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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Problem of the Week Archive => Topic started by: Borek on May 07, 2012, 12:35:46 PM

Title: Problem of the week - 07/05/2012
Post by: Borek on May 07, 2012, 12:35:46 PM: Air sucked from a garage was dried and pumped through a reactor filled with hopcalite. After some time temperature difference between entry and exhaust stabilized at 3.2°C. If air contains 21% oxygen by volume, has a specific heat (at constant pressure) of 0.2407 cal°C^-1g^-1, and if the heat of combustion of CO under constant pressure is 67655 cal, what was volume percent of CO in the air in the garage?
Title: Re: Problem of the week - 07/05/2012
Post by: AWK on May 10, 2012, 03:22:48 AM: What temperature of air in garage is?
Title: Re: Problem of the week - 07/05/2012
Post by: Borek on May 10, 2012, 03:38:50 AM: It doesn't matter.
Title: Re: Problem of the week - 07/05/2012
Post by: DrCMS on May 10, 2012, 08:37:56 AM: 0.0328%?
Title: Re: Problem of the week - 07/05/2012
Post by: Ann1234 on May 10, 2012, 09:41:22 PM: Quote from: Borek on May 07, 2012, 12:35:46 PM
Air sucked from a garage was dried and pumped through a reactor filled with hopcalite. After some time temperature difference between entry and exhaust stabilized at 3.2°C. If air contains 21% oxygen by volume, has a specific heat (at constant pressure) of 0.2407 cal°C^-1g^-1, and if the heat of combustion of CO under constant pressure is 67655 cal, what was volume percent of CO in the air in the garage?

0.03189%?
Title: Re: Problem of the week - 07/05/2012
Post by: Borek on May 11, 2012, 04:24:17 AM: Quote from: DrCMS on May 10, 2012, 08:37:56 AM
0.0328%?

Yes.

Compare S.H. Katz, D.A. Reynolds, H.W. Frevert and J.J. Bloomfield, U.S. Bur. Mines Tech. Papers 355 (1926) (if I understand correctly they also published related papers in 1932 and 1933 in J.Sci.Instruments and Chem.Zentr.).

Ann1234 - you are quite close, so I guess you have a small error in your calculations (like premature rounding of an intermediate result).
Title: Re: Problem of the week - 07/05/2012
Post by: AWK on May 11, 2012, 06:27:30 AM: Simple thermometric appratus for the estimation of carbon monoxide in air
Charles H. Lindsley1, John H. Yoe:
Quote
About 60% of the theoretically possible temperature rise is actually observed with the apparatus. By means of a calibration chart, the concentration of carbon monoxide present is read as a function of the temperature increase

Method is based on the above given paper.
Title: Re: Problem of the week - 07/05/2012
Post by: Borek on May 11, 2012, 06:56:42 AM: Quote from: AWK on May 11, 2012, 06:27:30 AM
Method is based on the above given paper.

Could be, I am quoting source as it was listed in the book from which I took the problem.

Calibration curve makes the measurement easier and faster, and takes some unpredictable factors into account. Problem was about theoretical approach and calculations are based on several assumptions (no heat loses, 100% conversion of CO to CO₂).

What I like about the problem is that it is about clever use of basic physics/chemistry for practical purposes. You can teach students about heat balance for months, but they don't know what for they learn it. Show them this question, explain how dangerous CO is, and chances are they will see it all makes sense.