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Lecture 19.3- Weak vs. Strong HONORS

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Lecture 19.3 for Honors Chemistry

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Lecture 19.3- Weak vs. Strong HONORS

  1. 1. BELLWORK- pH calcs <ul><li>Determine the pH of the following solutions. </li></ul><ul><li>[H + ] = 5.2x10 -9 M </li></ul><ul><li>[OH - ] = 4.9x10 -4 M </li></ul><ul><li>pOH = 5.7 </li></ul><ul><li>0.02M HNO 3 </li></ul><ul><li>0.10M NaOH </li></ul>
  2. 2. 19.3- Weak vs. Strong <ul><li>Lemons and grapefruits have a sour taste because they contain citric acid. </li></ul><ul><li>Sulfuric acid is a widely used industrial chemical that can quickly cause severe burns if it comes into contact with skin. </li></ul><ul><li>You will learn why some acids are weak and some acids are strong. </li></ul>
  3. 3. Strong acids and bases completely dissociate
  4. 4. <ul><li>AT EQUILIBRIUM </li></ul><ul><li>HCl + H 2 O  Cl - + H 3 O + </li></ul><ul><li>little lots lots </li></ul>Strong acids and bases completely dissociate
  5. 5. Weak acids and bases only partly dissociate.
  6. 6. <ul><li>When in water most of the weak acid will keep its proton attached. </li></ul>Weak acids and bases only partly dissociate.
  7. 7. <ul><li>When in water most of the weak acid will keep its proton attached. </li></ul><ul><li>Acetic acid(vinegar) is a weak acid. </li></ul>Weak acids and bases only partly dissociate.
  8. 8. <ul><li>When in water most of the weak acid will keep its proton attached. </li></ul><ul><li>Acetic acid(vinegar) is a weak acid. </li></ul><ul><li>AT EQUILIBRIUM </li></ul><ul><li>CH 3 COOH + H 2 O  CH 3 COO - + H 3 O + </li></ul><ul><li>lots little little </li></ul>Weak acids and bases only partly dissociate.
  9. 9. <ul><li>Which acid will produce more H+, </li></ul><ul><li>1M HCl or 1M acetic acid? </li></ul>
  10. 10. <ul><li>Which acid will produce more H+, </li></ul><ul><li>1M HCl or 1M acetic acid? </li></ul><ul><li>HCl is strong! </li></ul><ul><li>HC 2 H 3 COO is weak </li></ul>
  11. 11. Memorize this <ul><li>Recognize the name, formula, and relative strength (weak or strong) of the following: </li></ul><ul><li>STRONG ACIDS WEAK ACIDS </li></ul><ul><li>HCl hydrochloric acid CH 3 COOH </li></ul><ul><li>H 2 SO 4 sulfuric acid aka HC 2 H 3 O 2 or </li></ul><ul><li>HNO 3 nitric acid acetic acid (vinegar) </li></ul><ul><li>STRONG BASES WEAK BASES </li></ul><ul><li>NaOH sodium hydroxide NH 3 ammonia </li></ul><ul><li>KOH potassium hydroxide </li></ul>Arrhenius! Bronsted-Lowry!
  12. 12. <ul><li>A strong acid has a weak conjugate base. </li></ul><ul><li>A weak acid has a strong conjugate base. </li></ul><ul><li>A strong base has a weak conjugate acid. </li></ul><ul><li>A weak base has a strong conjugate acid. </li></ul>
  13. 13. Predict the products and label the conjugate acid-base pairs as weak or strong. <ul><li>NH 3 + HCl  _______ + _______ </li></ul><ul><li>CH 3 COOH + NH 3  _______ + _______ </li></ul>
  14. 14. <ul><ul><ul><li>An acid dissociation constant ( K a ) describes the equilibrium between an acid and the ions it forms. </li></ul></ul></ul><ul><ul><ul><li>HA ⇌ H + + A - </li></ul></ul></ul>
  15. 15. <ul><ul><li>Weak acids have small K a values. </li></ul></ul><ul><ul><li>The stronger an acid is, the larger is its K a value. </li></ul></ul>
  16. 16. <ul><ul><ul><li>The base dissociation constant ( K b ) describes the equilibrium of a base. </li></ul></ul></ul><ul><ul><ul><li>[HB + ][OH - ] </li></ul></ul></ul><ul><ul><ul><li> [B] </li></ul></ul></ul><ul><ul><ul><li>The larger the K b the more dissociation occurs, so the stronger the base. </li></ul></ul></ul>K b = ----------------

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