Final Report (vinegar Analysis)gpo-1.docx

CM011L: CHEMISTRY FOR ENGINEERS (LABORATORY) 3rd Quarter SY 2018-2019

Experiment No.1 Vinegar Analysis

Glennmar P. Otilla CM011L-B16

Department of Chemical, Biological, and Materials Engineering and Sciences Mapua University

ABSTRACT Vinegar is a common household ingredient which is about 4-5% acetic acid by mass. The experiment was conducted to determine the percent by mass of acetic acid in household vinegar (marca pina) using Titration technique. A technique in which the base (NaOH) the titrant, is added to the acid (vinegar sample) the analyte, with phenolphthalein (dye) which is an indicator, that changes color as a solution changes from having excess of acid or excess of base, or vice versa, and deionized water which is (previously boiled). On the first trial, fourteen point six (14.6) mL of sodium hydroxide (base) was used, resulting to 2.96% acetic acid in the vinegar sample. On the second trial, the amount of NaOH solution used was increased to fifteen point five (15.5) mL, resulting to an increased in percent (3.14%) which is because on the excessive water on the Erlenmeyer flask when it is washed after the first trial. The average percent by mass of acetic

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CM011L: CHEMISTRY FOR ENGINEERS (LABORATORY) 3rd Quarter SY 2018-2019

acid is 3.05% which is almost 1% lower than of usual. The reason behind is that the base has a lower concentration and the acid has a lower volume used in the experiment. When the concentration of the base is low, and the volume of the acid used is small, the percent by mass of acetic acid is lower than usual. And when the volume of the acid used is high, and the concentration of the titrant is also high, then the calculated percent of acetic acid in vinegar is also high than usual. Therefore, the molarity of the base and the volume of the acid use will affect the percent by mass of acetic acid in vinegar. And the vinegar sample (marca pina) has a lower percent of acetic acid by mass. INTRODUCTION Household vinegar is about 4-5% acetic acid by mass. A volumetric analysis or titration technique which is a common laboratory method that is used in determining the percent by mass of acetic acid in vinegar. Acid-base titration is important in counting concentration of acids and bases. The equivalence point in an acid-base titration is the point where the moles of the hydrogen ions (acid) is equal to the number of moles of the (base) or the hydroxide ions (Kotz and Purcell, 1987, p. 132). The point at which the equivalence point has been reached is called the theoretical endpoint. The titration is detected by some physical changes such as color change, to indicate the endpoint. By adding sodium hydroxide (NaOH) which is a basic solution, to the vinegar sample (Marca Pina), which is an acidic solution, a neutralization process occurs. An indicator known as phenolphthalein is also added to the vinegar. This indicator turns the solution to dark pink when more NaOH (base) is added to make the solution more basic. Thus, when the solution turns into persistent light pink, it indicates that the solution has been neutralized or the endpoint of titration is reached. The amount of NaOH used to standardize the vinegar can be used in determining the amount of acetic acid in vinegar as they are both at a 1:1 ratio as seen from the balanced equation.

ions in solution. In titration, standard solutions are now usually expressed in molarity (M). Molarity is the calculations of the concentration of a solution. This experiment is conducted to determine the percent by mass of acetic acid in household vinegar. MATERIALS AND METHODOLOGY List of Apparatus. 10-mL graduated cylinder, 50-mL graduated cylinder, 250-ml Erlenmeyer flask, 100-ml beaker, 25-mL hybrid burette, iron stand, burette clamp, and funnel. List of chemicals. 40 mL deionized water, 6 mL vinegar sample, 4 drops of phenolphthalein, 50 ml 0.1013 M NaOH, Titration setup. Approximately five (5) mL of standardized NaOH solution were added to the burette to clean its wall making sure that there is no certain drops cling inside the wall. Then the burette is clamped into the iron stand and filled with 0.1013 M NaOH solution using a 50-mL graduated cylinder to eliminate all air or bubbles in the burette. Excess NaOH solution is set aside in a 100-mL beaker. After ten to fifteen (10-15) seconds, the initial volume is read. (See Figure 1).

𝐶𝐻3𝑂𝑂𝐻(𝑎𝑞)+𝑁𝑎𝑂𝐻(𝑎𝑞)→𝐶𝐻3𝑂𝑂𝐻𝑁𝑎(𝑎𝑞)+𝐻2𝑂

The acid and base titrations used the Arrhenius theory. This theory stated that acid are substance which produce hydrogen ions in solution and bases are substance which produce hydroxide

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CM011L: CHEMISTRY FOR ENGINEERS (LABORATORY) 3rd Quarter SY 2018-2019

Preparing the Vinegar sample. Using a 10-mL graduated cylinder, three (3) mL of vinegar sample (Marca Pina) is introduced into a clean dry 250-mL Erlenmeyer flask. Then two (2) drops of phenolphthalein is added, and a twenty (20) mL of deionized water is combined to rinse the wall of the flask. (See figure 2).

Figure 2. Preparing the vinegar sample

Titrating the vinegar. A sheet of white paper beneath the flask is added to better see the changes in color. The NaOH solution from the burette is slowly added to the Vinegar sample, while swirling the flask during the addition until the endpoint is reached.

Figure 3. Titrating the vinegar

Repeat with the same vinegar. Refill the burette and repeat the titration once more with another sample of the same vinegar. Waste disposal. All test solutions and the NaOH solution in the burette can be discarded in the wastes bases container. Clean Up. The burette is rinse with a plenty of tap water and then with deionized water, discarding each rinse through the burette into the sink. Similarly rinse the flask and returned it dry.

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CM011L: CHEMISTRY FOR ENGINEERS (LABORATORY) 3rd Quarter SY 2018-2019

PRELIMINARY DATA SHEET

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CM011L: CHEMISTRY FOR ENGINEERS (LABORATORY) 3rd Quarter SY 2018-2019

FINAL DATA SHEET

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CM011L: CHEMISTRY FOR ENGINEERS (LABORATORY) 3rd Quarter SY 2018-2019

LABORATORY QUESTIONS AND ANSWERS Circle the questions that have been assigned. 1. Part A.2. A 20-ml volume of previously boiled, deionized water is added to the Erlenmeyer flask to prepare the sample for titration. Explain why these volume is not critical to the analysis. Because the volume of the vinegar which is too low (3ml) which indicates that a 20 ml of water is enough in the analysis of the percent of acetic acid of vinegar. The addition of a base (NaOH) which will not be too much in volume to the solution of water and vinegar will be the reason to neutralize the solution. Therefore a 20-ml deionized water is not critical for the analysis.

2. Part A.2.Previously boiled, deionized is unavailable. In a hurry to pursue the analysis, deionized water (not boiled) is added. How does this attempt to expedite the analysis effect the reported percent of acetic acid in vinegar: too high too low, or unaffected? Explain. Due to the addition of deionized water (not boiled) which we use in the experiment, it remains unaffected even though the result is too low, from the 4-5% acetic in vinegar, it is because the base (NaOH) has a lower concentration which will affect the number of moles of the acid that eventually be useful in determining the percent of acetic acid in vinegar. 3. Part A.2.and B.1. The 20-ml of water added to the Erlenmeyer flask is to be previously boiled, deionized water. Since water does absorbed C02 from the atmosphere and since CO2 dissolved in water causes it to be slightly acidic, will the use of deionized water that has not been previously boiled cause the mass of acetic

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CM011L: CHEMISTRY FOR ENGINEERS (LABORATORY) 3rd Quarter SY 2018-2019

acid in the vinegar to be calculated as too high or too low? Explain. Water absorbed carbon dioxide from the atmosphere and it will become slightly acidic which will cause on the result as too high in the reported percent acetic acid in vinegar because water should have a pH of 7. So when neutralized water is added to the vinegar sample, and then the base is added on it will become neutralize, but when water become slightly acidic, it will take more base to be added in order to neutralize the solution, that will eventually result on high percent of acetic acid in the vinegar on the calculations. 4. Part A.2. a.) In determining the percent acetic acid in vinegar, the mass of each vinegar sample is measured rather the volume. Explain. Because the mass of vinegar will be useful in determining the percent by mass of 6. decrease, or have no effect on the reported percent acetic acid in the vinegar? Explain. For example, if a chemist read immediately the initial volume at 0ml, then while preparing 20 ml of water, there is an amount of NaOH dripped from the burette, so it is not exactly at 0ml, during titration process, its final volume of the titrant use will increased. It is a good technique to wait for about 10-15 seconds before reading the Initial volume just because there is some flowing of fluid on the burette or the fluid is not still. Error to comply in this technique will affect the calculations of percent of acetic acid in vinegar. 7. Part B.1. The endpoint of the titration is overshot! Does this technique result in an increase, a decrease, or have no effect on the reported percent acetic acid in vinegar? Explain. During titration process, the analyte changes its color into light pink, due to the addition

acetic acid in vinegar with the formula: mass of acetic acid (g)/mass of vinegar (g)* 100= Percent by mass of acetic acid. b.) If the vinegar is measured volumetrically (e.g., pipet).What additional piece of data would be needed to complete the calculations for the experiment? The additional piece of data that will be helpful in the calculations on the experiment is the density of the vinegar which will be helpful in converting grams to mL, because density=g/ml. So given the volumetric measure of vinegar, and the density of the vinegar we can now get the mass in grams of the vinegar. 5. Part A.3. The burette is filled with NaOH titrant in the initial volume reading is immediately recorded without waiting the recommended 10-15 seconds. However, in Part B.1., the 10-15 seconds time lapse does occur before the reading is made. Thus this technique error result in an increase, a of the titrant. Persistent light pink indicates that the endpoint of titration is reached. But when you add even a small drop of titrant it will become dark pink which means that it is over titrated that will make the solution more basic, resulting in an increase on the percent of acetic acid compare on the reported percent of acetic acid which is about 45%.This is also an indicator that the chemist should do it all again from the beginning. 8. Part B.1. The wall of the flask is periodically rinse with the previously boiled, deionized water from the wash bottle. Does this titrimetric technique result in an increase, a decrease, or have no effect on the reported percent acetic acid in vinegar? Explain. When the titration end in the first trial. The neutralized solution is dispose into the sink with a plenty of water, then the Erlenmeyer flask is wash with water. Therefore, during the second trial it is not exactly 20ml of water is added into the flask because there is an amount of water that is

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CM011L: CHEMISTRY FOR ENGINEERS (LABORATORY) 3rd Quarter SY 2018-2019

present on the flask after it is being washed on the first trial. It will result in an increase percent of acetic acid in vinegar. 9. Part B.1. A drop of NaOH titrant, dispensed from the burette, adheres to the wall of the Erlenmeyer flask but is not washed into the vinegar with a wash bottle. Does this error in technique result in the reported percent of acetic acid being too high, too low, or unaffected? Explain. The percent of acetic acid in vinegar will result as too high because when the a drop of titrant will touch the wall of the Erlenmeyer flask, it will take too much time to flow down to the solution which will indicate that when the chemist read the volume of NaOH (titrant) used will increase than usual. Therefore, it is advice not to let the titrant touch the wall of the Erlenmeyer flask for better reading and computations.

(Trial 1)

(Trial 2)

As can be gleaned on the result, the NaOH solution used in the second trial was increased due to the excessive water in the Erlenmeyer flask when washed after the first trial. This indicates that the water used is not exactly 20-mL and it is a combination of tap and deionized water which resulting to more base to be added. The percent by mass of acetic acid is lower compare to the said percent (about 4-5%), the reason behind is that the base (NaOH) has lower concentration and that the acid (vinegar sample) is not too much acidic compare to the other brand. CONCLUSION

RESULTS During the first trial (left), a persistent pink color is achieved. Approximately fourteen point six (14.6) mL of 0.1013 M NaOH solution was used to neutralized the vinegar sample(Marca Pina), which then result to 2.96% of acetic acid in vinegar. While on the second trial (right), the endpoint of titration is reached with fifteen and a half (15.5) mL of the base (NaOH) solution is added to the sample, which result to 3.14% of acetic acid in vinegar. In general, the two trials is averaging 3.05% of acetic acid in the vinegar which is almost 1% low from the said 4-5% by mass of acetic acid of household vinegar (See reference).

The experiment was conducted to determine the percent by mass of acetic acid in household vinegar which is about 45% acetic acid by mass. But the results is seemly lower than usual which is about 3.05% by mass of acetic acid in average. When the base has lower concentration, and the vinegar sample used in the experiment is in small amount, the result is also lower than usual, and when the concentration is higher, then the sample is also increase in volume, the result will be much higher than usual. Therefore, the percent by mass of acetic acid in vinegar depends on the concentration of the base and the volume of the acid used. And the vinegar sample (marca pina) has lower percent of acetic acid by mass.

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CM011L: CHEMISTRY FOR ENGINEERS (LABORATORY) 3rd Quarter SY 2018-2019

REFERENCES

•

Books Beran, J. (n.d.). Laboratory manual For Principles of General Chemistry

Kotz, J. C., & Purcell, K. F. (1987). Chemistry amd Chemical Reactivity. Philadelphia: Saunders College Publishing, The Dryden Press . • Online Website (n.d.). Retrieved from https://www.google.com.ph/amp/s/school workhelper.net/titration-of-vinegar-labanswers/amp/ (n.d.). Retrieved from https://www.slideshare.net/mobile/AsyhS yiedah/chemistry-report-final (n.d.). Retrieved from https://archive.org/stream/TitrationLab/Ti trationLab_djvu.txt. (n.d.). Retrieved from https://www.bartleby.com/essay/Chemistr yAcid-base-Titration-F3DZXYYTJ.

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