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Chapter 5: Problem 25

Lewis \(^{12}\) describes the hazards of breathing air containing appreciable amounts of an asphyxiant (a gas that has no specific toxicity but, when inhaled, excludes oxygen from the lungs). When the mole percent of the asphyxiant in the air reaches \(50 \%,\) marked symptoms of distress appear, and at \(75 \%\) death occurs in a matter of minutes. A small storage room whose dimensions are \(2 \mathrm{m} \times 1.5 \mathrm{m} \times 3 \mathrm{m}\) contains a number of expensive and dangerous chemicals. To prevent unauthorized entry, the door to the room is always locked and can be opened with a key from either side. A cylinder of liquid carbon dioxide is stored in the room. The valve on the cylinder is faulty and some of the contents have escaped over the weekend. The room temperature is \(25^{\circ} \mathrm{C}\). (a) If the concentration of \(\mathrm{CO}_{2}\) reaches the lethal 75 mole \(\%\) level, what would be the mole percent of \(\mathrm{O}_{2} ?\) (b) How much \(\mathrm{CO}_{2}(\mathrm{kg})\) is present in the room when the lethal concentration is reached? Why would more than that amount have to escape from the cylinder for this concentration to be reached? (c) Describe a set of events that could result in a fatality in the given situation. Suggest at least two measures that would reduce the hazards associated with storage of this scemingly harmless substance.

Short Answer

Expert verified
a) About 25%, assuming \(\mathrm{O}_{2}\) takes up the largest portion of the remaining 25% not occupied by \(\mathrm{CO}_{2}\); b) Roughly 12.2 kg of \(\mathrm{CO}_{2}\) would be present in the room at a lethal concentration, but more than that amount must actually escape from the cylinder to displace the original air in the room; c) A fatal incident could occur if the \(\mathrm{CO}_{2}\) cylinder leaks over a weekend and an unsuspecting individual enters the room. For safety measures, regular checks and maintenance of cylinders, a gas detector, and good ventilation should be implemented.

Step by step solution

01

Calculate the mole percent of \(\mathrm{O}_{2}\)

The mole percent of a component in a mixture is the number of moles of that component divided by the total number of moles of all components. Since the mole percent of \(\mathrm{CO}_{2}\) is 75 %, the remaining 25 % must be composed of \(\mathrm{O}_{2}\) and other components. We can safely assume that the mole percent of \(\mathrm{O}_{2}\) will decrease but will constitute the majority of the remaining 25 %.
02

Determine the mass of \(\mathrm{CO}_{2}\) present in the room

First, the volume of the room in cubic meters needs to be calculated. This will be \(2 \mathrm{m} \times 1.5 \mathrm{m} \times 3 \mathrm{m} = 9 \mathrm{m^{3}}\). Then, used the ideal gas law (\(PV = nRT\)) to find the total number of moles of gas in the room. Here, P is the pressure (assumed to be 1 atm), V is the volume, n is the number of moles, R is the gas constant (0.0821 l atm K-\(^{1}\) mol-\(^{1}\)), and T is the temperature (298 K). Solving for n gives approximately 367 moles of gas in the room. 75% of this amount or approximately 275 moles is \(\mathrm{CO}_{2}\), which corresponds to about 12.2 kg when using the molar mass of \(\mathrm{CO}_{2}\) (44.01 g/mol).
03

Explain why more than the calculated amount must escape the cylinder

The calculated mass of \(\mathrm{CO}_{2}\) that must be present in the room for a lethal concentration does not consider that for \(\mathrm{CO}_{2}\) to occupy 75% of the room's volume, some of the original air in the room (made up of \(\mathrm{O}_{2}\), \(\mathrm{N}_{2}\), etc.) must be displaced and escape the room. Therefore, for 75% of the gas in the room to be \(\mathrm{CO}_{2}\), more than the calculated amount must leak from the cylinder.
04

Describe a plausible fatal sequence of events and suggest preventative measures.

A plausible sequence of events that could result in a fatality would be the valve on the \(\mathrm{CO}_{2}\) cylinder failing, releasing \(\mathrm{CO}_{2}\) into the room over a weekend. An individual entering the room on Monday morning would be exposed to a lethal concentration of \(\mathrm{CO}_{2}\). Preventative measures might include regularly checking and maintaining the valves on gas cylinders, installing a gas detector in the room, and ensuring that the room is well ventilated.

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Key Concepts

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

Asphyxiants
Asphyxiants are gases that can pose significant health risks even though they are not inherently toxic. They work by displacing oxygen in the air, making it difficult or impossible to breathe, which can lead to suffocation.
Unlike directly toxic gases, asphyxiants do not act by poisoning the body directly or by reacting chemically with biological tissues. Instead, their danger comes from reducing the concentration of oxygen available to living organisms.
  • A classic example of an asphyxiant is carbon dioxide ( CO_2 ), especially in confined spaces.
  • Breathing air with reduced oxygen levels can cause symptoms like dizziness, unconsciousness, or even death when the air is very low in oxygen concentration.
To mitigate the danger they pose, it's essential to ensure proper safety measures are in place when dealing with asphyxiants, especially in confined areas.
Gas Laws
Understanding gas laws is crucial when dealing with gases, especially in chemistry and physics. These laws explain how gases behave under various conditions of temperature, pressure, and volume.
The ideal gas law, for example, is often used to calculate the behavior of gases in a controlled environment: \( PV = nRT \).
  • Where \(P\) is the pressure, \(V\) is the volume, \(n\) is the number of moles of the gas, \(R\) is the ideal gas constant, and \(T\) is the temperature.
  • This equation allows for the determination of the number of moles in a given space, which can then be used to calculate the amount of a particular gas present in an environment.
In practical settings, such as the described scenario, gas laws help determine how much of an asphyxiant has leaked into the air and can predict the concentrations that might become hazardous.
Preventative Measures
Preventing accidents in environments where asphyxiants are stored involves a combination of safety practices. By implementing these measures, we reduce the risk of accidental exposure to harmful concentrations of gases.
Some effective preventative measures include:
  • Regularly inspecting and maintaining gas cylinders to ensure they are in good working order.
  • Installing gas detection alarms to alert personnel to dangerous gas concentrations.
  • Training staff on emergency procedures and the potential risks associated with chemical gases.
  • Limiting access to storage areas to only authorized personnel who are aware of the associated risks.
By focusing on these safety practices, it is possible to minimize hazards and maintain a safe working environment.
Chemical Storage
Proper storage of chemicals is vital to ensure the safety of personnel and the environment. When chemicals are stored incorrectly, they can become hazardous due to leaks or improper handling.
To safely store chemicals, consider the following guidelines:
  • Store chemicals in a well-ventilated area to prevent the accumulation of harmful gases.
  • Use appropriate containers that are designed for specific chemicals to prevent reactions.
  • Clearly label all containers with the chemical name and any hazard information.
  • Avoid storing incompatible chemicals together, as this can lead to dangerous reactions.
Safe chemical storage is a fundamental aspect of chemical safety protocols and can prevent incidents before they occur.
Ventilation
Ventilation plays a crucial role in maintaining air quality and safety where chemicals and gases are stored or used. Adequate ventilation ensures that any released gases, such as asphyxiants, are quickly dispersed and diluted.
Some tips to ensure proper ventilation include:
  • Installing mechanical ventilation systems to ensure a continuous supply of fresh air.
  • Using exhaust fans to remove contaminated air directly from the storage or work areas.
  • Regular checks and maintenance of ventilation systems to ensure they function efficiently.
By using proper ventilation, the risks associated with the accumulation of harmful gases are significantly minimized.
Safety Protocols
Implementing comprehensive safety protocols is key to preventing accidents involving hazardous chemicals. These protocols offer clear guidelines and procedures for handling emergencies and daily operations.
Here are some components of effective safety protocols:
  • Developing an emergency response plan for leaks or spills with clear instructions.
  • Conducting regular safety drills to ensure everyone knows what to do in an emergency.
  • Keeping safety equipment, such as respirators and fire extinguishers, accessible and in good condition.
  • Maintaining a safety data sheet (SDS) for all chemicals on-site to inform workers of the properties and hazards.
Comprehensive protocols ensure that everyone knows their role and can act swiftly to reduce risks and protect themselves and others.

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Most popular questions from this chapter

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.

A fuel cell is an electrochemical device that reacts hydrogen with oxygen from the air to produce water and DC electricity. A proposed application is replacement of the gasoline-fueled internal combustion engine in an automobile with a \(100 \mathrm{kW}\) fuel cell. You are on a summer internship with a gas supplier planning to transport hydrogen to service stations for use in cars powered by fuel cells. The hydrogen is to be transported in tube trailers, each of which has 10 tubes of length \(10.5 \mathrm{m}\) and diameter \(0.56 \mathrm{m}\). Hydrogen in the tubes at 2600 psig and an average temperature of \(298 \mathrm{K}\) is discharged at service stations to a final pressure of 55 psig. Refueling cach fuel-cell-powered automobile is estimated to require 4.0 kg of hydrogen. (a) You and your office-mate- an intern from a different university - have been asked to estimate the number of automobiles that can be refueled by one tube-trailer load of hydrogen. He does a very quick calculation and comes up with a value of 95 cars. Speculate how he did it and provide support for your speculation. What was his mistake? (b) Do the calculation using the SRK equation of state. Instead of using Eqs. \(5.3-11\) and \(5.3-13\) for the parameter \(\alpha,\) use the following correlation developed specifically for hydrogen: \(^{23}\) \(\alpha=1.202 \exp \left(-0.3228 T_{\mathrm{r}}\right)\) (c) Do the calculation using the law of corresponding states. (d) In which of the three estimates would you have the greatest confidence, and why?

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A slurry contains crystals of copper sulfate pentahydrate \(\left[\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}(\mathrm{s}), \text { specific gravity }=2.3\right]\) suspended in an aqueous copper sulfate solution (liquid SG \(=1.2\) ). A sensitive transducer is used to measure the pressure difference, \(\Delta P(\mathrm{Pa}),\) between two points in the sample container separated by a vertical distance of \(h\) meters. The reading is in turn used to determine the mass fraction of crystals in the slurry, \(x_{\mathrm{c}}(\mathrm{kg}\) crystals/kg slurry). (a) Derive an expression for the transducer reading, \(\Delta P(\mathrm{Pa}),\) in terms of the overall slurry density, \(\rho_{\mathrm{s}}\left(\mathrm{kg} / \mathrm{m}^{3}\right),\) assuming that the equation used to calculate the pressure head in Chapter 3 \(\left(P=P_{0}+\rho g h\right)\) is valid for this two-phase system. (b) Validate the following expression relating the overall slurry density to the liquid and solid crystal densities \(\left(\rho_{1} \text { and } \rho_{c}\right)\) and the mass fraction of crystals in the slurry: $$\frac{1}{\rho_{\mathrm{si}}}=\frac{x_{\mathrm{c}}}{\rho_{\mathrm{c}}}+\frac{\left(1-x_{\mathrm{c}}\right)}{\rho_{1}}$$ (c) Suppose \(175 \mathrm{kg}\) of the slurry is placed in the sample container with \(h=0.200 \mathrm{m}\) and a transducer reading \(\Delta P=2775\) Pa is obtained. Calculate \((\mathrm{i}) \rho_{\mathrm{s}_{\mathrm{s}},(\mathrm{ii})} x_{\mathrm{c}},\) (iii) the total slurry volume, (iv) the mass of crystals in the slurry, (v) the mass of anhydrous copper sulfate (CuSO \(_{4}\) without the water of hydration) in the crystals, (vi) the mass of liquid solution, and (vii) the volume of liquid solution. (d) Prepare a spreadsheet to generate a calibration curve of \(x_{c}\) versus \(\Delta P\) for this device. Take as inputs \(\rho_{\mathrm{c}}\left(\mathrm{kg} / \mathrm{m}^{3}\right), \rho_{1}\left(\mathrm{kg} / \mathrm{m}^{3}\right),\) and \(h(\mathrm{m}),\) and calculate \(\Delta P(\mathrm{Pa})\) for \(x_{\mathrm{c}}=0.0,0.05,0.10, \ldots, 0.60\) Run the program for the parameter values in this problem \(\left(\rho_{\mathrm{c}}=2300, \rho_{1}=1200, \text { and } h=0.200\right)\) Then plot \(x_{c}\) versus \(\Delta P\) (have the spreadsheet program do it, if possible), and verify that the value of \(x_{c}\) corresponding to \(\Delta P=2775\) Pa on the calibration curve corresponds to the value calculated in Part (c). (e) Derive the expression in Part (b). Take a basis of \(1 \mathrm{kg}\) of slurry \(\left[x_{\mathrm{c}}(\mathrm{kg}), V_{c}\left(\mathrm{m}^{3}\right)\right.\) crystals, \(\left.\left(1-x_{\mathrm{c}}\right)(\mathrm{kg}), V_{l}\left(\mathrm{m}^{3}\right) \text { liquid }\right],\) and use the fact that the volumes of the crystals and liquid are additive.

The bacteria acetobacter aceti convert ethanol to acetic acid in the presence of oxygen according to the reaction $$\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}+\mathrm{O}_{2} \rightarrow \mathrm{CH}_{3} \mathrm{COOH}+\mathrm{H}_{2} \mathrm{O}$$ In a continuous fermentation process, ethanol enters the top of the fermenter at a rate of \(145 \mathrm{kg} / \mathrm{h}\), and the air fed to the bottom of the fermenter is \(25 \%\) in excess of the amount required to consume all of the ethanol. A gas stream containing nitrogen and unreacted oxygen leaves the top of the fermenter, and a liquid stream containing acetic acid, water, and \(10 \%\) of the entering ethanol leaves the bottom. Assume that none of the ethanol, water, and acetic acid in the reactor is vaporized. The fermenter operates at \(30^{\circ} \mathrm{C},\) maintains a liquid \((\mathrm{SG}=0.95)\) height of \(4.5 \mathrm{m},\) and is open to the atmosphere (i.e., the pressure at the top of the fermenter is 1 atm). (a) What is the volumetric flow rate of air as it enters the bottom of the fermenter? What is the volumetric flow rate of gas leaving the top of the fermenter? (b) Assume a linear relationship between the fraction of oxygen reacted and the position of gas bubbles rising through the liquid in the fermenter: for example, half of the oxygen reacted is consumed in the bottom half of the fermenter. At the vertical midpoint of the fermenter, the average bubble diameter is \(1.5 \mathrm{mm}\). What is the average bubble diameter at the entry point of the air and as the gas leaves the liquid at the top of the fermenter?
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