CH204 Fall 2006 Cheat Sheet for Experiment 9. Acid-Base Equilibria 1Part 3. The Ionization Constant of Acetic Acid Solution: 10 ml of 1.6 M CH3COOH pH – measured Ka – ? Calculations: 1. x==−+ pH310]OH[ 2. Determine [CH3COO–] and [CH3COOH] from the following: CH3COOH + H2O CH3COO– + H3O+ (1.6 - x) x x 3. )6.1(]COOHCH[]COOCH][OH[K2333axx−==−+ Solution: 25 ml of 1.6 M NaCH3COO + 10 ml of 1.6 M CH3COOH CH3COOH + H2O CH3COO– + H3O+ (reversible) NaCH3COO → CH3COO– + Na+ (to completion) pH – measured Ka – ? Calculations: 1. pH310]OH[−+= 2. Determine [CH3COO–] in a new volume of 35 ml 3. Determine [CH3COOH] in a new volume of 35 ml 4. ]COOHCH[]COOCH][OH[K333a−+= Part 4. Buffering Capacity Solution: 30 ml of DI H2O + 2 ml of 3.0 M HCl HCl → H+ + Cl– (to completion) pH – measured pH (calculated) – ? Calculations: 1. Determine [HCl] in a new volume of 32 ml 2. [H+] = [HCl] 3. pHcalc = –log [H+]CH204 Fall 2006 Cheat Sheet for Experiment 9. Acid-Base Equilibria 2Solution: 30 ml of DI H2O + 2 ml of 3.0 M NaOH NaOH → Na+ + OH– (to completion) pH – measured pH (calculated) – ? Calculations: Use the same approach as shown above for the (H2O + 3.0 M HCl) solution. Remember, that [H+]×[ OH–] = 10–14 Solution: 30 ml of 1.6 M NaCH3COO + 30 ml of 1.6 M CH3COOH = 60 ml of the buffer pH – measured pH (calculated) – ? Calculations: 1. Determine [CH3COO–] in a new volume of 60 ml 2. Determine [CH3COOH] in a new volume of 60 ml 3. ]COOHCH[]COOCH[logpKpH33a−+= Use Ka = 1.76×10–5 Solution: 30 ml of the buffer (prepared previously) + 2 ml of 3.0 M HCl pH – measured pH (calculated) – ? Calculations: 1. Determine the number of moles of CH3COOH in solution: a 2. Determine the number of moles of CH3COO– in solution: b 3. Determine the number of moles of HCl added: x 4. H+ + CH3COO– → CH3COOH x b a start –x –x x change 0 (b – x) (a + x) after 5. COOHCH of molesCOOCH of moleslogpKpH33a−+= Use Ka = 1.76×10–5 Solution: 30 ml of the buffer (prepared previously) + 2 ml of 3.0 M NaOH OH– + CH3COOH → CH3COO– + H2O Calculations: Use the same approach as shown above for the (buffer + 3.0 M HCl)
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