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https://blackboard.nocccd.edu/bbcswebdavlpid-533736-dt-content-rid-2899762 1/courses/FULC161 CHEM103 12733/Case%20Scenario%20missing%20person%20inx20lakes pdr ie https blackboard.nocccd.edu/bbcswebdav/pid-533736-dt-conten rid-2899762 courses/FULC161 CHEM103 12733/CaseN620Scenariok2 0missing%20perse C YouTube Apple Bing Google istory of R. ds l Quizlet hoo Google Favorites Saint August...oyola Press 12733 CHEM Logging off your MY april 15. Ane A went missing from the Case Scenario: on April 15, a woman, Jane A. went missing from the Fullerton area. A family member filed missing person report and the police are investigating. A reliable confidential informer reports that a female body stuffed in an Igloo ice chest and dumped in the back of a van at a local lake in early May. Scuba divers have indeed found a van at the bottom ofthe lake and it appears there is might be an ice chest in the back of the van. The divers note two deployed airbag on the driver and passenger side of the van. Both airbags remain inflated even though they are under water. The inflated airbags might be an important piece of evidence as to how the van entered the lake and who was in the passenger seat. To preserve this evidence, tte police want to lift the van from the lake without exploding the airbags. As a forensic scientist, the police would like you o answer her following qurstions

Explanation / Answer

Presence of water may wash out most of the traces like hair, sweat, fabrics, etc. from the airbags. Howver, finger prints may be traced, if any.

Ans. The pressure at the bottom of the lake is always much greater than atmospheric pressure (1 atm.).

Assumed, the pressure at the bottom of the lake (at certain depth) is 2 atm.

Now, using ideal gas equation Ideal gas Law: pV = nRT

            Where, p = pressure in atm = 1 atm

            V = volume in L

            n = number of moles = 1           [standard condition]

            R = universal gas constant= 0.082057338 atm L mol-1K-1

P1V1 = nRT      - at bottom of the lake

V1 = nRT/ P1     ,

Assuming: volume, V of the maximally inflated airbag is fixed (it can reduce, but can’t increase).

            Temperature of the lake is equal to that of air, hence T is also constant.

P2V2 = nRT      - in open air (outside the lake)

V2 = nRT / P2

Comparing V1 and V2,

            V2 / V1 = P2 / P1 = 2/1

Or, V2 = 2 V1

That, when the car is pulled out of the lake into the air as such, the volume of the airbag increases 2 times that of the volume at the bottom of the lake. Thus, the airbag is most likely to burst and destruct the evidence.

To preserve the airbag as such, following two options are available-

I. Do not let the pressure decrease: Seal the whole car in a larger container at the bottom itself and airtight seal it including the water as surrounding around the car. The sealed outer container does not let the airbag inflate more because there is no more space for the bag to expand.

This procedure may be very expensive and time consuming. But it shall serve the purpose.

II. Reduce the temperature: Both the pressure and volume are inversely proportional to temperature.

If temperature is maintained below 22.40C, the airbag can be prevented from exploding.

Hang a large container (with upper top/ roof be able to be closed/opened) in the lake and carefully place the car in it. Displace the lake water () with chilled water by continuously pumping chilled water in the container.

V1 = nRT1 / P1 = nR (295.65 K) / 2P – at bottom of lake             [note: P1 = 2 atm]

V2 = nRT2 / P2 = nR T2 / 1.5 P   - in chilled water. Sine car is dipped in chilled water, the pressure is greater than that of atmospheric pressure.

Also, V2 must be equal or less than V1 to prevent bursting of airbag.

At, V1 = V2

            nR (295.65 K) / 2P = nR T2 / 1.5 P

            or, T2 = 221.73 K = - 520C

Cooling water to this temp. is also expensive.

However, closing the vessel airtight so that there is no void left shall work perfectly. Since, the vessel is completely filled with water and vessel is completely sealed, the airbag can’t expand. So, the car can be transported to lab in normally chilled water (say, around 40C) without causing airbags to burst.   

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