객관식
A solution of water (Kb=0.512 °C/m) and glucose boils at 103.56 °C. What is the molal concentration of glucose in this solution? Assume that the boiling point of pure water is 100.00 °C.
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14. Solutions
Boiling Point Elevation
객관식
Some people add salt to water, claiming that the salt raises the boiling point of the water, which makes the food cook faster. If 323 g of NaCl is added to a 2.54 L pot of water, what is the new boiling point of the solution?
A
101.3°C
B
102.0°C
C
99.8°C
D
100.5°C
검증된 단계별 안내1
Determine the molality of the NaCl solution. First, calculate the number of moles of NaCl using its molar mass. The molar mass of NaCl is approximately 58.44 g/mol. Use the formula: \( \text{moles of NaCl} = \frac{\text{mass of NaCl}}{\text{molar mass of NaCl}} \).
Calculate the molality of the solution. Molality (m) is defined as the number of moles of solute per kilogram of solvent. Assume the density of water is approximately 1 g/mL, so 2.54 L of water is 2540 g. Use the formula: \( m = \frac{\text{moles of NaCl}}{\text{mass of water in kg}} \).
Use the boiling point elevation formula to find the change in boiling point. The formula is \( \Delta T_b = i \cdot K_b \cdot m \), where \( i \) is the van't Hoff factor for NaCl (which is 2, since NaCl dissociates into two ions: Na\(^+\) and Cl\(^-\)), \( K_b \) is the ebullioscopic constant for water (0.512 °C kg/mol), and \( m \) is the molality.
Calculate the change in boiling point (\( \Delta T_b \)) using the values obtained in the previous steps.
Add the change in boiling point (\( \Delta T_b \)) to the normal boiling point of water (100°C) to find the new boiling point of the solution.
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