Problem 17 - Chemistry: The Central Science in SI Units, Global Edition

Question

A solid white substance \(A\) is heated strongly in the absence of air. It decomposes to form a new white substance \(\mathrm{B}\) and a gas C. The gas has exactly the same properties as the product obtained when carbon is burned in an excess of oxygen. Based on these observations, can we determine whether solids A and \(\mathrm{B}\) and gas \(\mathrm{C}\) are elements or compounds?

Step-by-Step Solution

Answer

Based on the given observations, we can determine that gas C (carbon dioxide) is a compound as it has the same properties as the product obtained when carbon is burned in an excess of oxygen. Solid A is most likely a compound since it decomposes into two different substances when heated. However, we cannot definitively conclude if solid B is an element or a compound based solely on the given observation.

Step 1: Identify the properties of each substance

A solid white substance (A) decomposes to form a new white solid substance (B) and a gas (C). The gas has the same properties as the product obtained when carbon is burned in an excess of oxygen.

Step 2: Determine the identity of gas C

Since the gas produced has the same properties as the product obtained when carbon is burned in an excess of oxygen, we can identify the gas as carbon dioxide (CO₂). Carbon dioxide is a compound, as it is formed by the combination of carbon (an element) and oxygen (another element).

Step 3: Determine the nature of solids A and B

We have limited information on A and B, but we do know that when solid A is heated strongly, it decomposes into solid B and the gas C (carbon dioxide/CO₂). The decomposition of solid A into two different substances suggests that it is most likely a compound, as elements tend to form compounds when heated, rather than breaking down further. As to solid B, we know a new white substance is formed from the decomposition process. Since we have no information beyond this, we cannot definitively conclude if it is an element or a compound based solely on the given observation. In conclusion, we can determine that gas C (carbon dioxide) is a compound, and solid A is most likely a compound. However, we do not have enough information to make a definitive conclusion about the nature of solid B as an element or a compound.

Key Concepts

Understanding Elements and Compounds

In chemistry, understanding the difference between elements and compounds is fundamental.
An **element** is a pure substance that cannot be broken down into simpler substances by chemical means. It consists of only one type of atom. Think of elements as the basic building blocks of matter. For example, carbon (C) and oxygen (O) are both elements.
A **compound**, on the other hand, is a substance formed when two or more different elements combine in a specific ratio through a chemical reaction. Compounds have different properties than the individual elements they are composed of. For instance, water ( H_2O ) is a compound made from hydrogen and oxygen, which are both elements.
Understanding this distinction helps in analyzing substances like the white solid A in our exercise. Since it decomposes to form new substances, it's likely a compound, not a simple element.

The Role of Carbon Dioxide in Chemistry

Carbon dioxide ( CO_2 ) is a common compound with fascinating properties and roles in our world. When carbon burns in the presence of oxygen, **carbon dioxide** is one of the primary products. This gas is essential in various biological and chemical processes.
- **Structure**: Carbon dioxide has one carbon atom covalently bonded to two oxygen atoms.
- **Occurrence**: It's found in Earth's atmosphere, contributing to the greenhouse effect and global warming.
- **Biological Role**: Plants use carbon dioxide during photosynthesis to produce oxygen and glucose as part of their energy cycle. Without it, life as we know it wouldn't exist.
Recognizing carbon dioxide in reactions, such as the decomposition described in the exercise, provides insights into the nature of the substances involved; here, it indicates that at least one part of the decomposition process involved a compound previously containing carbon.

Exploring Chemical Reactions and Decomposition

Chemical reactions are processes that lead to the transformation of one set of chemical substances to another. When a chemical reaction involves a compound breaking down into simpler substances, it is called **decomposition**.
- **Decomposition Reaction**: This is a type of chemical reaction where a single compound breaks down into two or more products.
- **Examples**: Heating calcium carbonate ( CaCO_3 ) is a classic example, where it decomposes into calcium oxide ( CaO ) and carbon dioxide ( CO_2 ).
In our exercise, heating the white solid A in the absence of air results in its decomposition, suggesting that A is composed of multiple elements bound together. The emergence of carbon dioxide as a product confirms that at least some portion of the reacting compound contained carbon.
Understanding these fundamentals of chemical reactions helps clarify how substances transform and interact.