The introduction of your report should be written on the on the topic of the role of indicators on acid base titrations.

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1 Experiment # 13A TITRATIONS INTRODUCTION: This experiment will be written as a formal report and has several parts: Experiment 13 A: Basic methods (accuracy and precision) (a) To standardize a base (~ 0.1M NaOH) using Potassium Hydrogen Phthalate (KHP), a monoprotic acid as a primary standard. (b) To use the standardized base to analyze a common acid (c) To use the common acid to analyze a common base Experiment 13 B: Potentiometric Titrations as a means of analysis The introduction of your report should be written on the on the topic of the role of indicators on acid base titrations. PRELAB READING ASSIGNMENT: Text Chapter 14 TECHNIQUES: The Pipet The Buret Precision and Significant Figures Writing a Formal Report PROCEDURE: NOTE: You will work individually. If your results do not agree to within 5 parts per thousand you should do extra titrations to a maximum of six. Part A: Standardization of a NaOH Solution 1. Obtain ~ 100 ml of NaOH solution from the stock bottle 2. Prepare the burette and fill with NaOH 3. Prepare three samples [1.4000g g] of KHP in clean and dry 125 ml Erlenmeyer flasks using the weighing by difference method. 4. Dissolve one KHP sample in ~50-75 ml of distilled water and titrate using phenolphthalein as the indicator. 5. Repeat for the other two KHP samples. Part B: Determination of the Molarity of Vinegar 6. Obtain approximately 50 ml of the vinegar. 7. Prepare a graduated pipette and transfer approximately / exactly 15 ml of vinegar to a 125 ml E- flask 8. Titrate using phenolphthalein indicator. 9. Using the volume of the sample of acid and the volume of NaOH, calculate how much acid would require 35 ml of base to reach the endpoint. 10. Calculate again using 40 ml. 11. Pipette two samples of vinegar within this range and titrate each sample, recording all volumes.

2 Part C: Determination of the Concentration of Drain Cleaner 12. Observe how to use a volumetric flask. (Include this in your report). 13. Ensure the appropriate titrations of the unknown acid from Part B give concentrations that agree to within +/ mol/l. Check with the instructor before proceeding. 14. Transfer (with a prepared volumetric pipette) approximately / exactly 10 ml of the drain cleaner to a 100 ml volumetric flask. Record actual volume in your notebook. 15. Add distilled water directly to the flask until the level reaches the line on the neck of the flask and mix appropriately. 16. Conduct a preliminary rough titration by placing approximately-exactly 10 ml of the acid solution in a 250 ml Erlenmeyer flask and titrating with your diluted drain cleaner. 20. Using the results from this titration, adjust the volume of acid in the flask so that you will titrate with at least 20 ml of the base. 21. Repeat until you have two titrations that give NaOH concentrations that agree to within +/ mol/l. What concentration of your original sample must have been NaOH? PART D BONUS: You will be given a liquid of unknown acidity, titrate this material to determine the concentration of acid or base assuming monoprotic stoichoimetry.

3 EXPERIMENT # 13A - Grade Sheet Name Date Bench # PURPOSE: Data Table I Standardization of a NaOH Solution Titration #1 KHP #2 KHP #3 KHP #4 KHP #5 KHP #6 KHP Mass of sample Final Initial Used Calculated Results (show one complete set of calculations on an attached page, do for all parts) Trial # g KHP Moles KHP NaOH Molarity NaOH 1 st Deviation 2 nd Deviation Average Molarity of NaOH = 1 st. If necessary = 2 nd.

4 Data Table II Determination of Concentration of Vinegar. Titration of Sample Final Base Initial Base Base Used Table for Calculated Results Trial # vinegar NaOH Moles NaOH Molarity Vinegar 1 st Deviation 2 nd Deviation (if needed) Average molarity = 1 st. If necessary = 2 nd.

5 Data Table III Determination of Concentration of Drain Cleaner. Titration of Acid Final Base Initial Base Base Used Table for Calculated Results Trial # vinegar Cleaner Moles NaOH Molarity Cleaner (dilute) Molarity Cleaner (original) 1 st Deviation 2 nd Deviation) Average molarity = 1 st. If necessary = 2 nd. QUESTIONS (answer on sheet attached to grade sheet) 1. Explain, using your results, how the accuracy and precision of one step related to the accuracy and precision of following steps. 2. Find out (from a referenced source) what the expected concentrations of vinegar and drain cleaner should be and compare with your results.

6 Experiment # 13B ACID BASE EQUILIBRIA: Potentiometric Titrations INTRODUCTION: In this experiment, you will approach some acid/base titrations from a different perspective. In these examples, you will know the molarity of both acid and base and you will use the titration results to determine how many ionizable protons an unknown acid has. You will also use titrations and titration curves to identify four unknown acids by observing which of the unknown solutions contain weak or strong, monoprotic or diprotic acids. PRELAB READING ASSIGNMENT: Text Chapter 14. TECHNIQUES: The Buret The Pipet EQUIPMENT REQUIRED: 4 clean 250 ml Erlenmeyer flasks 25 ml pipet and bulb 250 ml Nalgene bottle buret 4 50 ml beakers ph meter and probeware CHEMICALS SUPPLIED: unknown acids A, B, C, D metacresol purple indicator 0.1M NaOH PROCEDURE: Working in pairs 8. In this experiment, you will be repeating one or more of the titrations from the previous experiment, but you will be monitoring the ph. 9. Start with ml of your designated acid in a 250 ml beaker. 10. Add 3 6 drops of one of the indicator solutions (use a different one each time). 11. Set up beaker with ph meter (will be demonstrated). 12. Titrate with minimal washing with distilled water (none is best). 13. Record volume and ph readings with every ~ 0.4 change in ph until the ph is greater than Using clean glassware for each titration repeat this procedure for as many unknowns as possible. * For each titration you will have separate ph/volume readings because you should note the ph for every 0.4 change in ph. Near the endpoint you can expect large increases of ph with small volumes of base, so be very careful! * You will be expected to tabulate your data for submission with separate graphs of each data set (ph on y-axis, volume delivered on x-axis). On each plot, indicate the plotted equivalence point and the ph at that point, pka for the acid and ph range for colour changes.

7 EXPERIMENT # 13B - Grade Sheet Name Lab Day & Time Date Bench # PURPOSE: EXPERIMENTAL [Attach data tables and graphs]: Identification of the Unknown Acids [comment on how this experiment confirms or refutes conclusions from the previous experiment] Unknown A: Explanation: Unknown B: Explanation:

8 Unknown C: Explanation: Unknown D: Explanation: CONCLUSION:

9 TABLE OF INDICATORS

10 EXAMPLES OF TITRATION CURVES