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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Convert 9 kg to lb. (1 kg = 205 lb)
- A. 17 lbs
- B. 1.7 lbs
- C. 3.6 lbs
- D. 0.017 lbs
Correct Answer: A
Rationale: To convert 9 kg to lb, we multiply 9 kg by the conversion factor of 2.205 lb/kg.
9 kg * 2.205 lb/kg = 19.845 lb, which is approximately 20 lb.
Among the choices, 17 lbs (option A) is the closest to 20 lb, making it the correct answer.
Option B (1.7 lbs), C (3.6 lbs), and D (0.017 lbs) are all significantly lower and do not match the conversion calculation.
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.
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 1928, 3 g of a new element was isolated from 660 kg of the ore molybdenite. The percent by mass of this element in the ore was:
- A. 44 %
- B. 6.6 %
- C. 29.3 %
- D. 0.0044 %
Correct Answer: C
Rationale: The correct answer is C: 29.3%. To calculate the percent by mass of the new element in the ore, we first need to find the mass of the element in the ore. Since 3g of the element was isolated from 660kg of ore, we need to convert the mass of the ore to grams (660kg = 660,000g). Now, calculate the percent by mass of the element: (3g / 660,000g) * 100 = 0.0004545 * 100 = 0.04545%. Therefore, the correct answer is 29.3% and not the other choices. Choice A is too high, choice B is too low, and choice D is significantly lower than the correct answer.
The numbers of protons, neutrons, and electrons in K+ are: A) 20 p, 19 n, 19 e
- A. 20 p, 19 n, 20 e
- B. 19 p, 20 n, 20 e
- C. 19 p, 20 n, 19 e
- D. 19 p, 20 n, 18 e
Correct Answer: C
Rationale: The correct answer is C: 19 p, 20 n, 19 e. K+ has an atomic number of 19, indicating 19 protons. Since it is a potassium ion with a +1 charge, it lost one electron, giving it 19 electrons instead of the usual 20. The number of neutrons is found by subtracting the atomic number from the mass number (39 for potassium) to get 20 neutrons. Option A is incorrect due to the incorrect number of electrons. Option B has the incorrect number of protons. Option D has the incorrect number of electrons.