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Chapter 13: Problem 103

Instructions on a container of antifreeze (ethylene glycol; \(\left.\mathrm{fp},-12.6^{\circ} \mathrm{C}, \mathrm{bp}, 197.3^{\circ} \mathrm{C}\right)\) give the following volumes of Prestone to be used in protecting a \(12 \mathrm{qt}\) cooling system against freeze-up at different temperatures (the remaining liquid is water): \(10^{\circ} \mathrm{F}, 3 \mathrm{qt}\) \(0^{\circ} \mathrm{F}, 4 \mathrm{qt} ;-15^{\circ} \mathrm{F}, 5 \mathrm{qt} ;-34^{\circ} \mathrm{F}, 6 \mathrm{qt} .\) since the freezing point of the coolant is successively lowered by using more antifreeze, why not use even more than 6 qt of antifreeze (and proportionately less water) to ensure the maximum protection against freezing?

Short Answer

Expert verified
Using more than a certain proportion of antifreeze can lead to decreased cooling capabilities due to reduced water (which has a high heat capacity), a potential increase in the freezing point, and potentially cause mechanical problems due to increased solution viscosity.

Step by step solution

01

Understanding Freezing Point Depression

Freezing point depression is a colligative property of solutions. This means it depends on the amount of dissolved substances, not the type. When solute (like antifreeze) is added to a solvent (like water), it lowers the freezing point of the solvent. This property is why antifreeze is used in cooling systems. The more antifreeze, the lower the freezing point.
02

Importance of Balanced Proportions

Why not add more antifreeze for further protection? It's all about balance. The cooling capacity of the solution is not purely a role of antifreeze. Water has a notably high heat capacity, helping keep engines at an optimal operating temperature. If too much antifreeze is added, it could adversely affect the cooling capability of the system - the overall cooling capacity of the solution could decrease, causing the engine to overheat.
03

Understanding Concentration and Molality

Remember that the freezing point depression depends on the molality - the number of moles of solute (antifreeze) per kilogram of solvent (water). Replacing too much water with antifreeze would reduce this ratio, potentially causing a higher freezing point than desired.
04

Increasing Antifreeze beyond a Certain Point is Counter-Productive

The antifreeze usage beyond a certain point (given here as 6 quarts) would not only decrease the cooling efficiency but also potentially increase the freezing point of the solution. As higher concentrations also make the liquid more viscous, which can cause mechanical problems in the pumps and pipes of the cooling system.

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Most popular questions from this chapter

The aqueous solubility at \(20^{\circ} \mathrm{C}\) of \(\mathrm{Ar}\) at \(1.00 \mathrm{atm}\) is equivalent to \(33.7 \mathrm{mL} \mathrm{Ar}(\mathrm{g}),\) measured at STP, per liter of water. What is the molarity of Ar in water that is saturated with air at 1.00 atm and \(20^{\circ} \mathrm{C}\) ? Air contains \(0.934 \%\) Ar by volume. Assume that the volume of water does not change when it becomes saturated with air.

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