Ppt 5 p h and buffers

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Ppt 5 p h and buffers

  1. 1. Buffers SBI4U
  2. 2. <ul><li>Review of pH </li></ul><ul><li>pH is a measure of the acidity of a solution in the number of H + </li></ul><ul><li>pH scale: from 0-14 </li></ul><ul><li>Acidic solution = m ore H + = lower pH (pH<7) </li></ul><ul><li>Basic solution = l ess H + = higher pH (pH > 7) </li></ul><ul><li>Neutral solutions pH = 7 </li></ul>
  3. 3. Water
  4. 4. Bronsted-Lowry <ul><li>ACID: any molecule that will donate H + </li></ul><ul><li>BASE: any molecule that will accept H + </li></ul><ul><li>When HCl is placed in solution, it donates H + and is therefore a proton donor. </li></ul><ul><li>When NaOH is placed in solution, it removes H + from solution. NaOH is a proton acceptor. </li></ul><ul><li>HCl + N aOH     NaCl + H 2 O acid base conjugate conjugate </li></ul><ul><li>( H+ donor) ( H+ acceptor) base acid </li></ul><ul><li>Conjugate base – the species (salt) formed after an acid loses a proton. </li></ul><ul><li>Conjugate acid – the species formed after a base gains a proton. </li></ul>
  5. 5. Conjugate acid-base pairs
  6. 6. Try This: <ul><li>HCl + H 2 O  </li></ul>
  7. 7. Conjugate acid-base pairs
  8. 8. Arrhenius Theory <ul><li>Acids (same idea as Bronsted-Lowry) </li></ul><ul><li>An acid is something that contributes hydrogen ions (H + ) to solution. </li></ul><ul><li>For example: HCl in water ionizes to H + + Cl - . </li></ul><ul><li>HCl      H + + Cl - </li></ul><ul><li>Bases </li></ul><ul><li>A base is something that contributes hydroxide ions (OH - ) to solution. </li></ul><ul><li>For example: NaOH in water ionizes to Na + + OH - . </li></ul><ul><li>NaOH  Na + + OH - </li></ul><ul><li>Doesn’t take into consideration non-(OH) molecules. </li></ul>
  9. 9. Conjugate acid-base pairs Does this molecule have an OH?
  10. 10. What is a buffer? <ul><li>A buffer usually consists of a weak acid and its conjugate base in EQUILIBRIUM. Where the concentration of the acidic ion is equal to the concentration of the basic ion </li></ul><ul><li>H 2 O + CO 2  H 2 CO 3  HCO 3 + H + </li></ul><ul><ul><ul><ul><ul><li>weak acid process is limited (rxn is slow) </li></ul></ul></ul></ul></ul><ul><li>Buffers are able to resist changes in pH when LIMITED amounts of acid or base are added. </li></ul>What does a buffer do? Buffers help to maintain a constant pH (homeostasis). Buffers resist changes in pH through their ability to combine with both H+ ions and OH- ions.

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