EXP 9 and 10 Volumetric and Vinegar Analysis Lab Report.docx PDF

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Experiment 9 & 10: Volumetric and Vinegar Analysis (On-Campus Lab)

Exp. 9&10: Volumetric and Vinegar Analysis Ernesto Marin, Carrie Alcinord, Dylan Razack General Chemistry I (D06) Professor Richard H. Perry Laboratory Assistant: Skyler 10 - 04 - 2021

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Hypothesis Based on knowledge of household vinegar, the percent of acetic acid in vinegar should be between 4 and 5 percent if the experiment is conducted properly.

Abstract The purpose of the experiment is to prepare and standardize a sodium hydroxide solution, and to determine the molar concentration of a strong acid. The objective of this lab is to find and calculate the concentration of a strong base, percent by mass of an acetic acid in vinegar, and learn the titration technique. Experiment 9 focuses on volumetric analysis.

Introduction For this experiment, a volumetric analysis is used. Volumetric analysis is a chemical analysis that is performed primarily with the aid of volumetric glassware. (for example: pipette, burets, and volumetric flasks). For this analysis, a known quantity or a carefully measured amount of one substance reacts with a to-be-determined amount of another substance with the reaction occurring in an aqueous solution. The known amount of the substance for an analysis is generally measured and available in two ways: as a primary standard, or a standard solution. The method of this experiment requires a titration procedure. With the titration procedure, the reaction of the known substance with the substance to be analyzed, will occur in an aqueous solution. A volumetric analysis is usually conducted by titration. A titrant is a liquid that fills the burets and will dispense itself into a flask that contains an analyte with an indicator to help observe changes in pH levels. The change in the color of the indicator is called the endpoint. Phenolphthalein has no color when

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it is in an acidic solution and turns pink when the solution is basic. Dry potassium hydrogen phthalate is used as the primary acid standard to find the molar concentration of sodium hydroxide. The sodium hydroxide solution will then be called a secondary standard solution.

Procedure For experiment 9, an NaOH solution is prepared with a concentration. A more accurate molar concentration of the NaOH solution, which is the titrant, is determined using dry potassium hydrogen phthalate as a primary standard. For experiment 9, three clean 125-mL Erlenmeyer flaks for the titration. The first step is to dry the primary standard acid for several hours in a constant-temperature drying oven. After, 0.15 M of NaOH solution is needed. First, a 500-mL polyethylene bottle will need to be filled with 1/3 of deionized water cooled to room temperature. Afterwards, solid NaOH is added to the 500-mL polyethylene bottle. It is crucial to swirl the solution, rather than to shake. Finally, dilute the volume to ~500mL with the previously deionized water. Once the 0.15 M of NaOH solution is prepared, the primary standard acid is needed and this can be prepared by first calculating the mass of KHC8H4O4 which requires 1020 mL of the previously NaOH solution in order to reach the stoichiometric point. After, measure the mass on a tared piece of weighing paper and transfer to a clean, labeled flask. The next step in the procedure for experiment 9 is to prepare a clean buret and fill it with the NaOH solution and record its volume after 10 seconds. The last and most fundamental step in this procedure is to add the titrate the primary standard acid. Slowly add the NaOH titrant to the first acid sample. Swirl the flask after each addition, every so often. As the stoichiometric point nears, the solution will fade a light pink and this will indicate the endpoint of the titration. After the color persist for

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30 seconds, read and record the final volume of NaOH in the buret. To prepare and determine the unknown acidic concentration, collect a 125- or 250- mL flask and pipet 25.00 mL of acid solution and add two drops of phenolphthalein. Next, fill the buret with the standardized NaOH solution and after 10-15 seconds, read and record the initial volume. Titrate the acid sample to the phenolphthalein endpoint and record the final volume of titrant. Do this process for the second trial. For experiment 10, the procedure has a direct correlation to the procedure of experiment 9. To start the procedure for experiment 10, first the volume of vinegar is needed followed by preparing the vinegar sample. To prepare the vinegar sample, add the vinegar volume found previously and add two drops of phenolphthalein and rinse the walls of the flask with 20 mL of previously boiled, deionized water. Once this is complete, prepare the buret and titration set up. Rinse twice a 50- mL buret with the NaOH solution, and fill the buret with the standardized NaOH solution, and after 10-15 seconds, read and record the initial volume. To titrate the vinegar sample, slowly add the NaOH solution from the buret to the acid, swirling the flask after each addition, like it was done in experiment 9. Continue adding the NaOH titrant until the endpoint is reached. After 10 seconds, read and record the final volume.

Materials and Methods Please refer to Experiment 9 on pages 133-140 of Laboratory Manual for Principles of General Chemistry by J. A. Beran (10 th Ed.). 1. Deviation: two trials were done instead of three

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Results/Data Table 1: Standardization of a sodium hydroxide Solution through titration

Table 2: Volumetric analysis of a vinegar sample to find percentage of Acetic Acid

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Calculations Experiment 9: A3 Moles of KHC8H4O4 0.603 𝑔 𝐾𝐻𝐶 𝐻 𝑂 8

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204.22 𝑔/𝑚𝑜𝑙 𝐾𝐻𝐶 𝐻 𝑂 8

= 2. 95 * 10

−3

4 4

𝑚𝑜𝑙𝑒𝑠 𝐾𝐻𝐶8𝐻4𝑂4

A6 Volume of NaOH dispensed 17. 58 𝑚𝐿 𝑁𝑎𝑂𝐻 − 0. 37 𝑚𝐿 𝑁𝑎𝑂𝐻 = 17. 21 𝑚𝐿 𝑁𝑎𝑂𝐻 A7 Molar concentration of NaOH 3

𝑚𝑜𝑙𝑒𝑠 𝑁𝑎𝑂𝐻 = 𝑚𝑜𝑙𝑒𝑠 𝐾𝐻𝐶8𝐻4𝑂4 = 2. 95 * 10 𝑚𝑜𝑙𝑒𝑠 𝑁𝑎𝑂𝐻 3

2.95*10 𝑚𝑜𝑙𝑒𝑠 𝑁𝑎𝑂𝐻 17.21 𝑚𝐿 𝑁𝑎𝑂𝐻 * 0.001𝐿/𝑚𝐿

= 0. 1716 𝑚𝑜𝑙/𝐿 𝑁𝑎𝑂𝐻

A8 Average molar concentration of NaOH 0.1716 𝑚𝑜𝑙/𝐿 𝑁𝑎𝑂𝐻 + 0.1162 𝑚𝑜𝑙/𝐿 𝑁𝑎𝑂𝐻 2

= 0. 1439 𝑚𝑜𝑙/𝐿 𝑁𝑎𝑂𝐻

Experiment 10: A3 Mass of vinegar 90. 873 𝑔 − 81. 261 𝑔 = 9. 612 𝑔 B3 Volume of NaOH used 28. 34 𝑚𝐿 𝑁𝑎𝑂𝐻 − 13. 56 𝑚𝐿 𝑁𝑎𝑂𝐻 = 14. 78 𝑚𝐿 𝑁𝑎𝑂𝐻 B5 Moles of NaOH added 14. 78 𝑚𝐿 𝑁𝑎𝑂𝐻 * 0. 001 𝐿/𝑚𝐿 * 0. 1439 𝑚𝑜𝑙/𝐿 𝑁𝑎𝑂𝐻 = 2. 127 * 10 B6 Moles of CH3COOH in vinegar 𝑚𝑜𝑙𝑒𝑠 𝐶𝐻 𝐶𝑂𝑂𝐻 = 𝑚𝑜𝑙𝑒𝑠 𝑁𝑎𝑂𝐻 = 2. 127 * 10 3

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−3

𝑚𝑜𝑙𝑒𝑠 𝐶𝐻 𝐶𝑂𝑂𝐻 3

−3

𝑚𝑜𝑙𝑒𝑠 𝑁𝑎𝑂𝐻

B7 Mass of CH3COOH in vinegar 2. 127 * 10

−3

𝑚𝑜𝑙𝑒𝑠 𝐶𝐻3𝐶𝑂𝑂𝐻 * 60. 05 𝑔/𝑚𝑜𝑙 𝐶𝐻3𝐶𝑂𝑂𝐻 = 0. 1277 𝑔 𝐶𝐻3𝐶𝑂𝑂𝐻

B8 Percent by mass of CH3COOH in vinegar 0.1277 𝑔 𝐶𝐻 𝐶𝑂𝑂𝐻 3

9.612 𝑔 𝑣𝑖𝑛𝑒𝑔𝑎𝑟

* 100% = 1. 329% 𝐶𝐻3𝐶𝑂𝑂𝐻

Results and Discussion The purpose of this experiment was to be able to standardize the sodium in a NaOH solution. The molar concentration of a strong acid was determined throughout this experiment. In order to conduct these direct-related experiment, gravimetric analysis and volumetric analysis was necessary with the use of titration. In experiment 9, it was heavily focused on the KHC8H4O4. In experiment 10, the unknown substance, “Solar”, was used to determine the percent mass of acetic acid (CH3COOH) in vinegar.

This experiment was executed to determine the molar concentration of NaOH and the average percent by mass of acetic acid in unknown solution, “Solar”, using titration analysis. As we know, titration analysis is the process of chemical analysis that is performed primarily with the help of volumetric glassware like pipettes, burets and volumetric flaks. For a volumetric analysis procedure, a known quality or a carefully measured amount of one substance reacts with a to-be-determined amount of another substance with the reaction occurring in aqueous solution. For the acid-based titration studied in experiment 9, the titrant is a standard solution for sodium hydroxide analyte is KCH8H404. In experiment 10, the titrant is a standard solution of sodium hydroxide. The reaction is complete when the stoichiometric amounts of the reacting substances 7

are combined. In a titration, this is the stoichiometric point. In both experiment 9 and 10, the stoichiometric point for the acid-base titration is detected using a phenolphthalein indicator. In experiment 9, the sodium hydroxide solution was standardized with potassium hydrogen phthalate (KCH8H4O4) which is a white, crystalline, acidic sloid, which contains the properties of a primary solution and this is due to its high acidic status. In our experiment, we looked at different aspect with CH3COOH. We determined that the volume of the reactant was 14.78 mL, causing for the moles of NaOH added result in 0.00213 mol. Next, we determined the moles and mass of CH3COOH in vinegar since experiment 10 had us working with vinegar. Once calculated, the moles of CH3COOH were equal to the moles of NaOH added, 0.00213 moles. This is due to the 1:1 mole ratio within the experiment. Knowing the moles of CH3COOH within the vinegar, we were able to calculate the mass of CH3COOH which resulted in 0.128 g. By our results, we are able to see that CH3COOH does not weigh much. Moving to finding the percent mass and average mass, we were able to calculate it once the moles and mass of CH3COOH was found. We calculated the percent by mass of CH3COOH within the vinegar to be 1.33 % and the average percent by mass of CH3COOH to be 1.22%. There is not much difference in values from the individual percent by mass and the average percent by mass. This may be due to a mechanical error within the percent. Conclusions One error that occurred was during trial two of exp 9: too much NaOH was dispensed from the buret, this might have led to a lower molar concentration of NaOH in trial two, and thereby a lower average molar concentration. The results of the experiment was that we found the “solar” vinegar to have a composition of about 1.2185 percent acetic acid. This does not

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support our hypothesis, which was that the vinegar would contain about 4 to 5 percent acetic acid. Even accounting for the error made in experiment 9, the percentage acetic acid in the vinegar is much lower than expected. References Laboratory Manual for Principles of General Chemistry by J. A. Beran (10 th Ed.) pgs. 133-149

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