The mass density of a mixture of ethyl alcohol and water is \(950 \mathrm{~kg} / \mathrm{m}^{3} .\) Is the mixture mostly water, mostly alcohol, or about half and half? What is your reasoning?

When discussing the concept of density, it refers to the amount of mass per unit volume of a substance. In the case of mixtures like ethyl alcohol and water, density comparison helps us determine the composition of the mixture. The key factor we look at is the mixture's density relative to the known densities of the pure substances involved.

From the solved problem, we see that the density of the mixture is 950 kg/m³, which places it between the density of pure ethyl alcohol (789 kg/m³) and pure water (1000 kg/m³). By understanding that density is an intensive property – meaning it does not depend on the amount of substance but rather its identity – we recognize that the mixture's density being closer to that of water indicates a higher proportion of water to alcohol.

This method of comparison is useful in various applications such as quality control in manufacturing, determining the alcohol content in beverages, and even in forensic science where the composition of substances can be crucial evidence.

Water, with the chemical formula H2O, is one of the most well-studied substances due to its essential role in life on Earth. It is a polar molecule, which means it has a partial positive charge on one end and a partial negative charge on the other, making it an excellent solvent. This polarity also leads to hydrogen bonding, a special type of dipole-dipole attraction that contributes to water's unique properties.

• High Specific Heat: Water can absorb a lot of heat without a significant rise in temperature, meaning it's great for temperature regulation.
• Surface Tension: Due to hydrogen bonding, water has a high surface tension, allowing insects like water striders to walk on its surface.
• Density: Water has a maximum density at 4°C; below this temperature, it expands and becomes less dense, which is why ice floats on liquid water.

These properties make water an excellent reference point when comparing densities. Substances with a higher density than water will sink, while those with a lower density will float.

Ethyl alcohol, or ethanol, is another common substance with properties that distinctly differ from water. Ethanol has the chemical formula C2H5OH and is also polar, although less so than water, due to the presence of the hydrocarbon chain.

• Lower Density: With a density of about 789 kg/m³, ethanol is less dense than water, which is why it floats on water.
• Volatility: Ethanol is more volatile than water; it evaporates more readily due to weaker hydrogen bonds compared to water.
• Solubility: Ethanol is miscible with water in all proportions, which means it can be mixed with water to form a homogeneous solution at any ratio.

This lower density of ethanol compared to water is critical when analyzing mixtures of the two; the more ethanol present, the lower the overall density of the mixture. In practice, understanding ethanol's properties allows its use in various applications, from alcoholic beverages to biofuels and antiseptics.