ITC Final-Titration - Titration post lab PDF

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ITC-Titration

Katherine Mazella & Shyla Weller-Register

Introduction: The purpose of titration, both in general and for this specific experiment, is to determine the concentration of an unknown solution using the concentration of a known solution. The materials needed for general titration as well as this specific experiment are an acid, a base, an indicator, a buret, a stopcock, and a beaker. The titrant in titration is the known solution, which corresponds to the NaOH (base) in our specific experiment. An analyte in titration is the unknown solution, which corresponds to the vinegar (acid) in our specific experiment. An indicator in titration is the chemical that changes color to show when the endpoint of the titration is reached , which corresponds to the Turmeric in our specific experiment. An endpoint in titration is the point where the numbers of molecules in the reaction vessel match up perfectly [there is no excess of either chemical] , which corresponds to the reddish-orange color change in our specific experiment. The technique needing to be used along with the above materials is controlling the rate at which the titrant passes through the stopcock. The type of reaction being investigated in this experiment is an acid-base neutralization. The reagents utilized in this experiment are sodium hydroxide, and acetic acid. The purpose of sodium hydroxide is to act as the titrant, and the purpose of the acetic acid is to act as the analyte. Materials & Methods: The materials needed for this experiment are as follows: 15mL Acetic Acid(Vinegar), 30 mL of .5M NaOH solution, 5mL Turmeric Indicator, a 10 mL syringe, Two 100 mL beakers, Pipette, Test tube clamp, stopcock, Waste Container and two heavy items such as a textbook. The Methods used were as follows: Shyla poured the contents of the vinegar bottle into one of the 100 mL beakers. Shyla added approximately 4 mL vinegar to the other 100 mL beaker using a 10 mL syringe. Katherine recorded the actual volume to the nearest 0.05 mL under “Volume of Vinegar Used” in Data Table 2. Shyla added the 4 drops of indicator using a pipette to the 4 mL of vinegar in the 100 ml beaker and swirled it to distribute. Shyla removed the plunger and placed the stopcock onto the 10 mL syringe. Katherine arranged a work area to support the 10 mL syringe with attached stopcock directly above the 100 mL beaker. With plunger removed and the stopcock closed add slightly less than 10 mL of 0.500 M NaOH. Katherine recorded the starting volume to the nearest 0.05 mL in Data Table 1. Katherine then performed the acid-base titration through these simple steps: She added the base incrementally until she saw a fleeting color change when the base was added. She swirled the solution in the beaker constantly. After the color change she added the base dropwise until the solution being titrated turned reddish-orange at the addition of one drop. She recorded the amount of base, to nearest 0.05 mL, remaining in the syringe in Data Table 1. She calculated the “Moles of NaOH added” in Data Table 1, determined the “Moles CH3COOH neutralized” in Data Table2 , determined the “Concentration of CH3COOH in vinegar” using the “Moles CH3COOH neutralized” and “Volume of vinegar used (L).” Shyla then discarded the titrated solution from the Beaker into the waste container and rinsed the beaker as well as the pipette and the syringe. Shyla refilled the NaOH in the (buret) syringe. Katherine and Shyla repeated the titration at least two more times to obtain data from three successful trials. When they had completed 3 successful trials, they discarded the titration solution in the waste container. Then they discarded the excess base from the syringe into the waste container and cleaned and dried the syringe. Then they rinsed and dried all the equipment and capped the bottles tightly before placing them back in the large Ziplock for return.

ITC-Titration

Katherine Mazella & Shyla Weller-Register

Results: Molecular Formula: CH3COOH(aq)+ NaOH(aq) H2O(l)+ CH3COONa(aq) Complete Ionic Formula: Na+(aq) + OH-(aq) + CH3COOH(aq)CH3COO-(aq) + Na+(aq) + H2O(l)

ITC-Titration

Katherine Mazella & Shyla Weller-Register

Net Ionic Formula: OH-(aq) + CH3COOH(aq)  CH3COO-(aq) + H2O(l) Data Table 1-Amount of NaOH added Trial

Initial volume (mL)

Final volume (mL)

Change in volume (mL)

Moles of NaOH added (mol)

1

9.600

2.000

7.600

.0038

2

9.950

3.200

6.750

.0034

3

9.450

2.600

6.850

.0034

Data Table 2-Acetic acid in vinegar Trial

Moles CH COOH neutralized (mol)

Volume of vinegar used (mL)

3

Volume vinegar used (L)

Concentration of CH COOH in vinegar (M) 3

1

.0038

4.000

.0040

.9500

2

.0034

4.000

.0040

.8438

3

.0034

4.000

.0040

.8563

Data Table 3-Statistical analysis and comparison with “Typical” concentration of acetic acid in household vinegar Average concentration of CH COOH stock solution (M)

.8838

Standard deviation of concentration of CH COOH stock solution (M)

.0474

Acidity level (mass %) of acetic acid in typical household vinegar

5%

Concentration of acetic acid in typical household vinegar (M)

0.8351

Percent error*

5.831%

3

3

Discussion & Conclusion: The typical concentration of acetic acid in store bought vinegar is 4-8% by mass. Using the provided formulas and assuming a five percent concentration, we then calculated the molarity to be 0.8351. We had a 5.8% error, likely due to an error in titrating the solution or possible rounding errors, including assumptions for calculations. One main way to avoid or prevent the titration error is to go slower when titrating a solution to ensure maximum accuracy. One main way to avoid or prevent the rounding errors is to keep values in a calculator until a final answer is needed as well as keeping the number of significant figures consistent. If further investigations of this problem were to be conducted, they would entail more trials with possibly more vinegar to ensure that the ration of vinegar to one drop of the base could not cause this problem alone.

ITC-Titration

Katherine Mazella & Shyla Weller-Register

References:

“What Is a Titration.” What Is a Titration?, chemed.chem.purdue.edu/genchem/lab/techniques/titration/what.html Yool, Brooke. “What Is an Indicator for a Titration?” Sciencing, 2 Mar. 2019, sciencing.com/indicator-titration-6549531.html. “Titration.” www.chem.uiuc.edu/rogers/Text11/Tx115/tx115.html....