Which of the following is used as antifreeze in cars for cooling the engine? A.$10\% $ (V/V) ethanol solution in water B.$35\% $ (V/V) ethanol solution in glycol C.$45\% $ (V/V) ethanol solution in glycol D.$20\% $ (V/V) ethanol solution in water
Hint: Antifreeze is a substance that causes depression in the freezing point of a solution. Depression in freezing point is a colligative property and depends on the number of solute particles or impurities present in the solution.
Complete step by step answer: Antifreeze is used to lower the freezing point of a water based mixture. We know that water has good cooling properties and can thus be used vastly as a coolant. We add antifreeze in water and the mixture is used as a coolant in appliances and engines. We know that water on freezing forms ice. The volume of ice is greater than liquid water because of the structure of ice. So, if water is used alone as a coolant, it may freeze at lower temperatures. As water expands on freezing, it can cause the engine or the vehicle to burst. Thus, it is essential to decrease the freezing point of water in order to use it as a coolant. Solution of water with organic compounds are widely used as coolants. Alcohols are widely preferred for use as antifreeze in coolants as they have a high cryoscopic constant. We know that the depression in freezing point is directly proportional to the cryoscopic constant of the solute. Thus, $10\% $ (V/V) ethanol solution in water is used as antifreeze.
Thus, the correct option is A.
Note: We know from the knowledge of colligative properties that we can also use salt solutions as antifreeze. They also cause a higher depression in freezing point due to the dissociation in aqueous solution which increase the number of solute particles. However, salt solutions are corrosive in nature and can reduce the life of the engine. Thus, we prefer organic compounds as antifreeze.