Question

Hexane \(\left(\mathrm{C}_{6} \mathrm{H}_{14}, \text { density }=0.766 \mathrm{g} / \mathrm{cm}^{3}\right),\) perfluorohexane \(\left(\mathrm{C}_{6} \mathrm{F}_{14}, \text { density }=1.669 \mathrm{g} / \mathrm{cm}^{3}\right),\) and water are immiscible liquids; that is, they do not dissolve in one another. You place \(10 \mathrm{mL}\) of each in a graduated cylinder, along with pieces of high-density polyethylene (HDPE, density \(=0.97 \mathrm{g} / \mathrm{cm}^{3}\) ), polyvinyl chloride (PVC, \(\left.\text { density }\left.=1.36 \mathrm{g} / \mathrm{cm}^{3}\right), \text { and Teflon (density }=2.3 \mathrm{g} / \mathrm{cm}^{3}\right)\) None of these common plastics dissolves in these liquids. Describe what you expect to see.

Short answer

From top to bottom in the cylinder: hexane, HDPE, water, PVC, perfluorohexane, and Teflon.

Step-by-step solution

Identify the Density of Each Liquid

First, determine the density of each liquid involved in this problem: Hexane has a density of 0.766 g/cm³, perfluorohexane has a density of 1.669 g/cm³, and water has a density of 1.00 g/cm³. Based on density differences, the order of the liquids from top to bottom in a graduated cylinder should be hexane (least dense), water, and perfluorohexane (most dense).

Identify the Density of Each Plastic

Next, examine the density of each plastic: HDPE has a density of 0.97 g/cm³, PVC has a density of 1.36 g/cm³, and Teflon has a density of 2.3 g/cm³.

Determine the Layer Placement of Plastics

Plastics will float on liquids less dense than themselves and sink in liquids denser than themselves. HDPE, with a density of 0.97 g/cm³, will float on the water layer but sink in the hexane layer. PVC, with a density of 1.36 g/cm³, will float on the perfluorohexane layer but sink in the water layer. Teflon, with its density of 2.3 g/cm³, will sink to the bottom of the cylinder, beneath the perfluorohexane layer.

Describe the Final Arrangement

In the graduated cylinder, from top to bottom, expect hexane (least dense), HDPE (floating on water), water, PVC (floating on perfluorohexane), perfluorohexane, and lastly Teflon (resting at the very bottom).

Key concepts

Immiscible Liquids

Immiscible liquids are those that do not mix or dissolve in one another. This means they form distinct layers when placed in the same container. Think of oil and water as a classic example. Each liquid remains separate and forms layers based on their densities. In the exercise, we have hexane, water, and perfluorohexane. These liquids have different densities and are immiscible, allowing them to stack in layers within a graduated cylinder.

This separation occurs because the molecules of immiscible liquids are not attracted to each other, unlike miscible liquids that blend uniformly. Understanding this property helps in determining how substances will arrange themselves, which is key in many scientific experiments and industrial applications.

Mass and Volume

Mass and volume are core concepts when dealing with density. Mass is the amount of matter in an object and is usually measured in grams (g), while volume is the amount of space an object occupies, commonly measured in cubic centimeters (cm³) or milliliters (mL).

Density is calculated by dividing mass by volume (\( \text{Density} = \frac{\text{Mass}}{\text{Volume}} \)). This relationship helps us understand why substances with different densities create separate layers. An object with higher density compared to the liquid it's in will sink, whereas one with lower density will float. Understanding these concepts is essential in predicting the behavior of various materials in different liquids.

Graduated Cylinder

A graduated cylinder is a common laboratory tool used to measure the volume of liquids accurately. It is marked with volume units along its length and allows for precise measurement of liquid layers.

In experiments with immiscible liquids, a graduated cylinder helps visualize the separation of each layer. When you pour different liquids into it, denser liquids settle at the bottom, while less dense liquids float on top. This tool is crucial for observing how solid objects like plastics interact with these layers based on their densities.

• The transparency of the cylinder allows for easy observation.
• The cylindrical shape aids in layering liquids neatly.

Plastic Density Comparison

To compare the density of plastics, we look at how each plastic behaves in different layers of immiscible liquids. Plastics like HDPE, PVC, and Teflon have varying densities, which determine whether they float or sink.

HDPE, with a density of 0.97 g/cm³, will float on water but sink in hexane, as it is denser than hexane but less dense than water. PVC, at 1.36 g/cm³, will float on perfluorohexane because it is less dense than perfluorohexane but will sink in water. Teflon, being the most dense at 2.3 g/cm³, will settle at the bottom beneath all layers since it is denser than any of the liquids.

By understanding the densities, we can predict and explain the behavior of materials in various environments, which is valuable in designing and utilizing different materials based on their physical properties.