10 - Water equilibria, supplement, the six steps to solve acid base calculations

10 - Water equilibria, supplement, the six steps to solve acid base calculations

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Stepwise process for Working Acid/Base Equilibrium Problems (red stuff is not on exam 1) There are only six equations needed to solve acid base problems. There are only five possible variables to put into these equations: K a , K b , [H + ], [OH - ], C acid , C base Strong acid [H+] = Ca Strong base [OH-] = Cb Weak acid [H + ] = (K a C a ) 1/2 Weak base [OH - ] = (K b C b ) 1/2 Acid buffer [H + ] = K a C a /C b Basic buffer [OH - ] = K b C b /C a So there isn't a lot of complexity at the bottom of this. The hard part is figuring out which equation to use and what each of the variables is. To accomplish this task, we use the following procedure: 1) strip away all the extraneous information (spectator ions), 2) identify strong acids and bases, 3) identify weak acids and bases, 4) determine if you should neutralize, 5) perform neutralization calculation, 6) decide whether to work the problem as an acid or a base. Once these steps are done, the problem is greatly simplified to the point that you can use the table above to work a calculation. The back of this page shows every possible type of starting conditions and how they reduce to one of the problems above. 1) Getting rid of spectator ions . Always eliminate the ions that do nothing: all alkali metals and alkali earths (Na + , K + , Ca ++ ) and all conjugate bases of strong acids (Cl - , NO 3 - , ClO 4 - , I - , Br - ). Thus NH 4 Cl is NH 4 + NaOH is just OH - KCOOH is just COOH - 2) Identify strong acids and bases. Strong acids are HCl, HNO 3 , H 2 SO 4 , HClO

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10 - Water equilibria, supplement, the six steps to solve acid base calculations

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