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Acids and Bases

Acids and Bases. Properties of Acids. 1. Taste sour or tart and feels like water ex. Oranges, grapefruit, yogurt, sour milk, carbonated beverages, vinegar 2. React vigorously with many metals (produces hydrogen gas) 3. Electrolyte 4. Reacts with bases to make salt and water.

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Acids and Bases

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  1. Acids and Bases

  2. Properties of Acids 1. Taste sour or tart and feels like water ex. Oranges, grapefruit, yogurt, sour milk, carbonated beverages, vinegar 2. React vigorously with many metals (produces hydrogen gas) 3. Electrolyte 4. Reacts with bases to make salt and water

  3. Properties of Bases • Bitter taste • Feel smooth and slippery ex. Soap • Electrolyte • Reacts with acids to make salt and water

  4. Rules for Naming Acids

  5. Indicators Indicators A substance that turns one color in an acidic solution and another color in a basic solution Litmus paper comes from a species of lichens red indicates an acid and blue indicates a base Phenolphthalein clear indicator that turns pink in a base Methyl Blue Blue indicator that turns yellow in an acid

  6. Neutralization Reaction • Reaction of an acid with a base • The acid and the base are neutralized • Products of a neutralization reaction are always salt and water (DR reaction) HCl + NaOH  NaCl + HOH

  7. Arrhenius Definition of Acid and Base • An acid dissociates in water to produce hydrogen ions (H+) • A base dissociates in water to produce hydroxide ions (OH-) • Tell whether the following compounds are an Arrhenius Acid or Arrhenius Base • HCl • NaOH • KOH • HNO3

  8. Limitations of Arrhenius Definition • Restricts acids and bases to water solutions • Allows for only one type of base • the hydroxide ion

  9. Bronsted Lowry Lowry Bronsted y

  10. Bronsted – Lowry Definition • An acid is a substance that can donate H+ ions (proton donor) HCl with H2O • A base is any substance that can accept H+ ions (proton acceptor) NH3 with HCl to form NH4+ and Cl-. • Defines acids and bases independently of how they behave in water

  11. Lewis Definition • Acid • An atom, ion or molecule that accepts an electron pair to form a covalent bond. • Base • An atom, ion or molecule that donates an electron pair to form a covalent bond. • BF3 + F-→ BF4-

  12. Conjugate Acids and Bases • HCl (g) + H2O (l)  H3O+ (aq) + Cl- (aq) • Acid base conj. Acid conj. Base • NH3 (g) + H2O (l)  NH4+ (aq) + OH- (aq) • Base acid conj. Acid conj. Base • Water is Amphoteric (acts like an acid or a base) • A pair of compounds that differ by only one H+ are called a conjugate acid/base pair

  13. 100% Dissociation in Water Strong Acids • Hydrochloric - HCl • Hydrobromic - HBr • Hydroiodic - HI • Sulfuric - H2SO4 • Nitric - HNO3 • Perchloric – HClO4

  14. 100% Dissociation in Water Strong Bases • Lithium Hydroxide - LiOH • Sodium Hydroxide - NaOH • Potassium Hydroxide - KOH • Rubidium Hydroxide - RbOH • Cesium Hydroxide - CsOH • Calcium Hydroxide - CaOH • Barium Hydroxide - BaOH

  15. Dissociation Constants • Acid-dissociation constant (Ka) • Equilibrium constant for the reaction of an aqueous weak acid with water • Measures the strength of an acid • Base-dissociation constant (Kb) • Equilibrium constant for the reaction of an aqueous weak base with water • Measures the strength of a base

  16. Weak Acid and Weak Base Acetic Acid in water Reaction of NH3 in water

  17. pH • Concentration of hydronium ions (H3O+) in solution • Negative logarithm (to the base 10) of the H3O+ concentration • pH = -log[H3O+] • Greater concentration of H3O+ → lower the pH • Smaller concentration of H3O+→ higher the pH • pOH = concentration of hydroxide ions in solution • pOH = -log[OH-]

  18. pH Numerical Scale • Numbered 1-14 • < 7 is acidic • 7 is neutral • >7 is basic • pH of 7 means that the [H3O+] = [OH-] • [H3O+] = 1 x 10-7M • [OH-] = 1 x 10-7M • pH + pOH = 14

  19. Water • Amphoteric • Able to act like an acid or a base • Can react with itself • Two Water Molecules React to Form H3O+ and OH- • Dissociation constant for water (Kw) • Kw = [H3O+] [OH-] • Kw at 25°C is 1.00 x 10-14 • 1.00 x 10-14 = [H3O+] [OH-]

  20. Acid and Base Titrations

  21. Neutralization Reactions 1mol 2mol 1mol 2mol Neutralization is a process that occurs when an acid reacts with a base in the mole ratio specified by the balanced equation. It is not always a one-to-one ratio! Example: H2SO4(aq)+2NaOH (aq) Na2SO4(aq) + 2H2O(l) Two moles of the base NaOH are required to neutralize one mole of the acid H2SO4.

  22. Equivalence Point 2 H+ ions 2 OH- ions The number of moles of hydrogen ions equal the number of moles of hydroxide ion. In the previous example: H2SO4(aq)+2NaOH (aq)Na2SO4(aq) + 2H2O(l) To determine the concentration of the acid or base, a neutralization reaction using an indicator must be completed. This process is called titration.

  23. Equivalence Point Strong Acid titrated with a Strong Base: Weak acid titrated with a Strong Base:

  24. Titration A measured volume of an acid solution of an unknown concentration is added to a flask. Several drops of indicator are added to the solution while the flask is gently stirred. Measured volumes of base of a known concentration are mixed into the acid until the indicator just barely changes color.

  25. Titration The solution of known concentration is called the standard solution. The point at which the indicator changes color is the end point. The point of neutralization is the end point of the titration. You can use the same procedures to find the concentration of an acid using a standard base.

  26. Setup for titrating an acid with a base

  27. Types of Acid Base Reactions Strong Acid + Strong Base  Neutral Solution Strong Acid + Weak Base Acidic Solution Weak Acid + Strong Base  Basic Solution

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