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Chlorine is widely used to purify municipal water supplies and to treat swimming pool waters. Suppose that the volume of a particular sample of \(\mathrm{Cl}_{2}\) gas is \(8.70 \mathrm{~L}\) at \(119.3 \mathrm{kPa}\) and \(24^{\circ} \mathrm{C}\). (a) How many grams of \(\mathrm{Cl}_{2}\) are in the sample? (b) What volume will the \(\mathrm{Cl}_{2}\) occupy at STP? (c) At what temperature will the volume be \(15.00 \mathrm{~L}\) if the pressure is \(116.8 \mathrm{kPa}\) (d) At what pressure will the volume equal \(5.00 \mathrm{~L}\) if the temperature is \(58^{\circ} \mathrm{C} ?\)

Short Answer

Expert verified
29.50 g of \(\mathrm{Cl}_2\); 9.46 L at STP; 237.82°C for 15.00 L; 228.30 kPa for 5.00 L at 58°C.

Step by step solution

01

Calculate Moles of Chlorine Gas

First, we use the ideal gas law to find the number of moles of chlorine gas (\(\mathrm{Cl}_2\)). The ideal gas law equation is \(PV = nRT\), where \(P\) is pressure (in kPa), \(V\) is volume (in L), \(n\) is moles, \(R\) is the ideal gas constant (8.314 J/mol·K), and \(T\) is temperature in Kelvin. Convert the temperature from Celsius to Kelvin: \(T = 24 + 273.15 = 297.15\,\mathrm{K}\). Rearrange the ideal gas law to solve for \(n\): \[n = \frac{PV}{RT} = \frac{119.3 \times 8.70}{8.314 \times 297.15} = 0.416\,\mathrm{mol}\].
02

Convert Moles to Grams

To find how many grams of \(\mathrm{Cl}_2\) we have, we multiply the moles (calculated above) by the molar mass of \(\mathrm{Cl}_2\) (70.90 g/mol):\[\text{mass in grams} = 0.416 \times 70.90 = 29.50\,\mathrm{g}\].
03

Calculate Volume at STP

Standard Temperature and Pressure (STP) is defined as 0°C (273.15 K) and 100 kPa. Using the moles from Step 1 and the ideal gas law, solve for the new volume \(V_{STP}\): \[V_{STP} = \frac{nRT_{STP}}{P_{STP}} = \frac{0.416 \times 8.314 \times 273.15}{100} = 9.46\,\mathrm{L}\].
04

Find Temperature for Given Volume and Pressure

Using the ideal gas law, rearrange to find temperature \(T\) when volume is 15.00 L and pressure is 116.8 kPa: \[T = \frac{PV}{nR} = \frac{116.8 \times 15.00}{0.416 \times 8.314} = 510.97\,\mathrm{K}\]. Convert back to Celsius: \(T = 510.97 - 273.15 = 237.82\,\degree\mathrm{C}\).
05

Calculate Pressure for Given Volume and Temperature

To find pressure when the volume is 5.00 L and the temperature is 58°C (331.15 K), use the ideal gas law: \[P = \frac{nRT}{V} = \frac{0.416 \times 8.314 \times 331.15}{5.00} = 228.30\,\mathrm{kPa}\].

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Key Concepts

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

Chlorine gas
Chlorine gas, also known as  \( \text{Cl}_2\), is a diatomic molecule, meaning that each molecule consists of two chlorine atoms. This gas has numerous applications, particularly in disinfection. It is commonly used in water treatment facilities to purify water, making it safe for consumption, and in swimming pools to keep them sanitized. Chlorine gas is known for its pale green color and pungent smell.
Special precautions need to be taken when handling chlorine gas because it can be harmful or even dangerous at high concentrations. Its gas state allows it to be compressed and stored in pressurized containers, making it convenient for industrial and municipal use.
  • Chlorine gas is denoted chemically as \( \text{Cl}_2\).
  • It is essential for water purification and sanitation.
  • Safety measures are crucial when handling chlorine gas due to its toxic nature in high amounts.
Molar mass
The molar mass of a substance is a simple yet essential concept in chemistry. It refers to the mass of one mole of a chemical compound, expressed in grams per mole (g/mol). In this exercise, the molar mass of chlorine gas, \( \text{Cl}_2\), is calculated by summing up the molar masses of two chlorine atoms. Each chlorine atom has a molar mass of about 35.45 g/mol.
Therefore, for chlorine gas, the total molar mass comes out to be approximately 70.90 g/mol. Understanding molar mass is crucial because it allows us to convert between moles and grams, facilitating calculations in chemical reactions and processes.
  • Molar mass is used to convert moles of a substance to grams.
  • The molar mass of \( \text{Cl}_2\) is approximately 70.90 g/mol.
Pressure calculations
Pressure calculations are integral to working with gases, especially when using the ideal gas law. This law enables the determination of unknown variables like pressure, volume, or temperature when the other conditions are known. The key idea in pressure calculations is how pressure, along with volume and temperature, impacts the behavior of a gas.
In this exercise, we determine the pressure of chlorine gas when the volume and temperature change. The formula \(P = \frac{nRT}{V}\) allows us to find the new pressure by substituting known values of moles, temperature in Kelvin, and volume. Through this process, we calculate the adjusted pressure conditions for a given volume and temperature.
  • Pressure is measured in kilopascals (kPa) in this context.
  • The ideal gas law is used: \(PV=nRT\).
  • Tools like the ideal gas law are essential for predicting how gases behave under different conditions.
Temperature conversion
Temperature conversion is a necessary step in calculations involving gases because the ideal gas law needs temperature values in Kelvin, not Celsius.
To convert a temperature in Celsius to Kelvin, you simply add 273.15 to the Celsius temperature. This conversion ensures that we're using an absolute temperature scale, which is necessary for accurate gas calculations.
  • For example, \(24\, \degree\text{C}\) is converted to \(297.15\, \text{K}\).
  • Always add 273.15 to Celsius temperatures to get Kelvin.

Kelvin is preferred in gas law calculations because zero Kelvin represents absolute zero, the point where molecular motion stops. This makes it a more appropriate scale for a range of scientific calculations.

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Most popular questions from this chapter

A glass vessel fitted with a stopcock valve has a mass of \(337.428 \mathrm{~g}\) when evacuated. When filled with \(\mathrm{Ar}\), it has a mass of \(339.854 \mathrm{~g}\). When evacuated and refilled with a mixture of Ne and Ar, under the same conditions of temperature and pressure, it has a mass of \(339.076 \mathrm{~g}\). What is the mole percent of Ne in the gas mixture?

A \(334-\mathrm{mL}\) cylinder for use in chemistry lectures contains \(5.225 \mathrm{~g}\) of helium at \(23^{\circ} \mathrm{C}\). How many grams of helium must be released to reduce the pressure to 7.60 MPa assuming ideal gas behavior?

Suppose you are given two 2 -L flasks and told that one contains a gas of molar mass 28 , the other a gas of molar mass 56 , both at the same temperature and pressure. The mass of gas in the flask \(A\) is \(1.0 \mathrm{~g}\) and the mass of gas in the flask \(\mathrm{B}\) is \(2.0 \mathrm{~g}\). Which flask contains the gas of molar mass \(28,\) and which contains the gas of molar mass \(56 ?\)

You have a gas at \(25^{\circ} \mathrm{C}\) confined to a cylinder with a movable piston. Which of the following actions would double the gas pressure? (a) Lifting up on the piston to double the volume while keeping the temperature constant; (b) Heating the gas so that its temperature rises from \(25^{\circ} \mathrm{C}\) to \(50^{\circ} \mathrm{C}\), while keeping the volume constant; (c) Pushing down on the piston to halve the volume while keeping the temperature constant.

(a) Place the following gases in order of increasing average molecular speed at \(25^{\circ} \mathrm{C}: \mathrm{O}_{2}, \mathrm{Ar}, \mathrm{CO}, \mathrm{HCl}, \mathrm{CH}_{4} \cdot(\mathbf{b})\) Calculate the rms speed of CO molecules at \(25^{\circ} \mathrm{C}\). (c) Calculate the most probable speed of an argon atom in the stratosphere, where the temperature is \(0^{\circ} \mathrm{C}\).

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