QuestionQuestion

Acid-Base Titrations Questions
1. A solid diprotic weak acid, H2A (molecular weight = 128.9 g/mol) is used to standardize a KOH solution. When 0.4228 g of the acid is dissolved in 40.0 mL of water and then titrated to the phenolphthalein endpoint using KOH, it requires 19.28 mL of the KOH.
A. Write the balanced chemical equation for the reaction of H2A with KOH.
B. Using dimensional analysis, determine the mol of KOH required to reach the endpoint.
C. Calculate the molarity of the KOH solution.
2. Suppose that you used a known concentration (0.8442 M) of Ca(OH)2 to determine the concentration of an unknown HBr solution. If it takes 12.88 mL of the Ca(OH)2 solution to titrate 15.00 mL of the unknown HBr solution, what is the molarity of the HBr?
3. Determine if the following procedural errors would cause the calculated molarity of KOH to be higher or lower than the actual molarity of KOH? Or, would the error not affect the calculated molarity value? Briefly explain your answer in your own words. Answer in complete sentences.
A. The weak acid (H2A) was dissolved in 50.0 mL of water instead of 40.0 mL of water.
B. The KHP was not quantitatively transferred to the Erlenmeyer flask (meaning some of the KHP remained in the weighing boat or was spilled on the lab bench).
C. The titration wasn’t stopped until a dark pink color was reached instead of stopping a very light pink color.

Data:
A. Standardization of NaOH
                                                 Trial I                               Trial II
Mass of Weigh Boat (g)          ____________ ____________
Mass of Weigh Boat + KHP (g) ____________ ____________

Initial NaOH reading (mL)       ____________ ____________
Final NaOH reading (mL)       ____________ ____________

B. Standardization of HCl
                                                       Trial I                     Trial II
Volume HCl (mL)                   ____________           ____________
Initial NaOH Reading (mL)    ____________           ____________
Final NaOH Reading (mL)    ____________           ____________

Calculations
A. Standardization of NaOH
                                                 Trial I                   Trial II
Mass of KHP (g)             ____________       ____________
Mol of KHP (g)                ____________         ____________
Vol of NaOH (L)             ____________          ____________
Molarity, NaOH               __________ M           __________ M
Ave. Molarity of NaOH    __________ M

B. Standardization of HCl
                                     Trial I                     Trial II
Vol HCl (L)             ____________          ____________
Vol. NaOH (L)       ____________          ____________
Molarity HCl          __________ M          __________ M
Ave. Molarity of HCl   __________ M

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