Example Of Chem Lab Report

The Comprehensive Guide to Writing a Chemistry Lab Report: An Example and Explanation

Writing a clear and concise chemistry lab report is a crucial skill for any student. It's more than just recording your results; it's about demonstrating your understanding of the experiment, the underlying scientific principles, and your ability to analyze data and draw conclusions. This comprehensive guide provides a detailed example of a chemistry lab report, along with explanations for each section to help you master this important skill. We'll cover everything from the abstract to the discussion, ensuring you can confidently write your own reports.

I. Title: Determining the Molar Mass of an Unknown Volatile Liquid Using the Dumas Method

This title is clear, concise, and accurately reflects the experiment's purpose. It includes the key experimental technique (Dumas method) and the objective (determining molar mass).

II. Abstract

The abstract is a brief summary of the entire report (approximately 150-200 words). It should concisely state the purpose of the experiment, the methods used, the key results, and the conclusions drawn.

Example Abstract:

This experiment employed the Dumas method to determine the molar mass of an unknown volatile liquid. A sample of the unknown liquid was vaporized in a flask of known volume at a known temperature and pressure. The mass of the condensed vapor was then determined. Using the Ideal Gas Law (PV = nRT), the number of moles of the vapor was calculated. The molar mass was subsequently calculated by dividing the mass of the vapor by the number of moles. The experimentally determined molar mass was found to be 72.5 g/mol with a percent error of 3.8% compared to the literature value. This indicates a reasonable level of accuracy in the experimental procedure and data analysis. Sources of error and potential improvements to the experimental design are discussed.

III. Introduction

The introduction provides background information on the experiment's theoretical basis. It should explain the scientific principles involved and the purpose of the experiment. It should also briefly introduce the experimental method used.

Example Introduction:

The determination of molar mass is a fundamental concept in chemistry. Knowing the molar mass of a substance is crucial for various applications, including stoichiometric calculations, determining empirical and molecular formulas, and understanding the properties of molecules. Several methods exist for determining molar mass, including mass spectrometry and osmometry. This experiment utilizes the Dumas method, a classic technique for determining the molar mass of volatile liquids. The Dumas method relies on the Ideal Gas Law (PV = nRT), where P is pressure, V is volume, n is the number of moles, R is the ideal gas constant, and T is temperature. By measuring the mass, volume, temperature, and pressure of a vaporized sample, the number of moles can be calculated, and subsequently the molar mass. The objective of this experiment is to determine the molar mass of an unknown volatile liquid using this method and compare it to the literature value to assess the accuracy of the experiment.

IV. Materials and Methods

This section details the materials used and the step-by-step procedure followed. It should be written clearly and concisely, allowing another researcher to replicate the experiment.

Example Materials and Methods:

Materials:

• Unknown volatile liquid
• 125 mL Erlenmeyer flask
• Aluminum foil
• Rubber band
• Beaker
• Hot water bath
• Analytical balance
• Thermometer
• Barometer

Procedure:

1. Clean and dry a 125 mL Erlenmeyer flask and weigh it accurately using an analytical balance (mass 1).
2. Add approximately 5 mL of the unknown volatile liquid to the flask.
3. Cover the flask with aluminum foil, securing it tightly with a rubber band. Puncture a small hole in the foil to allow for vapor escape.
4. Carefully heat the flask in a boiling water bath until all the liquid has vaporized. Maintain the water bath temperature for at least 10 minutes to ensure equilibrium.
5. Remove the flask from the water bath and allow it to cool to room temperature. Carefully remove the foil.
6. Weigh the flask and its contents (mass 2).
7. Record the atmospheric pressure (P) using a barometer, the temperature (T) of the boiling water bath, and the volume (V) of the flask (determined by filling the flask with water and measuring the volume).

V. Results

This section presents the raw data collected during the experiment. This should include tables and/or graphs to clearly display the data. Calculations and relevant equations should also be shown here.

Example Results:

Table 1: Experimental Data

Calculations:

• Convert units: Convert temperature to Kelvin (T = 98.5 °C + 273.15 = 371.65 K), pressure to atmospheres (P = 762 mmHg * (1 atm/760 mmHg) = 1.003 atm), and volume to liters (V = 125 mL * (1 L/1000 mL) = 0.125 L).
• Calculate the number of moles (n): Using the Ideal Gas Law, PV = nRT, where R = 0.0821 L·atm/mol·K: n = PV/RT = (1.003 atm * 0.125 L) / (0.0821 L·atm/mol·K * 371.65 K) = 0.00410 moles
• Calculate the molar mass (M): M = mass/moles = 0.444 g / 0.00410 moles = 108.3 g/mol

VI. Discussion

This is the most crucial part of the lab report. Here, you analyze your results, explain any discrepancies, and discuss potential sources of error. You should also compare your results to literature values and discuss the implications of your findings.

Example Discussion:

The experimentally determined molar mass of the unknown volatile liquid was found to be 108.3 g/mol. This value differs from the expected value (assume the literature value is 112 g/mol for this example). This results in a percent error calculation of [(112-108.3)/112]*100% = 3.3%. The relatively small percent error suggests that the experiment was performed with reasonable accuracy.

Several sources of error could contribute to the discrepancy. One potential source is the incomplete vaporization of the liquid. If some liquid remained uncondensed, it would lead to an underestimation of the molar mass. Another source of error could be the small hole in the foil. If the hole was too large, some vapor might escape before being weighed, resulting in an underestimate of the molar mass. Conversely, if the hole was too small, there may have been issues with pressure equalization.

The accuracy of the barometer and thermometer readings also influence the results. Small inaccuracies in these measurements could propagate through the calculations, affecting the final molar mass. The purity of the unknown liquid is another important factor. Impurities could affect the measured mass and subsequently the calculated molar mass.

Future improvements could include using a larger flask to minimize the impact of error in volume measurement and ensuring complete vaporization by extending the heating time. Furthermore, using a more precise pressure gauge and thermometer could reduce uncertainties in those measurements. Careful attention to sealing the flask would also minimize vapor loss.

VII. Conclusion

The conclusion briefly summarizes the key findings and their implications. It restates the purpose of the experiment and states whether the objectives were achieved.

Example Conclusion:

This experiment successfully utilized the Dumas method to determine the molar mass of an unknown volatile liquid. The experimentally determined molar mass of 108.3 g/mol showed a reasonable degree of accuracy compared to the literature value, although some discrepancies were observed and attributed to potential sources of error, such as incomplete vaporization and limitations in measurement accuracy. The experiment reinforced the understanding of the Ideal Gas Law and the principles involved in determining molar mass. Future improvements to the experimental design are suggested to improve the accuracy and precision of the results.

VIII. References (if applicable)

If you used any external sources (textbooks, articles, etc.), list them here in a consistent format (e.g., APA, MLA). For this example, references are not necessary as the experiment is a standard procedure.

IX. Appendix (if applicable)

Any supplementary materials, such as raw data tables or calibration curves, can be included in the appendix. For this example, the detailed data is already included in the Results section, so an Appendix is not needed.

This detailed example provides a solid framework for writing a comprehensive chemistry lab report. Remember that clarity, accuracy, and a logical flow are key to a successful report. By following these guidelines and using this example as a template, you can confidently approach your future lab report writing assignments. Remember to always adapt these guidelines to the specifics of your individual experiment. The key is clear communication of your methodology, results, and interpretation.