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Chapter 3: Problem 11

What is a pure substance?

Short Answer

Expert verified
A pure substance is material that has uniform and unchanging composition; examples include elements like iron and compounds like water.

Step by step solution

01

Understanding a Pure Substance

A pure substance is a form of matter that has a consistent chemical composition and property throughout. It cannot be separated into components by physical methods (i.e., without breaking chemical bonds). Pure substances include elements and compounds.
02

Examples of Pure Substances

Provide examples of pure substances to help distinguish them from mixtures. For instance, iron, water, and carbon dioxide are pure substances because they consist only of one type of molecule or atom.
03

Identifying Pure Substances

Confirm that a substance is pure by checking if it has unique set of properties such as boiling point, melting point, and density. These properties are the same throughout the sample if it's pure.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Chemical Composition
Understanding the chemical composition of substances is crucial when studying matter. It refers to the identity and proportion of elements that make up a substance. Each pure substance has a specific chemical composition that remains unchanged, unless it undergoes a chemical reaction. For example, water (H2O) consists of two hydrogen atoms for every oxygen atom, a ratio that is constant for every sample of pure water. This distinct composition differentiates pure substances from mixtures, where the proportion of components can vary.
Physical Separation Methods
In contrast to chemical methods that involve breaking and forming bonds, physical separation methods rely on the physical differences between substances, such as density, solubility, or melting point, to separate them. Examples of such methods include filtration, distillation, and evaporation. While these techniques are effective for mixtures, they cannot isolate substances from a pure compound. For a pure substance, which has uniform properties throughout, physical separation methods would yield samples with the same properties and composition as the original.
Elements and Compounds
Elements and compounds represent two classes of pure substances. An element is a substance that consists of only one kind of atom, such as gold (Au) or oxygen (O2). A compound, on the other hand, contains two or more different atoms chemically bonded together, like sodium chloride (NaCl) or glucose (C6H12O6). Unlike mixtures, these substances cannot be divided into simpler materials by physical methods and maintain constant properties throughout a given sample.
Unique Properties of Substances
The unique properties of substances are intrinsic characteristics that help in identifying a pure substance and differentiating it from others. These include boiling point, melting point, and density. For instance, pure water boils at 100掳C at sea level, a property that can help confirm its purity. A substance's pure form will display these properties consistently throughout - meaning that no matter the sample size or location within the sample, these properties remain the same, indicating a homogeneous composition without impurities.

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Most popular questions from this chapter

The temperature in the South Pole during the Antarctic winter is so cold that planes cannot land or take off, effectively leaving the inhabitants of the South Pole isolated for the winter. The average daily temperature at the South Pole in July is \(-59.7{ }^{\circ} \mathrm{C}\). Convert this temperature to degrees Fahrenheit.

Classify each mixture as homogeneous or heterogeneous. (a) baby oil (b) chocolate chip cookie (c) water and gasoline (d) wine

The coldest temperature ever recorded in Iowa was \(-47{ }^{\circ} \mathrm{F}\) on February 3,1998 . Convert this temperature to kelvins and degrees Celsius.

Explain the difference between kinetic energy and potential energy.

Liquid helium boils at \(4.2 \mathrm{~K}\). Convert this temperature to degrees Fahrenheit and Celsius.
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