Dodecane, C12H26, is an unbranched alkane. Predict the following:
(a) Will it dissolve in water?
(b) Will it dissolve in hexane?
(c) Will it burn when ignited?
(d) Is it a liquid, solid, or gas at room temperature and atmospheric pressure?
(e) Is it more or less dense than water?
The Correct Answer and Explanation is :
Correct Answers:
(a) Will it dissolve in water?
No, dodecane will not dissolve in water.
(b) Will it dissolve in hexane?
Yes, dodecane will dissolve in hexane.
(c) Will it burn when ignited?
Yes, dodecane will burn when ignited.
(d) Is it a liquid, solid, or gas at room temperature and atmospheric pressure?
Dodecane is a liquid at room temperature and atmospheric pressure.
(e) Is it more or less dense than water?
Dodecane is less dense than water.
Explanation (300 words):
Dodecane (C₁₂H₂₆) is a hydrocarbon that belongs to the alkane family, characterized by nonpolar covalent bonds. Its properties are governed by its molecular structure and intermolecular forces.
(a) Solubility in water: Water is polar and forms strong hydrogen bonds, while dodecane is nonpolar and only experiences weak London dispersion forces. According to the principle “like dissolves like,” polar and nonpolar substances do not mix. Thus, dodecane does not dissolve in water.
(b) Solubility in hexane: Hexane is also a nonpolar solvent, like dodecane. Both compounds experience London dispersion forces, making them compatible. Consequently, dodecane dissolves readily in hexane.
(c) Combustibility: As a hydrocarbon, dodecane can undergo combustion in the presence of oxygen, producing carbon dioxide and water. This reaction is exothermic, meaning it releases energy. Hence, dodecane burns when ignited.
(d) Physical state: Dodecane has a boiling point of approximately 216°C and a melting point of -9.6°C. At room temperature (about 25°C) and atmospheric pressure, it exists as a liquid. Its high boiling point results from its relatively large molecular size, which increases intermolecular dispersion forces.
(e) Density: Dodecane’s density is approximately 0.75 g/cm³, which is lower than water’s density (1.0 g/cm³). This is typical for hydrocarbons, as they have less mass per unit volume due to weaker molecular packing and lower atomic mass of hydrogen and carbon compared to water’s oxygen and hydrogen atoms.
These properties highlight dodecane’s behavior as a nonpolar alkane suitable for nonpolar solvents and its utility as a combustible fuel or solvent.