Chemistry

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Which type of reaction is exemplified by the chemical equation KClO₃ → KCl + O₂?

  • A. Single replacement
  • B. Double replacement
  • C. Combustion
  • D. Decomposition
Correct Answer: D

Rationale: The chemical equation KClO₃ → KCl + O₂ represents a decomposition reaction. In a decomposition reaction, a single compound breaks down into two or more simpler substances. In this case, potassium chlorate (KClO₃) decomposes into potassium chloride (KCl) and oxygen gas (O₂). Therefore, the correct answer is D: Decomposition. This reaction is not a single replacement reaction (where one element replaces another in a compound), a double replacement reaction (where ions in two compounds exchange places), or a combustion reaction (which involves a substance reacting with oxygen to produce heat and light).

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What is the name for the horizontal rows of the periodic table?

  • A. groups
  • B. periods
  • C. families
  • D. sets
Correct Answer: B

Rationale: In the periodic table, the horizontal rows are called 'periods.' These periods represent the number of electron shells an element has. Each period starts a new energy level, indicating the elements' properties and atomic structure. 'Groups' refer to the vertical columns of the periodic table, each containing elements with similar chemical properties. 'Families' can also be used interchangeably with groups. 'Sets' is a vague term and not specifically related to the layout of the periodic table. Understanding the distinction between 'periods' and 'groups' is crucial in comprehending the organization and properties of elements in the periodic table.

Which of the following elements does not exist as a diatomic molecule?

  • A. boron
  • B. fluorine
  • C. oxygen
  • D. nitrogen
Correct Answer: A

Rationale: The correct answer is boron (A). Diatomic molecules consist of two atoms of the same element bonded together. Boron does not naturally form diatomic molecules in its elemental state. Fluorine (Fā‚‚), oxygen (Oā‚‚), and nitrogen (Nā‚‚) are examples of elements that exist as diatomic molecules in their elemental forms. Boron typically forms covalent bonds with other elements but does not naturally exist as a diatomic molecule.

What is the mass of ethyl alcohol that exactly fills a 200.0 mL container?

  • A. 157.8 g
  • B. 253.49 g
  • C. 0.0039 g
  • D. None of the above
Correct Answer: A

Rationale: To determine the mass of ethyl alcohol that fills a 200.0 mL container, we use the formula: Mass = Volume x Density. Given that the density of ethyl alcohol is 0.789 g/mL, multiplying the volume (200.0 mL) by the density gives us 200.0 mL x 0.789 g/mL = 157.8 g. Therefore, the correct answer is A, 157.8 g, representing the mass of ethyl alcohol that exactly fills the 200.0 mL container.

A block on your desk acts as a paperweight with measurements of 3 cm by 4 cm by 6 cm. The block has a mass of 184.32 g. What is its density?

  • A. 13,271.04 g/cm³
  • B. 2.56 g/cm³
  • C. 0.39 g/cm³
  • D. None of the above
Correct Answer: B

Rationale: Density is calculated by dividing mass by volume. To find the volume of the block, multiply its dimensions (3 cm x 4 cm x 6 cm = 72 cm³). Dividing the mass (184.32 g) by the volume (72 cm³) gives a density of 2.56 g/cm³. Therefore, the correct answer is B.

How are chemical equations typically written?

  • A. Products → Reactants
  • B. Reactants → Products
  • C. Reactants + Reactants
  • D. Products + Reactants
Correct Answer: B

Rationale: Chemical equations are typically written with reactants listed on the left side of the arrow and products on the right side. This convention signifies the progression of reactants transforming into products during a chemical reaction. Therefore, the correct way chemical equations are typically written is 'Reactants ā†’ Products.'

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