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Unformatted text preview: Nam es:_ CHEM 104
Workshop 9: Acid Base Calculations Today we will practice doing pH calculations at 298K. You will need the following equations:
pH = -log[H30+], pOH = -log [OH'], pH + pOH = 14, Kax Kb = Kw, pH = 12/2 (pKal + pKaz) Lets try and solve some problems: (30 pointsl 1. Calculate the pH of 0.25M NH3? (5 pts] 2. Consider a solution of the weak acid acetic acid [CH3COOH].
a] Calculate the concentration of this acid at pH 3.0. [5 pts) b) What is the resulting pH ifyou add 35 ml of 0.40 M NaOH to a 50 ml sample of this acid ifthe
concentration ofthe acetic acid is 0.50 M? [5 pts)
HINT: Think ab out doing a stoichiometric calculation first. N ashes: 3. The pH ofa barium hydroxide [Ba[OH]2] solution is 10.66 at 25°C.
a) What is the hydroxide ion concentration of this solution? [2 pts) b] If the solution volume is 250mL how many grams of Ba[OH)2 must have been used to make
this solution? (6 pts) 4. Potassium hydrogen carbonate (KHCOg) is a salt comprised ofa K+ cation and the HC03' anion. a) Write the two equilibrium expressions for this compound, one where it acts as an acid and
one where it acts as a base, and give the numerical values of Ka and Kb in each case. [4 pts) b] Calculate the pH ofa 0.10 M solution of KHCOg. (3 pts] EXTRA CREDIT: [5 pts) c) Does the pH you calculated in Q4 part b] make sense? Explain. ...
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- Fall '08