Spring 2009 CH302 Worksheet 5—How to Systematically Work Harder and Harder Acid Base Calculations Exactly the Same Way: Proof that the Seven Steps to Solving Acid Base Problems Work 1 Remove the spectator ions 2 Are there any strong acids or bases 3 Are there any weak acids or bases 4 Do I neutralize (are there both acids and bases and is at least on of them strong?) 5 Neutralize: convert everything to moles, write down neutralization reaction, perform limiting reagent calculation, convert back to molarity if necessary) 6 Select the appropriate acid base calculation and solve 7 Convert to appropriate final form (pH, pOH, H+, OH-) using 14 = pH + pOH and 14 = pKa + pKb Important: These calculations are based upon the following important assumptions: • Strong acids and bases completely dissociate • Weak acids and bases do not dissociate significantly (typically they will have K values <10-3) • The dissociation of water does not contribut4e significantly to pH (concentrations of dissolved solutions are large, > 10-4, and the K values are not near Kw, >10-11) In a nutshell, all of these problems are worked at high concentrations for a single equilibrium. When we get to complex equilibria you will learn how to tackle problems for which the assumptions do not hold. 1. What is the pOH of a 0.1 M HClO4 solution? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________. 2. What is the pH of a 0.1 M RbOH solution? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________. 3. What is the [H+] of a 0.1 M malonic acid with a Ka of 10-9 solution? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________.4. What is the pH of a 0.1 M lithium malonate solution? (Need a Kb? Look at the problem above.) 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________. 5. What is the [OH-] of a 0.01 M methylamine solution of Kb = 10-6? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________. 6. What is the pOH of a 0.01 M CH3NH3Br solution? (Need a Ka? Look at the problem above.) 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________. 7. What is the pH when equal volume mixtures of 0.2 M HClO4 and 0.2M LiClO4 are mixed? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________.8. What is the pH when 100 ml of 0.1 M HClO4 and 50 ml of 0.1 M Ba(OH)2 are mixed? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________. 9. What is the pH when 1 liter of 0.1 M HClO4 and 1 liter of 0.5M Ba(OH)2 are mixed? (this is the first problem to need a calculator) 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________. 10. What is the pOH when 100 ml of 0.1 M malonic acid and 100 ml of 0.1 M sodium malonate are mixed? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________. 10. What is the pH when 100 ml of 0.1 M methylamine and 100 ml of 0.1 M CH3NH3Br are mixed? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________.The next four calculations represent the titration of a weak base with a strong acid. Note the pH gets smaller and smaller as more acid is added. 11. What is the pH when no HBr is added to 100 ml of 0.1 M sodium malonate? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________. 12. What is the pH when 50 ml of 0.1 M HBr is added to 100 ml of 0.1 M sodium malonate? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________. 13. What is the pH when 100 ml of 0.1 M HBr is added to 100 ml of 0.1 M sodium malonate? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________. 14. What is the pH when 110 ml of 0.1 M HBr is added to 100 ml of 0.1 M sodium malonate? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________.The next four calculations represent the titration of a weak acid with a strong base Note the pH gets larger and larger as more base is added. 15. What is the pH when no LiOH is added to 200 ml of 0.05 M CH3NH3Br? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________. 16. What is the pH when 100 ml of 0.05 M LiOH is added to 200 ml of 0.05 M CH3NH3Br? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________. 17. What is the pH when 200 ml of 0.05 M LiOH is added to 200 ml of 0.05 M CH3NH3Br? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________. 18. What is the pH when 250 ml of 0.05 M LiOH is added to 200 ml of 0.05 M CH3NH3Br? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________.19. What is the pH when 10 ml of 0.1 M HClO3 is added to 100 ml of 0.1 M methylamine and 100 ml of 0.1 M CH3NH3Br? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________. 20. What is the pOH when 20 ml of 0.001 M KOH is added to 200 ml of 0.01 M malonic acid and 200 ml of 0.02 M sodium malonate are mixed? 1 2 3 4 5 6 7 What kind of acid base problem was this? ________________________________. Super-duper do it in your head pH problem. What is the pH when 10 ml of 0.1 M HClO3 and 20 ml of 0.05M Ba(OH)2 are added to 150 ml of 0.1 M methylamine and 75 ml of 0.2 M CH3NH3Br? Hint, put away your calculator and do it in your head. 1 2 3 4 5 6 7 What kind of acid base problem was this?
View Full Document
Unlocking...