Jul 30, 2015 - Viva Questions 1. What is a weak acid? Weak acid is a weak electrolyte, which ionises incompletely in aqueous solution. 2. What is PKa of a weak acid? PKa is a modern method of expressing the strength of weak of acids. It is mathematic
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Idea Transcript
Questions and Calculations
Weak Acid Dissociation Constant
1. If more than one trial was obtained, determine the average for each measurement. Calculate the pKa of each acid from the pH of the mixture.
2. Compare the pKa values of your unknown acids with the values in the table in the “Pre-Lab” portion of this experiment. Which of the five acids in that table do you think are your two unknowns?
3. Identify various possible sources of error in the experimental procedure you used.
4. (a) Using the mass of solid dissolved in 50.0-mL of water for your first unknown, calculate the concentration of the solution. Assume no volume change when the solid is dissolved. (b) Calculate the pH of this solution assuming your acid was a strong acid similar to HCl. (c) Compare the pH of the acid solution measured at the beginning of the experiment with the pH in Part (b) of this question. How do you account for the difference? (d) Calculate the percent ionization of your acid from the molar concentration determined in Part (a) and the pH of the acid solution measured before any base was added to the beaker.