Water is less dense than ethanol despite ethanol's larger molecular weight due to the polar molecular structure of water. The H-O-H angle creates a dipole moment, resulting in stronger intermolecular attractions among water molecules. This leads to water molecules being more closely packed compared to ethanol molecules, which do not exhibit the same level of attraction. Consequently, the density of water is higher than that of ethanol.
PREREQUISITESChemistry students, educators, and anyone interested in understanding the physical properties of liquids and the effects of molecular structure on density.
markosheehan said:Why is ethanol less dense than water if ethanol has a larger molecular weight. I think i heard it's something to do with water molecules being closer to each other. Why is this?
I like Serena said:Water has a polar molecular structure.
That is, the H-O-H atoms make an angle, causing a so called dipole moment, being negatively charged on one end, and positively charged on the other end.
Consequently $H_2O$ molecules have a stronger attraction to each other, and also to other polar molecules.