Title: Experimental Investigation of Vapor Molar Mass and Methodological Adaptations for Specific Substances

Categories: Chemistry

Understanding the molar mass of a vapor is crucial in various scientific applications, providing insights into the nature and composition of substances. In this experiment, we aim to determine the molar mass of a volatile liquid by employing a method involving controlled heating, condensation, and mass measurement. The process involves heating the volatile liquid to a known temperature, allowing the vapor to escape through a small orifice. Subsequently, the container is cooled to room temperature, causing the vapor to condense back into a liquid state, which is then accurately measured.

By knowing the volume of the container and the high-temperature conditions, and considering the atmospheric pressure through the orifice, we can calculate the moles of the substance and, consequently, derive its molar mass.

The experimental setup consists of a sealed container with a volatile liquid. This liquid is carefully heated to a predetermined temperature, causing it to vaporize. The container is equipped with a small orifice through which the vapor can escape.

Get quality help now
Sweet V
Sweet V
checked Verified writer

Proficient in: Chemistry

star star star star 4.9 (984)

“ Ok, let me say I’m extremely satisfy with the result while it was a last minute thing. I really enjoy the effort put in. ”

avatar avatar avatar
+84 relevant experts are online
Hire writer

It is important to note that the system remains open to the atmosphere through this orifice, allowing the gas to dissipate.

As the vapor exits the container, the cooling process begins. The container is gradually cooled to room temperature, prompting the vapor to condense back into a liquid state. At this point, the mass of the condensed liquid is measured with precision. The known volume of the container, along with the high-temperature conditions and atmospheric pressure, is utilized to calculate the moles of the substance.

To calculate the moles of the vapor, we utilize the ideal gas law, which relates pressure, volume, temperature, and the gas constant.

Get to Know The Price Estimate For Your Paper
Number of pages
Email Invalid email

By clicking “Check Writers’ Offers”, you agree to our terms of service and privacy policy. We’ll occasionally send you promo and account related email

"You must agree to out terms of services and privacy policy"
Write my paper

You won’t be charged yet!

The atmospheric pressure acting on the system through the orifice is considered, and by knowing the volume of the container, the moles of the substance can be determined.



  • P is the atmospheric pressure,
  • V is the volume of the container,
  • n is the moles of the substance,
  • R is the gas constant,
  • T is the temperature in Kelvin.

Once the moles of the substance are established, the molar mass is calculated by dividing the mass of the substance by the moles.

Molar Mass=Mass of SubstanceMoles of SubstanceMolar Mass=Moles of SubstanceMass of Substance​

This experiment is significant as it provides a practical approach to determining the molar mass of a vapor, contributing valuable data for understanding the composition and behavior of volatile substances. The methodology employed allows for accurate measurements, enhancing the reliability of the results obtained.

In conclusion, the experiment outlined above serves as a robust method for determining the molar mass of a vapor. Through controlled heating, condensation, and precise measurements, we can calculate the moles of the substance and subsequently derive its molar mass. This process not only deepens our understanding of the properties of volatile liquids but also highlights the importance of experimental techniques in scientific inquiry.

Equipment and Materials

a) Unidentified volatile liquid

b) Purified water

c) Elastic band

d) Bunsen burner

e) Erlenmeyer flask (100 mL)

f) Graduated cylinder (250 mL)

g) Tripod stand

h) Wire gauze

i) Needles or map pins

j) Aluminum foil square (2 inches)

k) Beaker (500 mL)

l) Weighing balance

m) Temperature gauge

The experimental endeavor has proven to be a success, culminating in the determination of the molar mass of the unidentified liquid as 30.625 g/mol. This calculation was executed utilizing the formula:


This outcome is indicative of the efficacy of the experimental procedure in yielding meaningful and reliable data. The application of the aforementioned formula facilitated the extraction of crucial information regarding the molar mass of the unknown liquid.

Moreover, it is paramount to underscore that the success of this experiment hinged on adhering to the principles of ideal gas behavior, particularly involving high temperatures and low pressures. These conditions were instrumental in ensuring that the gas under examination exhibited behavior consistent with ideal gas laws. The careful consideration of these factors underscores the importance of controlled environments in experiments aiming to elucidate the properties of gases.

In summation, the acquired results not only affirm the success of the experiment but also underscore the significance of ideal gas behavior principles in the determination of unknown gases. The application of fundamental gas laws, coupled with meticulous experimentation, contributes to the advancement of scientific understanding in this realm.

1) Impact of Insufficient Unknown Liquid:

If an insufficient quantity of the unknown liquid were utilized, it would adversely affect the accuracy of the experimental molar mass determination. This discrepancy arises from the fact that, upon heating, the insufficient amount of unknown liquid would fail to occupy the entire container, leading to a larger recorded volume in the equation (nRT)/PV. Consequently, the calculated molar mass would be underestimated, deviating from the actual value and compromising the accuracy of the results.

2) Major Sources of Experimental Error:

a) Inaccurate Volume Measurement: The precision of the volume measurement, crucially set at 2 mL, is pivotal for the accuracy of the experiment. Utilizing a 250 mL graduated cylinder demands meticulous attention to ensure that the volume of the unknown liquid is precisely 2 mL. Deviations from this target, whether exceeding or falling short, would introduce error into the results.

b) Hole Size in Aluminum Foil: The creation of a hole in the aluminum foil is a delicate step, requiring a needle with a minimal diameter. An excessively large hole would result in a greater quantity of vapor escaping, impacting the reliability of the measurements.

c) Handling of the Unknown Liquid: Correct handling of the volatile unknown liquid is imperative. Measurement and preparation should occur when the water is on the brink of reaching its boiling point. Any exposure beyond this critical moment may lead to premature evaporation, diminishing the accuracy of the molar mass determination.

d) Inaccurate Weight Measurement: Accurate weighing of the flask, cap, rubber band, and condensed vapor is crucial for precise results. Ensuring the balance is calibrated to 0.00 g before measurements mitigates external factors' impact, but slight errors may still occur.

e) Inaccurate Temperature Reading: Temperature readings must be taken precisely when the water is at its boiling point, using a reliable thermometer. Additionally, maintaining a constant temperature of 99°C during the 4-minute period when the Erlenmeyer flask is inserted into the boiling water is vital to minimize temperature-related errors.

In summary, meticulous attention to volume measurements, hole creation in the foil, handling of the unknown liquid, weight measurements, and temperature readings are critical aspects for minimizing experimental errors and enhancing the reliability of the molar mass determination.

3) Impact of Inadequate Drying of the Flask

If the flask is not meticulously wiped dry, residual water inside the flask will contribute to the overall mass of the flask and vapor. Consequently, the molar mass of the vapor will be inaccurately higher than it should be. The presence of water, even in small amounts, would artificially inflate the mass measurement, leading to a skewed calculation of the molar mass.

4) Modification for Isobutyl Alcohol

Isobutyl alcohol, with a boiling point of 108°C, necessitates a modification in the experimental procedure to determine its molar mass. Given that the boiling point exceeds that of water, the conventional hot-bath liquid, adjustments are required for an accurate assessment. To address this, ethylene glycol can be introduced to elevate the boiling point of the water. Alternatively, another suitable liquid, such as oil, could replace water in the hot-bath setup. This modification ensures that the experimental conditions align with the specific properties of isobutyl alcohol, facilitating an accurate and reliable determination of its molar mass. The adaptability of the experimental design showcases its versatility in accommodating different substances with distinct characteristics.

Considering the higher boiling point of isobutyl alcohol (108°C), adjustments to the standard experimental procedure are imperative for an accurate determination of its molar mass. As the boiling point surpasses that of water, typically used as the hot-bath liquid, the procedure must be adapted accordingly. One effective modification involves incorporating ethylene glycol into the hot-bath setup, elevating the boiling point of water to accommodate the higher temperature requirement of isobutyl alcohol. Alternatively, the substitution of water with a suitable liquid, such as oil, provides another viable approach. This modification ensures the experimental conditions align with the specific properties of isobutyl alcohol, facilitating a precise and reliable determination of its molar mass. This adaptability underscores the versatility of the experimental design in accommodating diverse substances with unique characteristics, enhancing the accuracy of the results.

Updated: Feb 19, 2024
Cite this page

Title: Experimental Investigation of Vapor Molar Mass and Methodological Adaptations for Specific Substances. (2024, Feb 06). Retrieved from https://studymoose.com/document/title-experimental-investigation-of-vapor-molar-mass-and-methodological-adaptations-for-specific-substances

Live chat  with support 24/7

👋 Hi! I’m your smart assistant Amy!

Don’t know where to start? Type your requirements and I’ll connect you to an academic expert within 3 minutes.

get help with your assignment