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Chemical Reactions: pH Equilibria
- 1. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Reversible Reactions and Chemical Equilibrium University of Lincoln presentation
- 11. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Units of K c Solution A Now try for solutions B and C
- 12. Acids and Bases This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
- 22. pK a values (data tables) This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Acid pK a Conjugate base H 3 PO 4 2.12 H 2 PO 4 - HNO 2 3.34 NO 2 - H 2 CO 3 6.37 HCO 3 - HCN 9.31 CN - HCO 3 - 10.25 CO 3 2-
- 24. Henderson-Hasselbach This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License For weak acids Use the equation with the example in the previous slide. Do you come to the same conclusion regarding the ratio of un-ionised to ionised acid molecules?
- 26. Henderson-Hasselbach This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License For weak bases Use the equation with the example in the previous slide. Do you come to the same conclusion regarding the ratio of un-ionised to ionised acid molecules?
- 34. Buffers This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
- 37. Buffers This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Henderson-Hasselbach equation Acidic buffers
- 40. An alkaline buffer: ammonia solution and ammonium chloride This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License Note the base/salt ratio What is the pH of a buffer with base:salt ratio = 1? Calculate the base:salt ratios for pH 8.5 and pH 10.5
Editor's Notes
- Strong acids dissociate completely in water. Concentrated acids contain several moles of substance per dm3.
- When an acid dissociated, the H+ ions actually combine with H2O to produce H30+ (oxonium ions, or hydroxonium ions). H+ + H2O ๏ฎ H3O+ A- is referred to as the conjugate base of the acid; I.e.the ions associated with the acid and capable of recombining with the H+ ion. More on this later. E.g. Ka values HCl = 7.2 x 10 10 acetic acid = 1.8 x 10-5
- Water can dissociate:I.e. separate into its ionic components. This dissociation is very partial, in fact one water molecule in 550 million is ionised at any given moment. Because of this to all intents and purposes the concentration of water is taken to be constant
- Kw is really Keq x another constant for H2O.
- Hopefully you have all used at some point universal pH paper green = 7 blue = very alkaline red = very acidic
- 0.1M HNO3 is fully ionised: HNO3 ๏ฎ H+ + NO3- thus, have 0.1moles in 1dm3 of H+ ions. Thus put 0.1 into equation to give a pH equalling 1. CH3COOH is partially ionised: CH3COOH ๏ซ CH3C00- + H+ only have 0.001 or 10-3 moles of H+ ions, thus pH = 3. A pH meter musing a H electrode to measure the pH of a solution.
- 0.1M NaOH - strong alkali-completely ionised NaOH ๏ฎ Na + + OH- Thus, 0.1M NaOH contains 0.1M of OH- ions in 1 dm3. Put into equation. 10-13 which gives a pH = 13.
- Used in the lab: reagents can be added to solutions without pH altering and reactions carried out. Absorption of CO2 and lab fumes may also the pH of a solution. 15.7 โ Housecroft โ P462 - 467 Making use of the partial dissociation of weak acids and bases
- P462
- P466 housecroft