1 / 6

Acid – Base Equilibria

Acid – Base Equilibria. Buffer Solutions: Question: Was the ICE Problem set up needed? Answer: No. The assumption of x << [HA], [A - ] is valid for all “traditional” buffers Traditional Buffer Weak acid (3 < pK a < 11) Ratio of weak acid to conjugate base in range 0.1 to 10

moira
Download Presentation

Acid – Base Equilibria

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Acid – Base Equilibria Buffer Solutions: Question: Was the ICE Problem set up needed? Answer: No. The assumption of x << [HA], [A-] is valid for all “traditional” buffers Traditional Buffer Weak acid (3 < pKa < 11) Ratio of weak acid to conjugate base in range 0.1 to 10 mM concentration range

  2. Acid – Base Equilibria Buffer Solutions: Since ICE not needed, can just use Ka equation Ka = [H+][A-]/[HA] = [H+][A-]o/[HA]o (always valid) (valid for traditional buffer) But log version more common pH = pKa + log([A-]/[HA]) Also known as Henderson-Hasselbalch Equation

  3. Acid – Base Equilibria Buffer Solutions: Ways to make buffer solution: Mix weak acid and conjugate base Add strong base to weak acid (weak acid must be in excess) – this converts some of the weak acid to its conjugate base Add strong acid to weak base (weak base must be in excess) – this converts some of weak base to its conjugate acid

  4. Acid – Base Equilibria Example Problems: How many moles of hydroxyl ammonium chloride (HONH3+Cl-) needs to be added to 500 mL of 0.020 M HONH2 to obtain a buffer solution with a pH of 6.20? The pKa for HONH3+ is 5.96. What is the pH of a solution made from mixing 400 mL of 0.018 M CH3CO2H (pKa = 4.75) with 100 mL of 0.024 M NaOH?

  5. Acid – Base Equilibria Last Example Problem: How many mL of 0.0500 M NaOH should be added to 50.0 mL of 0.00850 M methyl ammonium chloride (CH3NH3+Cl-) in order to make a buffer with a pH of 10.80? The pKa for CH3NH3+ is 10.645.

  6. Acid – Base Equilibria Additional Questions: Which of the following will result in a traditional buffer? 0.00100 M HNO3 + 0.00200 M NaNO3 0.010 M NH4Cl + 0.003 M NH3 1.0 x 10-5 M CH3CO2H + 0.010 M NaCH3CO2 0.0020 M HCl + 0.010 M CH3CO2H 0.0020 M HCl + 0.010 M NaCH3CO2

More Related