Find the acceptable concentration of CO

[s3a]

Homework Statement

Based on the “National Ambient Air Quality Objectives”, the acceptable hourly average concentration of carbon monoxide (CO) is 35 mg/m^3.

Find the acceptable concentration of CO in ppm if the temperature is -30 °C and pressure is 0.92 atm.

Express the concentration as a percent by volume.

Homework Equations

PV = nRT (maybe)

The Attempt at a Solution

Hello, everyone!

Could someone please help me understand how to do the problem above?

So far, I get the following.:
101.325 kPa * V = (35E-3 g / 28.01 g) mol * 8.31 kPa L / (mol K) * (-30 + 273.15) K

V = 0.0249180252056537913 L

Am I on the right track? If so, what do I do next? If not, then what must I do?

Any input would be greatly appreciated!

 

[Borek]

Write the ppm definition.

 

[epenguin]

Right equation, otherwise not really. We often get questions supposedly of chemistry here which are really problems of arithmetic that students learned years before starting chemistry.

You are given a concentration in mg/m^-3 at one T and P. You want to know in the first place the mg /m^-3 at another T, P. That is per unit volume - the volume in question, that is the m³ doesn't change. From your equation in 2 what remains the same between the two situations is P/R, can you see? That is the main bit of non-arithmetical knowledge. The other is knowing what is really meant by T in this context.

Work out the new mg/m^-3 then what that is in ppm.

 

[Borek]

You are given a concentration in mg/m-3 at one T and P.

Not exactly, original T and P are not given.

Work out the new mg/m^-3 then what that is in ppm.

As original statement doesn't contain any additional information, I am ready to assume it is to be understood as "35 mg/m³ at any conditions".

It doesn't say anything about whether is it ppm v/v or w/w, which makes it ambiguous and impossible to answer.

 

[s3a]

The way I read the question is 35 mg / m^3 at standard conditions is the legislative rule, and that what is sought is the adaption of the legislative rule to the new conditions ( -30 °C and 0.92 atm pressure).

Edit:
As for the ppm formula that you're asking for, according to this link ( https://sciencing.com/calculate-ppm-5194302.html ), it's weight / volume * 10^6.

 

[Borek]

The way I read the question is 35 mg / m^3 at standard conditions is the legislative rule, and that what is sought is the adaption of the legislative rule to the new conditions ( -30 °C and 0.92 atm pressure).

I am not convinced about the STP part, but you can definitely try this way. Note, that 35 mg of CO at STP means some easy to calculate volume in a well defined volume of air (1 m³). If you change T, P you change it for both gases. Will the ratio of volumes CO/air change? Will the molar ratio of CO/air change? Will the mass ratio of CO/air change? Does it make any sense to make these calculations?

As for the ppm formula that you're asking for, according to this link (...), it's weight / volume * 10^6.

Weight over volume - what units for weight, what units for volume? As long as they are not well defined there is no way to have an unambiguous result.

Compare http://www.chembuddy.com/?left=concentration&right=ppm-ppb-ppt

I still think assuming it is 35 mg per cubic meter of air regardless of T, P is the only way to add sense to the question.