Lab Report: Determining the Molecular Mass of Butane

Abstract

The objective of this experiment was to determine the molecular mass of butane (C4H10) using the ideal gas law (PV = nRT). Butane gas was chosen due to its behavior as an ideal gas under standard temperature and pressure conditions. The experiment involved collecting and testing butane gas using various equipment and measurements. Through calculations, the molecular mass of butane was determined.

Introduction

The molecular mass of a substance is a critical property in chemistry. In this experiment, we aimed to find the molecular mass of butane by applying the ideal gas law, which relates the pressure (P), volume (V), number of moles (n), and temperature (T) of a gas.

The ideal gas law is expressed as PV = nRT, where R is the ideal gas constant.

The materials used in the experiment included matches, a funnel, a bucket, a graduated cylinder, a thermometer, a lighter, a scale, and a wooden flint. These materials were essential for collecting and testing the butane gas under controlled conditions.

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Materials and Methods

Materials:

• Matches
• Funnel
• Bucket
• Graduated cylinder
• Thermometer
• Lighter
• Scale
• Wooden flint

Procedure:

1. Rinse the bucket and fill it three-fourths full of water.
2. Rinse all glassware to ensure cleanliness.
3. Place a thermometer in the bucket to measure the temperature of the water.
4. Record the initial pressure (P) as 760.4 mm of Hg or 1.03 atm.
5. Record the temperature as 22°C (295 K).
6. Weigh the dried lighter, record its weight before and after the experiment, and calculate the loss of gas (in grams) by subtracting the initial and final weights.
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7. Immerse a graduated cylinder in the bucket, ensuring there is no air inside.
8. Place a funnel at the bottom of the cylinder and position the lighter at the top of the funnel.
9. Strike the lighter continuously until at least 70 ml of gas has been collected in the cylinder.
10. Test the collected gas by lighting a match and placing it in the cylinder. Quickly remove the cylinder from the water and insert the lit flint into the gas.
11. Rinse all materials thoroughly.
12. Record the vapor pressure correction as 19.8 torr.

Results

Using the ideal gas law, PV = nRT, the following calculations were made to determine the molecular mass of butane:

1. Volume (V) in liters: 0.0399 L
2. Volume (V) in milliliters: 39.9 mL
3. Number of moles (n): 0.0017 moles

Here, R = 0.082 L·atm/(mol·K) and T = 295 K.

Conclusion

The experimental percent error was calculated to be 85%, and the percent yield was determined to be 185%. To enhance the accuracy of this lab, it is advisable to measure the mass of the lighter with greater precision, recording measurements to at least three decimal places. Additionally, while conducting the experiment, precautions should be taken to ensure there are no air bubbles in the cylinder when immersing the lighter. Lastly, when measuring the lighter, it is essential to ensure it is completely dry to prevent any discrepancies in the mass measurements.

Recommendations

Future experiments can focus on refining the techniques used in this experiment to reduce errors. Exploring different methods of gas collection and measurement may lead to more accurate results. Additionally, investigating the properties of other gases and their molecular masses can provide valuable insights into the behavior of ideal gases.