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EXPLORATION- Exercise 1 Determining the Concentration of Acetic Acid Procedure EXPERIMENTATION - In this exercise, you will determine the concentration of acetic acid (CH3COOH) in commercial distilled white vinegar. 1 EVALUATION ♥ Note: Please read all steps and safety information before starting the procedure. Gather the test tube holder, small stopcock, 10 mL syringe (titrator), and either 2 thick textbooks and the lab kit box or 5-6 thick textbooks. See Figure 4.
Figure 6. Titration setup. Note: It is important that the placement of the titrator allows for the white knob to be easily adjusted. If this is not the case, then either adjust the location of the books in the stack or slightly adjust where in the test tube clamp the titrator is located. 6 Use the empty, short-stem pipet to fill the titrator with 7-9 mL of distilled water. Note: It is important that you use distilled water for this step and not tap water. 7 Using both hands, one hand on the titrator and your other hand on the stopcock, practice releasing water from the titrator into the beaker. The goal is to be comfortable releasing only 1 drop at a time from the titrator. See Figure 7. 8 Themistry Imao Organicemistr Inorganic C Figure 7. Proper hand positioning for titration. When the open circle is facing you, the titrator is closed, when the open circle is directly under the titrator spout, the titrator is open and liquid will flow. When you are comfortable using the titrator, pour the water in the beaker down the drain, remove the titrator from the test tube clamp, and remove the stopcock from the titrator. Thoroughly dry each of these 3 items with paper towels.
2 3 Figure 4. Titrator and small stopcock. 5 Remove the plunger from the titrator and place it back in your lab kit box. Attach the stopcock to the tip of the titrator by placing the larger, clear, plastic end of the stopcock into the tip of the titrator and then twist the stopcock into place. The stopcock should fit tightly into the titrator so that the liquid will not leak. See Figure 5. 4 Stack the 5 textbooks or stack 2 textbooks on top of the lab kit box. Figure 5. Fitting the stopcock into the titrator. FIE Clamp the test tube holder around the middle of the titrator and slide the long end under the top 2 books in the stack. Place a sheet of white paper next to the bottom of the stack and set the 100 mL beaker on the sheet of white paper. The end of the stopcock should be located near the top of the beaker, approximately 1 cm above to 1 cm below the top of the beaker. See Figure 6. 471 Chernistry
8 9 directly under the titrator spout, the titrator is open and liquid will flow. When you are comfortable using the titrator, pour the water in the beaker down the drain, remove the titrator from the test tube clamp, and remove the stopcock from the titrator. Thoroughly dry each of these 3 items with paper towels. When all items are completely dry, reassemble the titration setup, as shown in Figure 6. 10 Put on your safety gloves and goggles. 11 With the stopcock in the closed position, fill the titrator with 9-10 mL of the 0.50 M NaOH. Note: The chemicals from the chemical bag will be used in additional experiments. Use only what is required for this experiment; when you have finished using the sodium hydroxide, put the lid back onto the chemical bottle and return it to the kit for future use. 12 Move the beaker away from the titrator and place a crumpled paper towel directly below the titrator. 13 Using the stopcock, allow a few drops of the NaOH to flow through the titrator into the paper towel. This will fill the tip of the titrator with NaOH solution and remove any air bubbles from the titrator. 14 Place the paper towel with the NaOH drops into the trash and reposition the clean, dry 100 mL beaker back in the titration setup, under the titrator. 15 Use the graduated cylinder to measure 5.0 mL of vinegar. 16 Pour the 5.0 mL of vinegar into the 100 mL beaker. Rinse the graduated cylinder with a small amount of distilled water and add to the beaker containing the 5.0 mL of vinegar. 17 Cut off the tip of the pipet with scissors and add 2 drops of phenolphthalein to the 5 mL of vinegar in the beaker. 18 Carefully swirl the mixture in the beaker to ensure that the indicator is incorporated into the vinegar; the solution will be colorless and clear. 19 Read the volume of NaOH in the titrator to the nearest 0.1 mL and record in Data Table 1 under "Initial NaOH Volume (mL)." next to "Trial 1". 20 Open the stopcock and add 1 drop of NaOH to the colorless and clear vinegar sample in the beaker. After the drop is added. gently swirl the beaker and observe the color for 5 seconds. Note: It is important to add the NaOH 1 drop at a time to avoid overshooting the titration.
Note: It is important to add the NaOH 1 drop at a time to avoid overshooting the titration. 21 Continue adding NaOH to the beaker, 1 drop at a time, swirling and observing after each drop until the color changes to a bright-pink color for at least 5 seconds. See Figure 8. Teaching Lab Science Courses MELUCHTMERRO 100ml 11 THE HIGH BOROSILICATE Gi TIR GLASS 3.3 Figure 8. Endpoint of titration. The titration is complete when the color changes to a bright pink for at least 5 seconds. 27 If necessary, add more NaOH to the titrator. 22 Read the volume of the NaOH solution remaining in the titrator and record this volume in Data Table 1 under "Final NaOH Volume (mL)", next to "Trial 1. 23 Determine the total volume of NaOH used by subtracting the final NaOH volume from the initial NaOH volume and record the total volume in Data Table 1. 24 Leave the titrator assembly intact. You will need it for future titrations in this experiment. 25 Pour the contents of the beaker down the drain and flush the drain with water. Thoroughly wash the beaker with soap and water to remove all of the vinegar/NaOH/indicator solution from the beaker. When the beaker is clean, rinse the beaker with distilled water and then thoroughly dry. 26 Place the clean and thoroughly dry beaker back in the titration setup, under the titrator. a of NaOH used in
Note: It is only necessary to add more NaOH to the titrator if there is less than 1 mL more than the total volume of NaOH used in the previous trial. For example, if the total volume of NaOH used in Trial 1 was 2.1 mL, then there needs to be at least 3.1 mL of NaOH in the titrator. 28 Repeat steps 15 through 27 two additional times (Trial 2 and Trial 3). 29 Average the results from the three trials and record in Data Table 1 and Data Table 2. 30 Using the following equation, determine the average concentration (moles per liter) of acetic acid (CH3COOH) present in your vinegar. Record the concentration in Data Table 2. M CH3COOH = L NaOH x % CH3COOH mol CH3COOH 1L vinegar mol NaOH L X 31 Using the following equation and your result from Step 30, determine % concentration (mass percent) of acetic acid (CH3COOH) in the vinegar and record it in Data Table 2. Note: The density of vinegar is 1.00 g/ml and the molecular mass of CH3COOH is 60.05 g/mol. 1L 1000 Cleanup: • Properly dispose of the chemicals in the titrator and beaker. 1 mol CH₂COOH 1 mol NaOH Wash and dry all equipment and return to the lab kit. 1 mL vinegar 1.006 g vinegar X X 1 0.0050 L vinegar 60.05 g CH₂COOH 1 mol CH3COOH * 100%
Experiment 1 Data Table 1: NaOH Titration Volume Initial NaOH Volume (mL) Trial 1 Trial 2 Trial 3 Average Volume of NaOH Used (mL): Data Table 1 Final NaOH Volume (mL) LOW COSUL EEE Datat Table 2 Total volume of NaOH used (mL)
xperiment 1 Data Table 2: Concentration of CH3COOH in Vinegar Average volume of NaOH used (mL) EEE Data Table 1 LAUL COOL EEE Datat Table 2 L Concentration of CH3COOH in vinegar (mol/L) % CH3COOH in vinegar