As the percentage of antifreeze in the coolant increases, __.
a. The freeze point decreases (up to a point)
b. The boiling point decreases
c. The heat transfer increases
d. All of the above
The Correct Answer and Explanation is:
Correct Answer: a. The freeze point decreases (up to a point)
Explanation (300+ words):
Antifreeze, commonly made of ethylene glycol or propylene glycol, is added to the coolant in a vehicle’s radiator system to alter the freezing and boiling characteristics of the coolant. The primary role of antifreeze is to prevent the coolant from freezing in cold conditions and from boiling in hot conditions.
A. The freeze point decreases (up to a point) – Correct
As the percentage of antifreeze in the coolant increases, the freezing point of the solution drops, meaning it can remain in liquid form at lower temperatures. This is due to freezing point depression, a colligative property in chemistry, where the addition of a solute (in this case, antifreeze) to a solvent (water) lowers the freezing point of the resulting solution. However, this effect only continues up to a certain concentration — typically around 60-70% antifreeze. Beyond this point, adding more antifreeze can raise the freezing point again, making the coolant less effective in cold weather.
B. The boiling point decreases – Incorrect
This statement is false. As antifreeze concentration increases, the boiling point of the coolant actually increases, not decreases. This is another colligative property called boiling point elevation. A higher antifreeze concentration allows the coolant to operate at higher temperatures without boiling, which is beneficial in preventing engine overheating.
C. The heat transfer increases – Incorrect
This is also false. Water is a better conductor of heat than antifreeze. Therefore, as the antifreeze concentration increases, the thermal conductivity decreases, which means the ability of the coolant to transfer heat actually reduces. High antifreeze concentrations can result in reduced efficiency in heat removal from the engine.
D. All of the above – Incorrect
Since both options B and C are incorrect, option D is also incorrect.
Conclusion:
The most accurate and scientifically supported choice is A: The freeze point decreases (up to a point), which reflects the key benefit of antifreeze in cold climates.