Lars observes a substance to be a solid and to float in water at room temperature ([tex]$23^{\circ} C$[/tex]). Based on the given properties, which substance is the most likely identity of this sample?
| Substance | Melting Point ([tex]$^{\circ} C$[/tex]) | Boiling Point ([tex]$^{\circ} C$[/tex]) | Density at Room Temperature ([tex]$g / cm^3$[/tex]) |
|---|---|---|---|
| carbon tetrachloride | -22.9 | 76.7 | 1.59 |
| cetyl alcohol | 49.3 | 344 | 0.811 |
| dichlorobenzene | 53.5 | 174 | 1.25 |
| Sulfur hexafluoride | -64 | -50.8 | 0.00617 |
A. carbon tetrachloride
B. cetyl alcohol
C. dichlorobenzene
D. sulfur hexafluoride
Answer (2)
Check the melting point of each substance to determine if it is a solid at 2 3 ∘ C .
Check the density of the solid substances to determine if they float in water (density less than 1 g / c m 3 ).
Carbon tetrachloride and sulfur hexafluoride are not solid at 2 3 ∘ C .
Dichlorobenzene is solid but sinks in water. Cetyl alcohol is solid and floats in water, so the answer is B .
Explanation
Problem Analysis We are looking for a substance that is a solid at 2 3 ∘ C and floats in water (density less than 1 g / c m 3 ). Let's analyze each substance.
Analyzing Carbon Tetrachloride Carbon tetrachloride: Melting point is − 22. 9 ∘ C . Since − 22.9 < 23 , it is a liquid at 2 3 ∘ C . So, it is not the substance we are looking for.
Analyzing Cetyl Alcohol Cetyl alcohol: Melting point is 49. 3 ∘ C . Since 23"> 49.3 > 23 , it is a solid at 2 3 ∘ C . Density is 0.811 g / c m 3 . Since 0.811 < 1 , it floats in water. This could be the substance we are looking for.
Analyzing Dichlorobenzene Dichlorobenzene: Melting point is 53. 5 ∘ C . Since 23"> 53.5 > 23 , it is a solid at 2 3 ∘ C . Density is 1.25 g / c m 3 . Since 1"> 1.25 > 1 , it sinks in water. So, it is not the substance we are looking for.
Analyzing Sulfur Hexafluoride Sulfur hexafluoride: Melting point is − 6 4 ∘ C . Since − 64 < 23 , it is a gas at 2 3 ∘ C . So, it is not the substance we are looking for.
Conclusion Based on the analysis, cetyl alcohol is the only substance that is a solid at 2 3 ∘ C and floats in water.
Examples
Understanding the properties of materials, such as melting point and density, is crucial in many real-world applications. For example, engineers need to select materials that remain solid at operating temperatures and float in water for designing marine equipment. Similarly, in the food industry, knowing the melting points of fats and oils helps in controlling the texture and stability of products. This problem demonstrates how these properties can be used to identify substances and predict their behavior in different conditions.
The substance that is a solid and floats in water at 23°C is cetyl alcohol, which has a melting point of 49.3°C and a density of 0.811 g/cm³. Carbon tetrachloride and sulfur hexafluoride are liquids or gases at this temperature, and dichlorobenzene, while solid, sinks in water. Therefore, the correct answer is B. cetyl alcohol.
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