Multiple Choice
Which of the following substances contains silica (SiO_2)?
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1. Intro to General Chemistry
Classification of Matter
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Which of the following is a mixture?
A
Brass
B
Pure water (H2O)
C
Carbon dioxide (CO2)
D
Air
Verified step by step guidance1
Understand the difference between a pure substance and a mixture. A pure substance has a fixed composition and distinct chemical properties, while a mixture contains two or more substances physically combined without fixed proportions.
Identify pure substances in the list: Pure water (H\_2O) and carbon dioxide (CO\_2) are pure substances because each consists of only one type of molecule with a fixed chemical formula.
Recognize that brass is an alloy, which is a solid mixture of two or more metals (usually copper and zinc). Since its components are physically combined and not chemically bonded in fixed ratios, brass is a mixture.
Consider air, which is a mixture of gases such as nitrogen, oxygen, carbon dioxide, and others. These gases are physically combined and can vary in proportion, making air a mixture.
Conclude that among the options, brass and air are mixtures, while pure water and carbon dioxide are pure substances.
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