Calculate Molar Mass of Acetone: 0.239g @766mm Hg & 100°C

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Discussion Overview

The discussion revolves around calculating the molar mass of acetone vapor given specific conditions of mass, pressure, and temperature. Participants explore the application of gas laws and the relationships between moles, mass, and volume in this context.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant presents an initial calculation but expresses uncertainty about the correctness of their approach.
  • Another participant suggests that the equations used may not be appropriate for the problem at hand.
  • A participant indicates they understand the concept of molar mass but struggles with deriving it from the provided data, noting a lack of thorough instruction from their teacher.
  • Another participant introduces the ideal gas law (PV=nRT) as a method to determine the number of moles, suggesting that this can be used to relate moles to grams.
  • One participant discusses the concept of standard temperature and pressure (STP) and how it relates to the exercise, noting that the conditions are not standard due to the higher temperature.
  • There is mention of using proportional relationships and the importance of understanding absolute temperature in calculations.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and approaches to the problem, with no consensus on the correct method or solution. Some participants agree on the relevance of the ideal gas law, while others question the appropriateness of their initial calculations.

Contextual Notes

There are unresolved issues regarding the application of gas laws under non-standard conditions and the specific definitions of terms like STP and NTP. Participants also express confusion about unit conversions and the role of the gas constant (R).

Who May Find This Useful

This discussion may be useful for students studying gas laws, molar mass calculations, or those seeking clarification on the relationships between pressure, volume, temperature, and moles in chemistry.

Hammertong
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A 125mL flask contains 0.239g of acetone vapor at 766mm Hg and 100*C. Calculate the molar mass of acetone.
766x125/373Kx273K/760=92.210mL
.239g/92.210/1000=2.592g/mL
Where am I going wrong? I have no idea if I'm anywhere close.
 
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Those equations aren't really what we want.

Hint: molar mass is the number of grams per moles.
 
I know what molar mass is, but I don't understand how to get it from what I'm given. My teacher goes over the equations once then moves on. Then he expects us to be able to do it backwards, forwards, and sideways.
I figured it out, I just needed to multiply my end answer by 22.4L to get weight of one mole at STP.
 
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Not sure anymore how all the units work; "R" is the complicated part, but the question seems like an ideal gas type. PV=nRT. You can determine the number of moles from that, "n". Next, you compare the number of moles to the number of grams of mass, which you are given.
 
These things are basically simple proportions.

A mole as you say occupies 22.4 l under standard conditions (still called STP or NTP?) . Got a texbook to check out how those are defined?
The exercise is not under standard conditions, but a higher temperature.
Again it is simple proportions - you have to know what absolute temperature means.
You do not need to use explicitly that equation - if you use the Charles temperature proportionality law you are using it implicitly anyway .
You can actually work out R from the above information.
Hope these thing become clear and simple. :smile:
 

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