Poisonous Gas Case

Question

Investigation

Gawain has been poisoned! The victim has been suffering from allergic reactions so his nose has been stuffed up all week while working in lab. Unusual headaches and nauseating feeling have brought him to the doctor who suspect that Gawain has been a victim of poison. Initial police investigation of the laboratory has obtained only a trace amount of a gas that appears to be the poison. Due to the limited quantity and instrumental malfunctions, only very rough analysis were performed on the potential poison.

The following are the results from analysis of the potential poison gas:

• The sample has a molecular mass under 100 amu/molecule

• The sample appears as a liquid when cooled to -40 oC (using a calcium chloride hexahydrate ice bath)

• The sample is made up of only two different elements.

Police also recovered 4 suspicious poisonous gas cylinders (found in separately locked cabinets) each belonging to one of the four other researchers sharing the lab with Gawain. The following are the other researchers who share the lab with Gawain and the physical properties of the four poisonous gases found in the gas cylinders.

Researcher Gas name Density (g/mL) bp (oC)

Mordred arsine 1.64 -62.5

Morgan tellurium hexafluoride 0.0106 -37.6

Vivien phosgene 4.25x10-3 8.3

Vortigern cyanogen 0.95 -21.1

1. Help the police with the investigation! The labels have fallen from the evidences and the four gas cylinders are now unidentified. The principal criminalist, who is sick at home today, has already examined the four poisonous gases and has described the procedure and recorded the following data. Help the police to identify the four cylinders so investigation may continue.

Procedures

Using liquid nitrogen for cooling, all 4 gases were liquefied and 1.00 g of each chemical was introduced to a separate 50.0 mL rigid sealed container, in which the chemicals were allowed to warm up to 25.0 oC. At least 10 minutes waiting time was used to allow all samples to establish thermal equilibrium with the controlled 25.0 oC environment The pressure measured from the gases in the containers are:

Cylinder ID P (atm)

A 4.946

B 2.025

C 6.278

D 9.403

*You will need to search for the chemical formulas or molar masses of the suspected gasses to help you match the labels to the gas cylinders

Cylinder ID Gas MW (g/mole) Gas Identity Chemical Formula

A

B

C

D

2. Use the information from the investigations and assuming the poison from which Gawain suffer is one of the four gases found in the cylinders in the lab, identify the potential poisonous gas. Explain how each clue is used in arriving at your conclusion.

3. Which researcher would you launch further investigation to better understand the potential motive for Gawain’s poisoning?

Answer 1

Hello, Jahnine,

A lot of work for some misplaced labels, but I think we can sort them out.

I couldn't enter the tables I prepared, due to lack of space in the=is reply box. I did upload them to https://docs.google.com/spreadsheets/d/1C-1WpjtIShbMXOdxUPneI0t9S7HwmRSfMP7XXdb9uI4/edit?usp=sharing

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Use the ideal gas law, PV=nRT, to determine the numer of moles contained in the 1.0 gram samples of gas. We want to solve for n, the number of moles. I don't have time to type in the actual calculations, but I'll do one. The rest follow the same format.

Cylinder A: PV=nRT

n = PV/RT

n = (4.946atm)*(0.05 L)/(0.08206 L*atm*K^-1mol^-1)(298K)

n = 0.01011 moles of gas in 1 gram of gas from cylinder A

We can now calculate a molar mass: 1 gram/(0.01011 mole) = 98.9g/mole

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This is repeated for the other gases. I got the following molar masses [table won't fit]:

Next we need to find the molar masses of the identified gases, along with their molecular formulas. [My table is too large to fit here - it is on the Google Sheet referenced above]

By matching the molar masses with those we calculated, we arrive at the following cylinder assignments: [This table will also not fit. On Google Sheets]

The published boiling points matched the ones provided, allowing additional verification. I went through this quickly, so double check the work. As far as what we might do next to confirm the culprit gas, we know it is under 100 g/mole. That eliminates TeF₆.

It forms a liquid by - 40C. It isn't clear whether a liquid forms at a higher temperature. Either phosgene or cyanogen would meet this boiling point observation. Futher verification of the gas ID would be possible with a more accurate boiling point measurement. Also, gas color or spectrographic analysis would lead to a firm ID. Sniffing the gas is also a possibile ID method, but not covered by health insurance.