To determine the correct substance that Lars observes, we need to consider the given properties of the substances and the conditions at room temperature (23°C).
Given data for each substance:
1. Carbon tetrachloride
- Melting Point: -22.9°C
- Boiling Point: 76.7°C
- Density: 1.59 g/cm³
2. Cetyl alcohol
- Melting Point: 49.3°C
- Boiling Point: 344°C
- Density: 0.811 g/cm³
3. Dichlorobenzene
- Melting Point: 53.5°C
- Boiling Point: 174°C
- Density: 1.25 g/cm³
4. Sulfur hexafluoride
- Melting Point: -64°C
- Boiling Point: -50.8°C
- Density: 0.00617 g/cm³
Conditions at room temperature:
- Temperature: 23°C
- Density of water: 1.0 g/cm³
To solve the problem, we need to find a substance that meets the following criteria at 23°C:
1. It is a solid.
2. It floats in water.
To be a solid:
- The room temperature (23°C) should be less than the melting point of the substance.
To float in water:
- The density of the substance must be less than the density of water (1.0 g/cm³).
Let's evaluate each substance:
1. Carbon tetrachloride:
- Melting Point: -22.9°C (23°C > -22.9°C, so it’s not a solid at room temperature)
2. Cetyl alcohol:
- Melting Point: 49.3°C (23°C < 49.3°C, so it’s a solid)
- Density: 0.811 g/cm³ (less than 1.0 g/cm³, so it will float)
3. Dichlorobenzene:
- Melting Point: 53.5°C (23°C < 53.5°C, so it’s a solid)
- Density: 1.25 g/cm³ (greater than 1.0 g/cm³, so it will sink)
4. Sulfur hexafluoride:
- Melting Point: -64°C (23°C > -64°C, so it’s not a solid at room temperature)
From this analysis, we can conclude that the only substance which is both a solid and floats in water at room temperature is cetyl alcohol.
Correct answer: B. Cetyl alcohol
