Determination of Acetic Acid Concentration in Vinegar

Lab - Determination of Acetic Acid Concentration in Vinegar Introduction Vinegar, a widely used preservative, cleaning product, and cooking ingredient, is a solution of acetic acid (HC2H3O2) and water. Different types of vinegar are produced through the fermentation of a wide variety of fruits and grains. Distilled white vinegar is produced by the fermentation of alcohol derived mainly from corn. A titration is the precise addition of a solution of known concentration and composition, called the titrant, to a solution of unknownconcentration or composition, called the analyte. In this acid-base titration, the titrant, sodium hydroxide, is delivered through a syringe in order to measure precisely (±0.1 mL) the volume of base added. In many traditional acidbase titrations, the titrant is added using a burette, a piece of glassware designed for adding known volumes of a solution to another container. Acetic acid can be neutralized with a strong base, such as sodium hydroxide, to form a salt and water. The concentration of acetic acid, the analyte, in vinegar can be determined through an acid-base titration. HC2H3O2 + NaOH → NaC2H3O2 + H2O At the equivalence point of a titration, the moles of acid exactly equalthe moles of base in solution. The equivalence point is achieved when sufficient titrant has been added to react with all of the analyte. The end point is the experimental estimate of the equivalence point, and is typically identified by a color change in an indicator solution. In a titration, there is a noticeable change in pH near the end point. A change in color of an indicator added to the analyte at the start of the titration is observed when the end point has been reached. The molarity and volume of the titrant are known, as is the volume of the analyte. To determine the concentration of the analyte, we use the following equation: #H+ x Ma x Va = #OH- x Mb x Vb Phenolphthalein is the indicator used in this experiment. Phenolphthalein is colorless in its acidic form and pink in its basic form Which substance is distilled white vinegar primarily made from? ANSWER: CORN Write and balance the equation for the neutralization of acetic acid by sodium hydroxide. CH3COOH + NaOH → CH3COONa +H2O Match the vocabulary term with it's meaning in terms of titrations: equivalence point: moles of acid equal moles of base End Point: indicator changes color Activity 1 - Titration of Vinegar with Sodium Hydroxide Completely read through all of the instructions below. Draw a diagram showing step-by-step what needs to be done in steps 1 through 17. Upload a picture of your diagram below. 1. Place the 10-mL graduated cylinder on the electronic balance. 2. Tare the balance. 3. Dispense approximately 5 mL of vinegar into the graduated cylinder with a plastic pipet. 4. Record the exact mass of vinegar in the data table for Vinegar Sample 1. 5. Calculate and record the exact volume of the vinegar using its density (1.005 g/mL). (You may need to go back and review how to density calculations from unit 1.) 6. Transfer the vinegar into the clean 25-mL Erlenmeyer flask. 7. Add 2 drops of phenolphthalein to the vinegar. 8. Transfer approximately 10 mL of 1 M sodium hydroxide (NaOH) to the small cup. This solution will be used to fill the syringe. 9. Fill the syringe with 1 M NaOH solution.Try to minimize the amount of air in the syringe. 10. Record the initial NaOH solution volume in the syringe to the nearest 0.1 mL in your data table. Be sure to read the volume of the syringe at the edge of the plunger. 11. Place the flask containing the vinegar on the white sheet of paper. The white background will make the color change more noticeable. 12. Add NaOH from the syringe in 0.5-mL increments, swirling the flask between each addition until a color change persists for a few seconds after the addition of the NaOH. 13. Add NaOH dropwise from the syringe, with constant swirling, until a single drop of NaOH causes a color change that persists for a few seconds after the addition. This indicates that the end point has been reached. 14. Once the end point has been reached, record the final volume of NaOH in the syringe in the data table. 15. Calculate the total volume of NaOH that was delivered to reach the end point and record the data in the data table. This can be done be initial NaOH volume minus the finan NaOH volume. 16. Dispose of the titrated vinegar sample in the sink. 17. Rinse the 25-mL flask three times with water. 18. Repeat these steps for Vinegar Sample 2 and Vinegar sample 3 in the data table. 19. Calculate the moles of NaOH delivered by using the volume of NaOH and the molarity of NaOH. (The volume needs to be in liters and the concentration of the NaOH is 1 M.) 20. The moles of acetic acid in sample is equal to the moles of NaOH delivered because the acid has one H+ and the base has one OH-. So it is a 1 to 1 ratio. 21. The mass of acetic acid in sample can be found by converting moles of acetic acid (HC2H3O2) to grams of acetic acid. (You may need to go back and review how to do mole calculations from unit 3.) 22. The calculated molarity of acetic acid in the sampled vinegar is found using the molarity equation: moles of solute divided by liters of total solution. 23. The calculated percent mass of acetic acid in sampled vinegar is found by taking the mass of acetic acid in the sample divided by the mass of the vinegar and multiplying by 100. 24. Once all three trials are done, you can calculate the average percent mass of acetic acid in sampled vinegar. Name of Vinegar Sample Mass of Vinegar Calculated Volume of Vinegar Vinegar Sample 2- Vinegar Sample 1Heinz (KIT) 10.05 g 10.00 g 10.05/1.005= 10mL Vinegar Sample 3 10.04 10.00/1.005= 9.5 mL 10.04/1.005= 9.99 mL Initial NaOH Volume in Syringe 9.0mL 9. 0 mL Final NaOH Volume in Syringe .3 mL .2 mL .4 mL 9.0 mL Volume of NaOH Delivered 8.7 mL 8.8 mL 8.6 mL Moles of NaOH Delivered .0087 mol .0088 mol .0086 mol Moles of Acetic Acid in Sample .0087 mol Mass of Acetic Acid in Sample (.0087/1)(60/1)= .552 g .0088 mol .0086 mol (.0088/1) (60/1)= .582g (.0086/1) (60/1)= .516 g Calculated Molarity of Acetic Acid in Vinegar .0087/18.75= .000464 M .0088/18.8= .000468 M .0086/18.64= .00463 M Calculated Percent Mass of Acetic Acid in Vinegar .552/10.05x100= 5.49% .582/10x100= 5.82% .516/10x100= 5.16 % Average Percent Mass of Acetic Acid in Vinegar 5.49+5.82+5.16/3= 5.49% Activity 2 - Titration of an Unknown Vinegar Sample with Sodium Hydroxide Activity 2 is an inquiry-based activity to demonstrate the learned technique of determining the acetic acid concentration in vinegar to a vinegar sample from your home. Each type of vinegar has a slightly different concentration of acetic acid. This activity requires the selection of a vinegar product from your home, a friend’s home, or a local restaurant. Only about a teaspoon of vinegar is needed. Attempt to find a different type of vinegar such as cider, malt, or balsamic vinegar. The vinegar included in this kit is white vinegar. Different brands of vinegar may also contain different amounts of acetic acid. Use the same procedure and the data table below to determine the acetic acid content in your vinegar sample. Upload a picture of you holding vinegar you chose to use in this activity. Be sure you are still wearing all your PPE. Name of Vinegar Sample- Rice Vingar Mass of Vinegar Calculated Volume of Vinegar Vinegar Sample 1 Vinegar Sample 2 9.48 g Vinegar Sample 3 9.57 g 9.48/1.005= 9.79 mL 9.54 g 9.57/1.005= 9.52 mL 9.54/1.005= 9.49 Initial NaOH Volume in Syringe 9.0 mL 9.0 mL 9.0 mL Final NaOH Volume in Syringe 1.2 1.5 1.3 Volume of NaOH Delivered 7.8 7.5 7.7 Moles of NaOH Delivered .0078 mol .0075 mol .0077 mol Moles of Acetic Acid in Sample .0078 mol Mass of Acetic Acid in Sample (.0078/1) (60/1)= .468 g .0075 mol .0077 mol (.0075/1) (60/1)= .45 g (.0077/1) (60/1)= .462 g Calculated Molarity of Acetic Acid in Vinegar .0078/17.28= .00451 M .0075/17.07= .00439 M .0077/17.24= .00406 M Calculated Percent Mass of Acetic Acid in Vinegar .468/9.48x100= 4.94 % .45/9.57x100= 4.70% .462/9.54x100= 4.84% Average Percent Mass of Acetic Acid in Vinegar 4.94+4.70+4.84/3= 4.82% Calculate the mass of NaOH required to make 0.40 L of a 0.50 M solution. Show all your work. .40L x (.5mol NaOH/1L) x (10 g NaOH/1 NaOH0)= 8.0 grams NaOH The Food and Drug Administration (FDA) mandates that all vinegar sold in the United States must have a minimum concentration of 4% acetic acid by mass. Calculate the minimum molarity of acetic acid in vinegar according to this standard. Assume the density of vinegar is the same as for water. 4%=4 grams mass= 100 grams density= mass/volume 1 g/ml = 100g/v V= 100 mL= .1 L moles of Acetic Acid- 4grams/60 g mol = .066 mol Molarity =.066 mol/.1 L = .66 Mol/L = answer List at least two possible sources of error from the experiment. Would these errors result in an overestimation or an underestimation of the concentration of acetic acid in the vinegar? one error could have been my measurements. if they were off then it would underestimate if I was under what my real value/ measurements were, but if I overestimated on my measurements then my numbers would be an overestimation. Another error could have been in the cleaning. I cleaned everything out 3 times, but if I didn't throughly clean it out the titration then the numbers could be off for my titration and then if there was more of the Phenolphthalein in the flask then my numbers would be off because I would have needed to use more drops than I had used and that is an underestimation.