To determine which substance can be a solid at room temperature (23°C) and float in water, we need to examine the melting point, boiling point, and density of each substance listed.
1. Carbon Tetrachloride:
- Melting Point: -22.9°C
- Boiling Point: 76.7°C
- Density at Room Temperature: 1.59 g/cm³
Analysis:
- At 23°C, carbon tetrachloride is above its melting point (-22.9°C) and below its boiling point (76.7°C), so it is in the liquid phase.
- Since its density (1.59 g/cm³) is greater than water's density (1.0 g/cm³), it sinks in water.
2. Cetyl Alcohol:
- Melting Point: 49.3°C
- Boiling Point: 344°C
- Density at Room Temperature: 0.811 g/cm³
Analysis:
- At 23°C, cetyl alcohol is below its melting point (49.3°C), so it is in solid phase.
- Since its density (0.811 g/cm³) is less than water’s density (1.0 g/cm³), it floats in water.
3. Dichlorobenzene:
- Melting Point: 53.5°C
- Boiling Point: 174°C
- Density at Room Temperature: 1.25 g/cm³
Analysis:
- At 23°C, dichlorobenzene is below its melting point (53.5°C), so it is in solid phase.
- However, its density (1.25 g/cm³) is greater than water’s density (1.0 g/cm³), so it sinks in water.
4. Sulfur Hexafluoride:
- Melting Point: -64°C
- Boiling Point: -50.8°C
- Density at Room Temperature: 0.00617 g/cm³
Analysis:
- At 23°C, sulfur hexafluoride is above both its melting point (-64°C) and its boiling point (-50.8°C), so it is in the gas phase.
Based on this analysis, the only substance that meets the criteria of being a solid at 23°C and floating in water due to its lower density than water (1.0 g/cm³) is cetyl alcohol.
Thus, the most likely identity of the substance observed by Lars is:
Answer: B. cetyl alcohol
