Question

Which of the following best describes the air around you on a typical day? (Assume the air is made up of \(\sim 80 \%\) nitrogen and \(\sim 20 \%\) oxygen. Ignore other gases such as water vapor and carbon dioxide. a. Air is a homogeneous mixture of gases because it generally contains the same ratio of gaseous substances from one region to another. b. Air is a heterogeneous mixture of gases because it contains different gaseous substances in unequal amounts. c. Air is a pure substance because it always has the same composition. d. Air is a compound because it is made up of nitrogen and oxygen, which are different elements. e. Air is an element because it contains nitrogen and oxygen, which are found in the periodic table.

Short answer

The correct answer is (a). Air is a homogeneous mixture of gases because it generally contains the same ratio of gaseous substances from one region to another.

Step-by-step solution

Understanding Homogeneous and Heterogeneous Mixtures

A homogeneous mixture is a mixture in which the components are evenly distributed and have a uniform composition. On the other hand, a heterogeneous mixture is a mixture in which the components are unevenly distributed and do not have a uniform composition.

Understanding Pure Substances and Compounds

A pure substance has a fixed composition and cannot be separated into simpler substances by physical methods. Compounds are pure substances made up of two or more elements chemically combined and can be separated into simpler substances by chemical methods.

Understanding Elements

An element is a pure substance that cannot be broken down into simpler substances by chemical methods and consists of only one type of atom.

Analyzing the Options

Now, let's analyze the given options: a. The air is homogeneous because it generally contains the same ratio of gaseous substances. This is quite true since the stated composition does not vary significantly from one region to another. This option seems like a good contender. b. The air is heterogeneous because it contains different gaseous substances in unequal amounts. This is not correct since although it contains different gases, the composition remains generally consistent and uniform. c. The air is a pure substance because it always has the same composition. This is not correct since the air is a mixture of different gases, not a pure substance. d. The air is a compound because it is made up of nitrogen and oxygen, which are different elements. This is not correct since the air is a mixture, not chemically bonded as a single compound. e. Air is an element because it contains nitrogen and oxygen, which are found in the periodic table. This is not correct since air is composed of elements, but it is not an element itself. Taking into account all the analysis made, the correct answer is: a. Air is a homogeneous mixture of gases because it generally contains the same ratio of gaseous substances from one region to another.

Key concepts

Air Composition

Air is a fascinating mixture that surrounds us every day. Understanding its composition is essential for grasping how it functions as a homogeneous mixture. The primary components of air are nitrogen and oxygen, but it's not just these gases alone.
There are also small amounts of other gases like argon, carbon dioxide, and traces of water vapor. However, for simplicity, we often focus on nitrogen and oxygen.

• Nitrogen makes up about 78% of the air we breathe.
• Oxygen accounts for approximately 21%.

These percentages can vary slightly depending on location and conditions, but in general, they remain consistent, forming a uniform arrangement.
This consistency across different regions is what makes air a homogeneous mixture rather than a heterogeneous one.

Nitrogen and Oxygen in Air

Nitrogen and oxygen are vital components of air, but they exist as separate gases, not combined chemically. This is crucial for distinguishing between a mixture and a compound.
Nitrogen, the most abundant, plays several roles:

• Essential for plant growth when combined with other elements.
• Inert nature prevents unwanted reactions.

Oxygen is equally important:

• Critical for respiration in living organisms.
• Supports combustion.

Their presence as separate gases rather than a single chemical entity emphasizes the mixed nature of air. This means that air is not a compound but a mixture of individual gases, each retaining its own properties.

Pure Substances and Mixtures

The distinction between pure substances and mixtures helps clarify why air is categorized as a homogeneous mixture.
Pure substances have a uniform composition and specific properties. They are either elements or compounds:

• Elements consist of a single type of atom.
• Compounds are composed of two or more elements chemically bonded together.

Mixtures, on the other hand, include multiple substances physically combined, not chemically.
By understanding this, it becomes clear that air, with its combination of nitrogen, oxygen, and other gases, does not fit the criteria for a pure substance. Instead, it's a uniform, well-distributed collection of different gases, exemplifying a homogeneous mixture.