Which of the following solutes, when dissolved in equal molal amounts in water, will raise the boiling point of water the most?

• A. C_6H_{12}O_6 (glucose)
• B. KNO_3
• C. NaCl
• D. CaCl_2

Answer: (D)

Verified step by step guidance

1. Understand that the boiling point elevation depends on the number of dissolved particles in solution, not just the amount of solute. This is a colligative property, which depends on the total concentration of solute particles.
2. Recall the boiling point elevation formula: \(\Delta T_b = i \cdot K_b \cdot m\), where \(\Delta T_b\) is the boiling point elevation, \(i\) is the van't Hoff factor (number of particles the solute dissociates into), \(K_b\) is the boiling point elevation constant for the solvent (water), and \(m\) is the molality of the solution.
3. Determine the van't Hoff factor \(i\) for each solute: glucose (\(C_6H_{12}O_6\)) does not dissociate, so \(i=1\); potassium nitrate (\(KNO_3\)) dissociates into \(K^+\) and \(NO_3^-\), so \(i=2\); sodium chloride (\(NaCl\)) dissociates into \(Na^+\) and \(Cl^-\), so \(i=2\); calcium chloride (\(CaCl_2\)) dissociates into \(Ca^{2+}\) and 2 \(Cl^-\) ions, so \(i=3\).
4. Since all solutes are dissolved in equal molal amounts, the difference in boiling point elevation depends on the van't Hoff factor \(i\). The solute with the highest \(i\) will produce the greatest boiling point elevation.
5. Conclude that \(CaCl_2\) with \(i=3\) will raise the boiling point of water the most compared to the other solutes listed.