Lab 7: My Second Acid-Base Titration

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Learning Outcomes

Upon completion of this lab, the student will be able to:

Perform another sodium hydroxide (NaOH) standardization titration to recheck its concentration
Use your standardized NaOH solution to perform a titration to determine the concentration of an unknown acid solution
Monitor the pH of a titration reaction

Introduction

Recall that a titration is an analytical quantitative technique used to determine the concentration of an acid or a base. Titrations play an important role in determining amount and purity in many manufacturing processes. These include food processing, textile, wood product manufacturing, petroleum, pharmaceuticals and chemical manufacturing. Titrations play a critical role in the manufacturing of biodiesel, water purification and waste water treatment and even in the production of various products in the dairy industry.

Experimental Design

Your solution of sodium hydroxide (NaOH) from the previous experiment whose concentration is known will be used for this experiment. You'll determine the exact concentration of a provided acid solution by titration with your standardized NaOH.

Fill in the worksheet as you perform today's experiment.

Reagents and Supplies

Your standardized solution of sodium hydroxide from last experiment, a provided unknown acid solution, a phenolphthalein solution, pH paper

(See posted Safety Data Sheets)

Procedure

Task 1: Recheck NaOH concentration

1. Perform one standardization titration to check the concentration of your NaOH solution following the steps from the previous experiment, Experiment 6.

Task 2: Titrations to Determine Unknown Acid Concentration

Unknown Solution: Acid (Flask)

Add 25 mL of unknown acid solution into a 125 mL Erlenmeyer flask.
Add one drop of phenolphthalein solution into the 125 mL Erlenmeyer flask.

Known Solution: Sodium Hydroxide (NaOH)

Clamp a burette to a burette stand.
Condition the burette by filling with water. Allow the water to drain. Water can be discarded in sink. Then rinse the burette with a few mL of your standardized sodium hydroxide solution (NaOH) from last week. Discard this rinse into waste. Finally, fill to slightly above the zero mark with the NaOH.
Drain enough NaOH so that there are no air bubbles in the tip of the burette and that the level of the NaOH is between 0.00mL and 1.00mL. Record the exact initial burette reading with appropriate significant figures and record this value with units.
Perform a fast titration. Record the volume of NaOH used to reach the endpoint.
Repeat steps 3-6 to perform a total of two slow titrations. Record the volume of NaOH used to reach the endpoint.

Task 3: Final slow titration while monitoring pH

Perform a third (and final) slow titration as you did in the steps above, but monitor the pH of your solution as you do so by using pH paper. First measure and record the pH of the acid solution in your flask before you add NaOH (this is labeled as 0.00 mL NaOH added in the table on your summary worksheet). Then you'll record the volume of NaOH added and the pH of the solution measured at this point as you perform your titration. You'll want to plan on getting two measurements before the equivalence point, one measurement at the equivalence point, and two measurements after the equivalence point. Use these values to fill out the chart in your worksheet.
Check with your instructor before cleaning up. Dispose all waste into appropriate waste disposal containers as instructed by your instructor. Clean and return all glassware. Place the burette upside down on the stand and turn the stop-cock to the open position to allow it to drain and dry.