Pure water boils at 100°C. What is the new boiling point of water after the addition of 13.12 g aluminum chloride, AlCl₃, to 615 g water?  

• A. 100.25°C
• B. 100.08°C
• C. 100.33°C
• D. 100.16°C

Answer: (C)

Verified step by step guidance

1. First, understand that the boiling point elevation is a colligative property, which means it depends on the number of solute particles in a solution, not their identity. The formula for boiling point elevation is 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 of the solvent, and m is the molality of the solution.
2. Calculate the molality (m) of the solution. Molality is defined as moles of solute per kilogram of solvent. First, find the moles of AlCl3 using its molar mass. The molar mass of AlCl3 is approximately 133.34 g/mol. Use the formula: moles = mass (g) / molar mass (g/mol).
3. Determine the van't Hoff factor (i) for AlCl3. When dissolved, AlCl3 dissociates into Al^3+ and 3 Cl^- ions, resulting in i = 4 because one formula unit of AlCl3 produces four ions.
4. Calculate the molality using the formula: m = moles of solute / mass of solvent (kg). Convert the mass of water from grams to kilograms by dividing by 1000.
5. Finally, use the boiling point elevation formula: ΔT_b = i * K_b * m. The ebullioscopic constant (K_b) for water is approximately 0.512°C kg/mol. Calculate ΔT_b and add it to the normal boiling point of water (100°C) to find the new boiling point.