How does adding antifreeze to a car's radiator affect the boiling point of the coolant?

• A. It decreases the boiling point of the coolant.
• B. It has no effect on the boiling point of the coolant.
• C. It increases the boiling point of the coolant.
• D. It causes the coolant to boil at a lower temperature than pure water.

Answer: (C)

Verified step by step guidance

1. Understand that antifreeze is typically a solute (such as ethylene glycol) added to the solvent, which is water in the car's radiator.
2. Recall the concept of boiling point elevation, a colligative property where adding a non-volatile solute to a solvent increases the boiling point of the solution compared to the pure solvent.
3. Apply the boiling point elevation formula: \(\Delta T_b = i \cdot K_b \cdot m\), where \(\Delta T_b\) is the increase in boiling point, \(i\) is the van't Hoff factor (number of particles the solute dissociates into), \(K_b\) is the ebullioscopic constant of the solvent, and \(m\) is the molality of the solution.
4. Recognize that adding antifreeze increases the molality \(m\) of the solution, thus increasing \(\Delta T_b\) and raising the boiling point of the coolant mixture above that of pure water.
5. Conclude that the presence of antifreeze in the radiator fluid causes the coolant to boil at a higher temperature, improving the engine's performance by preventing overheating.