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Questions and Answers
A pure substance can be separated into simpler substances by physical means.
A pure substance can be separated into simpler substances by physical means.
False (B)
Which of the following is NOT a characteristic of a pure substance?
Which of the following is NOT a characteristic of a pure substance?
What are the two main categories of pure substances?
What are the two main categories of pure substances?
Elements and compounds
A ______ is a uniform mixture with the same composition and properties throughout.
A ______ is a uniform mixture with the same composition and properties throughout.
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Which of the following is an example of a heterogeneous mixture?
Which of the following is an example of a heterogeneous mixture?
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Match the following terms with their definitions:
Match the following terms with their definitions:
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Explain how the melting point of a substance can indicate its purity.
Explain how the melting point of a substance can indicate its purity.
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All solutions are homogeneous mixtures.
All solutions are homogeneous mixtures.
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Flashcards
Pure Substances
Pure Substances
A pure substance is made of a single type of material and has fixed properties.
Characteristics of Pure Substances
Characteristics of Pure Substances
Fixed composition, constant properties; components can't be separated by physical means.
Elements
Elements
A pure substance that cannot be broken down into simpler substances using ordinary methods.
Compounds
Compounds
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Mixtures
Mixtures
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Homogeneous Mixtures
Homogeneous Mixtures
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Heterogeneous Mixtures
Heterogeneous Mixtures
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Separation of Mixtures
Separation of Mixtures
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Study Notes
Pure Substances
- Pure substances are composed of only one type of material.
- Their composition is fixed and constant.
- Properties such as melting point, boiling point, and density are fixed and constant.
- Components cannot be separated by physical processes.
- Examples include elements and compounds.
- To identify if a substance is pure, measure its melting or boiling point. Impurities lower the melting point and raise the boiling point.
Elements
- Elements are pure substances that cannot be broken down into simpler substances by ordinary physical or chemical processes.
- Elements are made of only one type of atom.
Compounds
- Compounds are pure substances formed from two or more different elements chemically bonded together in fixed proportions.
- Their properties are different from the properties of the individual elements.
Mixtures
- Mixtures consist of two or more substances (elements and/or compounds) physically combined in variable proportions.
- Each component retains its own properties.
- Composition can vary.
- Properties are variable; they are the average of the substances in the mixture.
- Components can be separated by physical means.
- Homogeneous mixtures are uniform throughout (e.g., solutions).
- Heterogeneous mixtures are not uniform (e.g., suspensions, colloids).
Comparing Compounds and Mixtures
| Feature | Compound (Pure Substance) | Mixture |
|---|---|---|
| Composition | Fixed | Variable |
| Separability | Cannot be separated by physical means | Can be separated by physical means |
| Properties | Different from constituent elements | Average of constituent substances |
Example: Iron and Sulfur
- Iron and sulfur mixture: mixture of yellow and silver spots, can be separated by magnet, sulfur dissolves in solvent.
- Iron sulfide compound: brown-black, cannot be separated by magnet, does not dissolve.
- Heat is involved in forming a compound, but not in a mixture.
- Different gases are released when compounds, like iron sulfide, react with acid compared to mixtures, like iron and sulfur.
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Description
Explore the concepts of pure substances, including elements and compounds, as well as mixtures. This quiz covers key properties that differentiate these categories and the methods used to identify purity. Test your understanding of the fundamental principles in chemistry related to composition and properties.
