Calculate Mass of NO2 in a Liter of Air

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Discussion Overview

The discussion revolves around calculating the mass of nitrogen dioxide (NO2) present in a liter of air, given its concentration in parts per million (ppm) and the number of air molecules in that volume. The scope includes homework-related problem-solving and mathematical reasoning involving conversions between molecules, moles, and mass.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant expresses uncertainty about how to approach the calculation, suggesting a conversion from molecules to moles and then to mass using the molar mass of NO2.
  • Another participant points out that with the given number of molecules in a liter of air, the concentration of NO2 can be calculated directly.
  • Some participants clarify the relationship between molar mass and atomic mass units (amu), indicating that the molar mass of NO2 is 46 g/mol.
  • There is a discussion about whether the ideal gas law is necessary for this calculation, with one participant stating it is not required.
  • One participant calculates the mass of NO2 using the number of molecules and molar mass, arriving at a value of 1.87 g, but expresses confusion about the expected answer.
  • Another participant provides a detailed breakdown of the calculation, confirming the number of NO2 molecules and relating it to the weight based on the known molar mass.
  • One participant suggests making an estimate based on the volume of gas at room temperature and pressure, indicating that the expected mass should be around 2 micrograms due to the low concentration of NO2.

Areas of Agreement / Disagreement

Participants generally agree on the approach to the calculation but express differing views on the necessity of using the ideal gas law and the interpretation of the results. The discussion remains unresolved regarding the final mass calculation, as participants arrive at different numerical values.

Contextual Notes

Some participants mention the need for conversions and the relationship between different units of mass, but there are no explicit resolutions to the mathematical steps involved in the calculations.

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Homework Statement


NO2 is a known air-pollutant resulting from the combustion of petroleum in vehicles. Suppose at 6:00 am, there are 0.920 ppm NO2 in a liter of air. Calculate the mass (in grams) of the NO2 present in a liter, assuming there are 2.46x10^22 molecules of air in 1.00 L. (1 ppm = 10-6)

Homework Equations


particle to mole to mass conversion
PV=nRT(maybe)

The Attempt at a Solution


I have no idea how to do this. The only thing I could think of is changing the number of molecules to some mass by changing it to moles than use the molar mass of NO2 to get mass
I would appreciate any help on this. Thanks.
 
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You are given the number of molecules in a liter of air
You know that 920/1000000 of these are NO2

Do you know the mass of NO2 in AMU?
Do you know the mass of a single AMU in grams
 
i know the molar mass of NO2 is 46g/mol. I don't think you need amu, unless the molar mass is the amu. Would I need to use the ideal gas law?
 
physicsman2 said:
i know the molar mass of NO2 is 46g/mol. I don't think you need amu, unless the molar mass is the amu.
The molar mass is the mass in grams of 1mole of molecules. An amu is 1g/1mole.
So you work out how many moles there are and multiply by 46h

Would I need to use the ideal gas law?
No
 
ok, so after dividing 2.46x10^22 by 6.022x10^23 and multiplying by 46, i get 1.87g. What do I have to do after this, I'm kinda confused. I know the answer should be 1.73x10^-6 but I don't know how to get it.
Thanks a lot.
 
There are 2.46x10^22 molecules in 1 litre of air
0.920ppm is NO2 so 0.92e-6 of these are NO2

So we have 2.46x10^22 * 0.92x10^-6 = 2.26x10^16 molecules of NO2 / litre
You know 6.02x10^23 molecues of NO2 weigh 46g

So how much does 2.26x10^16 molecules weigh?
 
ps with numbers like this it's always worth doing an estimate first.
We know that 1mol of a gas is 24litres at room temp/pressure
So 24litres would be 46g, then 1 litre NO2 is about 2g.

But we know that NO2 is only 1ppm - so the answer should be around 2 micro grams
 
thanks a lot. i see how that answer was found now.
 

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