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Which of the following describes atomic mass?
- A. Mass of protons and electrons
- B. Mass of neutrons and electrons
- C. Average mass of that element's isotopes
- D. Number of moles in a solution
Correct Answer: C
Rationale: The correct answer is C: Average mass of that element's isotopes. Atomic mass is the weighted average mass of the isotopes of an element, considering the natural abundance of each isotope. It is not just the sum of protons and neutrons or neutrons and electrons. Understanding atomic mass is crucial in chemistry as it helps in determining the molar mass of elements, which is essential in various chemical calculations such as stoichiometry and reaction equations.
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What distinguishes the 20 common amino acids from each other?
- A. Color
- B. Size
- C. R-group
- D. None of the above
Correct Answer: C
Rationale: The correct answer is C: R-group. The 20 common amino acids share a common backbone structure, but what differentiates them from each other is the side chain or R-group attached to this backbone. The R-group varies in composition and properties among the different amino acids, influencing their overall characteristics and functions. Options A and B are not the primary distinguishing factors among amino acids. Option D is incorrect as the R-group is the key feature that sets apart the 20 common amino acids, contributing to their individual identities and roles in biological processes.
What volume of silver will weigh exactly 2500.0 g? The density of silver is 10.5 g/cm³.
- A. 262.50 cm³
- B. 238.1 cm³
- C. 0.0042 cm³
- D. None of the above
Correct Answer: B
Rationale: To find the volume of silver, we use the formula: Volume = Mass / Density. Plugging in the given values, Volume = 2500.0 g / 10.5 g/cm³ = 238.1 cm³. Therefore, the correct answer is 238.1 cm³, which corresponds to option B.
Which of the following could be an empirical formula?
- A. C4H8
- B. C2H6
- C. CH
- D. C3H6
Correct Answer: C
Rationale: An empirical formula represents the simplest whole-number ratio of atoms in a compound. For a hydrocarbon compound consisting of carbon and hydrogen, the empirical formula should have the simplest ratio of carbon to hydrogen. Choice C, 'CH,' is the correct empirical formula as it represents a 1:1 ratio of carbon to hydrogen atoms, indicating the simplest ratio. Choices A, B, and D have multiple atoms of carbon and hydrogen, which do not represent the simplest whole-number ratio. Therefore, 'CH' is the empirical formula that best fits the definition.
What is the density of carbon tetrachloride if a flask weighing 345.8 g is filled with 225 mL of the liquid, and the total weight of the flask and liquid is 703.55 g?
- A. 1.59 g/mL
- B. 2.76 g/mL
- C. 1.4 g/mL
- D. None of the above
Correct Answer: A
Rationale: To find the density of carbon tetrachloride, we first need to determine the weight of the liquid only. The weight of the liquid can be calculated by subtracting the weight of the empty flask from the total weight of the flask and liquid: 703.55 g - 345.8 g = 357.75 g. Now, using the volume of the liquid (225 mL) and its weight (357.75 g), we can calculate the density: Density = Mass/Volume = 357.75 g / 225 mL ĉ� 1.59 g/mL. Therefore, the correct answer is A, 1.59 g/mL.
What is the term for the reactant that is entirely consumed in a reaction?
- A. limiting reactant
- B. reducing agent
- C. reaction intermediate
- D. reagent
Correct Answer: A
Rationale: The term for the reactant that is entirely consumed in a reaction is the limiting reactant. The limiting reactant is crucial in determining the maximum amount of product that can be formed as it is fully consumed in the reaction. The other choices, reducing agent, reaction intermediate, and reagent, do not specifically refer to the reactant that is completely consumed during the reaction process. Identifying the limiting reactant is essential for calculating the theoretical yield of a reaction and understanding the stoichiometry of the reaction.