Question

Hydrometers are used to determine the density of water in car radiators, these tools have lines on them to indicate the density of the liquid they are placed into. Since density varies as a function of the amount of antifreeze (ethylene glycol) added, it is possible to determine the percentage of antifreeze in the radiator and the temperature at which it would freeze. Knowing the density of ethylene glycol to be 0.958 and the density for water is ~1.0, would a radiator containing fluid with a density of 0.976 or 0.989 be better prepared for cold weather? Explain.

Answer 1

At lower temperatures, molecules move slower, collide easily, does not move farther apart, and therefore occupy less space for the same amount of mass. Thus, the density (mass to volume ratio) of a fluid is generally inversely related to its temperature.

The radiator with a specific gravity of 0.976 has more anti-freeze than the one with a specific gravity of 0.989, and thus will not freeze at a lower temperature.

Also, lower density (0.976) indicates a higher percentage or concentration of ethylene glycol, hence a greater freezing point depression.