At approximately what minimum percentage of ethanol by volume does an ethanol-water solution remain liquid and not freeze at standard household freezer temperatures (about -18^ext{o}C)?

• A. 40%
• B. 20%
• C. 50%
• D. 35%

Answer: (C)

Verified step by step guidance

1. Understand that the freezing point of a solution depends on the concentration of solutes—in this case, ethanol in water. Ethanol lowers the freezing point of water due to freezing point depression.
2. Recall that pure water freezes at 0\^\{\circ\}C, and pure ethanol freezes at about -114\^\{\circ\}C. Mixing ethanol and water creates a solution with a freezing point somewhere between these values, depending on the ethanol concentration.
3. Recognize that standard household freezers operate around -18\^\{\circ\}C, so the ethanol concentration must be high enough to lower the freezing point of the solution below this temperature to remain liquid.
4. Use or refer to a phase diagram or freezing point data for ethanol-water mixtures, which shows the relationship between ethanol volume percentage and freezing point. Identify the minimum ethanol percentage where the freezing point is below -18\^\{\circ\}C.
5. Conclude that the minimum ethanol volume percentage to keep the solution liquid at -18\^\{\circ\}C is approximately 50%, as lower percentages freeze at higher temperatures.