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ACIDS, BASES & SALTS

ACIDS, BASES & SALTS. The Arrhenius Theory of Acids and Bases. Arrhenius Theory of Acids and Bases:. an acid contains hydrogen and ionizes in solutions to produce H + ions: HCl  H + (aq) + Cl - (aq). Arrhenius Theory of Acids and Bases:.

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ACIDS, BASES & SALTS

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  1. ACIDS, BASES & SALTS

  2. The Arrhenius Theory of Acids and Bases

  3. Arrhenius Theory of Acids and Bases: an acid contains hydrogen and ionizes in solutions to produce H+ ions: HCl  H+(aq) + Cl-(aq)

  4. Arrhenius Theory of Acids and Bases: a base contains an OH- group and ionizes in solutions to produce OH- ions: NaOH  Na+(aq) + OH-(aq)

  5. Neutralization • Neutralization: the combination of H+ with OH- to form water. • H+(aq) + OH-(aq) H2O (l) • Hydrogen ions (H+)in solution form hydronium ions (H3O+)

  6. In Reality… H+ + H2O  H3O+ Hydronium Ion (Can be used interchangeably with H+)

  7. Commentary on Arrhenius Theory… One problem with the Arrhenius theory is that it’s not comprehensive enough. Some compounds act like acids and bases that don’t fit the standard definition.

  8. Bronsted-Lowry Theory of Acids & Bases

  9. Bronsted-Lowry Theory of Acids & Bases: • An acid is a proton (H+) donor • A base is a proton (H+) acceptor

  10. for example… Proton transfer HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq) Base Acid

  11. Water is a proton donor, and thus an acid. another example… CONJUGATE BASE ACID NH3(aq) + H2O(l) NH4+ (aq) + OH- (aq) BASE CONJUGATE ACID Ammonia is a proton acceptor, and thus a base

  12. Conjugate acid-base pairs • Conjugate acid-base pairs differ by one proton (H+) A conjugate acid is the particle formed when a base gains a proton. A conjugate base is the particle that remains when an acid gives off a proton.

  13. Examples: In the following reactions, label the conjugate acid-base pairs: • H3PO4 + NO2- HNO2 + H2PO4- • CN- + HCO3- HCN + CO32- • HCN + SO32- HSO3- + CN- • H2O + HF  F- + H3O+ acid base c. acid c. base base acid c. acid c. base acid base c. base c. acid c. base c. acid base acid

  14. Amphoteric Substances A substance that can act as both an acid and a base (depending on what it is reacting with) is termed amphoteric. Water is a prime example.

  15. ACIDS Have a sour taste Change the color of many indicators Are corrosive (react with metals) Neutralize bases Conduct an electric current BASES Have a bitter taste Change the color of many indicators Have a slippery feeling Neutralize acids Conduct an electric current Properties of Acids and Bases

  16. Other Household Acids and Bases • Antacid: a weak base that neutralizes excess stomach acid. • The pH of shampoo is generally kept between 5 and 8. • Lemon juice is an acid that is sometimes used to help keep fruit looking fresh. What will happen to left apple?

  17. Indicators- “Way Cool” Cyber-lab: http://www.miamisci.org/ph/phlemon.html

  18. Strength of Acids and Bases • A strong acid dissociates completely in sol’n: • HCl  H+(aq) + Cl-(aq) • A weak acid dissociates only partly in sol’n: • HNO2 H+(aq) + NO2-(aq) • A strong base dissociates completely in sol’n: • NaOH  Na+(aq) + OH-(aq) • A weak base dissociates only partly in sol’n: • NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)

  19. The Lewis Theory of Acids and Bases

  20. The Lewis Theory of Acids & Bases • Lewis acid: a substance that can accept an electron pair to form a covalent bond (electron pair acceptor). • Lewis base: a substance that can donate an electron pair to form a covalent bond (electron pair donor).

  21. Neutralization • Neutralization: the formation of a coordinate covalent bond in which both electrons originated on the same (donor) atom.

  22. Example 1: • Ionization of NH3: • NH3 + H2O  NH4+ + OH- base + acid .. .. H H - ..  .. .. + H O H H N H O H H N H + H

  23. Example 2: • Auto-ionization of water: • H2O + H2O  H3O+ + OH- + acid .. .. base .. .. - ..  .. .. + H O H H O H O H H O H + H

  24. Example 3: • Reaction of NH3 with HBr (a Lewis AND a Bronsted-Lowry acid-base reaction): • NH3 + HBr  NH4+ + Br- base + acid .. .. H H -  .. .. .. + H Br H N H Br H N H + H

  25. Acid Base Theories Lewis Bronsted-Lowry Arrhenius

  26. SUMMARY OF ACID-BASE THEORIES

  27. Acid-Base Reactions • Neutralization reactions: reactions between acids and metal hydroxide bases which produce a salt and water. • H+ ions and OH- ions combine to form water molecules: • H+(aq) + OH-(aq) H2O(l)

  28. Example 1: the reaction of HCl and NaOH (there are 3 ways to write the chemical equation): • Balanced formula unit equation: • HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq) • Total ionic equation: • H+(aq)+Cl-(aq)+Na+(aq)+OH-(aq)H2O(l)+Na+(aq)+Cl-(aq) • Net ionic equation: • H+(aq) + OH-(aq)  H2O(l)

  29. Example 2: Write the 3 types of equations for the reaction of hydrobromic acid, HBr, with potassium hydroxide, KOH. • Balanced formula unit equation: • HBr(aq) + KOH(aq) H2O(l) + KBr(aq) • Total ionic equation: • H+(aq)+Br-(aq)+K+(aq)+OH-(aq)H2O(l)+K+(aq)+Br-(aq) • Net ionic equation: • H+(aq) + OH-(aq) H2O(l)

  30. Example 3: Write the 3 types of equations for the reaction of nitric acid, HNO3, with calcium hydroxide, Ca(OH)2. • Balanced formula unit equation: • 2HNO3(aq) + Ca(OH)2(aq) 2H2O(l) + Ca(NO3)2(aq) • Total ionic equation: • 2H+(aq)+2NO3-(aq)+Ca2+(aq)+2OH-(aq)2H2O(l)+Ca2++2NO3-(aq) • Net ionic equation: • H+(aq) + OH-(aq) H2O(l)

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