Some Basic Concepts of Chemistry: Matter, Pure Substances & Mixtures: 25 flashcards
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1. What is matter?
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Anything that occupies space and has mass.
2. What is chemistry the study of?
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Matter, its physical and chemical properties, and the physical and chemical changes it undergoes under different conditions.
3. Why is chemistry called the central science?
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Because physics, biology, applied sciences and earth/space sciences all depend on chemical knowledge.
4. What are the two main branches of matter by chemical composition?
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Pure substances and mixtures.
5. What defines a pure substance?
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A definite chemical composition, and therefore definite properties, regardless of origin.
6. What are the two types of pure substances?
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Elements and compounds.
7. What is an element?
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A pure substance containing only one kind of atom.
8. What is a compound?
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A pure substance made of two or more elements chemically combined in a fixed ratio.
9. How are elements classified?
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As metals, nonmetals and metalloids.
10. What are typical properties of metals?
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Lustrous, malleable and good conductors.
11. What are metalloids?
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Elements that show properties of both metals and nonmetals.
12. What defines a mixture?
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Two or more substances not chemically combined, with no definite composition and no definite properties.
13. What are the two types of mixtures?
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Homogeneous and heterogeneous mixtures.
14. What is a homogeneous mixture?
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A mixture that is uniform throughout, with the same composition in every part.
15. What is a heterogeneous mixture?
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A mixture that is visibly non-uniform, with different parts having different compositions.
16. Why can mixtures be separated by physical methods?
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Because their ingredients are not chemically combined.
17. Why do compounds require chemical methods to break apart?
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Because their elements are chemically bonded together.
18. Is water an element or a compound?
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A compound — hydrogen and oxygen chemically combined in a fixed ratio.
19. Is tap water a pure substance?
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No, it is a homogeneous mixture of water with dissolved salts and gases.
20. Is air a pure substance?
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No, it is a homogeneous mixture of gases.
21. Give an example of a heterogeneous mixture.
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Sand mixed with iron filings, or oil floating on water.
22. Give an example of a homogeneous mixture.
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Salt dissolved in water, or clean air.
23. What is the two-question test for classifying matter?
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First: is the composition fixed? If yes, second: is it one element or more than one?
24. Why do a compound's properties differ from its constituent elements?
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Because the elements are chemically combined, not merely blended — e.g. water versus hydrogen and oxygen.
25. What does 'pure' mean in chemistry?
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Having a fixed chemical composition and fixed properties — not merely clean-looking or unadulterated.
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