2.Titration of vinegar with standardized NaOH solution Use the standardized NaOH solution to complete the rest of the titrations for this lab experiment. Be sure to record the exact concentration of the NaOH that you and your partner calculated. Remember, this is your reserve of NaOH solution for use in all your titrations for the remainder of the lab experiment - do not waste it! Use the same buret that you used for standardizing the sodium hydroxide solution. Check that the buret still drains cleanly. Add 2-3 drops of phenolphthalein indicator solution to each of the Erlenmeyer flasks containing your vinegar solutions. Note:Students with red-green colorblindness may use thymolphthalein indicator solution. The color change for these indicators is colorless (in acidic medium) to blue (in basic medium). Before titrating the first vinegar sample, adjust and record the initial level of the base in the buret to the nearest 0.02 mL in your lab notebook. You should begin with the meniscus exactly on a calibration mark and record the exact initial volume. Titrate the first vinegar sample until a very pale pink color persists in the solution for more than 20 seconds. Record the final volume reading of the buret in your lab notebook. Repeat the titration procedure on the vinegar samples 2 and 3. STUDENT ASSIGNMENTS I. Pre-laboratory Preparation Prior to attending the laboratory period, complete the following activities in an organized manner in your laboratory notebook. This assignment is due at the beginning of the lab period. A. Introductory StatementIn a short paragraph, summarize in your own words (not the lab manual’s), the purpose, theory and procedure for this laboratory exercise.B. Pre-laboratory Questions / Activities 1.What does it mean to “standardize the NaOH solution”? Why can the molarity of the NaOH solution not be determined accurately based on the mass of NaOH dissolved in water? Consider the following scenario: 4.000 g of solid, reagent grade NaOH was dissolved in enough water to make 1.00 L of solution. What is the calculated molarity of the solution? Is the true molarity greater than, less than, or equal to this calculated value? Explain. 2.What is a primary standard and what primary standard will be used to standardize the NaOH solution in this lab? 3.What is an indicator and what purpose does it serve in a titration? Name the acid-base indicator that you will use in this lab experiment. How will it signal changes during your titration? If 24.5 mL of base are required to reach the color endpoint of an acid/base titration, what volume (more than, less than, or equal to this amount) of base is actually needed to reach the stoichiometric endpoint? Explain.
Lab 5 – Page 6 of 8
You've reached the end of your free preview.
Want to read all 8 pages?
- Fall '12
- Chemistry, Sodium hydroxide, KHP