Nokea
Many classic experiments have given us indirect evidence of the nature of the atom. Which of the experiments listed below did not give the results described?
- A. The Rutherford experiment proved the Thomson "plum- pudding" model of the atom to be essentially correct.
- B. The Rutherford experiment was useful in determining the nuclear charge on the atom.
- C. Millikan's oil-drop experiment showed that the charge on any particle was a simple multiple of the charge on the electron.
- D. The electric discharge tube proved that electrons have a negative charge.
Correct Answer: A
Rationale: The correct answer is A because the Rutherford experiment actually disproved the Thomson "plum-pudding" model of the atom. Rutherford's experiment involved firing alpha particles at a thin gold foil and observing their scattering patterns. The results showed that atoms have a small, dense, positively charged nucleus, which contradicted the Thomson model. Choice B is correct as the experiment was indeed useful in determining the nuclear charge on the atom. Choice C is incorrect because Millikan's oil-drop experiment determined the charge on the electron, not just that it was a simple multiple. Choice D is incorrect as the electric discharge tube did show that electrons have a negative charge.
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Which one of the following statements about atomic structure is false?
- A. An atom is mostly empty space.
- B. Almost all of the mass of the atom is concentrated in the nucleus.
- C. The protons and neutrons in the nucleus are very tightly packed.
- D. The number of protons and neutrons is always the same in the neutral atom.
Correct Answer: D
Rationale: The correct answer is D because the statement that the number of protons and neutrons is always the same in a neutral atom is false. In a neutral atom, the number of protons equals the number of electrons, not the number of neutrons. Neutrons are not always equal to the number of protons.
A: An atom is mostly empty space - Correct. This is true because the nucleus is very tiny compared to the overall size of the atom.
B: Almost all of the mass of the atom is concentrated in the nucleus - Correct. This is true because protons and neutrons have much more mass than electrons.
C: The protons and neutrons in the nucleus are very tightly packed - Correct. This is true because protons and neutrons are densely packed within the nucleus.
A quantitative observation
- A. contains a number and a unit
- B. does not contain a number
- C. always makes a comparison
- D. must be obtained through experimentation E) is none of these KEY: Chemistry | general chemistry | general concepts | scientific methodMSC: Conceptual
Correct Answer: A
Rationale: The correct answer is A because a quantitative observation must contain both a number and a unit to provide a specific measurement. This ensures the observation is precise and can be accurately communicated. The other choices are incorrect because B is vague, C is not a requirement for quantitative observations, and D is not true as quantitative observations can also be obtained through measurements, not just experimentation.
How many significant figures are there in the number 0006428?
- A. 7
- B. 3
- C. 8
- D. 4
Correct Answer: D
Rationale: The correct answer is D: 4. Significant figures are non-zero digits and zeros between them. In this case, only digits 6, 4, 2, and 8 are non-zero, making them all significant. Zeros before the first non-zero digit are not significant, so the zeros before 6 are not counted. Hence, there are 4 significant figures in the number 0006428.
Choice A (7) is incorrect because it includes all digits, including the leading zeros, which are not significant. Choice B (3) is incorrect because it only considers the non-zero digits, excluding the zeros between them. Choice C (8) is incorrect because it counts all digits including leading zeros, which are not significant.
A metric unit for length is
- A. gram
- B. milliliter
- C. yard
- D. kilometer
Correct Answer: D
Rationale: The correct answer is D: kilometer. A kilometer is a metric unit for length because it is used to measure long distances. In the metric system, length is typically measured in meters, and a kilometer is equal to 1000 meters. This makes it a suitable unit for measuring larger distances efficiently.
Explanation for incorrect choices:
A: Gram is a unit of mass, not length.
B: Milliliter is a unit of volume, not length.
C: Yard is a unit of length, but it is not a metric unit. The metric system uses meters and its derivatives for length measurements.
The element rhenium (Re) exists as two stable isotopes and 18 unstable isotopes. Rhenium-185 has in its nucleus
- A. 75 protons, 75 neutrons
- B. 75 protons, 130 neutrons
- C. 130 protons, 75 neutrons
- D. 75 protons, 110 neutrons
Correct Answer: A
Rationale: The correct answer A is determined by knowing that the atomic number of rhenium is 75. Since the element is rhenium-185, the sum of protons and neutrons must equal 185. As the atomic number is 75, the number of protons is 75. Therefore, the number of neutrons is 185 - 75 = 110. Thus, rhenium-185 has 75 protons and 110 neutrons. Choices B, C, and D are incorrect as they do not adhere to the correct number of protons and neutrons in the nucleus of rhenium-185.