91Ó°ÊÓ

Phosgene (CCl, O) is a colorless gas that was used as an agent of chemical warfare in World War I. It has the odor of new-mown hay (which is a good warning if you know the smell of new-mown hay). Pete Brouillette, an innovative chemical engincering student, came up with what he believed was an effective new process that utilized phosgene as a starting material. He immediately set up a reactor and a system for analyzing the reaction mixture with a gas chromatograph. To calibrate the chromatograph (i.e., to determine its response to a known quantity of phosgene), he evacuated a 15.0 cm length of tubing with an outside diameter of \(0.635 \mathrm{cm}\) and a wall thickness of \(0.559 \mathrm{mm}\), and then connected the tube to the outlet valve of a cylinder containing pure phosgene. The idea was to crack the valve, fill the tube with phosgene, close the valve, feed the tube contents into the chromatograph, and observe the instrument response. What Pete hadn't thought about (among other things) was that the phosgene was stored in the cylinder at a pressure high enough for it to be a liquid. When he opened the cylinder valve, the liquid rapidly flowed into the tube and filled it. Now he was stuck with a tube full of liquid phosgene at a pressure the tube was not designed to support. Within a minute he was reminded of a tractor ride his father had once given him through a hayfield, and he knew that the phosgene was leaking. He quickly ran out of the lab, called campus security, and told them that a toxic leak had occurred, that the building had to be evacuated, and the tube removed and disposed of properly. Personnel in air masks shortly appeared, took care of the problem, and then began an investigation that is still continuing. (a) Show why one of the reasons phosgene was an effective weapon is that it would collect in low spots soldiers often mistakenly entered for protection. (b) Pete's intention was to let the tube equilibrate at room temperature ( \(23^{\circ} \mathrm{C}\) ) and atmospheric pressure. How many gram-moles of phosgene would have been contained in the sample fed to the chromatograph if his plan had worked? (c) The laboratory in which Pete was working had a volume of \(2200 \mathrm{ft}^{3}\), the specific gravity of liquid phosgene is \(1.37,\) and Pete had read somewhere that the maximum "safe" concentration of phosgene in air is \(0.1 \mathrm{ppm}\) \(\left(0.1 \times 10^{-6} \mathrm{mol} \mathrm{CCl}_{2} \mathrm{O} / \mathrm{mol}\) air) \right. Would the "safe" concentration have been exceeded if all the liquid phosgene in the tube had evaporated into the room? Even if the limit would not have been exceeded, give several reasons why the lab would still have been unsafe. (d) List several things Pete did (or failed to do) that made his experiment unnecessarily hazardous.

Step by step solution

01

Step 1(a): Understanding Phosgene Gas Weight

Phosgene gas is heavier than air. This means when released, it tends to sink and collect in low-lying areas, such as trenches or bunkers. Therefore soldiers seeking safety in these lower spots would be in danger of inhalation.

02

Step 2(b): Applying the Ideal Gas Law

For here, use the Ideal Gas Law, which is \(PV = nRT\). Pete wants the tube to have atmospheric pressure, which is \(1 atm\). The volume can be found by calculating a cylinder's volume formula \(\pi r^2 h\), where \(r\) (the radius) is half the diameter and \(h\) (height) is the length of the tube. The gas constant (R) is \(0.0821 L*atm/mol*K\) and the temperature is \(23^{\circ}C\) which needs to be converted to Kelvin by adding \(273.15\). Solving for \(n\) (moles), we can get the answer.

03

Step 3(c): Estimating Safe Concentration

The quantity of phosgene the tube can hold can be found from its volume and the specific gravity of phosgene which allows us to find the weight of the phosgene that would be in the tube. Using the molar mass of phosgene (\(98.92 g/mol\)), we can find the moles of phosgene gas. Then, figure out the volume of air in the laboratory by converting the given volume to liters. Thus, the concentration of phosgene can be found by dividing the moles of phosgene by the total moles of air (using the ideal gas law again to find moles of air), which can be compared to the safe limit.

04

Step 4(d): Evaluating Safety Procedures

There are several safety rules that Pete neglected which led to a hazardous situation. Some include lack of personal protective equipment, incorrect storage, and mishandling of chemicals, lack of understanding/assessment of the reactivity of substances, and lack of preparation for potential incidents. Proper knowledge and protocols need to be followed to prevent such incidents.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Phosgene Characteristics

Phosgene is a colorless gas with the chemical formula \(\text{COCl}_2\). It was infamously used as a chemical warfare agent during World War I due to its ability to cause severe respiratory damage. One key characteristic of phosgene is its density, which is greater than that of air. As a result, phosgene tends to settle in low-lying areas.
This property made it particularly hazardous on the battlefield, as it would collect in trenches and bunkers.
Phosgene has a distinctive musty smell similar to that of new-mown hay, which can act as a warning of its presence. However, the smell may not be strong enough to provide timely detection, especially when inhaled in small concentrations. It was this property that led to its accidental release being detected by Pete in the exercise.

• Colorless gas
• Heavier than air
• Distinctive smell akin to fresh-cut hay
• Used in chemical warfare due to its toxic effects

Ideal Gas Law

The Ideal Gas Law is a fundamental equation in chemistry that describes the relationship between pressure, volume, temperature, and the number of moles of a gas. It is expressed as \( PV = nRT \), where \( P \) is the pressure, \( V \) is the volume, \( n \) is the number of moles, \( R \) is the universal gas constant, and \( T \) is the temperature in Kelvin.
This equation assumes that the gas behaves ideally—meaning its molecules have negligible volume and do not interact with one another. While not always perfectly accurate, it provides a good approximation for many gases in a range of conditions.
In Pete's scenario, he intended to use the Ideal Gas Law to calculate the moles of phosgene that would fit in the tube at atmospheric pressure and room temperature. By identifying the dimensions of the tube and converting necessary units, he could have used the law to finalize his setup safely.

• Describes gas behavior
• Equation: \( PV = nRT \)
• Useful for calculating moles of gas

Laboratory Safety

Laboratory safety is crucial when handling chemicals, especially hazardous ones like phosgene. Proper safety protocols prevent accidents and ensure a safe working environment. It's essential to understand the properties of the chemicals involved and use appropriate protective gear such as gloves, masks, and goggles.
Another key aspect is the awareness and preparedness for handling emergencies. As illustrated in Pete's case, failing to assess the state of phosgene in the storage cylinder led to an unsafe scenario. Laboratory setups must be risk-assessed, and equipment should be checked for adequacy in handling different states of chemicals (liquid vs. gas).

• Use of personal protective equipment
• Knowledge of chemical properties and behavior
• Risk assessment before experiments
• Emergency preparedness and response plans

Chemical Hazard Analysis

Conducting a thorough chemical hazard analysis is essential before any experiment involving potentially dangerous substances. This process involves identifying and understanding the hazards associated with each chemical, such as toxicity, reactivity, and environmental effects.
For phosgene, the key hazards include its toxicity at low concentrations and its reactivity that can lead to leaks. Such assessments help in planning safe handling, storage, and disposal methods.
In Pete's experiment, a proper chemical hazard analysis might have revealed the risks of filling the tube with liquid phosgene under high pressure, prompting a reconsideration of his approach to using phosgene or investing in more suitable containment.

• Identify chemical hazards
• Assess risks in different conditions
• Ensure safe storage and handling
• Implement precautions and response strategies