Nokea
The pressure of the earth's atmosphere at sea level is . What is the pressure when expressed in ? (54 cm = 1 in., 205 lb = 1 kg)
- A. 2.62 105
- B. 1.03 107
- C. 5.02 104
- D. 4.30 100
Correct Answer: A
Rationale: The correct answer is A: 2.62 × 10^5. To convert atmospheric pressure from inches of mercury to pascals, we use the conversion factor 1 in. = 2.54 cm and the standard atmospheric pressure at sea level (29.92 in. Hg). First, convert 29.92 in. Hg to cm Hg (29.92 in. × 2.54 cm/in.), then convert cm Hg to Pa (1 atm = 101325 Pa). Follow these steps to get the correct answer. Choice B (1.03 × 10^7) is incorrect as it is too high. Choice C (5.02 × 10^4) is incorrect as it is too low. Choice D (4.30 100) is not a valid numerical expression.
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The density of liquid mercury is 6 g/mL. What is its density in units of ? (54 cm = 1 in., 205 lb = 1 kg)
- A. 1.57 10 2
- B. 4.91 10 1
- C. 1.01 10 1
- D. 7.62 10 2
Correct Answer: C
Rationale: To find the density of liquid mercury in units of g/cm³, we need to convert the density from g/mL to g/cm³. The conversion factor is 1 mL = 1 cm³. Given the density of mercury as 6 g/mL, it is equivalent to 6 g/cm³. Therefore, the correct answer is 1.01 x 10¹ g/cm³ (choice C).
Choice A: 1.57 x 10² is too large for the density of liquid mercury.
Choice B: 4.91 x 10¹ is incorrect as it does not match the calculated density.
Choice D: 7.62 x 10² is significantly higher than the actual density of liquid mercury.
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.
The cargo of uranium hexafluoride weighed kg and was contained in 30 drums, each containing L of UF . What is the density (g/mL) of uranium hexafluoride?
- A. 1.53 g/mL
- B. 5.11 g/mL
- C. 2.25 g/mL
- D. 0.196 g/mL
Correct Answer: C
Rationale: To find the density, we first calculate the total volume of uranium hexafluoride. Since each drum contains 15 L, the total volume is 30 drums * 15 L/drum = 450 L. Next, convert the mass from kg to g (1 kg = 1000 g). Density = mass/volume. Density = (mass in g) / (volume in mL). Since the mass is in g, we need to convert the volume from L to mL (1 L = 1000 mL). Density = (mass in g) / (volume in mL) = (mass in g) / (volume in L * 1000). Density = (mass in g) / (450 L * 1000) = (mass in g) / 450000 mL. Therefore, the density is the mass divided by 450000. The correct answer is C: 2.25 g/mL. Choice A is incorrect as it is too low
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.
You measure water in two containers: a 10-mL graduated cylinder with marks at every mL, and a 1-mL pipet marked at every 1 mL. If you have some water in each of the containers and add them together, to what decimal place could you report the total volume of water?
- A. 0.01 mL
- B. 0.1 mL
- C. 1 mL
- D. 10 mL
Correct Answer: C
Rationale: The correct answer is C: 1 mL. When adding volumes measured in different containers, you should report the result to the least precise measurement scale, which is the 1 mL pipet in this case. The graduated cylinder measures to the nearest mL, so the total volume should be rounded to the nearest whole mL. Reporting to a decimal place of 0.01 mL or 0.1 mL would imply a level of precision greater than what the equipment can provide. Choice D is incorrect as it exceeds the maximum volume capacity of the containers and is not relevant to the precision of the measurements.