1. Acids/Bases Lesson 14 Buffers

2. Buffer Solutions Buffer solutions are equilibrium systems, which maintain a relatively constant pH when small amounts of acids or bases are added. How can you prepare a buffer? You need a high concentration of weak acid or a weak base, and add to it its conjugate acid or its conjugate base also in high concentrations. This combination is known as a BUFFER.

3. Buffer Solutions Acid Buffer Recipe Weak Acid + Salt (conjugate base) HF NaF *Na + is a spectator Buffer EquationSame as weak acid HF ⇋ H + +F -

4. [High][low][High] [HF] is high and [H + ] is low because HF is a weak acid. [F - ] is high due to adding the salt NaF. This buffer solution can shift left or right and the [H + ] and the pH remains fairly constant.

5. Note on buffers A solution of CH 3 COOH by itself cannot act as a buffer because the concentration of CH 3 COO - would be too small and will not satisfy the conditions of a buffer system. A buffer requires large amounts of both the acid and its conjugate. This is why we mix the weak acid or base with its conjugate salt.

6. Acidic buffer Mix 1.0 mol of acetic acid (CH 3 COOH ) and 1.0 mol of sodium acetate (NaCH 3 COO) and dilute to 1.0 L of solution

7. Base Buffer Recipe Weak Base + Salt (conjugate acid) NH 3 NH 4 Cl *Cl - spectator Buffer EquationSame as weak base NH 3 +H 2 O ⇋ NH 4 + +OH - [High][High][Low]

8. Fill in the blanks to get buffer solutions. Acidconjugate Base from a salt HCNNaCN H 2 CO 3 NaHCO 3 H 3 PO 4 NaH 2 PO 4 CH 3 COOHKCH 3 COO NaHCO 3 Na 2 CO 3 NaH 2 PO 4 Na 2 HPO 4

9. How buffers work… The ‘buffering effect’ works due to the fact that the value of the ratio: [conjugate acid] remains fairly constant. [conjugate base] * This ratio does not change much when a small amount of either an acid or a base is added to the buffer system. Why ??? The conjugate acid present can react with the added OH to neutralize it, and the conjugate base present can react with the added H 3 O to neutralize it.

10. Buffer Animation Buffer Animation 1

11. Buffer Application 1.Pick the two buffer solutions A.NH 4 Cland HCl B.NaClandNaOH C.HCNandNaCN D.NH 4 ClandNH 3

12. 2.Write the equations for the above two buffer solutions. Label the concentrations as high or low.

13. 3.A few drops of 0.10 M NaOH is added to a buffer solution at pH = 5.00. The new pH could be: A4.98 B.5.02 C.8.05 D.2.11

14. Buffers in biological systems

16. Homework Read page 182 and 183 for “Buffers in biological systems”, must know these systems and how they work. Page 181: #132,133,138,139 Page 183: #143 on buffers…interesting story/question.