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ACIDS AND BASES

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  1. ACIDS AND BASES www.lab-initio.com

  2. Section 18.1 Introduction to Acids and Bases • Identify the physical and chemical properties of acids and bases. • Classify solutions as acidic, basic, or neutral. • Compare the Arrhenius and Brønsted-Lowry models of acids and bases. Different models help describe the behavior of acids and bases. Section 18-1

  3. Some common acids: • Sulfuric acid, H2SO4 • Hydrochloric acid, HCl • Nitric acid, HNO3 • Carbonic acid, H2CO3 • Phosphoric acid, H3PO4 • Acetic acid, HC2H3O2

  4. Some common bases: • Sodium hydroxide, NaOH • Calcium hydroxide, Ca(OH)2 • Potassium hydroxide, KOH • Magnesium hydroxide,Mg(OH)2 • Aluminum hydroxide, Al(OH)3 • Ammonia, NH3

  5. The Arrhenius Model • The Arrhenius model states that an acid is a substance that contains hydrogen and ionizes to produce hydrogen ions in aqueous solution, and a base is a substance that contains a hydroxide group and dissociates to produce a hydroxide ion in solution. Section 18-1

  6. The Arrhenius Model (cont.) • Arrhenius acids and bases • HCl ionizes to produce H+ ions. • HCl(g) → H+(aq) + Cl–(aq) • NaOH dissociates to produce OH– ions. • NaOH(s) → Na+(aq) + OH–(aq) • Some solutions produce hydroxide ions even though they do not contain a hydroxide group. Section 18-1

  7. Properties of Acids and Bases (cont.) • The usual solvent for acids and bases is water—water produces equal numbers of hydrogen and hydroxide ions in a process called self-ionization. • H2O(l) + H2O(l) ↔ H3O+(aq) + OH–(aq) • The hydronium ion is H3O+. Section 18-1

  8. Properties of Acids and Bases (cont.) • All water solutions contain hydrogen ions (H+) and hydroxide ions (OH–). • An acidic solutioncontains more hydrogen ions than hydroxide ions. • A basic solutioncontains more hydroxide ions than hydrogen ions. Section 18-1

  9. The Brønsted-Lowry Model • The Brønsted-Lowry Model of acids and bases states that an acid is a hydrogen ion donor, and a base is a hydrogen ion acceptor. • The Brønsted-Lowry Model is a more inclusive model of acids and bases. Section 18-1

  10. The Brønsted-Lowry Model (cont.) • A conjugate acidis the species produced when a base accepts a hydrogen ion. • A conjugate baseis the species produced when an acid donates a hydrogen ion. • A conjugate acid-base pair consists of two substances related to each other by donating and accepting a single hydrogen ion. Section 18-1

  11. The Brønsted-Lowry Model (cont.) • Hydrogen fluoride—a Brønsted-Lowry acid • HF(aq) + H2O(l) ↔ H3O+(aq) + F–(aq) • HF = acid, H2O = base, H3O+ = conjugate acid, F– = conjugate base Section 18-1

  12. The Brønsted-Lowry Model (cont.) • Ammonia— Brønsted-Lowry base • NH3(aq) + H2O(l) ↔ NH4+(aq) + OH–(aq) • NH3 = base, H2O(l) = acid, NH4+ = conjugate acid, OH– = conjugate base • Substances that can act as acids or bases are called amphoteric. Section 18-1

  13. Acts as both an acid and a base Water is amphoteric: HCl + H2O  H3O+ + Cl-1 Proton acceptor NH3 + H2O  NH4+1 + OH- Proton donor

  14. HCl + SO3-2 HSO3-1 + Cl- CONJUGATE ACID CONJUGATE BASE ACID BASE

  15. NH3 + HNO2 NO2-1 + NH4+ CONJUGATE BASE BASE CONJUGATE ACID ACID

  16. Monoprotic and Polyprotic Acids • An acid that can donate only one hydrogen ion is a monoprotic acid. • Only ionizable hydrogen atoms can be donated. Section 18-1

  17. Monoprotic and Polyprotic Acids (cont.) • Acids that can donate more than one hydrogen ion are polyprotic acids. Section 18-1

  18. Properties of Acids • Acids are proton (hydrogen ion, H+) donors • Acids have a pH lower than 7 • Acids taste sour • Acids effect indicators • Blue litmus turns red • Methyl orange turns red • Acids react with active metals, producing H2 • Acids react with carbonates • Acids neutralize bases

  19. Acids Effect Indicators Bluelitmus paper turnsredin contact with an acid. Methyl orange turnsredwith addition of an acid

  20. Acids React with Active Metals Acids react with active metals to form salts and hydrogen gas. Mg + 2HCl  MgCl2 + H2(g) Zn + 2HCl  ZnCl2 + H2(g) Mg + H2SO4 MgSO4 + H2(g)

  21. AcidsReact withCarbonates 2HC2H3O2+Na2CO3 2 NaC2H3O2 + H2O + CO2

  22. Effects of Acid Rain on Marble(calcium carbonate) George Washington: BEFORE George Washington: AFTER

  23. Properties of Bases • Bases are proton (hydrogen ion, H+) acceptors • Bases have a pH greater than 7 • Bases taste bitter • Bases effect indicators • Red litmus turns blue • Phenolphthalein turns purple • Solutions of bases feel slippery • Bases neutralize acids

  24. Bases Effect Indicators Red litmus paper turns blue in contact with a base. Phenolphthalein turns bright pinkin a base.

  25. A B C D Section 18.1 Assessment A conjugate acid is formed when: A.a base accepts a hydrogen ion B.an acid accepts a hydrogen ion C.an acid donates a hydrogen ion D.a base donates a hydrogen ion Section 18-1