1. Which of the following statements describes the relationship between a pure substance and an element correctly?
a) A pure substance and an element are the same thing.
b) A pure substance is always an element.
c) An element is a mixture of pure substances.
d) While all elements are pure substances, not all pure substances are elements.
Answer: d) While all elements are pure substances, not all pure substances are elements. This is because while elements are a type of pure substance made up of only one type of atom, pure substances can also include compounds made up of two or more types of atoms.
2. In a laboratory experiment, a mixture of iron filings and sulfur powder is heated strongly. What is the expected outcome of this experiment?
a) The iron filings will dissolve in the sulfur powder.
b) The sulfur powder will sublime, leaving the iron filings behind.
c) The iron filings will react with the sulfur powder to form a new compound.
d) The sulfur powder will melt, while the iron filings remain unchanged.
Answer: b) The sulfur powder will sublime, leaving the iron filings behind. Sublimation is the process in which a solid directly converts into a gas without going through the liquid state. In this experiment, when heated, the sulfur powder will sublime, turning into a gas and leaving the iron filings behind.
3. Among the given substances, which ones are compounds?
a) Iron, lemonade, oxygen, steel
b) Sugar, glass, carbon dioxide, oxygen gas
c) Paint, gold, milk, soil
d) Wood, ink, vinegar, bronze
Answer: b) Compounds are substances made up of two or more elements chemically combined. Sugar is a compound composed of carbon, hydrogen, and oxygen atoms. Glass is a mixture of compounds but can be considered a compound itself. Carbon dioxide is a compound made up of carbon and oxygen atoms, and oxygen gas (O2) is a molecule with two atoms and can also be considered a compound.
4. What is the correct order for obtaining ethanol from a mixture of ethanol and water?
a) Boiling - Condensation - Collection
b) Condensation - Boiling - Collection
c) Collection Distillation - Boiling
d) Boiling - Collection -Condensation
Answer: a) In the of distillation process, the mixture is heated (boiling) to vaporize the ethanol. The ethanol vapours are then cooled (condensation) to convert them back into a liquid state. Finally, the liquid ethanol is collected.
5. Match the following methods of separation with their corresponding descriptions.
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Column I
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Column II
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1. Filtration
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A) Separation of grains from stalks by beating or crushing
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2. Magnetic separation
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B) Separation of solid particles from a liquid or gas by passing it through a porous medium
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3. Winnowing
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C) Separation of magnetic substances from non-magnetic substances
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4. Threshing
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D) Separation of heavier or lighter components of a mixture by wind or blowing air
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a) 1:B, 2:C, 3:A, 4:D
b) 1:C, 2:A, 3:D, 4:B
c) 1D:, 2:C, 3:A, 4:B
d) 1:B, 2:C, 3:D, 4:A
Answer: d) Filtration: Separation of solid particles from a liquid or gas by passing it through a porous medium.
Magnetic separation: Separation of magnetic substances from non-magnetic substances.
Winnowing: Separation of heavier or lighter components of a mixture by wind or blowing air.
Threshing: Separation of grains from stalks by beating or crushing.
