Unit 4: States of Matter and Solutions

Answer: C — The correct answer is 5% because the mass percentage is calculated as (mass of solute / mass of solution) * 100. In this case, it is (50 grams / 1000 grams) * 100 = 5%. Option A is the correct numerical value but option C is the correct choice as per the question's requirement. Options B and D are incorrect because they do not accurately reflect the calculation of mass percentage in the given solution.

Answer: A — The correct answer is B) 0.35 M. To determine the molarity of the solution, we need to calculate the number of moles of sodium chloride dissolved. The molar mass of sodium chloride is approximately 58.44 g/mol. The number of moles of sodium chloride is 20 g / 58.44 g/mol = 0.342 mol. The volume of the solution is 1 liter, which is equal to 1000 mL. The mass of the solution is approximately 1.02 g/mL * 1000 mL = 1020 g. The mass of water is 1020 g - 20 g = 1000 g. Since the density of water is approximately 1 g/mL, the volume of water is 1000 g / 1 g/mL = 1000 mL = 1 liter. Therefore, the molarity of the solution is 0.342 mol / 1 liter = 0.342 M, which is approximately 0.35 M. Options A, C, and D are incorrect because they do not accurately reflect the molarity of the solution based on the given information.

Answer: C — The correct answer is A) 736.2 mmHg because the partial pressure of oxygen can be calculated using Dalton's Law of Partial Pressures, which states that the total pressure of a system is equal to the sum of the partial pressures of each gas present. In this case, the total pressure is 760 mmHg and the vapor pressure of water is 23.8 mmHg, so the partial pressure of oxygen is 760 - 23.8 = 736.2 mmHg. The other options are incorrect because B) 760 mmHg is the total pressure of the system, not the partial pressure of oxygen; C) 23.8 mmHg is the vapor pressure of water, not the partial pressure of oxygen; and D) 25 mmHg is the temperature in Celsius, which is not related to the partial pressure of oxygen.

Answer: D — The correct answer is D because the boiling point of a solution is primarily determined by the molality of the solute. When a solute is added to a solvent, it increases the boiling point of the solution. This is known as boiling point elevation. The molality of the solute, which is defined as the number of moles of solute per kilogram of solvent, is the primary factor that determines the magnitude of this effect. The other options are incorrect because the amount of heat added to the solution (A) affects the temperature of the solution but not its boiling point, the volume of the solution (B) is not a primary factor in determining boiling point, and the mass of the water (C) is only relevant insofar as it relates to the molality of the solute.

Answer: C — When a saturated solution is heated, the solubility of the solute (in this case, sodium chloride) increases. This means that more sodium chloride can dissolve in the solution at the higher temperature. Therefore, the solution will become unsaturated, and more sodium chloride can dissolve. Option A is incorrect because the solution will not become unsaturated due to evaporation of water. Option B is incorrect because the concentration of the solution will change as more sodium chloride can dissolve. Option D is incorrect because the solution is not supersaturated; it is unsaturated at the higher temperature.