Brass is a substitutional alloy consisting of a solution of copper and zinc. A particular sample of red brass consisting of 80.0 % Cu and 20.0 % Zn by mass has a density of 8750 kg/m3. (b) What is the molarity of Zn in the solution?
Ch.13 - Properties of Solutions
Chapter 13, Problem 60a
Breathing air that contains 4.0 % by volume CO2 over time causes rapid breathing, throbbing headache, and nausea, among other symptoms. What is the concentration of CO2 in such air in terms of (a) mol percentage,

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Start by understanding that the problem provides the concentration of CO2 as a volume percentage, which is 4.0% by volume.
Recall that for gases, volume percentage is equivalent to mole percentage under the same conditions of temperature and pressure, due to Avogadro's law.
Since the volume percentage is given as 4.0%, the mole percentage of CO2 is also 4.0%.
This is because, under the same conditions, equal volumes of gases contain an equal number of moles.
Therefore, the concentration of CO2 in terms of mole percentage is the same as the volume percentage, which is 4.0%.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Mole Fraction and Mol Percentage
Mole fraction is a way of expressing the concentration of a component in a mixture, defined as the ratio of the number of moles of that component to the total number of moles of all components. Mol percentage is simply the mole fraction multiplied by 100, providing a percentage representation of the component's concentration in the mixture.
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Gas Laws
Gas laws describe the behavior of gases in relation to pressure, volume, and temperature. Understanding these laws, particularly Dalton's Law of Partial Pressures, is essential for analyzing gas mixtures, as it states that the total pressure of a gas mixture is equal to the sum of the partial pressures of each individual gas.
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Combined Gas Law
Volume Percent Concentration
Volume percent concentration expresses the amount of a substance in a mixture as a percentage of the total volume. In the context of gases, it indicates the volume of a specific gas relative to the total volume of the gas mixture, which is particularly useful for understanding the composition of air and its effects on health.
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Constant-Volume Calorimetry
Related Practice
Textbook Question
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Textbook Question
Caffeine (C8H10N4O2) is a stimulant found in coffee and tea. If a solution of caffeine in the solvent chloroform (CHCl3) has a concentration of 0.0500 m, calculate (b) the mole fraction of caffeine in the solution.
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Open Question
During a person’s typical breathing cycle, the CO2 concentration in the expired air rises to a peak of 4.6% by volume. (b) What is the molarity of the CO2 in the expired air at its peak, assuming a body temperature of 37 °C?
Textbook Question
Breathing air that contains 4.0 % by volume CO2 over time causes rapid breathing, throbbing headache, and nausea, among other symptoms. What is the concentration of CO2 in such air in terms of (b) molarity, assuming 1 atm pressure and a body temperature of 37 °C?
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Open Question
You make a solution of a nonvolatile solute with a liquid solvent. Indicate whether each of the following statements is true or false. (a) The freezing point of the solution is higher than that of the pure solvent. (b) The freezing point of the solution is lower than that of the pure solvent.
Textbook Question
You make a solution of a nonvolatile solute with a liquid solvent. Indicate if each of the following statements is true or false. (a) The freezing point of the solution is unchanged by addition of the solvent.
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