Textbook Question
Commercial concentrated aqueous ammonia is 28% NH3 by mass and has a density of 0.90 g/mL. What is the molarity of this solution?
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Ch.13 - Properties of Solutions
Chapter 13, Problem 57b
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?
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Determine the mass of zinc in a given volume of the brass sample. Assume a convenient volume, such as 1 m^3, for simplicity.
Calculate the mass of zinc in the assumed volume using the percentage composition: \( \text{mass of Zn} = 0.20 \times \text{total mass of brass} \).
Convert the mass of zinc to moles using the molar mass of zinc (65.38 g/mol).
Calculate the volume of the solution in liters. Since the density is given in kg/m^3, convert the volume from m^3 to liters (1 m^3 = 1000 L).
Determine the molarity of zinc by dividing the number of moles of zinc by the volume of the solution in liters.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Molarity
Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. It is expressed in moles per liter (mol/L) and is crucial for understanding how much of a substance is present in a given volume of solution. To calculate molarity, one must know the mass of the solute, its molar mass, and the total volume of the solution.
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Molarity
Density
Density is the mass of a substance divided by its volume, typically expressed in kg/m³ or g/cm³. In the context of solutions, density can help determine the mass of solute present in a specific volume of solution. Knowing the density of the brass sample allows for the calculation of the total mass of the solution, which is essential for finding the molarity of the zinc component.
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Substitutional Alloys
Substitutional alloys are formed when atoms of the solute metal replace some of the atoms in the solvent metal's crystal lattice. In the case of brass, zinc atoms substitute for copper atoms, affecting the physical properties of the alloy. Understanding the composition of substitutional alloys is important for calculating the proportions of each metal, which is necessary for determining the molarity of the components in the solution.
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Related Practice
Textbook Question
Commercial concentrated aqueous ammonia is 28% NH3 by mass and has a density of 0.90 g/mL. What is the molarity of this solution?
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Textbook Question
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. (a) What is the molality of Zn in the solid solution?
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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 (a) mol percentage,
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