Calculating Air Pressure: Ideal Gas Law Homework Solution

[aaronfue]

Homework Statement

I'm trying to calculate the air pressure from some data that I have.

#1. Calculate the cylinder pressure. (barometric pressure=765 mmHg, h=35mm)

#2. Calculate the moles of air using low temperature and volume and cylinder pressure above. (Low temp=50.0deg Celsius, vol=4.0mL, R=62.36)

#3. Calculate the air pressure using the high temperature reading from data. (High temp = 80deg Celsius)

Homework Equations

Ideal Gas Law
PV=nRT

The Attempt at a Solution

I have converted the temps to Kelvin and the mL to L. I have also made a -0.2 mL correction to my volume.

Question #1= 768 mm Hg

Question #2 = 1.448×10^-4 mol air

Question #3 = The question doesn't say to use the volume for that high temp, so I use it anyways. Another classmate got 420 mm Hg. But I don't get that. I get 480+ mm Hg.

Should I use the volume from question #2 since #3 doesn't specify?

The data that was collected is the same as my classmates but I don't know where I am making my mistake!

I would appreciate any assistance with this!

 

[Borek]

Cylinder? h? You have to explain what you are talking about.

 

[aaronfue]

Cylinder? h? You have to explain what you are talking about.

I'm eventually going to find the enthalpy of vaporization of water. The pressure of the cylinder is what needs to be determined which is asked in the first question.

The value of h is given in the first question in parenthesis. I was able to calculate the cylinder pressure. I just needed help with my moles of air from the second question.

 

[Borek]

You have still not explained what the h is. I can do some guessing, but that would be a waste of time, as I don't know what is the setup, if the cylinder is rigid, or closed with a piston, why the pressure inside is different from atmospheric and so on. Basically I know nothing.

 

[DeeNos]

It looks like you have correctly used the ideal gas law to calculate the cylinder pressure and the moles of air. For question #3, it is not specified which volume to use, so you can use the same volume from question #2. However, it is important to note that the ideal gas law assumes constant volume, so using the same volume for both low and high temperatures may not be accurate. It would be better to use the volume at the high temperature, if possible.

As for the discrepancy between your answer and your classmate's, it may be due to rounding errors or different values used for R. I would recommend checking your calculations and making sure you are using the same values for R as your classmate. If you are still unsure, it would be best to consult with your teacher or classmates for clarification.