Problem 79 - Chemistry The Central Science In Si Units

Question

Hexane (density \(=0.659 \mathrm{~g} / \mathrm{mL}\) ) and acetic acid (density = \(1.0446 \mathrm{~g} / \mathrm{mL}\) ) do not form a solution when mixed but are separate in distinct layers. A piece of oak wood (density \(\left.=900 \mathrm{~kg} / \mathrm{m}^{3}\right)\) is placed inside a test tube containing hexane and acetic acid solution; sketch how the three substances would position themselves.

Step-by-Step Solution

Answer

Hexane on top, oak wood in the middle, acetic acid at the bottom.

Step 1: Convert wood density to g/mL

First, convert the oak wood density from kg/m³ to g/mL, as hexane and acetic acid densities are in g/mL. We know 1 kg/m³ = 0.001 g/mL, therefore, divide 900 kg/m³ by 1000 to get 0.900 g/mL.

Step 2: Compare Densities to Determine Layer Order

Compare the densities of the three substances: hexane (0.659 g/mL), acetic acid (1.0446 g/mL), and oak wood (0.900 g/mL). The substance with the lowest density will be on top, and the one with the highest density on the bottom. The order from top to bottom based on their densities will be hexane, then wood, and then acetic acid.

Step 3: Visualize the Layer Arrangement

Sketch the test tube: The least dense hexane layer will be at the top due to its lighter density, followed by the oak wood in the middle, since its density is higher than hexane but lower than acetic acid. Acetic acid forms the bottom layer as it has the highest density.

Key Concepts

Layering of Liquids

In the fascinating world of liquids, the concept of layering occurs when different substances with varying densities are poured into a container. Each substance forms a distinct layer, with the least dense floating on top and the most dense sinking to the bottom. This natural separation arises due to the differences in mass and volume of the substances, which determine their density. In our exercise, we have hexane, acetic acid, and an oak wood piece.

• Hexane - It has the lowest density among the three, measuring at 0.659 g/mL. Because of this, it forms the topmost layer.
• Oak Wood - With a density of 0.900 g/mL (after converting from kg/m³), it finds its place in the middle.
• Acetic Acid - The densest of the trio, at 1.0446 g/mL, occupies the bottom layer.

This concept not only helps in visualizing how different substances interact when mixed but also illuminates characteristics such as buoyancy and material properties.

Density Conversion

Density conversion is a critical process when comparing substances measured in different units, as seen in our exercise. The oak wood's density needed conversion from kg/m³ to g/mL to compare it accurately with hexane and acetic acid, both already in g/mL.

• To convert 1 kg/m³ = 0.001 g/mL.
• Thus, for oak wood, 900 kg/m³ is equivalent to 900 x 0.001 = 0.900 g/mL.

This simple yet important conversion step allows us to make precise comparisons, aiding our understanding of how different materials interact in the same environment. Consistent units are essential for correct density calculations and visualization of liquid layering.

Relative Density

Relative density, or specific gravity, compares the density of a substance to that of a reference, usually water. It sheds light on whether a substance will float or sink in reference liquids.

• Hexane's Relative Density - With a density less than 1 g/mL, it floats on water and situates at the top in our liquid mix.
• Oak Wood's Relative Density - It is also less than 1 g/mL after conversion, indicating buoyancy in pure water but placing it above acetic acid due to acetic acid's higher density.
• Acetic Acid's Relative Density - Having a density greater than 1 g/mL implies it sinks in water, and in our mix, it forms the bottom layer under hexane and the oak wood.

Understanding relative density helps predict and explain the behavior of substances in various solvents and environments, providing insights into applications spanning from industrial processes to natural phenomena.