Multiple Choice
What is the boiling point of a solution of 0.150 mole Al(NO3)3 in 0.500 kg of water, given that the ebullioscopic constant (Kb) is 0.512°C m⁻¹?
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14. Solutions
Boiling Point Elevation
Multiple Choice
What mass in grams of NaCl would need to be added to 2951 g of water to increase the boiling temperature of the solution by 1.500°C? (Kb for water is 0.5100°C/m)
A
135.0 g
B
67.5 g
C
270.0 g
D
45.0 g
Verified step by step guidance1
Identify the formula for boiling point elevation: ΔT_b = i * K_b * m, where ΔT_b is the change in boiling point, i is the van't Hoff factor, K_b is the ebullioscopic constant, and m is the molality of the solution.
Determine the van't Hoff factor (i) for NaCl. Since NaCl dissociates into two ions (Na^+ and Cl^-), i = 2.
Rearrange the formula to solve for molality (m): m = ΔT_b / (i * K_b). Substitute the given values: ΔT_b = 1.500°C, i = 2, and K_b = 0.5100°C/m.
Calculate the molality (m) using the rearranged formula. This will give you the moles of solute per kilogram of solvent.
Convert the molality to mass of NaCl. Use the molality to find the moles of NaCl needed, then multiply by the molar mass of NaCl (58.44 g/mol) to find the mass in grams. Remember to convert the mass of water from grams to kilograms when using the molality formula.
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