Why does increasing the concentration of sugar in water cause the boiling point of the solution to become higher?

• A. Sugar molecules reduce the vapor pressure of the solution, requiring a higher temperature for boiling.
• B. Sugar molecules increase the vapor pressure of the solution, causing it to boil at a lower temperature.
• C. Sugar acts as a catalyst, speeding up the boiling process and raising the boiling point.
• D. Sugar reacts chemically with water to form a compound with a higher boiling point.

Answer: (A)

Verified step by step guidance

1. Understand that boiling occurs when the vapor pressure of a liquid equals the external atmospheric pressure.
2. Recognize that adding a non-volatile solute like sugar to water lowers the vapor pressure of the solution because sugar molecules do not evaporate and interfere with water molecules escaping into the vapor phase.
3. Recall the concept of boiling point elevation, a colligative property, which states that the boiling point of a solvent increases when a solute is dissolved in it due to the lowering of vapor pressure.
4. Use the qualitative relationship: since the vapor pressure is reduced, the solution must be heated to a higher temperature to reach the atmospheric pressure and boil.
5. Conclude that sugar molecules cause the boiling point of the solution to increase by reducing the vapor pressure, not by chemical reaction or catalysis.