Nokea
What can be predicted by using the periodic table?
- A. The properties of each element
- B. The charges of polyatomic ions
- C. The number of isotopes for each element
- D. The potential for discovering new elements
Correct Answer: A
Rationale: The periodic table organizes elements based on their properties, such as atomic number, electron configuration, and chemical behavior. By examining an element's position on the periodic table, one can predict its properties, including its physical and chemical characteristics, reactivity, and other behaviors. This predictive ability is one of the fundamental strengths of the periodic table in understanding and working with elements. Therefore, the correct answer is A, as the periodic table allows for the prediction of the properties of each element based on its location and characteristics within the table.
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What is the density of iron when 28.5g of iron shot is added to a graduated cylinder containing 45.5mL of water, causing the water level to rise to the 49.1mL mark?
- A. 0.63 g/mL
- B. 7.92 g/mL
- C. 0.58 g/mL
- D. None of the above
Correct Answer: B
Rationale: To determine the density of iron, we use the formula: Density = Mass / Volume. The mass of the iron is given as 28.5g. The volume of water displaced by the iron is the final volume (49.1mL) minus the initial volume (45.5mL), resulting in 3.6mL. Therefore, the density of iron can be calculated by dividing the mass of iron (28.5g) by the volume of water displaced (3.6mL), giving us 7.92 g/mL. Therefore, choice B, 7.92 g/mL, is the correct answer.
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).
In a double replacement reaction, which of the following occurs?
- A. Energy in the form of heat or light is not always produced.
- B. The reactants can involve a variety of elements.
- C. A gas, solid precipitate, or compound forms in the exchange of ions.
- D. All of the above.
Correct Answer: C
Rationale: In a double replacement reaction, two compounds exchange ions to form two new compounds. This often results in the formation of a gas, a solid precipitate, or a new compound. Choice A is not always true as energy production can vary in different reactions. Choice B is not a defining characteristic of double replacement reactions, as the reactants can involve a variety of elements. Therefore, the correct answer is C, as it accurately describes a common outcome of double replacement reactions.
Will solids always sink in liquids?
- A. True, a solid is hard, and liquids are not.
- B. True, solids are heavier than liquids.
- C. False, solids have a smooth surface so they will float.
- D. False, it depends on the density of the solid and liquid.
Correct Answer: D
Rationale: Solids will not always sink in liquids. Whether a solid sinks or floats in a liquid depends on the relative densities of the solid and the liquid. If the density of the solid is greater than that of the liquid, it will sink. If the density of the solid is less than that of the liquid, it will float. Therefore, it is incorrect to state that solids will always sink in liquids without considering their respective densities. The weight or hardness of the solid and the smoothness of its surface do not determine whether it will sink or float in a liquid. The critical factor is the density relationship between the solid and the liquid.
Identify the reactants in the chemical reaction below: CH₄ + 2O₂ → CO₂ + 2H₂O
- A. CHâ‚„ and Oâ‚‚
- B. COâ‚‚ and Hâ‚‚O
- C. Both
- D. None of the above
Correct Answer: A
Rationale: Reactants in a chemical reaction are the initial substances that are transformed into products. In this reaction, CHâ‚„ (methane) and Oâ‚‚ (oxygen) are the reactants, as they are the starting materials that undergo a chemical change to form COâ‚‚ (carbon dioxide) and 2Hâ‚‚O (water). The equation clearly shows that CHâ‚„ and Oâ‚‚ are on the left side of the reaction arrow, indicating that they are the reactants. Therefore, the correct answer is A: CHâ‚„ and Oâ‚‚.