Problem 63 - Chemistry and Chemical Reactivity

Question

Three liquids of different densities are mixed. Because they are not miscible (do not form a homogeneous solution with one another), they form discrete layers, one on top of the other. Sketch the result of mixing carbon tetrachloride \(\left(\mathrm{CCl}_{4}, d=1.58 \mathrm{g} / \mathrm{cm}^{3}\right),\) mercury \((d=\) \(\left.13.546 \mathrm{g} / \mathrm{cm}^{3}\right),\) and water \(\left(d=1.00 \mathrm{g} / \mathrm{cm}^{3}\right)\)

Step-by-Step Solution

Answer

Mercury is at the bottom, carbon tetrachloride in the middle, and water on top.

Step 1: List Densities

First, note down the densities of the liquids: \( \text{CCl}_4 \) has a density of 1.58 g/cm³, mercury has a density of 13.546 g/cm³, and water has a density of 1.00 g/cm³.

Step 2: Determine Order

Arrange the liquids in order of their densities from highest to lowest. Mercury (13.546 g/cm³) has the highest density, carbon tetrachloride (1.58 g/cm³) is in the middle, and water (1.00 g/cm³) has the lowest density.

Step 3: Sketch Layers

Draw a container and sketch the layers based on their densities. At the bottom, place mercury, followed by carbon tetrachloride in the middle, and water on the top.

Key Concepts

Immiscible Liquids

Immiscible liquids are types of liquids that do not mix to form a single homogeneous phase. Instead, these liquids retain distinct layers when combined in a container. The word 'immiscible' originates from the Latin word 'miscere', meaning 'to mix', with the prefix 'im-' indicating 'not'.
In practical terms, when two immiscible liquids, such as oil and water, are placed in a shared container, they will separate into two distinct layers rather than blending together.

• This occurrence is often due to differences in polarity. For example, water is a polar molecule while many oils are non-polar, preventing them from mixing.
• It is important to recognize immiscible liquids because understanding this concept allows for the correct prediction of how liquids will behave when combined in scenarios such as chemical experiments or cooking.

Thus, knowing whether liquids are immiscible helps us understand the fundamental interactions between different substances.

Liquid Layering

Liquid layering occurs when immiscible liquids are poured into a container, each settling into a separate layer based on their densities. When various liquids of different densities are mixed, they automatically organize themselves from the heaviest at the bottom to the lightest at the top.
In the provided exercise, mercury sits at the bottom layer due to its high density, carbon tetrachloride forms the middle layer, and water stays at the top since it is the least dense of the three liquids.

• This sorting effects occur because gravitity exerts force on each liquid according to its mass per unit volume or density.
• Layering provides a visual representation of the relative densities of the liquids involved.

Liquid layering helps in easily identifying and separating immiscible liquids based on their physical properties.

Densities of Substances

The density of a substance refers to its mass per unit of volume, commonly expressed in grams per cubic centimeter (g/cm³) or kilograms per cubic meter (kg/m³). Density provides key insights into how different substances will behave when they come into contact with one another.
The density values of liquids in an experiment, like in the original exercise, can determine the layering order when they are combined: mercury with a density of 13.546 g/cm³, carbon tetrachloride at 1.58 g/cm³, and water at 1.00 g/cm³.

• Knowledge of densities allows us to predict which liquid will float on top of another.
• Fluids with lower densities ascend, while those with higher densities descend in a container.

This property is essential in both natural phenomena and industrial applications where density-based separation is used.

Density-Based Separation

Density-based separation exploits the differences in densities between substances to separate them from each other. This method is frequently used in various scientific and industrial processes to systematically and efficiently segregate mixtures into their individual components.
For example, during oil spill clean-ups, skimmers are used to separate the oil from water by taking advantage of their differing densities. In the given exercise scenario, this method appears vividly as the three liquids form stacked layers based solely on their densities.

• Separations based on density are useful because they require minimal energy input compared to other techniques, relying instead on gravitational force.
• This separation technique allows for recovery and reuse of materials, benefitting sustainable practices.

Density-based separation is a practical application of both science and engineering for solving everyday problems and managing environmental issues efficiently.