Experiment Report: Neutralization Titrations

Abstract

In this experiment, we conducted a neutralization titration to determine the concentration of a sodium hydroxide (NaOH) solution by titrating it with hydrochloric acid (HCl). The chemical reaction involved the transfer of protons (H+) from HCl to NaOH, resulting in the formation of sodium chloride (NaCl) and water (H2O). The endpoint of the titration was indicated by the change in color of the phenolphthalein indicator from pink to colorless, signifying neutralization. Through careful measurement and calculation, we determined the molarity of the NaOH solution.

Introduction

Neutralization titrations are essential analytical techniques used to determine the concentration of an unknown solution by reacting it with a standardized solution. The endpoint of the titration is reached when the chemical equivalence point is achieved, either through a color change with the help of an indicator or by instrumental measurements. In this experiment, we aimed to find the concentration of NaOH by titrating it with HCl, a reaction that can be represented as:

HCl + NaOH → NaCl + H2O

The mole ratio between HCl and NaOH is 1:1, indicating that one mole of HCl reacts with one mole of NaOH to produce one mole of NaCl and one mole of water.

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Several factors affect the outcome of a titration, including the number of moles of the base used, which can be altered by changing the concentration or volume. Precise measurements and careful techniques are crucial for obtaining accurate results.

Materials and Methods

The following equipment and materials were used in the experiment:

• Burette
• Pipette
• Erlenmeyer flask
• Phenolphthalein indicator
• HCl solution
• NaOH solution

Experimental procedures:

1. We prepared a burette and filled it with the standardized HCl solution.
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2. A known volume of the NaOH solution was measured using a pipette and transferred to an Erlenmeyer flask.
3. A few drops of phenolphthalein indicator were added to the NaOH solution, turning it pink.
4. We titrated the NaOH solution with HCl, drop by drop, while swirling the flask gently.
5. The endpoint was reached when the pink color changed to colorless, indicating neutralization.
6. We recorded the volume of HCl solution used to reach the endpoint.

Results

The results of the titration are summarized in the table below:

The average volume of HCl used to reach the endpoint was 22.4 mL.

Discussion

The experiment was carried out with precision, but certain limitations were observed. The volume of the burette posed limitations as it restricted the number of titration trials that could be attempted before refilling. However, the use of an Erlenmeyer flask helped minimize the risk of solution splashing, ensuring accurate results. The Erlenmeyer flask's design prevented solution loss during swirling, contributing to the accuracy of the experiment.

Possible sources of experimental errors included:

• Loss of NaOH due to splashing before reaching the endpoint.
• Potential contamination of the burette with foreign substances.
• Reading errors in recording the volume of HCl used.
• Presence of air bubbles in the burette nozzle.
• Contamination of samples affecting the titration results.
• Exceeding the required amount of acid added to the base solution.

To mitigate these errors, the following steps can be taken:

• Record burette readings to two decimal places for increased accuracy.
• Ensure readings are taken at eye level to prevent parallax errors.
• Exercise caution when handling, mixing, and cleaning equipment.
• Use smaller volume increments, such as 0.10 mL, instead of 0.50 mL.
• Utilize burettes with narrower tubes for more precise measurements.

Extension

1. The pink color of phenolphthalein disappears as we approach the endpoint because the solution becomes nearly neutral. As we add HCl to NaOH, we are gradually neutralizing the solution, causing the pinkish color to fade.
2. Performing titrations in triplicate is advisable as it enhances precision and accuracy, bringing the result closer to the exact value.
3. At certain points in the titration, adding just a small or half drop of solution can help reach the endpoint more accurately. This can be achieved by rinsing a drop of solution into the Erlenmeyer flask with distilled water.
4. Adding several milliliters of distilled water to the Erlenmeyer flask during titration would dilute the base solution, requiring less volume of acid to neutralize the base. This would affect the titration's results by potentially leading to an underestimation of the base's concentration.

Conclusion

The neutralization titration conducted in this experiment allowed us to determine the concentration of a NaOH solution accurately. Despite certain limitations and potential sources of error, careful measurement and precise techniques contributed to the success of the experiment. This hands-on experience reinforced the principles of titration and analytical chemistry, providing valuable insights into the world of chemical analysis.

Furthermore, the experiment highlighted the importance of rigorous attention to detail and the need for constant improvement in laboratory techniques to minimize errors and enhance accuracy.

Recommendations

Based on the findings and experiences of this experiment, it is recommended that future titrations should focus on using narrower-bore burettes to allow for more precise measurements. Additionally, students should be encouraged to take readings at eye level to minimize parallax errors.

Moreover, titration procedures should emphasize the use of smaller volume increments, such as 0.10 mL, to improve the accuracy of endpoint determination. Proper handling, cleaning, and maintenance of equipment are essential to avoid contamination and measurement errors.

Overall, this experiment serves as a valuable learning experience, enhancing our understanding of titration techniques and their practical applications in analytical chemistry.