Ch.1 - Introduction: Matter, Energy, and Measurement

Problem 17

Chapter 1, Problem 17

A solid white substance A is heated strongly in the absence of air. It decomposes to form a new white substance 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 B and gas C are elements or compounds?

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Identify the gas C by analyzing the information given: it has exactly the same properties as the product obtained when carbon is burned in excess oxygen. Burning carbon in excess oxygen produces carbon dioxide (CO\_2), which is a compound, not an element.

Since gas C is carbon dioxide (a compound), consider the decomposition reaction of solid A into solid B and gas C. This suggests that solid A contains carbon and oxygen in some form, and upon heating, it breaks down to release CO\_2 gas.

Analyze the nature of solids A and B: since A decomposes to form B and CO\_2, both A and B are likely compounds because elements do not typically decompose to form other solids plus a compound gas without changing their elemental identity.

Conclude that gas C is a compound (carbon dioxide), and solids A and B are also compounds, based on the decomposition behavior and the identity of the gas produced.

Summarize that none of the substances A, B, or C are elements; instead, A and B are compounds, and C is a compound gas formed from the decomposition of A.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Thermal Decomposition

Thermal decomposition is a chemical process where a compound breaks down into simpler substances when heated, often without oxygen. It helps identify whether a substance is a compound by observing if it splits into different products upon heating.

Identification of Gases by Properties

Gases can be identified by comparing their physical and chemical properties to known substances. Since gas C has the same properties as the product of carbon burning in oxygen (carbon dioxide), it suggests gas C is CO2, a compound, not an element.

Distinguishing Elements from Compounds

Elements are pure substances that cannot be broken down further by chemical means, while compounds consist of two or more elements chemically combined. Observing decomposition into different substances indicates the original solid is a compound, while the products may be elements or compounds.

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