MCAT General Chemistry Question 121: Answer and Explanation
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Question: 121
1. An aqueous solution was prepared by mixing 70 g of an unknown nondissociating solute into 100 g of water. The solution has a boiling point of 101.11°C. What is the molar mass of the solute?
(Note:)
- A.
- B.
- C.
- D.
Correct Answer: A
Explanation:
The equation ΔTb = iKbm can be used to solve this problem. The change in boiling point is 101.11 - 100 = 1.11°C. Then, we can plug that into:
The van 't Hoff factor for this solute is 1 because the molecule does not dissociate into smaller components. Then, we can convert to grams of solute using the definition of molality:
The mass used in this equation is 0.1 kg because 100 mL of water has a mass of 0.1 kg. Then, we can determine the molar mass:
which is closest to choice (A).