Answer Happy

Name: CHEMISTRY LAB EXPERIMENT #8 "Acid-Base Titration" Introduction: Many laboratories analyze consumer products to determine accuracy in the labeling of a product. The very common and simple technique of titration is demonstrated in this experiment. A titration is an analytical procedure in which a reaction is run under carefully controlled conditions. The stoichiometric volume of one reactant of known concentration, the titrant that is required to react with another reactant of unknown concentration, the analyte, is measured. The concentration of the analyte is determined from the concentration and volume of the titrant and the stoichiometry of the reaction between them. A buret, which contains the titrant, is calibrated so the volume of solution that it delivers can be determined with high accuracy and precision. Titrant is added to the analyte until the stoichiometric volume of the titrant has been added - this is called the equivalence point, at which the volume of titrant delivered by the buret is read. Usually, the volume readings are estimated to the nearest 0.01 mL. The delivery of the titrant is adjusted with the stopcock on the buret. With practice, one can dispense fractions of a drop of titrant and control the procedure well enough that replicated titrations agree within 0.10 L. For this lab, you will need your titrations to agree within 0.50 mL. (Your instructor will approve your data during the lab period). The equivalence point can be determined by two methods. The pH can be monitored during the titration with a pH electrode, and the equivalence point identified as the point of most rapid pH change. The equivalence point can also be determined visually with an indicator. The indicator, which is a substance that changes color near the equivalence point, is added to the analyte solution. Since the color change is near but not exactly at the equivalence point, the point at which the color change occurs is called the endpoint. Indicators are chosen so the endpoint is very close to the equivalence point. It is important to keep a titration well mixed, so the titrant and analyte can contact each other in a uniform fashion and react rapidly with each other. Either manual swirling of the beaker or mechanical stirring can be used. Materials and Fruinmana Do
Materials and Equipment Required Ring Stand Buret Clamp Universal Clamp Buret (25 or 50 mL) pH Electrode (Vernier) Hand-Held Vernier Unit Balance; Top Loader Graph Paper (for analysis) 10 mL Grad. Cylinder 50 mL Grad. Cylinder 50 mL Beaker 250 mL Beaker (reaction) 2 of 100 mL Beaker (waste) Stir Bar Hotplate with stirring capabilities 0.50 M NaOH (x.ssss verified) Vinegar, Commercial-white) Phenolphthalein Indicator Background: The most common type of titration is the acid-base titration. In this experiment you will determine the concentration of acetic acid, HC₂H₂O₂, in commercial vinegar. Vinegar is a mixture of acetic acid and water. In this titration aqueous NaOH is the titrant, and vinegar is the analyte. We assume that the strong base and the weak acid react completely according to the net equation: HC₂H₂O₂ (aq) + OH (aq) ====== C₂H₂O₂ (aq) + H₂0 (1) (1) The balanced equation shows 1:1 stoichiometry, so we can assume and write: TER20
uses Unless you need to edit, it's safer to sta The balanced equation shows 1:1 stoichiometry, so we can assume and write: (2) Moles of HC₂H₂O₂ reacting = moles OH added Or more generally: Moles of acid reacting = moles of base reacting In the titration of the acetic acid with aqueous NaOH, phenolphthalein is used as the indicator. Phenolphthalein is nearly colorless in an acidic solution BUT turns pink at a pH of about 8. This indicates that the base has neutralized the acid. As you titrate the vinegar, you will observe that the pink color is more persistent as you add more base. This is a signal to slow the addition of the base and control it carefully. The endpoint has bee reached when a faint pink color persists for at least 30 seconds. It is easy to overshoot the endpoint. If this happens you will have a dark purple-pink solution, and you may have to repeat the trial titration. Note that the volume measurements in titrations are usually reported to four significant figures, so the concentrations are usually reported to four significant figures as well. Procedure: 1) Obtain a clean, dry 10 ml graduated cylinder 2) Using a clean, dry 50 ml beaker, obtain about 25 mL of vinegar 3) Condition the 10 ml graduated cylinder with vinegar solution before using it. This is done by adding a little vinegar solution to the graduated cylinder, swirl so that the sides are coated with vinegar and then discard the remaining vinegar. Repeat this procedure 1 or 2 more times to ensure that the graduated cylinder is conditioned. 4) Measure the mass of an empty 250 ml beaker and record this value in the Preliminary data table. Using the 10 ml graduated cylinder, transfer @ 7.0 mL of the vinegar into the beaker. Weigh the beaker + vinegar together and record the mass in the Prelim Data Table as well 5) Add @ 40 ml of deionized water (using a separate graduated cylinder) and 3 drops of phenolphthalein solution to the beaker containing the vinegar.
6) Obtain @50 ml of 0.5 M NaOH (get the exact concentration from the bottle or your instructor) in a clean, dry 100 ml beaker. Record the exact concentration from the bottle of NaOH and enter that value in Preliminary Data Table. 7) Condition the 25.0 ml buret with NaOH solution as directed by your instructor. 8) Fill the buret with NaOH and carefully clamp it to the ring stand. Make sure to fill the tip with NaOH solution by draining some solution from the tip into a waste beaker. Record the initial volume of NaOH in the buret in Date Table 2. 9) Carefully slide the stir bar into the 250 ml beaker containing the vinegar solution while tilting to avoid to avoid splashing or damage to the beaker. Position the stir plate under the 250 ml beaker and begin stirring slowly. 10) Carefully position the pH electrode in the 250 mL beaker until about ½ inch of the tip is in the solution. Clamp the pH electrode to the ring stand with the clamp provided. Be sure that the stir bar will not strike the pH electrode. If necessary, add more water. 11) Position the buret so that the tip of the buret is just inside the beaker. 12) Take an initial pH reading and the initial volume of the NaOH in the buret and record both values in Data Table 1 Titration Time 13) Open the stopcock of the buret and add @ 2 mL of titrant (NaOH) to the contents of the beaker. Stir about 10 seconds then read the exact volume on the buret, and enter this value- and the pH reading - in Data Table 1 (second data point). 14) Continue to add titrant in 2.0 mL increments and record the buret and pH values in Data Table 2. Stop at 8.0 mL of titrant volume. 15) After @ 8.0 mL of titrant has been added, the increment of titrant addition should be decreased as the endpoint is closer. Add titrant in @ 1.0 mL increments of less until a total of 11.0 ml of titrant has been added. Then reduce the amount of titrant additions to 0.5 mL or less. Record the incremental additions (Vol. of NaOH and pH) in Data Table 1. At this point, the pH should change more than 0.3 pH units per addition, signaling the
Table 2. Stop at 15) After @ 8.0 ml of titrant has been added, the increment decreased as the endpoint is closer. Add titrant in @ 1.0 ml increments of less until a total of 11.0 mL of titrant has been added. Then reduce the amount of titrant additions to 0.5 ml or less. Record the incremental additions (Vol. of NaOH and pH) in Data Table 1. At this point, the pH should change more than 0.3 pH units per addition, signaling the titration endpoint. You will see a faint pink color appear and then quickly fade. When the color begins to disappear mor slowly, slow the addition of titrant to a dropwise rate. Rinse the walls of the beaker and the tip of the buret with deionized water from a wash bottle as you approach the final endpoint. This ensures that all of the NaOH delivered from the buret ends up in the reaction mixture. The endpoint has been reached when the faint pink color lasts for at least 10 seconds. Record the equivalence point readings (volume of NaOH added and pH) in Table 2. 16) To finish generating the titration curve, return to 1 ml increments of titrant as the changes in pH decrease beyond the equivalence point. Do not stop the titration until you have added approximately 5 mL of titrant beyond the equivalence point. I At this point notify your instructor so that a review of your data can be made. Once your instructor approves your work to this point, as well as the data you have annerated on will be instructed to perform a carand identical in procedural titration
Mailings Review ses. Unless you need to edit it's safer to stay in Protected View. Ena At this point notify your instructor so that a review of your data can be made. Once your instructor approves your work to this point, as well as the data you have generated, you will be instructed to perform a second (identical in procedure) titration with your existing setup. Second Titration: 17) Refill your buret, clean your reaction beaker (spent solutions can be discarded into the sink with water washings), rinse the pH probe, and transfer a second 7.0 ml. portion of vinegar to your reaction beaker, get the total vinegar + beaker weight, add the drops of the indicator, dilute the solution with deionized water, and add the pertinent readings to the "Second Trial" columns in Data Table II. 18) Complete the second titration, entering all required data in Data Table 2 (total volume of NaOH delivered and pH readings). 19) Complete the entire second titration per steps #8 thru # 16. When the second titration is complete, notify your instructor for inspection. Once your data on the second titration has been approved, disassemble and clean the equipment, and dispose of all solutions per your instructor's directions. Data Analysis 1) Construct/Draw a curve of your titration using one of your titration trials. The vertical axis (y-axis) should be in pH units, from 0 to 14. The horizontal axis (x-axis) should be in "ml titrant added", from 0 to just past the final volume of titrant added. 2) Mark your titration curve to indicate the exact position (on the curve) where your indicator kept the faint pink color for at least 20 seconds 3) Using the data from your titration experiment, calculate the concentration (molarity) of the acetic acid (in the vinegar). Remember VA MA= VB MB Add all required information in Data Table 1
Add all required information in Data Table 1 4) Also, answer the following questions. Remember that your titration curve MUST be submitted, as well as the data tables as written. No exceptions. General Questions: 1) What was the color of the solution below pH of 8.0 ?? What was the color of the solution above pH of 8.0 ?? Name: Partner's Name: Date: 2) Calculate the number of millimoles of NaOH required to reach the endpoint (equivalence point) for each of the two titrations. Show one calculation completely (below), and enter that data in Data Table 2 I 3) How many millimoles of acetic acid are in each vinegar sample? Show one calculation completely (below) and enter that data in Data Table 2.
4) What is the mass of acetic acid in each vinegar sample? Show one calculation completely (below) and record that data in Data Table 2. 5) What is the molarity of the acetic acid in each vinegar sample? Show one calculation completely (below) and record that data in Data Table 2. 6) What is the mass percent of acetic acid in each vinegar sample? Show one calculation completely (below) and record that data in Data Table 2. Data Tables Next Page Please note that this submission of the completed laboratory experiment will include 1) the graphical data as requested, 2) answers to the questions above, 3) the completed Data Page., and your signed Flowchart.
Name: DETAILED DATA PAGE Preliminary Data Trail 1 Concentration of NaOH (M) Weight of 250 mL Beaker (g) Weight of Beaker + Acid Weight of Acid Data Table No. 1-Titration Details (Data Obtained in Lab) Component Trial 1 Trial 1. Trial 2 Trial 2 Data Point # Total ml NaOH pH of Titrant Total ml NaOH Ph of Titrant 1 2 3 4 5 6 7 8 9 Partner's 10 11 12 13 14 D 1 ) Trial 2
nd View Saved to this PC- Mallings Review View Help es Unies as need to edit, it's safer to stay in Protected Component Trial 1 Trial 1 Data Point & Total ml NaOH pH of Titrant 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 A 6 FF 7 Search (Alt- a L 47 8 Enable Editing Trial 2 Trial 2 Total ml NaOH Ph of Titrant 1 C F9 ( 9 = O H prt sc home ·
es. Unless you need to edit, it's safer to stay Name: Data Table 2-Compiled Data NaOH Concentration (M) NaOH Init. Vol. in Buret (ml) NaOH Final Vol (ml) at Equiv. pH Final Reading at Equiv. Minimoles NaOH at Equiv. Minimoles Acid at Equiv. Molarity of Acid at Equiv. Mass of acid at Equiv. % Acid at Equiv. Instructor's Approval of Data (end of lab). Partner's Name: Trial #1 Date: I Trial #2