Question

Comment on whether each of the following is a homogeneous mixture or a heterogeneous mixture: (a) air in a closed bottle, (b) air over New York City.

Short answer

(a) Homogeneous; (b) Heterogeneous.

Step-by-step solution

Understanding Mixtures

Before we classify each example, recall that a homogeneous mixture has the same uniform appearance and composition throughout while a heterogeneous mixture consists of visibly different substances or phases.

Evaluate Air in a Closed Bottle

Air in a closed bottle is an example of a homogeneous mixture. This is because the composition of gases (mainly nitrogen, oxygen, and small amounts of other gases) is uniform throughout the bottle, resulting in a consistent mixture.

Evaluate Air Over New York City

Air over New York City can be considered a heterogeneous mixture. This is due to the presence of varying levels of pollutants, dust, smoke, and other particles that create differences in composition across different areas and times.

Comparison and Conclusion

Compare the two examples to see how one maintains uniformity while the other does not. In summary, a closed environment like a bottle maintains a homogeneous mixture, whereas the dynamic and varying environment over a city results in a heterogeneous mixture.

Key concepts

Homogeneous Mixtures

When we think of homogeneous mixtures, imagine something that looks the same no matter where you sample it from. These mixtures are consistent in appearance and composition because their components are evenly distributed. For instance, air in a closed bottle is a perfect example of a homogeneous mixture.

• The gases within—mainly nitrogen, oxygen, and small amounts of others like carbon dioxide—are uniformly spread.
• This uniformity ensures that no matter where you check within the bottle, the composition seems the same.
• Such mixtures often need no shaking or stirring, as their uniformity is natural and stable.

Even though we can't "see" the individual gases, their even distribution makes it a true homogeneous mixture.

Heterogeneous Mixtures

Heterogeneous mixtures, on the other hand, have visibly different components or phases. This means their composition is not the same throughout. When you look at air over New York City, you find a heterogeneous mixture.

• This is because the air contains varying elements like pollutants, dust, and smoke.
• These differences can change from one part of the city to another, or even from one moment to the next.
• Therefore, if you sample the air in different places around the city, you'll likely find differences.

This variability is a hallmark of a heterogeneous mixture—what you see and measure can change depending on where you check.

Composition

Composition refers to the types and amounts of substances within a mixture. In both homogeneous and heterogeneous mixtures, understanding composition is key to determining their nature.

• In homogeneous mixtures, since the composition is uniform, you consistently get the same blend of substances everywhere in the sample, like air in a closed bottle.
• In heterogeneous mixtures, the composition can differ from place to place, such as in the air over New York City with its uneven distribution of pollutants and natural air elements.
• Being aware of a mixture’s composition helps us predict its behavior, such as how it will react with other substances or how it might be filtered or divided.

Thus, a basic grasp of composition forms the foundation for classifying mixtures.

Gases

Gases play a vital role in mixtures, as they easily combine to form either homogeneous or heterogeneous mixtures. In the context of air:

• Gases like nitrogen and oxygen are primary components, with others like carbon dioxide being secondary.
• When confined in a controlled environment like a bottle, these gases blend into a homogeneous mixture.
• In open and dynamic environments, such as a city, these gases mix with particles and pollutants, resulting in a heterogeneous mixture.

Understanding gases and their behavior in mixtures helps clarify how the same substance can be part of both homogeneous and heterogeneous contexts.