Nokea
The statement “The total mass of materials is not affected by a chemical change in thosematerials” is called a(n)
- A. observation
- B. measuremen t
- C. theory
- D. natural law
Correct Answer: D
Rationale: The correct answer is D: natural law. A natural law describes a consistent pattern or behavior in the natural world, such as the conservation of mass in a chemical reaction. This principle states that the total mass of materials before and after a chemical change remains constant. Observations (A) are factual statements based on data, measurements (B) involve quantifying properties, and theories (C) are explanations based on evidence, but none specifically address the consistent behavior of mass in chemical changes as a natural law does.
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20 protons
- A. 22 protons
- B. 20 protons
- C. 18 electrons
- D. 22
Correct Answer: A
Rationale: The correct answer is A. Since the question states that there are 20 protons, option A with 22 protons is incorrect. Option B with 20 protons matches the given information, making it the correct answer. Option C with 18 electrons is unrelated to the given information about protons. Option D with just the number 22 is irrelevant and does not provide any information about protons.
Which statement is not correct?
- A. The mass of an alpha particle is 7300 times that of the electron.
- B. An alpha particle has a 2+ charge.
- C. Three types of radioactive emission are gamma rays, beta rays, and alpha particles.
- D. A gamma ray is high-energy light.
Correct Answer: D
Rationale: The correct answer is D because gamma rays are not light but a form of electromagnetic radiation with high energy. Gamma rays have no charge and are produced from the nucleus. Choice A is correct as an alpha particle is heavier than an electron. Choice B is correct as an alpha particle has a 2+ charge. Choice C is correct as these are types of radioactive emissions.
We generally report a measurement by recording all of the certain digits plus uncertain digit(s).
- A. no
- B. one
- C. two
- D. three
Correct Answer: B
Rationale: Step 1: In measurement, certain digits are the numbers that are known for sure.
Step 2: Uncertain digits are the last digit that is estimated or measured.
Step 3: We record all the certain digits and one uncertain digit to indicate the precision of the measurement.
Step 4: Choice A is incorrect because we do include uncertain digit(s) in the measurement.
Step 5: Choice C and D are incorrect as including two or three uncertain digits would provide excessive precision beyond what is known for certain.
In 1984, some drums of uranium hexafluoride were lost in the English Channel, which is known for its cold water (about 17°C). The melting point of uranium hexafluoride is 148°F. In what physical state is the uranium hexafluoride in these drums?
- A. solid
- B. liquid
- C. gas
- D. a mixture of solid and liquid
Correct Answer: A
Rationale: The correct answer is A: solid. Uranium hexafluoride has a melting point of 148°F, which is equivalent to approximately 64.4°C. Since the water temperature in the English Channel is only about 17°C, the uranium hexafluoride would be below its melting point and thus in a solid state. The other choices are incorrect because the temperature is not high enough for it to be in a liquid or gaseous state, and there is no indication of it being a mixture of solid and liquid based on the given information.
In March 2008, gold reached a milestone value of $1000 per troy ounce. At that price, what was the cost of a gram of gold? (1 troy ounce = 10 g)
- A. less than $1
- B. between $1 and $10
- C. between $10 and $50
- D. between $50 and $100
Correct Answer: C
Rationale: To find the cost of a gram of gold at $1000 per troy ounce, we divide $1000 by 10 (since 1 troy ounce = 10g). This gives us $100 per gram. Therefore, the correct answer is C: between $10 and $50. Option A is incorrect as it is less than $1, option B is incorrect as it is between $1 and $10, and option D is incorrect as it is between $50 and $100.