Lab Write Up Example Chemistry

The Ultimate Guide to Writing a Chemistry Lab Report: A Comprehensive Example

Writing a comprehensive chemistry lab report can seem daunting, especially for beginners. However, with a structured approach and a clear understanding of the key components, crafting a high-quality report becomes manageable and even enjoyable. This guide provides a complete example of a chemistry lab report, walking you through each section with detailed explanations and tips to help you excel in your chemistry studies. We'll cover everything from the abstract to the discussion, ensuring you understand the importance of each section and how to write effectively for a scientific audience.

Introduction: Understanding the Purpose of a Lab Report

The primary purpose of a chemistry lab report is to communicate your experimental findings clearly and concisely to others. It’s a formal record of your scientific investigation, allowing others to understand your methods, results, and conclusions. A well-written report demonstrates not only your experimental skills but also your understanding of the underlying chemical principles. This report should be written in a professional and objective manner, avoiding subjective opinions or personal biases. Keywords frequently used in chemistry lab reports include experimental design, data analysis, error analysis, chemical reactions, stoichiometry, spectroscopy, and titration.

Example Lab Report: Determination of the Molar Mass of a Volatile Liquid

This example focuses on a common experiment: determining the molar mass of a volatile liquid using the ideal gas law. This experiment involves measuring the mass and volume of a volatile liquid vaporized in a flask, allowing the calculation of molar mass using the ideal gas equation (PV = nRT).

1. Title: Determination of the Molar Mass of an Unknown Volatile Liquid

The title should be concise and clearly state the purpose of the experiment.

2. Abstract: A Concise Summary of the Experiment

The abstract is a brief summary of the entire report (typically 150-200 words). It should include:

• The purpose of the experiment: To determine the molar mass of an unknown volatile liquid.
• A brief description of the methodology: The ideal gas law was used to calculate the molar mass. The volatile liquid was vaporized in a flask, and its mass, volume, temperature, and pressure were measured.
• Key results: The experimental molar mass of the unknown volatile liquid was determined to be [insert your calculated value] g/mol.
• Major conclusions: The experimental molar mass is comparable/significantly different to the expected molar mass of [mention the suspected substance, if any] due to [mention potential sources of error].

Example Abstract: This experiment aimed to determine the molar mass of an unknown volatile liquid using the ideal gas law (PV = nRT). The volatile liquid was vaporized in a pre-weighed flask of known volume, and the mass of the condensed vapor was determined. The temperature and pressure of the system were also measured. Using these values, the molar mass was calculated to be 72.5 g/mol. This value is reasonably close to the expected molar mass of the suspected substance, acetone (58.08 g/mol), indicating a successful experiment, although minor discrepancies suggest potential sources of error such as incomplete vaporization or slight variations in temperature and pressure.

3. Introduction: Background and Theory

This section provides background information on the theoretical principles relevant to the experiment. This includes:

• Definition of molar mass: Explanation of molar mass and its significance.
• The ideal gas law (PV = nRT): Detailed explanation of the ideal gas law, including definitions of each variable (P = pressure, V = volume, n = number of moles, R = ideal gas constant, T = temperature).
• Derivation of the molar mass equation: Show how the ideal gas law can be rearranged to solve for molar mass.
• Limitations of the ideal gas law: Discuss situations where the ideal gas law may not be accurate (high pressure, low temperature).

Example Introduction: Molar mass, defined as the mass of one mole of a substance, is a fundamental property used to understand and quantify chemical reactions. The ideal gas law, PV = nRT, describes the relationship between the pressure (P), volume (V), number of moles (n), ideal gas constant (R), and temperature (T) of an ideal gas. Since n = mass/molar mass (m/M), we can rearrange the ideal gas law to solve for molar mass (M): M = mRT/PV. This equation forms the basis of this experiment. However, it's important to note that the ideal gas law is an approximation and may not hold perfectly under all conditions, particularly at high pressures or low temperatures where intermolecular forces become significant.

4. Materials and Methods: Experimental Procedure

This section details the materials used and the step-by-step procedure followed. Be precise and clear, allowing another scientist to replicate your experiment.

• List of materials: Include all chemicals and equipment used, specifying quantities and concentrations.
• Step-by-step procedure: Describe the experimental procedure in chronological order, using concise and precise language. Include diagrams if necessary.

Example Materials and Methods:

Materials:

• Unknown volatile liquid (~5 mL)
• 125 mL Erlenmeyer flask
• Aluminum foil
• Boiling water bath
• Beaker (250 mL)
• Analytical balance
• Thermometer
• Barometer

Procedure:

1. Clean and dry a 125 mL Erlenmeyer flask.
2. Weigh the empty flask and aluminum foil cover accurately.
3. Add approximately 3-5 mL of the unknown volatile liquid to the flask.
4. Carefully cover the flask with the aluminum foil, creating a snug seal, and make a small hole in the foil to allow for pressure equalization.
5. Submerge the flask in a boiling water bath until all the liquid has vaporized.
6. Remove the flask from the boiling water bath and allow it to cool to room temperature.
7. Carefully wipe off any condensed water on the outside of the flask.
8. Weigh the flask, foil, and condensed vapor accurately.
9. Record the temperature of the boiling water bath and the atmospheric pressure.
10. Calculate the molar mass using the ideal gas law.

5. Results: Presentation of Data and Calculations

This section presents your experimental data and calculations in a clear and organized manner. Use tables and graphs to present your data effectively.

• Data table: Present your raw data in a neatly organized table.
• Sample calculations: Show the detailed calculation of the molar mass using the ideal gas law, using data from your table. Include units throughout your calculations.
• Graphs (if applicable): Use graphs to visualize your data if appropriate.

Example Results:

Table 1: Experimental Data

Sample Calculation:

Mass of vapor (m) = 0.787 g Volume of flask (V) = 125 mL = 0.125 L Temperature (T) = 99.5 °C = 372.65 K Atmospheric pressure (P) = 762 mmHg = 1.00 atm (approx.) Ideal gas constant (R) = 0.0821 L·atm/mol·K

M = mRT/PV = (0.787 g)(0.0821 L·atm/mol·K)(372.65 K) / (1.00 atm)(0.125 L) = 72.5 g/mol

6. Discussion: Analysis and Interpretation of Results

This section is crucial for demonstrating your understanding of the experiment and its implications.

• Comparison of experimental and expected values: Compare your experimental molar mass with the expected molar mass (if known). Discuss any discrepancies and potential sources of error.
• Error analysis: Quantify the uncertainty in your measurements and calculations. Identify potential systematic and random errors and their impact on your results.
• Limitations of the experiment: Discuss limitations of the experiment and how they might be addressed in future experiments.
• Suggestions for improvement: Offer suggestions for improving the accuracy and precision of the experiment.

Example Discussion: The experimental molar mass of the unknown volatile liquid was determined to be 72.5 g/mol. While this value is not precisely the same as the expected molar mass of acetone (58.08 g/mol), the discrepancy could be attributed to several factors. Incomplete vaporization of the liquid could lead to an overestimation of the molar mass. Slight variations in temperature and pressure readings could also introduce errors. Furthermore, the ideal gas law is an approximation, and deviations from ideality could contribute to discrepancies. Improvements to the experimental procedure could include ensuring complete vaporization by using a longer heating time and employing more precise measuring instruments. More controlled temperature and pressure conditions could also reduce uncertainty.

7. Conclusion: Summary of Findings

This section briefly summarizes the main findings and conclusions of the experiment. Restate your key findings and their implications in a concise manner.

Example Conclusion: This experiment successfully demonstrated a method for determining the molar mass of a volatile liquid using the ideal gas law. The experimental molar mass of 72.5 g/mol obtained is relatively close to the expected molar mass of acetone, suggesting that the unknown liquid is likely acetone. The observed discrepancy highlights the importance of careful measurements and consideration of potential sources of error.

8. References: Citation of Sources

List any references you cited in your report using a consistent citation style (e.g., APA, MLA).

9. Appendix (Optional): Raw Data and Supporting Information

This section can include supplementary data or information that is not included in the main body of the report. This might include raw data tables, calibration curves, or detailed calculations.

This detailed example provides a solid framework for writing a high-quality chemistry lab report. Remember to always tailor your report to the specific requirements of your instructor and the experiment you are conducting. By following these guidelines, you will be able to produce clear, concise, and insightful reports that effectively communicate your scientific findings. Remember to always practice proper laboratory safety procedures when conducting experiments.