Question

Which of the following are solutions? (a) Italian salad dressing (b) Rubbing alcohol (c) Algae in pond water (d) Mouthwash

Short answer

Rubbing alcohol and mouthwash are solutions.

Step-by-step solution

Define a Solution

A solution is a homogeneous mixture where the components are uniformly distributed, and only one phase is present. Typically, it consists of a solute dissolved in a solvent.

Analyze Italian Salad Dressing

Italian salad dressing is typically a heterogeneous mixture containing oil, vinegar, herbs, and spices. Because the components separate and it contains multiple phases, it's not a solution.

Analyze Rubbing Alcohol

Rubbing alcohol is generally a homogeneous mixture of isopropanol and water. Since the alcohol and water combine into one clear phase, it qualifies as a solution.

Analyze Algae in Pond Water

Pond water with algae contains visible particles of algae mixed with water, making it a heterogeneous mixture. Since it has multiple phases, it is not a solution.

Analyze Mouthwash

Mouthwash is typically a homogeneous mixture of water, alcohol, coloring, and flavoring agents. As it appears as one uniform phase, mouthwash is considered a solution.

Key concepts

Homogeneous Mixture

A homogeneous mixture is a type of mixture in which the components are distributed uniformly throughout the substance. This means that no matter where you take a sample from, you will find the same composition. An easy way to remember this is to think about mixing sugar in water. Once it's dissolved, every sip you take is the same.

• The components are mixed at the molecular level.
• There are no visible boundaries between different components.
• It forms a single phase, typically liquid.

Solutions are a common example of homogeneous mixtures, blending substances so well that they appear as one phase. This uniformity is what qualifies substances like rubbing alcohol and mouthwash as examples of solutions.

Heterogeneous Mixture

In contrast to homogeneous mixtures, heterogeneous mixtures are those where the composition varies from one part to another. They consist of visibly different substances or phases, meaning that you can usually see the distinct parts in the mixture.

• The components of the mixture remain separate and can be identified visually.
• It can consist of two or more phases.
• The mixture is not uniform throughout.

An example of a heterogeneous mixture is Italian salad dressing. The oil, vinegar, and herbs do not mix uniformly, creating distinct layers. Similarly, pond water with algae is heterogeneous due to the visible separation between water and algae.

Solute and Solvent

Understanding solutions involves recognizing the roles of solutes and solvents. The solute is the substance that gets dissolved, like sugar in our earlier example, while the solvent is the substance that does the dissolving, like water.

• The solute is generally present in a smaller amount.
• The solvent is the larger component, capable of dissolving the solute.
• Both parts must be compatible for a solution to form.

In a solution like rubbing alcohol, water acts as the solvent and isopropanol as the solute. Together, they mix uniformly to form a homogeneous solution.

Phases in Mixtures

The concept of phases in mixtures is crucial to understanding why some mixtures are solutions and others are not. A phase refers to any part of a system that has uniform composition and properties. In a mixture:

• A single phase means a mixture is homogeneous.
• Multiple phases indicate a heterogeneous mixture.
• Phases can be solid, liquid, or gas.

When substances blend into one phase, such as with mouthwash, they form a solution. However, when a mixture like Italian salad dressing displays oil and vinegar in separate phases, it remains heterogeneous. Recognizing phases helps distinguish between different types of mixtures.